# A search for time-dependent astrophysical neutrino emission with IceCube
data from 2012 to 2017

R. Abbasi  Department of Physics, Loyola University Chicago, Chicago, IL
60660, USA  M. Ackermann  DESY, D-15738 Zeuthen, Germany  J. Adams  Dept. of
Physics and Astronomy, University of Canterbury, Private Bag 4800,
Christchurch, New Zealand  J. A. Aguilar  Université Libre de Bruxelles,
Science Faculty CP230, B-1050 Brussels, Belgium  M. Ahlers  Niels Bohr
Institute, University of Copenhagen, DK-2100 Copenhagen, Denmark  M. Ahrens
Oskar Klein Centre and Dept. of Physics, Stockholm University, SE-10691
Stockholm, Sweden  C. Alispach  Département de physique nucléaire et
corpusculaire, Université de Genève, CH-1211 Genève, Switzerland  A. A. Alves
Jr  Karlsruhe Institute of Technology, Institute for Astroparticle Physics,
D-76021 Karlsruhe, Germany  N. M. Amin  Bartol Research Institute and Dept. of
Physics and Astronomy, University of Delaware, Newark, DE 19716, USA  K.
Andeen  Department of Physics, Marquette University, Milwaukee, WI, 53201, USA
T. Anderson  Dept. of Physics, Pennsylvania State University, University Park,
PA 16802, USA  I. Ansseau  Université Libre de Bruxelles, Science Faculty
CP230, B-1050 Brussels, Belgium  G. Anton  Erlangen Centre for Astroparticle
Physics, Friedrich-Alexander-Universität Erlangen-Nürnberg, D-91058 Erlangen,
Germany  C. Argüelles  Department of Physics and Laboratory for Particle
Physics and Cosmology, Harvard University, Cambridge, MA 02138, USA  S. Axani
Dept. of Physics, Massachusetts Institute of Technology, Cambridge, MA 02139,
USA  X. Bai  Physics Department, South Dakota School of Mines and Technology,
Rapid City, SD 57701, USA  A. Balagopal V  Dept. of Physics and Wisconsin
IceCube Particle Astrophysics Center, University of Wisconsin–Madison,
Madison, WI 53706, USA  A. Barbano  Département de physique nucléaire et
corpusculaire, Université de Genève, CH-1211 Genève, Switzerland  S. W.
Barwick  Dept. of Physics and Astronomy, University of California, Irvine, CA
92697, USA  B. Bastian  DESY, D-15738 Zeuthen, Germany  V. Basu  Dept. of
Physics and Wisconsin IceCube Particle Astrophysics Center, University of
Wisconsin–Madison, Madison, WI 53706, USA  V. Baum  Institute of Physics,
University of Mainz, Staudinger Weg 7, D-55099 Mainz, Germany  S. Baur
Université Libre de Bruxelles, Science Faculty CP230, B-1050 Brussels, Belgium
R. Bay  Dept. of Physics, University of California, Berkeley, CA 94720, USA
J. J. Beatty  Dept. of Astronomy, Ohio State University, Columbus, OH 43210,
USA  Dept. of Physics and Center for Cosmology and Astro-Particle Physics,
Ohio State University, Columbus, OH 43210, USA  K.-H. Becker  Dept. of
Physics, University of Wuppertal, D-42119 Wuppertal, Germany  J. Becker Tjus
Fakultät für Physik & Astronomie, Ruhr-Universität Bochum, D-44780 Bochum,
Germany  C. Bellenghi  Physik-department, Technische Universität München,
D-85748 Garching, Germany  S. BenZvi  Dept. of Physics and Astronomy,
University of Rochester, Rochester, NY 14627, USA  D. Berley  Dept. of
Physics, University of Maryland, College Park, MD 20742, USA  E. Bernardini
DESY, D-15738 Zeuthen, Germany  D. Z. Besson  Dept. of Physics and Astronomy,
University of Kansas, Lawrence, KS 66045, USA  G. Binder  Dept. of Physics,
University of California, Berkeley, CA 94720, USA  Lawrence Berkeley National
Laboratory, Berkeley, CA 94720, USA  D. Bindig  Dept. of Physics, University
of Wuppertal, D-42119 Wuppertal, Germany  E. Blaufuss  Dept. of Physics,
University of Maryland, College Park, MD 20742, USA  S. Blot  DESY, D-15738
Zeuthen, Germany  S. Böser  Institute of Physics, University of Mainz,
Staudinger Weg 7, D-55099 Mainz, Germany  O. Botner  Dept. of Physics and
Astronomy, Uppsala University, Box 516, S-75120 Uppsala, Sweden  J. Böttcher
III. Physikalisches Institut, RWTH Aachen University, D-52056 Aachen, Germany
E. Bourbeau  Niels Bohr Institute, University of Copenhagen, DK-2100
Copenhagen, Denmark  J. Bourbeau  Dept. of Physics and Wisconsin IceCube
Particle Astrophysics Center, University of Wisconsin–Madison, Madison, WI
53706, USA  F. Bradascio  DESY, D-15738 Zeuthen, Germany  J. Braun  Dept. of
Physics and Wisconsin IceCube Particle Astrophysics Center, University of
Wisconsin–Madison, Madison, WI 53706, USA  S. Bron  Département de physique
nucléaire et corpusculaire, Université de Genève, CH-1211 Genève, Switzerland
J. Brostean-Kaiser  DESY, D-15738 Zeuthen, Germany  A. Burgman  Dept. of
Physics and Astronomy, Uppsala University, Box 516, S-75120 Uppsala, Sweden
R. S. Busse  Institut für Kernphysik, Westfälische Wilhelms-Universität
Münster, D-48149 Münster, Germany  M. A. Campana  Dept. of Physics, Drexel
University, 3141 Chestnut Street, Philadelphia, PA 19104, USA  C. Chen  School
of Physics and Center for Relativistic Astrophysics, Georgia Institute of
Technology, Atlanta, GA 30332, USA  D. Chirkin  Dept. of Physics and Wisconsin
IceCube Particle Astrophysics Center, University of Wisconsin–Madison,
Madison, WI 53706, USA  S. Choi  Dept. of Physics, Sungkyunkwan University,
Suwon 16419, Korea  B. A. Clark  Dept. of Physics and Astronomy, Michigan
State University, East Lansing, MI 48824, USA  K. Clark  SNOLAB, 1039 Regional
Road 24, Creighton Mine 9, Lively, ON, Canada P3Y 1N2  L. Classen  Institut
für Kernphysik, Westfälische Wilhelms-Universität Münster, D-48149 Münster,
Germany  A. Coleman  Bartol Research Institute and Dept. of Physics and
Astronomy, University of Delaware, Newark, DE 19716, USA  G. H. Collin  Dept.
of Physics, Massachusetts Institute of Technology, Cambridge, MA 02139, USA
J. M. Conrad  Dept. of Physics, Massachusetts Institute of Technology,
Cambridge, MA 02139, USA  P. Coppin  Vrije Universiteit Brussel (VUB), Dienst
ELEM, B-1050 Brussels, Belgium  P. Correa  Vrije Universiteit Brussel (VUB),
Dienst ELEM, B-1050 Brussels, Belgium  D. F. Cowen  Dept. of Astronomy and
Astrophysics, Pennsylvania State University, University Park, PA 16802, USA
Dept. of Physics, Pennsylvania State University, University Park, PA 16802,
USA  R. Cross  Dept. of Physics and Astronomy, University of Rochester,
Rochester, NY 14627, USA  P. Dave  School of Physics and Center for
Relativistic Astrophysics, Georgia Institute of Technology, Atlanta, GA 30332,
USA  C. De Clercq  Vrije Universiteit Brussel (VUB), Dienst ELEM, B-1050
Brussels, Belgium  J. J. DeLaunay  Dept. of Physics, Pennsylvania State
University, University Park, PA 16802, USA  H. Dembinski  Bartol Research
Institute and Dept. of Physics and Astronomy, University of Delaware, Newark,
DE 19716, USA  K. Deoskar  Oskar Klein Centre and Dept. of Physics, Stockholm
University, SE-10691 Stockholm, Sweden  S. De Ridder  Dept. of Physics and
Astronomy, University of Gent, B-9000 Gent, Belgium  A. Desai  Dept. of
Physics and Wisconsin IceCube Particle Astrophysics Center, University of
Wisconsin–Madison, Madison, WI 53706, USA  P. Desiati  Dept. of Physics and
Wisconsin IceCube Particle Astrophysics Center, University of
Wisconsin–Madison, Madison, WI 53706, USA  K. D. de Vries  Vrije Universiteit
Brussel (VUB), Dienst ELEM, B-1050 Brussels, Belgium  G. de Wasseige  Vrije
Universiteit Brussel (VUB), Dienst ELEM, B-1050 Brussels, Belgium  M. de With
Institut für Physik, Humboldt-Universität zu Berlin, D-12489 Berlin, Germany
T. DeYoung  Dept. of Physics and Astronomy, Michigan State University, East
Lansing, MI 48824, USA  S. Dharani  III. Physikalisches Institut, RWTH Aachen
University, D-52056 Aachen, Germany  A. Diaz  Dept. of Physics, Massachusetts
Institute of Technology, Cambridge, MA 02139, USA  J. C. Díaz-Vélez  Dept. of
Physics and Wisconsin IceCube Particle Astrophysics Center, University of
Wisconsin–Madison, Madison, WI 53706, USA  H. Dujmovic  Karlsruhe Institute of
Technology, Institute for Astroparticle Physics, D-76021 Karlsruhe, Germany
M. Dunkman  Dept. of Physics, Pennsylvania State University, University Park,
PA 16802, USA  M. A. DuVernois  Dept. of Physics and Wisconsin IceCube
Particle Astrophysics Center, University of Wisconsin–Madison, Madison, WI
53706, USA  E. Dvorak  Physics Department, South Dakota School of Mines and
Technology, Rapid City, SD 57701, USA  T. Ehrhardt  Institute of Physics,
University of Mainz, Staudinger Weg 7, D-55099 Mainz, Germany  P. Eller
Physik-department, Technische Universität München, D-85748 Garching, Germany
R. Engel  Karlsruhe Institute of Technology, Institute for Astroparticle
Physics, D-76021 Karlsruhe, Germany  J. Evans  Dept. of Physics, University of
Maryland, College Park, MD 20742, USA  P. A. Evenson  Bartol Research
Institute and Dept. of Physics and Astronomy, University of Delaware, Newark,
DE 19716, USA  S. Fahey  Dept. of Physics and Wisconsin IceCube Particle
Astrophysics Center, University of Wisconsin–Madison, Madison, WI 53706, USA
A. R. Fazely  Dept. of Physics, Southern University, Baton Rouge, LA 70813,
USA  S. Fiedlschuster  Erlangen Centre for Astroparticle Physics, Friedrich-
Alexander-Universität Erlangen-Nürnberg, D-91058 Erlangen, Germany  A.T.
Fienberg  Dept. of Physics, Pennsylvania State University, University Park, PA
16802, USA  K. Filimonov  Dept. of Physics, University of California,
Berkeley, CA 94720, USA  C. Finley  Oskar Klein Centre and Dept. of Physics,
Stockholm University, SE-10691 Stockholm, Sweden  L. Fischer  DESY, D-15738
Zeuthen, Germany  D. Fox  Dept. of Astronomy and Astrophysics, Pennsylvania
State University, University Park, PA 16802, USA  A. Franckowiak  Fakultät für
Physik & Astronomie, Ruhr-Universität Bochum, D-44780 Bochum, Germany  DESY,
D-15738 Zeuthen, Germany  E. Friedman  Dept. of Physics, University of
Maryland, College Park, MD 20742, USA  A. Fritz  Institute of Physics,
University of Mainz, Staudinger Weg 7, D-55099 Mainz, Germany  P. Fürst  III.
Physikalisches Institut, RWTH Aachen University, D-52056 Aachen, Germany  T.
K. Gaisser  Bartol Research Institute and Dept. of Physics and Astronomy,
University of Delaware, Newark, DE 19716, USA  J. Gallagher  Dept. of
Astronomy, University of Wisconsin–Madison, Madison, WI 53706, USA  E. Ganster
III. Physikalisches Institut, RWTH Aachen University, D-52056 Aachen, Germany
S. Garrappa  DESY, D-15738 Zeuthen, Germany  L. Gerhardt  Lawrence Berkeley
National Laboratory, Berkeley, CA 94720, USA  A. Ghadimi  Dept. of Physics and
Astronomy, University of Alabama, Tuscaloosa, AL 35487, USA  C. Glaser  Dept.
of Physics and Astronomy, Uppsala University, Box 516, S-75120 Uppsala, Sweden
T. Glauch  Physik-department, Technische Universität München, D-85748
Garching, Germany  T. Glüsenkamp  Erlangen Centre for Astroparticle Physics,
Friedrich-Alexander-Universität Erlangen-Nürnberg, D-91058 Erlangen, Germany
A. Goldschmidt  Lawrence Berkeley National Laboratory, Berkeley, CA 94720, USA
J. G. Gonzalez  Bartol Research Institute and Dept. of Physics and Astronomy,
University of Delaware, Newark, DE 19716, USA  S. Goswami  Dept. of Physics
and Astronomy, University of Alabama, Tuscaloosa, AL 35487, USA  D. Grant
Dept. of Physics and Astronomy, Michigan State University, East Lansing, MI
48824, USA  T. Grégoire  Dept. of Physics, Pennsylvania State University,
University Park, PA 16802, USA  Z. Griffith  Dept. of Physics and Wisconsin
IceCube Particle Astrophysics Center, University of Wisconsin–Madison,
Madison, WI 53706, USA  S. Griswold  Dept. of Physics and Astronomy,
University of Rochester, Rochester, NY 14627, USA  M. Gündüz  Fakultät für
Physik & Astronomie, Ruhr-Universität Bochum, D-44780 Bochum, Germany  C.
Haack  Physik-department, Technische Universität München, D-85748 Garching,
Germany  A. Hallgren  Dept. of Physics and Astronomy, Uppsala University, Box
516, S-75120 Uppsala, Sweden  R. Halliday  Dept. of Physics and Astronomy,
Michigan State University, East Lansing, MI 48824, USA  L. Halve  III.
Physikalisches Institut, RWTH Aachen University, D-52056 Aachen, Germany  F.
Halzen  Dept. of Physics and Wisconsin IceCube Particle Astrophysics Center,
University of Wisconsin–Madison, Madison, WI 53706, USA  M. Ha Minh  Physik-
department, Technische Universität München, D-85748 Garching, Germany  K.
Hanson  Dept. of Physics and Wisconsin IceCube Particle Astrophysics Center,
University of Wisconsin–Madison, Madison, WI 53706, USA  J. Hardin  Dept. of
Physics and Wisconsin IceCube Particle Astrophysics Center, University of
Wisconsin–Madison, Madison, WI 53706, USA  A. A. Harnisch  Dept. of Physics
and Astronomy, Michigan State University, East Lansing, MI 48824, USA  A.
Haungs  Karlsruhe Institute of Technology, Institute for Astroparticle
Physics, D-76021 Karlsruhe, Germany  S. Hauser  III. Physikalisches Institut,
RWTH Aachen University, D-52056 Aachen, Germany  D. Hebecker  Institut für
Physik, Humboldt-Universität zu Berlin, D-12489 Berlin, Germany  K. Helbing
Dept. of Physics, University of Wuppertal, D-42119 Wuppertal, Germany  F.
Henningsen  Physik-department, Technische Universität München, D-85748
Garching, Germany  E. C. Hettinger  Dept. of Physics and Astronomy, Michigan
State University, East Lansing, MI 48824, USA  S. Hickford  Dept. of Physics,
University of Wuppertal, D-42119 Wuppertal, Germany  J. Hignight  Dept. of
Physics, University of Alberta, Edmonton, Alberta, Canada T6G 2E1  C. Hill
Dept. of Physics and Institute for Global Prominent Research, Chiba
University, Chiba 263-8522, Japan  G. C. Hill  Department of Physics,
University of Adelaide, Adelaide, 5005, Australia  K. D. Hoffman  Dept. of
Physics, University of Maryland, College Park, MD 20742, USA  R. Hoffmann
Dept. of Physics, University of Wuppertal, D-42119 Wuppertal, Germany  T.
Hoinka  Dept. of Physics, TU Dortmund University, D-44221 Dortmund, Germany
B. Hokanson-Fasig  Dept. of Physics and Wisconsin IceCube Particle
Astrophysics Center, University of Wisconsin–Madison, Madison, WI 53706, USA
K. Hoshina  Dept. of Physics and Wisconsin IceCube Particle Astrophysics
Center, University of Wisconsin–Madison, Madison, WI 53706, USA  F. Huang
Dept. of Physics, Pennsylvania State University, University Park, PA 16802,
USA  M. Huber  Physik-department, Technische Universität München, D-85748
Garching, Germany  T. Huber  Karlsruhe Institute of Technology, Institute for
Astroparticle Physics, D-76021 Karlsruhe, Germany  K. Hultqvist  Oskar Klein
Centre and Dept. of Physics, Stockholm University, SE-10691 Stockholm, Sweden
M. Hünnefeld  Dept. of Physics, TU Dortmund University, D-44221 Dortmund,
Germany  R. Hussain  Dept. of Physics and Wisconsin IceCube Particle
Astrophysics Center, University of Wisconsin–Madison, Madison, WI 53706, USA
S. In  Dept. of Physics, Sungkyunkwan University, Suwon 16419, Korea  N.
Iovine  Université Libre de Bruxelles, Science Faculty CP230, B-1050 Brussels,
Belgium  A. Ishihara  Dept. of Physics and Institute for Global Prominent
Research, Chiba University, Chiba 263-8522, Japan  M. Jansson  Oskar Klein
Centre and Dept. of Physics, Stockholm University, SE-10691 Stockholm, Sweden
G. S. Japaridze  CTSPS, Clark-Atlanta University, Atlanta, GA 30314, USA  M.
Jeong  Dept. of Physics, Sungkyunkwan University, Suwon 16419, Korea  B. J. P.
Jones  Dept. of Physics, University of Texas at Arlington, 502 Yates St.,
Science Hall Rm 108, Box 19059, Arlington, TX 76019, USA  R. Joppe  III.
Physikalisches Institut, RWTH Aachen University, D-52056 Aachen, Germany  D.
Kang  Karlsruhe Institute of Technology, Institute for Astroparticle Physics,
D-76021 Karlsruhe, Germany  W. Kang  Dept. of Physics, Sungkyunkwan
University, Suwon 16419, Korea  X. Kang  Dept. of Physics, Drexel University,
3141 Chestnut Street, Philadelphia, PA 19104, USA  A. Kappes  Institut für
Kernphysik, Westfälische Wilhelms-Universität Münster, D-48149 Münster,
Germany  D. Kappesser  Institute of Physics, University of Mainz, Staudinger
Weg 7, D-55099 Mainz, Germany  T. Karg  DESY, D-15738 Zeuthen, Germany  M.
Karl  Physik-department, Technische Universität München, D-85748 Garching,
Germany  A. Karle  Dept. of Physics and Wisconsin IceCube Particle
Astrophysics Center, University of Wisconsin–Madison, Madison, WI 53706, USA
U. Katz  Erlangen Centre for Astroparticle Physics, Friedrich-Alexander-
Universität Erlangen-Nürnberg, D-91058 Erlangen, Germany  M. Kauer  Dept. of
Physics and Wisconsin IceCube Particle Astrophysics Center, University of
Wisconsin–Madison, Madison, WI 53706, USA  M. Kellermann  III. Physikalisches
Institut, RWTH Aachen University, D-52056 Aachen, Germany  J. L. Kelley  Dept.
of Physics and Wisconsin IceCube Particle Astrophysics Center, University of
Wisconsin–Madison, Madison, WI 53706, USA  A. Kheirandish  Dept. of Physics,
Pennsylvania State University, University Park, PA 16802, USA  J. Kim  Dept.
of Physics, Sungkyunkwan University, Suwon 16419, Korea  K. Kin  Dept. of
Physics and Institute for Global Prominent Research, Chiba University, Chiba
263-8522, Japan  T. Kintscher  DESY, D-15738 Zeuthen, Germany  J. Kiryluk
Dept. of Physics and Astronomy, Stony Brook University, Stony Brook, NY
11794-3800, USA  S. R. Klein  Dept. of Physics, University of California,
Berkeley, CA 94720, USA  Lawrence Berkeley National Laboratory, Berkeley, CA
94720, USA  R. Koirala  Bartol Research Institute and Dept. of Physics and
Astronomy, University of Delaware, Newark, DE 19716, USA  H. Kolanoski
Institut für Physik, Humboldt-Universität zu Berlin, D-12489 Berlin, Germany
L. Köpke  Institute of Physics, University of Mainz, Staudinger Weg 7, D-55099
Mainz, Germany  C. Kopper  Dept. of Physics and Astronomy, Michigan State
University, East Lansing, MI 48824, USA  S. Kopper  Dept. of Physics and
Astronomy, University of Alabama, Tuscaloosa, AL 35487, USA  D. J. Koskinen
Niels Bohr Institute, University of Copenhagen, DK-2100 Copenhagen, Denmark
P. Koundal  Karlsruhe Institute of Technology, Institute for Astroparticle
Physics, D-76021 Karlsruhe, Germany  M. Kovacevich  Dept. of Physics, Drexel
University, 3141 Chestnut Street, Philadelphia, PA 19104, USA  M. Kowalski
Institut für Physik, Humboldt-Universität zu Berlin, D-12489 Berlin, Germany
DESY, D-15738 Zeuthen, Germany  K. Krings  Physik-department, Technische
Universität München, D-85748 Garching, Germany  G. Krückl  Institute of
Physics, University of Mainz, Staudinger Weg 7, D-55099 Mainz, Germany  N.
Kurahashi  Dept. of Physics, Drexel University, 3141 Chestnut Street,
Philadelphia, PA 19104, USA  A. Kyriacou  Department of Physics, University of
Adelaide, Adelaide, 5005, Australia  C. Lagunas Gualda  DESY, D-15738 Zeuthen,
Germany  J. L. Lanfranchi  Dept. of Physics, Pennsylvania State University,
University Park, PA 16802, USA  M. J. Larson  Dept. of Physics, University of
Maryland, College Park, MD 20742, USA  F. Lauber  Dept. of Physics, University
of Wuppertal, D-42119 Wuppertal, Germany  J. P. Lazar  Department of Physics
and Laboratory for Particle Physics and Cosmology, Harvard University,
Cambridge, MA 02138, USA  Dept. of Physics and Wisconsin IceCube Particle
Astrophysics Center, University of Wisconsin–Madison, Madison, WI 53706, USA
K. Leonard  Dept. of Physics and Wisconsin IceCube Particle Astrophysics
Center, University of Wisconsin–Madison, Madison, WI 53706, USA  A.
Leszczyńska  Karlsruhe Institute of Technology, Institute for Astroparticle
Physics, D-76021 Karlsruhe, Germany  Y. Li  Dept. of Physics, Pennsylvania
State University, University Park, PA 16802, USA  Q. R. Liu  Dept. of Physics
and Wisconsin IceCube Particle Astrophysics Center, University of
Wisconsin–Madison, Madison, WI 53706, USA  E. Lohfink  Institute of Physics,
University of Mainz, Staudinger Weg 7, D-55099 Mainz, Germany  C. J. Lozano
Mariscal  Institut für Kernphysik, Westfälische Wilhelms-Universität Münster,
D-48149 Münster, Germany  L. Lu  Dept. of Physics and Institute for Global
Prominent Research, Chiba University, Chiba 263-8522, Japan  F. Lucarelli
Département de physique nucléaire et corpusculaire, Université de Genève,
CH-1211 Genève, Switzerland  A. Ludwig  Dept. of Physics and Astronomy,
Michigan State University, East Lansing, MI 48824, USA  Department of Physics
and Astronomy, UCLA, Los Angeles, CA 90095, USA  W. Luszczak  Dept. of Physics
and Wisconsin IceCube Particle Astrophysics Center, University of
Wisconsin–Madison, Madison, WI 53706, USA  Y. Lyu  Dept. of Physics,
University of California, Berkeley, CA 94720, USA  Lawrence Berkeley National
Laboratory, Berkeley, CA 94720, USA  W. Y. Ma  DESY, D-15738 Zeuthen, Germany
J. Madsen  Dept. of Physics and Wisconsin IceCube Particle Astrophysics
Center, University of Wisconsin–Madison, Madison, WI 53706, USA  K. B. M. Mahn
Dept. of Physics and Astronomy, Michigan State University, East Lansing, MI
48824, USA  Y. Makino  Dept. of Physics and Wisconsin IceCube Particle
Astrophysics Center, University of Wisconsin–Madison, Madison, WI 53706, USA
P. Mallik  III. Physikalisches Institut, RWTH Aachen University, D-52056
Aachen, Germany  S. Mancina  Dept. of Physics and Wisconsin IceCube Particle
Astrophysics Center, University of Wisconsin–Madison, Madison, WI 53706, USA
I. C. Mariş  Université Libre de Bruxelles, Science Faculty CP230, B-1050
Brussels, Belgium  R. Maruyama  Dept. of Physics, Yale University, New Haven,
CT 06520, USA  K. Mase  Dept. of Physics and Institute for Global Prominent
Research, Chiba University, Chiba 263-8522, Japan  F. McNally  Department of
Physics, Mercer University, Macon, GA 31207-0001, USA  K. Meagher  Dept. of
Physics and Wisconsin IceCube Particle Astrophysics Center, University of
Wisconsin–Madison, Madison, WI 53706, USA  A. Medina  Dept. of Physics and
Center for Cosmology and Astro-Particle Physics, Ohio State University,
Columbus, OH 43210, USA  M. Meier  Dept. of Physics and Institute for Global
Prominent Research, Chiba University, Chiba 263-8522, Japan  S. Meighen-Berger
Physik-department, Technische Universität München, D-85748 Garching, Germany
J. Merz  III. Physikalisches Institut, RWTH Aachen University, D-52056 Aachen,
Germany  J. Micallef  Dept. of Physics and Astronomy, Michigan State
University, East Lansing, MI 48824, USA  D. Mockler  Université Libre de
Bruxelles, Science Faculty CP230, B-1050 Brussels, Belgium  G. Momenté
Institute of Physics, University of Mainz, Staudinger Weg 7, D-55099 Mainz,
Germany  T. Montaruli  Département de physique nucléaire et corpusculaire,
Université de Genève, CH-1211 Genève, Switzerland  R. W. Moore  Dept. of
Physics, University of Alberta, Edmonton, Alberta, Canada T6G 2E1  R. Morse
Dept. of Physics and Wisconsin IceCube Particle Astrophysics Center,
University of Wisconsin–Madison, Madison, WI 53706, USA  M. Moulai  Dept. of
Physics, Massachusetts Institute of Technology, Cambridge, MA 02139, USA  R.
Naab  DESY, D-15738 Zeuthen, Germany  R. Nagai  Dept. of Physics and Institute
for Global Prominent Research, Chiba University, Chiba 263-8522, Japan  U.
Naumann  Dept. of Physics, University of Wuppertal, D-42119 Wuppertal, Germany
J. Necker  DESY, D-15738 Zeuthen, Germany  L. V. Nguyễn  Dept. of Physics and
Astronomy, Michigan State University, East Lansing, MI 48824, USA  H.
Niederhausen  Physik-department, Technische Universität München, D-85748
Garching, Germany  M. U. Nisa  Dept. of Physics and Astronomy, Michigan State
University, East Lansing, MI 48824, USA  S. C. Nowicki  Dept. of Physics and
Astronomy, Michigan State University, East Lansing, MI 48824, USA  D. R.
Nygren  Lawrence Berkeley National Laboratory, Berkeley, CA 94720, USA  A.
Obertacke Pollmann  Dept. of Physics, University of Wuppertal, D-42119
Wuppertal, Germany  M. Oehler  Karlsruhe Institute of Technology, Institute
for Astroparticle Physics, D-76021 Karlsruhe, Germany  A. Olivas  Dept. of
Physics, University of Maryland, College Park, MD 20742, USA  E. O’Sullivan
Dept. of Physics and Astronomy, Uppsala University, Box 516, S-75120 Uppsala,
Sweden  H. Pandya  Bartol Research Institute and Dept. of Physics and
Astronomy, University of Delaware, Newark, DE 19716, USA  D. V. Pankova  Dept.
of Physics, Pennsylvania State University, University Park, PA 16802, USA  N.
Park  Dept. of Physics and Wisconsin IceCube Particle Astrophysics Center,
University of Wisconsin–Madison, Madison, WI 53706, USA  G. K. Parker  Dept.
of Physics, University of Texas at Arlington, 502 Yates St., Science Hall Rm
108, Box 19059, Arlington, TX 76019, USA  E. N. Paudel  Bartol Research
Institute and Dept. of Physics and Astronomy, University of Delaware, Newark,
DE 19716, USA  P. Peiffer  Institute of Physics, University of Mainz,
Staudinger Weg 7, D-55099 Mainz, Germany  C. Pérez de los Heros  Dept. of
Physics and Astronomy, Uppsala University, Box 516, S-75120 Uppsala, Sweden
S. Philippen  III. Physikalisches Institut, RWTH Aachen University, D-52056
Aachen, Germany  D. Pieloth  Dept. of Physics, TU Dortmund University, D-44221
Dortmund, Germany  S. Pieper  Dept. of Physics, University of Wuppertal,
D-42119 Wuppertal, Germany  A. Pizzuto  Dept. of Physics and Wisconsin IceCube
Particle Astrophysics Center, University of Wisconsin–Madison, Madison, WI
53706, USA  M. Plum  Department of Physics, Marquette University, Milwaukee,
WI, 53201, USA  Y. Popovych  III. Physikalisches Institut, RWTH Aachen
University, D-52056 Aachen, Germany  A. Porcelli  Dept. of Physics and
Astronomy, University of Gent, B-9000 Gent, Belgium  M. Prado Rodriguez  Dept.
of Physics and Wisconsin IceCube Particle Astrophysics Center, University of
Wisconsin–Madison, Madison, WI 53706, USA  P. B. Price  Dept. of Physics,
University of California, Berkeley, CA 94720, USA  B. Pries  Dept. of Physics
and Astronomy, Michigan State University, East Lansing, MI 48824, USA  G. T.
Przybylski  Lawrence Berkeley National Laboratory, Berkeley, CA 94720, USA  C.
Raab  Université Libre de Bruxelles, Science Faculty CP230, B-1050 Brussels,
Belgium  A. Raissi  Dept. of Physics and Astronomy, University of Canterbury,
Private Bag 4800, Christchurch, New Zealand  M. Rameez  Niels Bohr Institute,
University of Copenhagen, DK-2100 Copenhagen, Denmark  K. Rawlins  Dept. of
Physics and Astronomy, University of Alaska Anchorage, 3211 Providence Dr.,
Anchorage, AK 99508, USA  I. C. Rea  Physik-department, Technische Universität
München, D-85748 Garching, Germany  A. Rehman  Bartol Research Institute and
Dept. of Physics and Astronomy, University of Delaware, Newark, DE 19716, USA
R. Reimann  III. Physikalisches Institut, RWTH Aachen University, D-52056
Aachen, Germany  M. Renschler  Karlsruhe Institute of Technology, Institute
for Astroparticle Physics, D-76021 Karlsruhe, Germany  G. Renzi  Université
Libre de Bruxelles, Science Faculty CP230, B-1050 Brussels, Belgium  E.
Resconi  Physik-department, Technische Universität München, D-85748 Garching,
Germany  S. Reusch  DESY, D-15738 Zeuthen, Germany  W. Rhode  Dept. of
Physics, TU Dortmund University, D-44221 Dortmund, Germany  M. Richman  Dept.
of Physics, Drexel University, 3141 Chestnut Street, Philadelphia, PA 19104,
USA  B. Riedel  Dept. of Physics and Wisconsin IceCube Particle Astrophysics
Center, University of Wisconsin–Madison, Madison, WI 53706, USA  S. Robertson
Dept. of Physics, University of California, Berkeley, CA 94720, USA  Lawrence
Berkeley National Laboratory, Berkeley, CA 94720, USA  G. Roellinghoff  Dept.
of Physics, Sungkyunkwan University, Suwon 16419, Korea  M. Rongen  III.
Physikalisches Institut, RWTH Aachen University, D-52056 Aachen, Germany  C.
Rott  Dept. of Physics, Sungkyunkwan University, Suwon 16419, Korea  T. Ruhe
Dept. of Physics, TU Dortmund University, D-44221 Dortmund, Germany  D.
Ryckbosch  Dept. of Physics and Astronomy, University of Gent, B-9000 Gent,
Belgium  D. Rysewyk Cantu  Dept. of Physics and Astronomy, Michigan State
University, East Lansing, MI 48824, USA  I. Safa  Department of Physics and
Laboratory for Particle Physics and Cosmology, Harvard University, Cambridge,
MA 02138, USA  Dept. of Physics and Wisconsin IceCube Particle Astrophysics
Center, University of Wisconsin–Madison, Madison, WI 53706, USA  S. E. Sanchez
Herrera  Dept. of Physics and Astronomy, Michigan State University, East
Lansing, MI 48824, USA  A. Sandrock  Dept. of Physics, TU Dortmund University,
D-44221 Dortmund, Germany  J. Sandroos  Institute of Physics, University of
Mainz, Staudinger Weg 7, D-55099 Mainz, Germany  M. Santander  Dept. of
Physics and Astronomy, University of Alabama, Tuscaloosa, AL 35487, USA  S.
Sarkar  Dept. of Physics, University of Oxford, Parks Road, Oxford OX1 3PU, UK
S. Sarkar  Dept. of Physics, University of Alberta, Edmonton, Alberta, Canada
T6G 2E1  K. Satalecka  DESY, D-15738 Zeuthen, Germany  M. Scharf  III.
Physikalisches Institut, RWTH Aachen University, D-52056 Aachen, Germany  M.
Schaufel  III. Physikalisches Institut, RWTH Aachen University, D-52056
Aachen, Germany  H. Schieler  Karlsruhe Institute of Technology, Institute for
Astroparticle Physics, D-76021 Karlsruhe, Germany  P. Schlunder  Dept. of
Physics, TU Dortmund University, D-44221 Dortmund, Germany  T. Schmidt  Dept.
of Physics, University of Maryland, College Park, MD 20742, USA  A. Schneider
Dept. of Physics and Wisconsin IceCube Particle Astrophysics Center,
University of Wisconsin–Madison, Madison, WI 53706, USA  J. Schneider
Erlangen Centre for Astroparticle Physics, Friedrich-Alexander-Universität
Erlangen-Nürnberg, D-91058 Erlangen, Germany  F. G. Schröder  Karlsruhe
Institute of Technology, Institute for Astroparticle Physics, D-76021
Karlsruhe, Germany  Bartol Research Institute and Dept. of Physics and
Astronomy, University of Delaware, Newark, DE 19716, USA  L. Schumacher  III.
Physikalisches Institut, RWTH Aachen University, D-52056 Aachen, Germany  S.
Sclafani  Dept. of Physics, Drexel University, 3141 Chestnut Street,
Philadelphia, PA 19104, USA  D. Seckel  Bartol Research Institute and Dept. of
Physics and Astronomy, University of Delaware, Newark, DE 19716, USA  S.
Seunarine  Dept. of Physics, University of Wisconsin, River Falls, WI 54022,
USA  S. Shefali  III. Physikalisches Institut, RWTH Aachen University, D-52056
Aachen, Germany  M. Silva  Dept. of Physics and Wisconsin IceCube Particle
Astrophysics Center, University of Wisconsin–Madison, Madison, WI 53706, USA
B. Smithers  Dept. of Physics, University of Texas at Arlington, 502 Yates
St., Science Hall Rm 108, Box 19059, Arlington, TX 76019, USA  R. Snihur
Dept. of Physics and Wisconsin IceCube Particle Astrophysics Center,
University of Wisconsin–Madison, Madison, WI 53706, USA  J. Soedingrekso
Dept. of Physics, TU Dortmund University, D-44221 Dortmund, Germany  D. Soldin
Bartol Research Institute and Dept. of Physics and Astronomy, University of
Delaware, Newark, DE 19716, USA  G. M. Spiczak  Dept. of Physics, University
of Wisconsin, River Falls, WI 54022, USA  C. Spiering  DESY, D-15738 Zeuthen,
Germany  J. Stachurska  DESY, D-15738 Zeuthen, Germany  M. Stamatikos  Dept.
of Physics and Center for Cosmology and Astro-Particle Physics, Ohio State
University, Columbus, OH 43210, USA  T. Stanev  Bartol Research Institute and
Dept. of Physics and Astronomy, University of Delaware, Newark, DE 19716, USA
R. Stein  DESY, D-15738 Zeuthen, Germany  J. Stettner  III. Physikalisches
Institut, RWTH Aachen University, D-52056 Aachen, Germany  A. Steuer
Institute of Physics, University of Mainz, Staudinger Weg 7, D-55099 Mainz,
Germany  T. Stezelberger  Lawrence Berkeley National Laboratory, Berkeley, CA
94720, USA  R. G. Stokstad  Lawrence Berkeley National Laboratory, Berkeley,
CA 94720, USA  T. Stuttard  Niels Bohr Institute, University of Copenhagen,
DK-2100 Copenhagen, Denmark  G. W. Sullivan  Dept. of Physics, University of
Maryland, College Park, MD 20742, USA  I. Taboada  School of Physics and
Center for Relativistic Astrophysics, Georgia Institute of Technology,
Atlanta, GA 30332, USA  F. Tenholt  Fakultät für Physik & Astronomie, Ruhr-
Universität Bochum, D-44780 Bochum, Germany  S. Ter-Antonyan  Dept. of
Physics, Southern University, Baton Rouge, LA 70813, USA  S. Tilav  Bartol
Research Institute and Dept. of Physics and Astronomy, University of Delaware,
Newark, DE 19716, USA  F. Tischbein  III. Physikalisches Institut, RWTH Aachen
University, D-52056 Aachen, Germany  K. Tollefson  Dept. of Physics and
Astronomy, Michigan State University, East Lansing, MI 48824, USA  L.
Tomankova  Fakultät für Physik & Astronomie, Ruhr-Universität Bochum, D-44780
Bochum, Germany  C. Tönnis  Institute of Basic Science, Sungkyunkwan
University, Suwon 16419, Korea  S. Toscano  Université Libre de Bruxelles,
Science Faculty CP230, B-1050 Brussels, Belgium  D. Tosi  Dept. of Physics and
Wisconsin IceCube Particle Astrophysics Center, University of
Wisconsin–Madison, Madison, WI 53706, USA  A. Trettin  DESY, D-15738 Zeuthen,
Germany  M. Tselengidou  Erlangen Centre for Astroparticle Physics, Friedrich-
Alexander-Universität Erlangen-Nürnberg, D-91058 Erlangen, Germany  C. F. Tung
School of Physics and Center for Relativistic Astrophysics, Georgia Institute
of Technology, Atlanta, GA 30332, USA  A. Turcati  Physik-department,
Technische Universität München, D-85748 Garching, Germany  R. Turcotte
Karlsruhe Institute of Technology, Institute for Astroparticle Physics,
D-76021 Karlsruhe, Germany  C. F. Turley  Dept. of Physics, Pennsylvania State
University, University Park, PA 16802, USA  J. P. Twagirayezu  Dept. of
Physics and Astronomy, Michigan State University, East Lansing, MI 48824, USA
B. Ty  Dept. of Physics and Wisconsin IceCube Particle Astrophysics Center,
University of Wisconsin–Madison, Madison, WI 53706, USA  M. A. Unland
Elorrieta  Institut für Kernphysik, Westfälische Wilhelms-Universität Münster,
D-48149 Münster, Germany  J. Vandenbroucke  Dept. of Physics and Wisconsin
IceCube Particle Astrophysics Center, University of Wisconsin–Madison,
Madison, WI 53706, USA  D. van Eijk  Dept. of Physics and Wisconsin IceCube
Particle Astrophysics Center, University of Wisconsin–Madison, Madison, WI
53706, USA  N. van Eijndhoven  Vrije Universiteit Brussel (VUB), Dienst ELEM,
B-1050 Brussels, Belgium  D. Vannerom  Dept. of Physics, Massachusetts
Institute of Technology, Cambridge, MA 02139, USA  J. van Santen  DESY,
D-15738 Zeuthen, Germany  S. Verpoest  Dept. of Physics and Astronomy,
University of Gent, B-9000 Gent, Belgium  M. Vraeghe  Dept. of Physics and
Astronomy, University of Gent, B-9000 Gent, Belgium  C. Walck  Oskar Klein
Centre and Dept. of Physics, Stockholm University, SE-10691 Stockholm, Sweden
A. Wallace  Department of Physics, University of Adelaide, Adelaide, 5005,
Australia  T. B. Watson  Dept. of Physics, University of Texas at Arlington,
502 Yates St., Science Hall Rm 108, Box 19059, Arlington, TX 76019, USA  C.
Weaver  Dept. of Physics and Astronomy, Michigan State University, East
Lansing, MI 48824, USA  A. Weindl  Karlsruhe Institute of Technology,
Institute for Astroparticle Physics, D-76021 Karlsruhe, Germany  M. J. Weiss
Dept. of Physics, Pennsylvania State University, University Park, PA 16802,
USA  J. Weldert  Institute of Physics, University of Mainz, Staudinger Weg 7,
D-55099 Mainz, Germany  C. Wendt  Dept. of Physics and Wisconsin IceCube
Particle Astrophysics Center, University of Wisconsin–Madison, Madison, WI
53706, USA  J. Werthebach  Dept. of Physics, TU Dortmund University, D-44221
Dortmund, Germany  M. Weyrauch  Karlsruhe Institute of Technology, Institute
for Astroparticle Physics, D-76021 Karlsruhe, Germany  B. J. Whelan
Department of Physics, University of Adelaide, Adelaide, 5005, Australia  N.
Whitehorn  Dept. of Physics and Astronomy, Michigan State University, East
Lansing, MI 48824, USA  Department of Physics and Astronomy, UCLA, Los
Angeles, CA 90095, USA  K. Wiebe  Institute of Physics, University of Mainz,
Staudinger Weg 7, D-55099 Mainz, Germany  C. H. Wiebusch  III. Physikalisches
Institut, RWTH Aachen University, D-52056 Aachen, Germany  D. R. Williams
Dept. of Physics and Astronomy, University of Alabama, Tuscaloosa, AL 35487,
USA  M. Wolf  Physik-department, Technische Universität München, D-85748
Garching, Germany  K. Woschnagg  Dept. of Physics, University of California,
Berkeley, CA 94720, USA  G. Wrede  Erlangen Centre for Astroparticle Physics,
Friedrich-Alexander-Universität Erlangen-Nürnberg, D-91058 Erlangen, Germany
J. Wulff  Fakultät für Physik & Astronomie, Ruhr-Universität Bochum, D-44780
Bochum, Germany  X. W. Xu  Dept. of Physics, Southern University, Baton Rouge,
LA 70813, USA  Y. Xu  Dept. of Physics and Astronomy, Stony Brook University,
Stony Brook, NY 11794-3800, USA  J. P. Yanez  Dept. of Physics, University of
Alberta, Edmonton, Alberta, Canada T6G 2E1  S. Yoshida  Dept. of Physics and
Institute for Global Prominent Research, Chiba University, Chiba 263-8522,
Japan  T. Yuan  Dept. of Physics and Wisconsin IceCube Particle Astrophysics
Center, University of Wisconsin–Madison, Madison, WI 53706, USA  Z. Zhang
Dept. of Physics and Astronomy, Stony Brook University, Stony Brook, NY
11794-3800, USA

(August 27, 2024)

###### Abstract

High-energy neutrinos are unique messengers of the high-energy universe,
tracing the processes of cosmic-ray acceleration. This paper presents analyses
focusing on time-dependent neutrino point-source searches. A scan of the whole
sky, making no prior assumption about source candidates, is performed, looking
for a space and time clustering of high-energy neutrinos in data collected by
the IceCube Neutrino Observatory between 2012 and 2017. No statistically
significant evidence for a time-dependent neutrino signal is found with this
search during this period since all results are consistent with the background
expectation. Within this study period, the blazar 3C 279, showed strong
variability, inducing a very prominent gamma-ray flare observed in 2015 June.
This event motivated a dedicated study of the blazar, which consists of
searching for a time-dependent neutrino signal correlated with the gamma- ray
emission. No evidence for a time-dependent signal is found. Hence, an upper
limit on the neutrino fluence is derived, allowing us to constrain a hadronic
emission model.

††thanks: also at Università di Padova, I-35131 Padova, Italy††thanks: also at
National Research Nuclear University, Moscow Engineering Physics Institute
(MEPhI), Moscow 115409, Russia††thanks: also at Earthquake Research Institute,
University of Tokyo, Bunkyo, Tokyo 113-0032, Japan††thanks: also at National
Research Nuclear University, Moscow Engineering Physics Institute (MEPhI),
Moscow 115409, Russia

##  1 Introduction

The cosmic-ray energy spectrum is observed from the sub-GeV region to ultra
high energies in the $10^{20}$ eV range. While the lowest-energy cosmic rays
are thought to originate from Galactic supernova explosions (Baade & Zwicky,
1934), extragalactic objects, such as gamma-ray bursts and active galactic
nuclei (Waxman & Bahcall, 1999; Mannheim et al., 2001), are candidates to
explain the highest energy part of the spectrum. However, none of these
hypotheses has been experimentally verified and the origin of cosmic rays
remains mostly unknown.

Cosmic rays themselves don’t point back at their exact origin because they are
deflected by magnetic fields on their way to Earth. It is however possible to
get this information through some of the secondary particles cosmic rays
produce in the vicinity of their sources. Indeed, cosmic rays interact with
gas and radiation near their accelerating sites, leading to the production of
charged and neutral pions, which in turn produce neutrinos and photons. Those
two particles are indirect messengers that have the potential to point back at
cosmic ray sources, as they are both neutral and thus not sensitive to
magnetic fields. However, photon detection alone is delicate; many different
phenomena can be responsible for their emission and the photons detected at
Earth or by satellites are not necessarily the same as the ones that were
produced by cosmic-ray interaction. Photons are also produced in leptonic
processes such as bremsstrahlung, inverse Compton scattering and synchrotron
radiation, which would be overlaid to the photons produced in hadronic
processes, alongside the neutrinos. Neutrinos, on the other hand, can only
have hadronic origin. They are powerful messengers since they pass through the
universe basically undisturbed. At the same time, this implies a challenge for
their detection. The observation of both neutrinos and gamma rays from a same
source is a smoking gun to trace cosmic-ray sources.

The IceCube detector has been able to address the neutrino challenge and has
reported the detection of a cosmic neutrino flux at the level of few events
per year above $\sim 50$ TeV on top of the softer atmospheric neutrino and
muon background (Aartsen et al., 2013a, 2014b, 2015a). Even if the sources of
those high-energy neutrinos are still unknown, some evidence for possible
candidates started to show up in recent observations. In 2017, a very high-
energy neutrino event, IceCube-170922A, was detected. It triggered an alert
and a follow-up in the event’s direction and in various photon bands was
realized by several independent experiments. Evidence for a blazar in a
flaring state, TXS 0506+056, consistent with the direction of the neutrino
event, was first claimed by the _Fermi_ gamma-ray satellite, then confirmed by
the MAGIC telescopes and also other high-energy gamma-ray experiments (Aartsen
et al., 2018a; Abeysekara et al., 2018). The analysis reported a coincidence
between IceCube-170922A and the flare of TXS 0506+056 which was inconsistent
with a background fluctuation at the level of 3$\sigma$. In addition to that,
a time-dependent search, similar to what is described in this paper, was
conducted on 9.5 years of archival data and revealed a 3.5$\sigma$ evidence
for neutrino emission in the direction of this blazar during a $\sim 110$-day
period in 2014-2015 (Aartsen et al., 2018b), this time not accompanied by an
observed blazar flare. Those observations combined together make TXS 0506+056
the first blazar associated with a significant neutrino excess. However, only
$\sim 1\%$ of the diffuse flux previously observed in IceCube can be
attributed to this single source (Aartsen et al., 2018).

In 2019, a search for astrophysical neutrino point-like sources was conducted
on 10 years of IceCube data. Several types of analysis were realized. Very
interestingly, the scan of the whole sky, using neutrino-data only, revealed a
clustering of high-energy neutrinos, exceeding the background expectation at
the level of 2.9$\sigma$, at a location in the sky coinciding with the Seyfert
II galaxy NGC 1068 (Aartsen et al., 2019). In addition to the all-sky
analysis, a catalog of sources observed in gamma rays was constructed. All
sources considered together, the catalog of the Northern hemisphere was found
to be inconsistent with a background-only hypothesis at 3.3$\sigma$. This
result is mostly due to excesses found in the neutrino data in the directions
of the Seyfert II galaxy NGC 1068, the blazar TXS 0506+056, and the BL Lacs
PKS 1424+240 and GB6 J1542+6129. Those results, together with flaring
observations from the direction of TXS 0506+056, motivate searches for
neutrino sources whose emission is time-dependent, which can provide
complementary information to the time-integrated analyses.

In this paper we illustrate a dedicated search for time-dependent signals
performed on IceCube data from 2012 to 2017, which consists of looking for a
space and time clustering of high-energy neutrinos above 1 TeV, scanning the
whole sky. It updates the previous search which used IceCube data from 2008 to
2012 (Aartsen et al., 2015b). Time-dependent studies are relevant since, for
flares below about 100 days, they have a better discovery potential than time-
integrated searches (Aartsen et al., 2015b).

One time-variable source of special interest is the blazar 3C 279, a
frequently studied flat spectrum radio quasar (FSRQ) at redshift $z=0.536$. It
has been observed since the end of the 1980s in radio (Aller et al., 1987),
optical and infrared (Kidger et al., 1990) and X-ray bands (Makino et al.,
1989) and the first gamma-ray observation was achieved in 1991 by the EGRET
experiment (Hartman et al., 1992; Maraschi et al., 1992). More recently, the
Fermi-Large Area Telescope (LAT) detected two prominent gamma-ray flares, in
December 2013 (Hayashida et al., 2015) and on 2015 June 16, the latter being
exceptionally bright (Cutini, 2015; Hayashida et al., 2015), thus making this
blazar one of the brightest objects ever observed at such high energies and
such distances. For one day, the Fermi-LAT experiment detected a flux
exceeding the steady flux of the source by more than forty times. This is the
historically highest gamma-ray luminosity observed from 3C 279, including also
past EGRET observations, with a $\gamma$ ray isotropic luminosity reaching
$\sim 10^{49}$ erg s-1. Moreover, a minute-timescale variability of the blazar
is reported (Ackermann et al., 2016), with the flux doubling in less than 10
minutes, which is a very rare event. This allows us to explore compatibility
of observations with purely leptonic standard models of FSRQs, in which gamma
rays are produced by external radiation comptonization (ERC) (Sikora et al.,
2009) or hadronic models. In the ERC model, depending on assumptions, a high
Lorentz factor ($>50$) and extremely low jet magnetization or a Lorentz factor
of 120 are required (Ackermann et al., 2016). An alternative leptonic model
would imply a magnetically dominated jet still with a high Lorentz factor of
about 25 (Ackermann et al., 2016). In this paper, we focus on hadronic models,
which, as explained above, foresee interactions of protons with ordinary
matter or radiation. In particular, we constrain the model in Halzen &
Kheirandish (2016). The analysis of IceCube data, driven by the Fermi-LAT
gamma-ray data, gives an opportunity to test this model for the 2015 flare of
3C 279.

##  2 IceCube detector and data sample

The IceCube detector is a cubic kilometer volume of instrumented ice located
at the geographic South Pole. Its construction was completed in the austral
summer 2010-2011. The detector consists of 86 strings, each holding 50 digital
optical modules (DOMs) deployed at a depth between 1450 m and 2450 m below the
ice surface. The DOMs are spaced vertically by 17 m and each one hosts a
10-inch photomultiplier tube (Abbasi et al., 2010) and associated electronics
(Abbasi et al., 2009) protected from the high pressure by a glass sphere. The
horizontal separation between strings is 125 m. The detection is indirect,
i.e. neutrinos interact with the Antarctic ice and produce secondary charged
particles such as muons or electrons. Photomultiplier tubes (PMTs) in the DOMs
observe Cherenkov radiation from those charged particles. The PMT signals are
digitized in the DOMs, and transmitted to the surface.

Muon neutrinos can undergo charged-current interactions in the vicinity or
inside the instrumented region, resulting in muon tracks. Cascades originate
from charged-current interactions of $\nu_{e}$ and $\nu_{\tau}$ and from
neutral-current interactions of all neutrino flavours. Track-like events have
an angular resolution typically $\leq 0.8^{\circ}{\textdegree}$ at $\sim$ TeV
energies and poor energy resolution of the order of a factor of two, while
cascade events have about 15% deposited energy resolution, but only
10${}^{\circ}{\textdegree}$ angular resolution above some tens of TeV (Aartsen
et al., 2014a). The analyses reported in this paper rely on good pointing
capabilities and therefore uses a sample of muon-track events. Neutrino event
candidates arriving from the Northern hemisphere (up-going events) are mostly
composed of mis-reconstructed down-going muon events and of atmospheric
neutrinos with energies above about 100 GeV. The latter constitute the
dominant background in this hemisphere. The Southern hemisphere is dominated
by down-going atmospheric muons. Therefore a higher energy threshold is
applied to reduce them (Aartsen et al., 2017).

The event selections used in the time-dependent analysis are different for the
first 3 years and the last 2.5 years of data. Therefore, the two data sets are
treated independently and the analysis is performed separately on each of
them. Both data sets were recorded with the full configuration of IceCube. The
all-sky scan uses a sample of about $3.5\times 10^{5}$ good quality tracks
(“through-going tracks”) in the Southern and the Northern hemispheres
collected from 2012 May to 2015 May. For a detailed description of the event
sample, see Aartsen et al. (2014c). To this sample, also the Medium Energy
Starting Events (MESE) lower-energy sample is added (Aartsen et al., 2016).
The MESE down-going sample is selected by eliminating tracks, mostly due to
atmospheric muons, starting outside a fiducial volume inside the instrumented
region. In this way, it is possible to select neutrino events with their
vertex in the fiducial region.

From 2015 April to 2017 November a slightly different selection of muon tracks
is used: the real-time event selection developed for the gamma-ray follow-up
(GFU) program (Aartsen et al., 2017). This sample includes $5.7\times 10^{5}$
tracks.

For the analysis of the blazar 3C 279, we use a subsample of 11 days of the
through-going tracks and the MESE sample, centered around the bright flare of
the blazar, which happened on 2015 June 16. Given that the data selection is
the same, the background probability functions (see Sec. 3.2) for the blazar
analysis were built based on the full period of data between 2012 and 2015.
All samples are summarized in Tab. 1.

Table 1: Summary of the data used in the reported analyses. Each line corresponds to one of the analysis, with the columns giving the specific data selection used, the number of tracks included, the start and end dates of the data and the livetime of the data. Analysis | Number through-going | Number MESE | Number GFU | Start day | End day | Lifetime
---|---|---|---|---|---|---
tracks | tracks | tracks |  |  | (days)
All-sky scan I | 338588 | 603 | - | 15.05.2012 | 18.05.2015 | 1057.54
All-sky scan II | - | - | 571595 | 24.04.2015 | 01.11.2017 | 886.90
3C 279 flare analysis | 3429 | 6 | - | 11.06.2015 | 22.06.2015 | 12.04

The analysis performance strongly depends on the pointing precision and the
effective area, which are described in Abbasi et al. (2011b). The pointing
accuracy is estimated through the median of the distribution of the angle
between the true neutrino direction and the reconstructed muon obtained from
Monte Carlo simulations as a function of energy. Fig. 1 shows this angle for
through-going tracks in both the Southern (green) and the Northern (dashed
blue) sky, as well as for the declination band of 1${}^{\circ}{\textdegree}$
around the blazar 3C 279 (dashed green line). Above 10 TeV, the resolution is
below 0.5${}^{\circ}{\textdegree}$. The MESE angular resolution is shown in
red. It is worse than for the through-going tracks due to the fact that events
starting inside the detector have a shorter lever arm.

Figure 1: Median angular resolution (defined as the median angle between the
reconstructed muon track and the parent neutrino direction from simulation) as
a function of neutrino energy for the through-going muon tracks data set shown
for Northern declinations (dashed blue line), for Southern declinations (solid
green line), for a declination band of 1∘ around 3C 279 declination (dashed
green line) and for the starting muon tracks (MESE) data set (dashed red
line).

The angular resolution of the GFU data set is very similar to the through-
going tracks and is shown in Aartsen et al. (2017). The direction of the
tracks is calculated through an iterative maximum likelihood method. The
uncertainty of the reconstructed direction is estimated by the 1$\sigma$
contour of the likelihood space around the minimum, which is estimated by a
method fitting a two-dimensional parabola, called “paraboloid”, to the
likelihood landscape (Neunhoffer, 2006). Fig. 2 shows the effective area for
the through-going and the MESE selections in the Southern hemisphere (left)
and in the Northern hemisphere (right). The effective area is optimal at the
location of 3C 279 (green line), since the source is very close to the horizon
where the Earth absorption of high-energy neutrinos is negligible. The
effective area for the GFU sample is comparable to that of the through-going
tracks, as shown in Fig. 3 in Aartsen et al. (2017).

Figure 2: IceCube effective area as a function of neutrino energy for the
through-going muon and starting muon (MESE) tracks data sets in the Southern
hemisphere (left) and for the through-going muon tracks data set in the
Northern hemisphere (right). The effective area is averaged over the solid
angle in each declination range.

##  3 Analysis method

The analysis is based on a standard point-source unbinned likelihood method
which compares two hypotheses (Braun et al., 2008, 2010a; Aartsen et al.,
2015b):

  * •

$\mathcal{H}_{0}$, the null hypothesis, which assumes that all events in the
data set are due to an isotropic background.

  * •

$\mathcal{H}_{1}$, which assumes that measured data are the result of the
above described background and in addition a point-source astrophysical
neutrino signal following a $\frac{dN}{dE}\propto E^{-\gamma}$ spectrum.

To quantify the probability that the data is not compatible with the null
hypothesis, a test statistic is defined as:

$TS=-2\log\frac{P(Data|\mathcal{H}_{0})}{P(Data|\mathcal{H}_{1})}.$ (1)

A larger TS value indicates a smaller compatibility with background. The
probability of observing the data given a certain hypothesis, as written in
the TS definition, is given by a likelihood function. The likelihood function
contains parameters that are fitted in the analysis and is defined as:

$\mathcal{L}(\vec{x}_{s},n_{s},\gamma,...)=\prod_{i=0}^{N}(\frac{n_{s}}{N}S_{i}+(1-\frac{n_{s}}{N})B_{i})$
(2)

where $i$ runs over the number of events $N$, $\vec{x}_{s}$ is the source
position, $n_{s}$ is the number of signal events, $\gamma$ is the source
spectral index and $S_{i}$ and $B_{i}$ are respectively the signal and the
background probability density functions (PDFs).

The signal PDF is composed of a spatial, energy and time PDF

$S_{i}=P_{i}^{sig}(\sigma_{i},\vec{x}_{i}|\vec{x}_{s})\cdot\epsilon_{i}^{sig}(E_{i},\delta_{i}|\gamma)\cdot
T_{i}^{sig},$ (3)

where $P_{i}^{sig}$ is the spatial PDF and $\epsilon_{i}^{sig}$ is the energy
PDF. They are described in Aartsen et al. (2013b). The time PDF $T_{i}^{sig}$
is specific to each analysis and will be described in the corresponding
sections. The background PDF

$B_{i}=P_{i}^{bkg}(\delta_{i})\cdot\epsilon_{i}^{bkg}(E_{i},\delta_{i})\cdot
T_{i}^{bkg}$ (4)

has the same structure as the signal PDF and is decribed in Aartsen et al.
(2013b).

The background spatial PDF $P_{i}^{bkg}(\delta_{i})$ gives the density of
atmospheric neutrinos and muons with respect to the declination $\delta_{i}$
of the event $i$. It is uniform in right ascension when we consider data over
a sufficiently long period. For short time scales, of the order of less than a
day, a dependency in right ascension appears. This is caused by the fact that
incoming neutrinos aligned with the strings of the detector are better
reconstructed. This effect fades away with Earth rotation. In order to treat
correctly short time scales, the right ascension-independent PDF is multiplied
by a local coordinate distribution, $P_{i}^{bkg}(\phi_{i},cos\theta_{i})$,
which depends on both the zenith $\theta$ and the azimuth $\phi$ angle for
each event $i$ (Christov, 2016). It is to be noticed that at the South Pole
the relation between the zenith $\theta_{i}$ and the declination $\delta_{i}$
is largely simplified to $\delta_{i}=-90^{\circ}+\theta_{i}$. This is
important because it means that the background variation at the local detector
level (zenith) is equivalent to its variation in equatorial coordinates
(declination).

The energy PDF gives the probability of finding an event with measured energy
$E_{i}$ coming from the atmospheric background at the declination of the event
$\delta_{i}$. $E_{i}$ is an energy proxy of the true neutrino energy based on
the visible muon energy in the detector.

Finally, the time-dependent term of the background PDF is taken to be constant
for the background even though some seasonal variations are observed in the
atmospheric event rates due to changes of the atmosphere density (Abbasi et
al., 2011a). These variations are at the level of $\pm 15\%$ of the rate of
down-going muons, but are much reduced for up-going neutrinos coming from all
latitudes across the Earth.

###  3.1 Time PDF of the all-sky scans

The time-dependent term, $T_{i}^{sig}$ is defined by a Gaussian function, with
width $\sigma_{T}$ and mean $T_{0}$:

$T_{i}^{sig}=\frac{1}{\sqrt{2\pi}\sigma_{T}}e^{\left(-\frac{(t_{i}-T_{0})^{2}}{2\sigma^{2}_{T}}\right)},$
(5)

where $t_{i}$ is the arrival time of the $i^{th}$ event. We tested also step
functions to represent a flare, but the results do not change in a significant
way.

In order to avoid an undesired bias of the fit towards short flares in a
specific time period, a penalizing term $T/\sqrt{2\pi}\sigma_{T}$ is added to
the original test statistics, as explained in Braun et al. (2010b):

$TS=-2\log\left[\frac{T}{\sqrt{2\pi}\hat{\sigma}_{T}}\times\frac{\mathcal{L}(n_{s}=0)}{\mathcal{L}(\hat{n}_{s},\hat{\gamma}_{s},\hat{\sigma}_{T},\hat{T}_{0})}\right]$
(6)

where $\hat{n}_{s}$, $\hat{\gamma}_{s}$, $\hat{\sigma}_{T}$, $\hat{T}_{0}$ are
the best-fit values of the parameters defined above.

The all-sky scan is realized by creating a $0.1^{\circ}{}\times 0.1^{\circ}{}$
grid covering the whole sky, for declinations between $-85^{\circ}{}$ to
$+85^{\circ}{}$ (not enough statistics are collected at the poles to apply the
analysis there) and by fitting the free parameters in order to maximize the
likelihood at each point. This results in a TS value at each point of the sky
grid.

This analysis is performed to determine the hottest spots in the Northern and
in the Southern sky. In order to calculate the post trial values of the TS for
the hottest spots, we need to account for all the directions looked at.
Because the sample is background-dominated, we use ‘pseudo-experiments’
(trials) containing only background created by assigning a random location in
the sky (right ascension) to each event (Aartsen et al., 2015b). By applying
this procedure, which preserves the distributions in detector
coordinates111This is because the distribution of events is expected to be
flat in right ascension due to the continuous flux of atmospheric neutrinos
and muons, the Earth rotation and the fact that the acquisition is continuous
and has no stop at a fixed time every day., we make sure that no real signal,
that could potentially be contained in the sample, remains in the trial
sample.

The performance of the analysis can be estimated in terms of the sensitivity,
defined as the average number of signal events ($n_{s}$) required so that 90%
of the generated ‘equivalent’ experiments have a TS greater than 50% of the
background trials (i.e. where no signal events are injected on top of the
background events), and in terms of the discovery potential, defined as the
$n_{s}$ required so that 50% of the trials have a TS greater than $5\sigma$ of
the background distribution, i.e. a $p$-value of $3\times 10^{-7}$. The
average number of events observed from a source is directly related to its
flux. The usual way of representing it in time-dependent analyses is through
the time-integrated flux or through the fluence, which is the energy-flux
integrated over the time of the selected flare and over the energy interval,
limited to the 5% and the 95% energy percentiles of the event sample (Aartsen
et al., 2015b). Sensitivity and discovery potential in terms of $n_{s}$ and
time-integrated flux are shown in Figs. 3 and 4 as a function of the logarithm
of the duration of the flare for the periods from 2012 to 2015 (IC86 II-IV)
and from 2015 to 2017 (IC86 V-VII), respectively.

Figure 3: The 5$\sigma$ discovery potential (solid black line) and the
sensitivity (dashed blue line) for IC86 II-IV shown in terms of the mean
number of signal events ($n_{s}$) (left) and in terms of the time-integrated
flux (right) for a fixed source in the Northern hemisphere at +16∘ in
declination (top) and in the Southern hemisphere at -16∘ (bottom) with an $\rm
E^{-2}$ spectrum.

Figure 4: The 5$\sigma$ discovery potential (solid black line) and the
sensitivity (dashed blue line) for IC86 V-VII shown in terms of the mean
number of signal events ($n_{s}$) (left) and in terms of the time-integrated
flux (right) for a fixed source in the Northern hemisphere at +16∘ in
declination (top) and in the Southern hemisphere at -16∘ (bottom) with an $\rm
E^{-2}$ spectrum.

###  3.2 Time PDF of 3C 279 flare analysis

The 3C 279 flare analysis is a triggered time-dependent point-source analysis,
i.e. its search time window is determined by the flaring behavior of the
source in gamma rays. To build such an analysis, the gamma-ray information is
combined together with the neutrino information.

The gamma-ray emission of 3C 279 is recorded by Fermi-LAT and its light curve,
shown in Fig. 5, is produced through an aperture photometry analysis222Because
of its fast execution and simplicity, this analysis method was preferred to a
full-likelihood approach, despite the better flux precision of the latter, as
the resulting light curve is only used in the time-dependent analysis for the
variability of its relative flux (see Sec. 3.2). using a one-day binning. With
the help of the analysis tools provided by the Fermi-LAT collaboration (Fermi
Science Tools v10r0p5
package333https://fermi.gsfc.nasa.gov/ssc/data/analysis/documentation/), open
access photometric data from Fermi-LAT are downloaded. We use photons of the
P8R3$\\_$SOURCE class with front and back conversions (Atwood et al., 2013).
Those photons are then selected within $2^{\circ}{}$ from the source, in order
to further reduce the background. Photon events with zenith angles greater
than $90^{\circ}{}$ are excluded to avoid contamination due to the Earth’s
albedo. The photon energy range goes from 100 MeV to 500 GeV as recommended by
the Fermi-LAT collaboration.

Figure 5: Integral photon flux above 100 MeV of the 3C 279 blazar with one-day
binning, produced using aperture photometry. The data come from Fermi-LAT.

After the light curve is created, it is de-noised using the Bayesian block
method (Scargle et al., 2013; Resconi et al., 2009). It allows to remove the
non-representative fluctuations of the emission and to keep only the main
features of the light curve. The light curve is modeled into blocks, each
meant to represent a Poisson distribution with a constant mean, extending for
a certain duration. The parameter of the Bayesian blocks, called $F_{B}$, was
set to 5, following a previous study on similar IceCube data (Aartsen et al.,
2015b). A representation of a light curve turned into Bayesian blocks can be
seen in Fig. 6 (a).

The gamma-ray and neutrinos data are analyzed over a period of 11 days, from
2015 June 11 to 2015 June 22, which is chosen to isolate the bright flare and
whose exact duration was selected based on a series of tests, aiming at
maximizing the 5$\sigma$ discovery potential (50% C.L.).

The likelihood function of this analysis follows the general form defined in
Eq. 2. The background PDF is described by Eq. 4. The signal spatial and energy
PDFs are defined in Eq. 3, while the signal time PDF is specific to the
triggered analysis. It depends on two parameters, fit in the likelihood
maximization: the time lag, $D_{t}$, and the threshold, $f_{th}$.

The time lag describes a shift of the entire light curve in time in the range
of plus or minus half a day. This tolerance accounts for binning effects,
when, for example, a photon flare is spread between contiguous one-day bins
and not fully contained within them. While this is relevant for a light curve
containing a single flare, such a binning effect would be averaged out when
dealing with multiple flares.

If we assume that the gamma rays recorded in the light curve are produced via
hadronic interactions of cosmic rays, a higher astrophysical neutrino flux is
expected where a higher gamma-ray flux is detected. However, the neutrino
background should stay constant. This provides an opportunity to restrict the
search for astrophysical neutrinos to the periods of enhanced gamma-ray
activity, thus maximizing the signal while reducing the background. The
neutrino signal enhancement might be even larger during flares, since in many
models of neutrino emission, the neutrino-production efficiency is actually
doubly enhanced during flares, due to the fact that both the proton injection
and the target photon field are expected to be enhanced at the same time
(Oikonomou et al., 2019).

The flux level at which we consider the object to be in a flaring state is not
well defined. The threshold, which is a parameter of the fit, determines where
the source is considered in flaring state since it results from the likelihood
method optimisation of the signal over background. The construction of the
signal time PDF from the variation of the threshold is illustrated by Fig. 6.
Below the threshold, the time PDF is defined as zero. Above the threshold, the
time PDF is defined by the area of the light curve normalized to one, as shown
in Fig. 6 (b). The value of the threshold is varied during the likelihood
maximization.

Figure 6: (a) The threshold (red) is varied within the flux range defined by
the denoised gamma-ray light curve (blue). It defines a region where the
source denoised gamma-ray lightcurve (blue) indicates a high-state. (b) The
time PDF is constructed from the light curve and the value of the threshold.

The test statistic is defined as

$TS=-2\log\left[\frac{\mathcal{L}(n_{s}=0)}{\mathcal{L}(\hat{n}_{s},\hat{\gamma}_{s},\hat{D}_{t},\hat{f}_{th})}\right]$
(7)

with $\hat{n}_{s}$, $\hat{\gamma}_{s}$, $\hat{D}_{t}$, $\hat{f}_{th}$ the
best-fit values for the number of signal events, the spectral index, the time
lag and the threshold of the time PDF, respectively. Notice that in the fit
the parameter $\gamma_{s}$ is allowed to vary between 1 and 4.

The $5\sigma$ discovery potential and the sensitivity of this analysis, shown
in Fig. 7, are functions of the value of the threshold, $f_{th}$, given in
terms of flux. The discovery potential and the sensitivity are largely
insensitive to the threshold, even though there is a small tendency for them
to improve with larger threshold. The reason for this is that the higher the
threshold is, the more the time PDF is restricted to a short period and the
less background is included in the fit. Logically, fewer events are needed in
order to make a discovery in such case. An average of 3 events is required for
a discovery while about 2 events are needed to reach the 90% sensitivity
level.

Figure 7: Sensitivity and 5$\sigma$ discovery potential for the 11-day flare
analysis in number of neutrino signal events as a function of the gamma-ray
threshold level in daily bins.

##  4 Results

###  4.1 Time-dependent all-sky scans

####  4.1.1 IC86 II-VI analysis

The all-sky scan is realized by running the fit, resulting in a TS (Eq. 6), at
each point of a $0.1^{\circ}{}$ x $0.1^{\circ}{}$ grid over the sky (except
the poles). Each TS is converted into a $p$-value, assuming that the TS
distribution follows a $\chi^{2}$ distribution of three degrees of freedom,
even though four parameters are fitted in the analysis. Indeed, due to
correlations between parameters and some having limited ranges, a $\chi^{2}$
distribution of three degrees of freedom was found to be the one best-
representing the TS distribution. Fig. 8 shows a sky map of the entire sky in
equatorial coordinates for the period from 2015 to 2017 and reports the
$p$-value found at each point of the grid.

The $p$-values shown in the sky map are pre-trial $p$-values. The most
significant spot in each hemisphere is circled in black on the sky map in Fig.
8. The hottest spot overall was found in the Northern hemisphere at (RA,
Dec)=($170.4^{\circ}{},28.0^{\circ}{}$)444All equatorial coordinates are
quoted for the J2000 epoch.. The best fit parameters of the Gaussian time PDF
are $\hat{T}_{0}=56167.27$ MJD and $\hat{\sigma}_{T}=40.01$ days. The fitted
number of signal events is $\hat{n}_{s}=11.79$ and the fitted spectral index
is $\hat{\gamma}=2.11$. The pre-trial significance is $1.38\times 10^{-6}$,
which results in a post-trial $p$-value of 17.7%. The inferred post-trial
$p$-value for the Southern hemisphere is 24.2%. These values are compatible
with a statistical fluctuation of the background. The observed $p$-value from
data together with the distribution of TS from pseudo-experiments are shown in
the left panels of Fig. 9 and 10.

Figure 8: IC86 II-IV skymap in equatorial coordinates showing the pre-trial
$p$-values for the best-fit flare hypothesis tested in each direction of the
sky. The strongest time-dependent Gaussian-like signal was found in the
Northern sky at (RA, Dec) = (170.4∘, 28.0∘), with post-trial $p$-value of
17.7%. The solid black curve indicates the Galactic plane and the hottest spot
in each hemisphere is circled.

In order to help visualize how the different terms of the likelihood
contribute to each event, a weight $w_{i}$ is defined for each event as the
ratio between the signal and background PDF of the event without the time
term:

$w_{i}=\frac{P_{i}^{sig}(\sigma_{i},\vec{x}_{i}|\vec{x}_{s})\cdot\epsilon_{i}^{sig}(E_{i},\delta_{i}|\gamma)}{P_{i}^{bkg}(\phi_{i},\theta_{i})\cdot\epsilon_{i}^{bkg}(E_{i},\delta_{i})}$
(8)

When the weights are then plotted on the time axis, they immediately allow to
visualize which part of the likelihood (spatial/energy or time) dominates the
significance. The right panels of Fig. 9 and 10 show the time-independent
weights (Eq. 8) at a source direction $\vec{x}_{s}$ defined by the hottest
spot in the Northern and Southern hemisphere respectively. The best-fit
Gaussian time structure with mean $\hat{T}_{0}$ and sigma $\hat{\sigma}_{0}$
is overlaid.

Figure 9: Northern hemisphere: Left: expected background $p$-value
distribution obtained from scrambled data in green compared to the measured
most significant pre-trial $p$-value (shown as the black vertical dashed line)
in the Northern sky. The inferred post-trial $p$-value is 17.7%. Right: the
time-independent event weights, evaluated for the IC86 II-IV data in the
Northern hemisphere, at a source direction $\vec{x}_{s}$ defined by the
hottest spot (RA, Dec) = (170.4∘, 28.0∘). The best-fit Gaussian time PDF is
shown in black (dashed), with mean $\hat{T}_{0}$ and sigma $\hat{\sigma}_{0}$.

Figure 10: Southern hemisphere: Left: expected background $p$-value
distribution obtained from scrambled data in green compared to the measured
most significant pre-trial $p$-value (shown as the black vertical dashed line)
in the Southern sky. The inferred post-trial $p$-value is 24.2%. Right: the
time-independent event weights, evaluated for the IC86 II-IV data in the
Southern hemisphere, at a source direction $\vec{x}_{s}$ defined by the
hottest spot (RA, Dec) = (89.45∘, -35.95∘). The best-fit Gaussian time PDF is
shown in black (dashed), with mean $\hat{T}_{0}$ and sigma $\hat{\sigma}_{0}$.

####  4.1.2 IC86 V-VII analysis

The time period of 2015 to 2017 was treated separately from the previous time
period since a different event selection was applied. Fig. 11 shows the sky
map for the period 2012 to 2015, displaying the pre-trial $p$-values. The most
significant value for each hemisphere is circled. The hottest region is found
in the Northern hemisphere, like in the previous analysis period, at
coordinates (RA, Dec) = ($77.7^{\circ}{},2.6^{\circ}{}$). The pre-trial
$p$-value is $1.3\times 10^{-6}$, with the best-fit number of signal events
being $\hat{n}_{s}=25.27$ for a flux with spectral index $\hat{\gamma}=2.55$
and the most significant time clustering centered at $\hat{T}_{0}=57573.85$
MJD, with a Gaussian width $\hat{\sigma}_{0}=189.6$ days. This results in a
post-trial $p$-value of 18.8%.

Figure 11: IC86 V-VII skymap in equatorial coordinates showing the pre-trial
$p$-value for the best-fit flare hypothesis tested in each direction of the
sky. The strongest time-dependent Gaussian-like signal was found in the
Northern sky at (RA, Dec) = (77.7∘ , 2.6∘), with post-trial significance of
18.8%. The solid black curve indicates the Galactic plane and the hottest
spots are circled in each hemisphere.

The right panel of Fig. 12 (13) shows the time-independent weights in blue, at
a source direction $\vec{x}_{s}$ defined by the hottest spot in the Northern
(Southern) hemisphere and the associated best-fit Gaussian in black. The
corresponding histograms of background trials and the observed $p$-value
(vertical black dashed line) are displayed in Fig. 12 (13) for the Northern
(Southern) hemisphere.

In Fig. 12, we can see that the best-fit Gaussian encompasses almost the
entire analysis period. Given that no finer structure is found, the fit tries
to maximize the test statistics by including as much background as possible,
hence the largest Gaussian width is preferred.

Figure 12: Northern hemisphere: Left: expected background $p$-value
distribution obtained from scrambled data in green compared to the measured
most significant pre-trial $p$-value (shown as the black vertical dashed line)
in the Northern sky. The inferred post-trial $p$-value is 18.8%. Right: The
time-independent event weights, evaluated for the IC86 V-VII data in the
Northern hemisphere, at a source direction $\vec{x}_{s}$ defined by the
hottest spot (RA, Dec) = (77.65∘, 2.55∘). The best-fit Gaussian time PDF is
shown in black (dashed), with mean $\hat{T}_{0}$ and sigma $\hat{\sigma}_{0}$.

Figure 13: Southern hemisphere: Left: expected background $p$-value
distribution obtained from scrambled data in green compared to the measured
most significant pre-trial $p$-value (shown as the black vertical dashed line)
in the Southern sky. The inferred post-trial $p$-value is 81.5%. Right: The
time-independent event weights, evaluated for the IC86 V-VII data in the
Southern hemisphere, at a source direction $\vec{x}_{s}$ defined by the
hottest spot (RA, Dec) = (9.85∘, -31.05∘). The best-fit Gaussian time PDF is
shown in black (dashed), with mean $\hat{T}_{0}$ and sigma $\hat{\sigma}_{0}$.

No significant excess is found in the Southern hemisphere (Fig. 13) with a
post-trial $p$-value of more than 80%.

Tab. 2 summarizes the results for each data period and each hemisphere,
listing the coordinates of the hottest spot, the best-fit parameters and the
pre-trial and post-trial $p$-values. In both cases, the smallest $p$-values
were observed in the Northern hemisphere, where a longer duration flare, with
a harder emission spectrum, was found. None of those results is significant.

Table 2: Summary of all-sky scan results.  Data set | RA (J2000) | Dec (J2000) | Number of signal events | Spectral index | Gaussian mean | Gaussian width | p-value | p-value
---|---|---|---|---|---|---|---|---
| (∘) | (∘) | $\hat{n}_{s}$ | $\hat{\gamma}$ |  $\hat{T}_{0}$ (MJD) |  $\hat{\sigma}_{T}$ (days) | pre-trial | post-trial
IC86 II-IV |  |  |  |  |  |  |  |
South | 89.45 | -35.95 | 7.48 | 2.85 | 56808.46 | 4.013 | $1.38\times 10^{-6}$ | 24.2%
North | 170.35 | 27.95 | 11.79 | 2.11 | 56167.27 | 40.01 | $1.14\times 10^{-6}$ | 17.7%
IC86 V-VII |  |  |  |  |  |  |  |
South | 9.85 | -31.05 | 2.99 | 3.55 | 57216.78 | 0.021 | $6.19\times 10^{-6}$ | 81.5%
North | 77.65 | 2.55 | 25.27 | 2.25 | 57573.85 | 189.6 | $1.3\times 10^{-6}$ | 18.8%

####  4.1.3 Results of the scans at the location of TXS 0506+056

Aartsen et al. (2018b) performed a dedicated time-dependent analysis at the
position of the blazar TXS 0506+056, (RA, Dec,) = ($77.4^{\circ}{}$,
$+5.7^{\circ}{}$), motivated by the detection of IceCube-170922A, and found a
$3.5\sigma$ excess (post-trial $p$-value = $3\times 10^{-5}$), corresponding
to $13\pm 5$ signal events in the time period between 2012 and 2015. The
excess doesn’t appear significant in the present analysis, even though the
data and the analysis method are the same. This is explained by the fact that
this work scans the entire sky while Aartsen et al. (2018b) is solely
inspecting TXS 0506+056 direction. Since a grid of $0.1^{\circ}{}\times
0.1^{\circ}{}$ over the whole sky is analyzed, the final $p$-values are
penalized by large trial factors, which reduce their significance. It is
interesting to note that the second most significant hot spot (pre-trial
$p$-value = $9.2\times 10^{-6}$) of the 2012-2015 analysis is found at (RA,
Dec,) = ($77.55^{\circ}{}$, $+5.65^{\circ}{}$), which is consistent with the
location of TXS 0506+056. Moreover, applying the analysis at the exact TXS
0506+056 location as a further check, this work finds a similar excess of
events ($\hat{n}_{s}=13.55$) as reported by Aartsen et al. (2018b) in the time
period of 2012 to 2015, with a pre-trial $p$-value of $1.65\times 10^{-5}$ and
a pre-trial $p$-value of $3.2\times 10^{-2}$ in the time period of 2015 to
2017, consistent with the pre-trial $p$-values found by Aartsen et al.
(2018b).

###  4.2 3C 279 flare analysis

This analysis looks for high-energy neutrino candidate events clustered in
space around 3C 279, which is located in the Southern sky at (RA,
Dec)=($194.047^{\circ}{}$, $-5.789^{\circ}{}$), and in the time period defined
by the blazar gamma-ray light curve. The result of the analysis is shown in
Fig. 14. The left panel displays the background TS values found by running the
analysis on $10^{6}$ scrambled data sets. The result of the analysis performed
on real data is marked with the black vertical dashed line. A final $p$-value
of 19% is obtained, which is compatible with background.

The right panel of Fig. 14 shows the time-independent neutrino event weights
as defined by Eq. 8. The best-fit value of the threshold is $\rm 2.44\times
10^{-15}\leavevmode\nobreak\ photons\leavevmode\nobreak\
cm^{-2}\leavevmode\nobreak\ s^{-1}$, which is consistent with 0. This means
that the time PDF is above this value and includes all 11 days. Tab. 3
summarizes the best-fit values of the parameters. The best-fit number of
signal events is $\hat{n}_{s}=0.48$, the spectral index $\hat{\gamma}$ is 2.45
and the lag was fit to its maximum value, i.e. $0.5$ day.

Figure 14: Result of the 11-day (MJD 57184 - 57195 ) analysis. Left: test statistics for $10^{6}$ background trial scrambled data in green. The black dashed line shows the TS value resulting from the analysis. Right: The red line is the denoised light curve of 3C 279. The blue vertical lines represent IceCube events selected by the analysis and their size is given by the product of the signal over the background spatial and energy PDFs. The threshold is not represented since it was fitted to zero. No correlation is found between the flare of 3C 279 and neutrinos detected by IceCube.  Table 3: Results of the 3C 279 flare analysis  Number of signal events | Spectral index | Threshold | Lag | Test statistic |  $p$-value
---|---|---|---|---|---
$\hat{n}_{s}$ | $\hat{\gamma}$ | (photons cm-2 s-1) | (days) |  |
0.48 | 2.45 | 0 | 0.5 | 0.16 | 19%

Four events are visible in the right plot of Fig. 14, but a total of nine
contributed to the likelihood. However their time-independent weight is so
small that they are not represented in the plot. One may notice that two
events around 57188 MJD are quite close in time. More details about the nine
events can be found in Tab. 4, which shows the time, coordinates, weights and
visible reconstructed muon energy of each detected event in the 11-day
analysis.

Table 4: IceCube events contributing to the likelihood fit, at the position of 3C 279, in the time period MJD 57184 - 57195.  Event time | $w_{i}$ | RA (J2000) | Dec (J2000) | Angular error (1$\sigma$) | $\rm\log_{10}({E_{\mu}}(GeV))$
---|---|---|---|---|---
(MJD) | ($\rm\log_{10}{(spatialWeight\cdot energyWeight)}$) | (∘) | (∘) | (∘) |
57185.41 | -6.13 | 194.91 | -3.35 | 0.37 | 2.81
57185.72 | -2.98 | 190.00 | 1.56 | 1.59 | 2.75
57186.27 | 3.82 | 193.95 | -4.99 | 0.46 | 3.26
57187.77 | 0.35 | 187.34 | -4.69 | 1.91 | 3.07
57187.79 | 0.55 | 195.35 | -3.89 | 0.57 | 3.10
57189.15 | -3.30 | 187.78 | 12.07 | 3.73 | 2.87
57189.50 | -3.50 | 197.67 | -1.82 | 0.94 | 2.87
57191.44 | 3.85 | 194.95 | -6.02 | 0.60 | 4.01
57194.61 | -3.81 | 195.93 | 2.15 | 1.44 | 2.89

The spatial distribution of the events found in $\pm 5^{\circ}$ around 3C 279
is shown in Fig. 15. The position of 3C 279 is marked with a red cross. The
color scale represents the energy weight while the circles shows the angular
error associated with each event. The four events which are the closest to the
source have the highest energy and a fairly good angular precision and are the
ones seen in Fig 14.

Figure 15: Location in declination and right ascension of the IceCube events
detected in the 11 days of the analysis. 3C 279 is represented by the red
cross. The color scale shows the energy weight and the circles the angular
uncertainty (i.e. paraboloid sigma, cf. Sec. 2). Nine events are detected in
total, but five have a weight close to zero, which probably means background

.

###  4.3 Upper limit on a hadronic model

The number of neutrinos expected to be detected at IceCube in association to
the huge flare of 3C 279 is estimated by Halzen & Kheirandish (2016), for a
purely hadronic gamma-ray production mechanism. Considering the one day of
highest emission of 3C 279 and taking into account IceCube’s efficiency, the
authors find that about 4 (2) events should be detected in time and space
coincidence with the blazar flare for $pp$ ($p\gamma$) interactions. Since
this analysis did not find any excess of neutrinos following the gamma-ray
time profile from the direction of the blazar, we can constrain the emission
model of Halzen & Kheirandish (2016) by setting an upper limit on the number
of neutrino events emitted by the source.

Halzen & Kheirandish (2016) assume that the observed gamma rays in the MeV-TeV
energy range are produced in a hadronic scenario, i.e. from protons colliding
with radiation or gas surrounding the blazar. In this mechanism, charged and
neutral pions are created and decay in turn, producing neutrinos and high-
energy gamma rays. In order to derive the expected number of neutrinos that
should be detected in IceCube, the neutrino flux has first to be related to
the observed gamma-ray flux. Following estimates (Halzen & Hooper, 2005) and
using energy conservation, one can write:

$\int_{E_{\gamma}^{\text{min}}}^{E_{\gamma}^{\text{max}}}E_{\gamma}\frac{dN_{\gamma}}{dE_{\gamma}}dE_{\gamma}=K\int_{E_{\gamma}^{min}}^{E_{\gamma}^{max}}E_{\nu}\frac{dN_{\nu}}{dE_{\nu}}dE_{\nu}$
(9)

where the gamma-ray spectrum is defined as

$\frac{dN_{\gamma}}{dE_{\gamma}}=A_{\gamma}E_{\gamma}^{-\alpha}$ (10)

where

$A_{\gamma}=\frac{F_{\gamma}}{\int_{E_{\gamma}^{\text{min}}}^{E_{\gamma}^{\text{max}}}E_{\gamma}^{-\alpha}dE_{\gamma}}$
(11)

with $\alpha=2.1$ the measured spectral index, $\rm F_{\gamma}=24.3\times
10^{-6}\leavevmode\nobreak\ photons\leavevmode\nobreak\
cm^{-2}\leavevmode\nobreak\ s^{-1}$ the average daily flux during the one day
of highest emission (Ackermann et al., 2016), $E_{\gamma}^{\text{min}}=0.1$
GeV and $E_{\gamma}^{\text{max}}=300$ GeV. The factor $K$ indicates the ratio
between the number of gamma rays and the number of neutrinos. For proton
interactions with radiation,
$K_{p\gamma}=\frac{\text{BR}_{\gamma}}{\text{BR}_{\nu}}=\frac{5/8}{3/8}=1.7$
and for $pp$ interactions,
$K_{pp}=\frac{\text{BR}_{\gamma}}{\text{BR}_{\nu}}=\frac{1/2}{1/2}=1$. $\rm
BR_{\gamma}$ and $\rm BR_{\nu}$ are the branching ratio of gamma rays and
neutrinos, respectively. They are calculated in the same way as in Halzen &
Kheirandish (2016), the only difference being that we also consider
synchrotron radiation or Compton scattering from the positrons produced by
charged pions, which produces additional gamma rays.

The neutrino spectrum is derived from Eq. 9:

$\frac{dN_{\nu}}{dE_{\nu}}\approx
A_{\nu}E_{\nu}^{-2}\approx\frac{A_{\gamma}E_{\gamma,min}^{-\alpha+2}}{(\alpha-2)K\ln(E_{\nu,\text{max}}/E_{\nu,\text{min}})}E_{\nu}^{-2}$
(12)

Following the steps described in Halzen & Kheirandish (2016) and integrating
Eq. 12, the expected number of muon neutrinos in IceCube is

$N_{\nu_{\mu}+\bar{\nu}_{\mu}}=t\int_{E_{\nu}^{\text{min}}}^{E_{\nu}^{\text{max}}}\frac{1}{3}\frac{dN_{\nu}}{dE_{\nu}}A_{\text{eff}}(E_{\nu},\delta)dE$
(13)

where we choose $t=86400$ s, $1$ TeV$\leq E_{\nu}\leq$10 PeV and the
declination band of 3C 279, $-6.289^{\circ}{}\leq\delta\leq-5.289^{\circ}{}$.
The factor $\frac{1}{3}$ accounts for neutrino oscillations.
$A_{\text{eff}}(E_{\nu},\delta)$ is IceCube effective area at the declination
of 3C 279 and is shown by the dashed green line in Fig. 2.

In order to compare against the model of Halzen & Kheirandish (2016), a 90%
C.L. upper limit is calculated with the 3C 279 flare analysis. In this
calculation, the injected signal is defined by a point-source at the location
of 3C 279 emitting a flux proportional to $E^{-2}$, having fixed a high
threshold in order to effectively reduce the emission time to the same assumed
in Ref. Halzen & Kheirandish (2016), corresponding to 1 day on 2015 June 16,
when the highest emission was observed. The signal strength at which 90% of
pseudo-experiments had a larger TS than the observed value corresponds to a
mean of 2.18 signal events, which is slightly larger than the number of events
needed to reach the sensitive region. This number of events translates to a
time-integrated flux of
$E^{2}\frac{1}{A_{\text{eff}}}\frac{dN}{dE}\rm=4.24\cdot
10^{-2}\leavevmode\nobreak\ GeV/cm^{2}$.

The expected number of muon neutrino tracks in IceCube,
$N_{\nu_{\mu}+\bar{\nu}_{\mu}}$, is calculated from Eq. 13. Following the
approach of Halzen & Kheirandish (2016), different neutrino energy ratios,
$E_{\nu,\text{max}}/E_{\nu,\text{min}}$, which represent the energy interval
over which proton interactions produce gamma rays from pions, are tested and
shown in Fig. 16 and Fig. 17. The minimum neutrino energy,
$E_{\nu,\text{min}}$ is directly derived from the minimum energy of the
protons, which dependins on the value of the Lorentz factor of the jet of the
blazar that is considered. The exact calculations are described by Eq. 4 to 7
in Halzen & Kheirandish (2016). Once $E_{\nu,\text{min}}$ is set,
$E_{\nu,\text{max}}$ is determined from the chosen neutrino energy ratio.

Fig. 16 shows the number of expected muon neutrino tracks in IceCube as a
function of the Lorentz factor of the jet of the blazar $\Gamma$ in the case
of $pp$ interactions (right) and as a function of $E_{\gamma}^{o}/\Gamma^{2}$
, with $E_{\gamma}^{o}$ the energy of the target photons, in the case of
$p\gamma$ interactions (left). The blue line corresponds to
$E_{\nu,\text{max}}/E_{\nu,\text{min}}=10^{3}$, the green line to
$E_{\nu,\text{max}}/E_{\nu,\text{min}}=10^{5}$ and the red line to
$E_{\nu,\text{max}}/E_{\nu,\text{min}}=10^{8}$. The black dashed line
represents the 90% CL upper limit corresponding to the one-day block on June
16 derived from this analysis. Model parameters which lie above the dashed
line are excluded.

Figure 16: Left: Number of expected muon neutrino tracks in IceCube for
$p\gamma$ interactions vs. $E_{\gamma}^{o}/\Gamma^{2}$ , with $E_{\gamma}^{o}$
the energy of the target photons as derived from Halzen & Kheirandish (2016).
The different colors represent different energy ranges where neutrinos are
produced. The black dashed line represents the 90% CL upper limit
corresponding to the one-day block on June 16 derived from the analysis. The
parameter space above the dashed line is excluded. Right: Number of expected
muon neutrino tracks in IceCube vs. jet Lorentz factor $\Gamma$ in the case of
$pp$ interactions, as derived in Halzen & Kheirandish (2016). The different
colors represent different neutrino production energy ranges. The black dashed
line represents the 90% CL upper limit corresponding to the one-day block on
June 16 derived from the analysis. The parameter space above the dashed line
is excluded.

Only a small fraction of the parameter space can be excluded by this analysis,
assuming the smallest ratio $E_{\nu,\text{max}}/E_{\nu,\text{min}}$, which
represents the energy interval over which proton interactions produce gamma
rays from pions. In the case of $p\gamma$ interactions large
$E_{\gamma}^{o}/\Gamma^{2}$ ($>10^{3}$) can be excluded, while for the $pp$
scenario small $\Gamma$ ($<20$) are disfavored.

Fig. 17 gives the same information as Fig. 16 in two dimensions. The colored
regions correspond to the expected number of events. The parameter spaces on
the left of the black lines are excluded.

Figure 17:  Contour plots showing the expected number of muon neutrino tracks
in IceCube for $p\gamma$ (left) and for $pp$ (right) interactions. The black
line represents the 90% CL upper limit corresponding to the one-day block on
June 16 derived from the analysis. The parameter space on the left of the
black line is excluded.

##  5 Summary

In this paper, we reported a time-dependent all-sky scan on IceCube data from
2012 to 2017. The analysis searches each direction in the sky for an excess of
neutrino events in space and time above the expected background. No
assumptions on the potential sources of neutrinos are made. The most
significant result corresponds to a $p$-value of 17.7%, which is compatible
with background. It is obtained at the beginning of the analyzed period, the
best-fit Gaussian time structure having its mean on 2012 August 28 and a width
of 40 days, and lies in the Northern hemisphere at the position (RA, Dec) =
($170.4^{\circ},28.0^{\circ}$).

Within the analyzed period, the blazar 3C 279, already well-known for its high
variability, went through a brief but extremely intense gamma-ray flare which
was recorded by the Fermi-LAT experiment. In order to analyze this interesting
event, a dedicated time-dependent search was performed at the location of the
blazar and during 11 days around the peak of the flare, which happened on 2015
June 16. Assuming that the neutrino emission would follow the intensity of the
detected gamma rays, we defined the signal time PDF directly from the gamma-
ray light curve of 3C 279, obtained from Fermi-LAT. The analysis resulted in a
$p$-value of 19%, which is compatible with background.

The 90% C.L. upper limit for the day of most intense gamma-ray activity of the
blazar was calculated and used to constrain the neutrino emission model
presented in Halzen & Kheirandish (2016). This model, which is purely
hadronic, estimates the number of neutrinos that should be detected by IceCube
as function of the Lorentz boost of the jet of the blazar $\Gamma$ and of the
energy of the target photons $E_{\gamma}^{o}$. Different neutrino energy
intervals over which proton interactions would produce gamma rays from pions
were calculated and the results were expressed as a function of the neutrino
energy ratio, $E_{\nu,\text{max}}/E_{\nu,\text{min}}$. Assuming the smallest
ratio of neutrino energies leads to the most stringent limits, where large
$E_{\gamma}^{o}/\Gamma^{2}$ ($>10^{5}$) are excluded in case of p$\gamma$
interactions, while small $\Gamma$ ($<20$) are disfavored for the $pp$
scenario.

## Acknowledgements

The IceCube collaboration acknowledges the significant contributions to this
manuscript from Stéphanie Bron and Teresa Montaruli. The authors gratefully
acknowledge the support from the following agencies and institutions: USA –
U.S. National Science Foundation-Office of Polar Programs, U.S. National
Science Foundation-Physics Division, Wisconsin Alumni Research Foundation,
Center for High Throughput Computing (CHTC) at the University of
Wisconsin–Madison, Open Science Grid (OSG), Extreme Science and Engineering
Discovery Environment (XSEDE), Frontera computing project at the Texas
Advanced Computing Center, U.S. Department of Energy-National Energy Research
Scientific Computing Center, Particle astrophysics research computing center
at the University of Maryland, Institute for Cyber-Enabled Research at
Michigan State University, and Astroparticle physics computational facility at
Marquette University; Belgium – Funds for Scientific Research (FRS-FNRS and
FWO), FWO Odysseus and Big Science programmes, and Belgian Federal Science
Policy Office (Belspo); Germany – Bundesministerium für Bildung und Forschung
(BMBF), Deutsche Forschungsgemeinschaft (DFG), Helmholtz Alliance for
Astroparticle Physics (HAP), Initiative and Networking Fund of the Helmholtz
Association, Deutsches Elektronen Synchrotron (DESY), and High Performance
Computing cluster of the RWTH Aachen; Sweden – Swedish Research Council,
Swedish Polar Research Secretariat, Swedish National Infrastructure for
Computing (SNIC), and Knut and Alice Wallenberg Foundation; Australia –
Australian Research Council; Canada – Natural Sciences and Engineering
Research Council of Canada, Calcul Québec, Compute Ontario, Canada Foundation
for Innovation, WestGrid, and Compute Canada; Denmark – Villum Fonden and
Carlsberg Foundation; New Zealand – Marsden Fund; Japan – Japan Society for
Promotion of Science (JSPS) and Institute for Global Prominent Research (IGPR)
of Chiba University; Korea – National Research Foundation of Korea (NRF);
Switzerland – Swiss National Science Foundation (SNSF); United Kingdom –
Department of Physics, University of Oxford.

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