# Search for Astrophysical Neutrinos from 1FLE Blazars with IceCube

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  J.M.
Alameddine Dept. of Physics, TU Dortmund University, D-44221 Dortmund, Germany
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  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  Y. Ashida  Dept. of
Physics and Wisconsin IceCube Particle Astrophysics Center, University of
Wisconsin–Madison, Madison, WI 53706, USA  S. Athanasiadou  DESY, D-15738
Zeuthen, Germany  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  M. Baricevic  Dept.
of Physics and Wisconsin IceCube Particle Astrophysics Center, University of
Wisconsin–Madison, Madison, WI 53706, USA  S. W. Barwick Dept. of Physics and
Astronomy, University of California, Irvine, CA 92697, USA  V. Basu Dept. of
Physics and Wisconsin IceCube Particle Astrophysics Center, University of
Wisconsin–Madison, Madison, WI 53706, USA  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  J. Beise Dept.
of Physics and Astronomy, Uppsala University, Box 516, S-75120 Uppsala, Sweden
C. Bellenghi  Physik-department, Technische Universität München, D-85748
Garching, Germany  S. Benda  Dept. of Physics and Wisconsin IceCube Particle
Astrophysics Center, University of Wisconsin–Madison, Madison, WI 53706, USA
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 also at Università di Padova, I-35131
Padova, Italy  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  F. Bontempo  Karlsruhe Institute of
Technology, Institute for Astroparticle Physics, D-76021 Karlsruhe, Germany
J. Y. Book Department of Physics and Laboratory for Particle Physics and
Cosmology, Harvard University, Cambridge, MA 02138, USA  J. Borowka  III.
Physikalisches Institut, RWTH Aachen University, D-52056 Aachen, 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  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  B. Brinson  School of Physics and Center for
Relativistic Astrophysics, Georgia Institute of Technology, Atlanta, GA 30332,
USA  S. Bron  Département de physique nucléaire et corpusculaire, Université
de Genève, CH-1211 Genève, Switzerland  J. Brostean-Kaiser  DESY, D-15738
Zeuthen, Germany  R. T. Burley  Department of Physics, University of Adelaide,
Adelaide, 5005, Australia  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
E. G. Carnie-Bronca  Department of Physics, University of Adelaide, Adelaide,
5005, Australia  C. Chen School of Physics and Center for Relativistic
Astrophysics, Georgia Institute of Technology, Atlanta, GA 30332, USA  Z. Chen
Dept. of Physics and Astronomy, Stony Brook University, Stony Brook, NY
11794-3800, USA  D. Chirkin Dept. of Physics and Wisconsin IceCube Particle
Astrophysics Center, University of Wisconsin–Madison, Madison, WI 53706, USA
K. 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  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  A. Connolly  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  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  C. Dappen  III. Physikalisches Institut,
RWTH Aachen University, D-52056 Aachen, Germany  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 and Astronomy,
University of Alabama, Tuscaloosa, AL 35487, USA  D. Delgado López Department
of Physics and Laboratory for Particle Physics and Cosmology, Harvard
University, Cambridge, MA 02138, 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  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 Centre
for Cosmology, Particle Physics and Phenomenology - CP3, Université catholique
de Louvain, Louvain-la-Neuve, Belgium  T. DeYoung Dept. of Physics and
Astronomy, Michigan State University, East Lansing, MI 48824, USA  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
M. Dittmer  Institut für Kernphysik, Westfälische Wilhelms-Universität
Münster, D-48149 Münster, Germany  H. Dujmovic Karlsruhe Institute of
Technology, Institute for Astroparticle Physics, D-76021 Karlsruhe, Germany
M. A. DuVernois Dept. of Physics and Wisconsin IceCube Particle Astrophysics
Center, University of Wisconsin–Madison, Madison, WI 53706, 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  Karlsruhe Institute of
Technology, Institute of Experimental Particle Physics, D-76021 Karlsruhe,
Germany  H. Erpenbeck  III. Physikalisches Institut, RWTH Aachen University,
D-52056 Aachen, 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
K. L. Fan  Dept. of Physics, University of Maryland, College Park, MD 20742,
USA  A. R. Fazely Dept. of Physics, Southern University, Baton Rouge, LA
70813, USA  A. Fedynitch Institute of Physics, Academia Sinica, Taipei, 11529,
Taiwan  N. Feigl  Institut für Physik, Humboldt-Universität zu Berlin, D-12489
Berlin, Germany  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  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
A. Garcia Department of Physics and Laboratory for Particle Physics and
Cosmology, Harvard University, Cambridge, MA 02138, USA  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  N. Goehlke
Karlsruhe Institute of Technology, Institute of Experimental Particle Physics,
D-76021 Karlsruhe, Germany  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  S. Griswold
Dept. of Physics and Astronomy, University of Rochester, Rochester, NY 14627,
USA  C. Günther  III. Physikalisches Institut, RWTH Aachen University, D-52056
Aachen, Germany  P. Gutjahr Dept. of Physics, TU Dortmund University, D-44221
Dortmund, 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  H. Hamdaoui  Dept. of Physics and Astronomy, Stony Brook
University, Stony Brook, NY 11794-3800, 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,
Massachusetts Institute of Technology, Cambridge, MA 02139, USA  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  P.
Hatch  Dept. of Physics, Engineering Physics, and Astronomy, Queen’s
University, Kingston, ON K7L 3N6, Canada  A. Haungs Karlsruhe Institute of
Technology, Institute for Astroparticle Physics, D-76021 Karlsruhe, Germany
K. Helbing Dept. of Physics, University of Wuppertal, D-42119 Wuppertal,
Germany  J. Hellrung  III. Physikalisches Institut, RWTH Aachen University,
D-52056 Aachen, 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
L. Heuermann  III. Physikalisches Institut, RWTH Aachen University, D-52056
Aachen, Germany  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 The
International Center for Hadron Astrophysics, 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  K. Hoshina  also at Earthquake Research
Institute, University of Tokyo, Bunkyo, Tokyo 113-0032, Japan  Dept. of
Physics and Wisconsin IceCube Particle Astrophysics Center, University of
Wisconsin–Madison, Madison, WI 53706, USA  W. Hou  Karlsruhe Institute of
Technology, Institute for Astroparticle Physics, D-76021 Karlsruhe, Germany
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
K. Hymon  Dept. of Physics, TU Dortmund University, D-44221 Dortmund, Germany
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 The International Center for Hadron
Astrophysics, 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  M. Jin
Department of Physics and Laboratory for Particle Physics and Cosmology,
Harvard University, Cambridge, MA 02138, USA  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  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  L. Kardum  Dept. of Physics,
TU Dortmund University, D-44221 Dortmund, 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  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  K. Kin  Dept.
of Physics and The International Center for Hadron Astrophysics, Chiba
University, Chiba 263-8522, Japan  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  A. Kochocki Dept. of Physics and
Astronomy, Michigan State University, East Lansing, MI 48824, 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  T. Kontrimas  Physik-
department, Technische Universität München, D-85748 Garching, 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  T. Kozynets  Niels Bohr Institute, University
of Copenhagen, DK-2100 Copenhagen, Denmark  E. Krupczak  Dept. of Physics and
Astronomy, Michigan State University, East Lansing, MI 48824, USA  E. Kun
Fakultät für Physik & Astronomie, Ruhr-Universität Bochum, D-44780 Bochum,
Germany  N. Kurahashi Dept. of Physics, Drexel University, 3141 Chestnut
Street, Philadelphia, PA 19104, USA  N. Lad  DESY, D-15738 Zeuthen, Germany
C. Lagunas Gualda DESY, D-15738 Zeuthen, Germany  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  J. W. Lee Dept. of Physics, Sungkyunkwan University,
Suwon 16419, Korea  K. Leonard Dept. of Physics and Wisconsin IceCube Particle
Astrophysics Center, University of Wisconsin–Madison, Madison, WI 53706, USA
A. Leszczyńska Bartol Research Institute and Dept. of Physics and Astronomy,
University of Delaware, Newark, DE 19716, USA  M. Lincetto  Fakultät für
Physik & Astronomie, Ruhr-Universität Bochum, D-44780 Bochum, Germany  Q. R.
Liu Dept. of Physics and Wisconsin IceCube Particle Astrophysics Center,
University of Wisconsin–Madison, Madison, WI 53706, USA  M. Liubarska  Dept.
of Physics, University of Alberta, Edmonton, Alberta, Canada T6G 2E1  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 Wisconsin IceCube Particle Astrophysics Center, University of
Wisconsin–Madison, Madison, WI 53706, USA  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  S. Mancina  Dept. of
Physics and Wisconsin IceCube Particle Astrophysics Center, University of
Wisconsin–Madison, Madison, WI 53706, USA  W. Marie Sainte  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  I. Martinez-Soler
Department of Physics and Laboratory for Particle Physics and Cosmology,
Harvard University, Cambridge, MA 02138, USA  R. Maruyama Dept. of Physics,
Yale University, New Haven, CT 06520, USA  S. McCarthy  Dept. of Physics and
Wisconsin IceCube Particle Astrophysics Center, University of
Wisconsin–Madison, Madison, WI 53706, USA  T. McElroy  Dept. of Physics,
University of Alberta, Edmonton, Alberta, Canada T6G 2E1  F. McNally
Department of Physics, Mercer University, Macon, GA 31207-0001, USA  J. V.
Mead  Niels Bohr Institute, University of Copenhagen, DK-2100 Copenhagen,
Denmark  K. Meagher Dept. of Physics and Wisconsin IceCube Particle
Astrophysics Center, University of Wisconsin–Madison, Madison, WI 53706, USA
S. Mechbal  DESY, D-15738 Zeuthen, Germany  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 The International
Center for Hadron Astrophysics, Chiba University, Chiba 263-8522, Japan  S.
Meighen-Berger Physik-department, Technische Universität München, D-85748
Garching, Germany  Y. Merckx  Vrije Universiteit Brussel (VUB), Dienst ELEM,
B-1050 Brussels, Belgium  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  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 and
Wisconsin IceCube Particle Astrophysics Center, University of
Wisconsin–Madison, Madison, WI 53706, USA  T. Mukherjee  Karlsruhe Institute
of Technology, Institute for Astroparticle Physics, D-76021 Karlsruhe, Germany
R. Naab DESY, D-15738 Zeuthen, Germany  R. Nagai Dept. of Physics and The
International Center for Hadron Astrophysics, 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 Dept. of Physics and Astronomy,
Michigan State University, East Lansing, MI 48824, USA  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  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
B. Oeyen Dept. of Physics and Astronomy, University of Gent, B-9000 Gent,
Belgium  A. Olivas  Dept. of Physics, University of Maryland, College Park, MD
20742, USA  J. Osborn  Dept. of Physics and Wisconsin IceCube Particle
Astrophysics Center, University of Wisconsin–Madison, Madison, WI 53706, 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, Engineering Physics, and Astronomy,
Queen’s University, Kingston, ON K7L 3N6, Canada  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  L. Paul  Department of Physics, Marquette University, Milwaukee, WI,
53201, USA  C. Pérez de los Heros Dept. of Physics and Astronomy, Uppsala
University, Box 516, S-75120 Uppsala, Sweden  L. Peters  III. Physikalisches
Institut, RWTH Aachen University, D-52056 Aachen, Germany  J. Peterson  Dept.
of Physics and Wisconsin IceCube Particle Astrophysics Center, University of
Wisconsin–Madison, Madison, WI 53706, USA  S. Philippen  III. Physikalisches
Institut, RWTH Aachen University, D-52056 Aachen, 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 Physics Department, South
Dakota School of Mines and Technology, Rapid City, SD 57701, USA  Y. Popovych
Institute of Physics, University of Mainz, Staudinger Weg 7, D-55099 Mainz,
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  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  J. Rack-
Helleis  Institute of Physics, University of Mainz, Staudinger Weg 7, D-55099
Mainz, Germany  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  Z. Rechav  Dept. of
Physics and Wisconsin IceCube Particle Astrophysics Center, University of
Wisconsin–Madison, Madison, WI 53706, USA  A. Rehman Bartol Research Institute
and Dept. of Physics and Astronomy, University of Delaware, Newark, DE 19716,
USA  P. Reichherzer  Fakultät für Physik & Astronomie, Ruhr-Universität
Bochum, D-44780 Bochum, 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  E. J. Roberts  Department of
Physics, University of Adelaide, Adelaide, 5005, Australia  S. Robertson
Dept. of Physics, University of California, Berkeley, CA 94720, USA  Lawrence
Berkeley National Laboratory, Berkeley, CA 94720, USA  S. Rodan  Dept. of
Physics, Sungkyunkwan University, Suwon 16419, Korea  G. Roellinghoff  Dept.
of Physics, Sungkyunkwan University, Suwon 16419, Korea  M. Rongen Institute
of Physics, University of Mainz, Staudinger Weg 7, D-55099 Mainz, Germany  C.
Rott Department of Physics and Astronomy, University of Utah, Salt Lake City,
UT 84112, USA  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  J. Saffer
Karlsruhe Institute of Technology, Institute of Experimental Particle Physics,
D-76021 Karlsruhe, Germany  D. Salazar-Gallegos Dept. of Physics and
Astronomy, Michigan State University, East Lansing, MI 48824, USA  P.
Sampathkumar  Karlsruhe Institute of Technology, Institute for Astroparticle
Physics, D-76021 Karlsruhe, Germany  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
M. Santander Dept. of Physics and Astronomy, University of Alabama,
Tuscaloosa, AL 35487, USA  S. Sarkar Dept. of Physics, University of Alberta,
Edmonton, Alberta, Canada T6G 2E1  S. Sarkar Dept. of Physics, University of
Oxford, Parks Road, Oxford OX1 3PU, UK  K. Satalecka DESY, D-15738 Zeuthen,
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  S. Schindler
Erlangen Centre for Astroparticle Physics, Friedrich-Alexander-Universität
Erlangen-Nürnberg, D-91058 Erlangen, 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  Physik-department, Technische
Universität München, D-85748 Garching, Germany  G. Schwefer  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  A. Sharma  Dept. of Physics and Astronomy, Uppsala University, Box 516,
S-75120 Uppsala, Sweden  S. Shefali  Karlsruhe Institute of Technology,
Institute of Experimental Particle Physics, D-76021 Karlsruhe, Germany  N.
Shimizu  Dept. of Physics and The International Center for Hadron
Astrophysics, Chiba University, Chiba 263-8522, Japan  M. Silva Dept. of
Physics and Wisconsin IceCube Particle Astrophysics Center, University of
Wisconsin–Madison, Madison, WI 53706, USA  B. Skrzypek  Department of Physics
and Laboratory for Particle Physics and Cosmology, Harvard University,
Cambridge, MA 02138, 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  A. Sogaard  Niels Bohr Institute, University of Copenhagen, DK-2100
Copenhagen, Denmark  D. Soldin  Bartol Research Institute and Dept. of Physics
and Astronomy, University of Delaware, Newark, DE 19716, USA  C. Spannfellner
Physik-department, Technische Universität München, D-85748 Garching, Germany
G. M. Spiczak Dept. of Physics, University of Wisconsin, River Falls, WI
54022, USA  C. Spiering 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  T. Stezelberger
Lawrence Berkeley National Laboratory, Berkeley, CA 94720, USA  T. Stürwald
Dept. of Physics, University of Wuppertal, D-42119 Wuppertal, Germany  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  S. Ter-
Antonyan Dept. of Physics, Southern University, Baton Rouge, LA 70813, USA  W.
G. Thompson Department of Physics and Laboratory for Particle Physics and
Cosmology, Harvard University, Cambridge, MA 02138, USA  J. Thwaites  Dept. of
Physics and Wisconsin IceCube Particle Astrophysics Center, University of
Wisconsin–Madison, Madison, WI 53706, USA  S. Tilav  Bartol Research Institute
and Dept. of Physics and Astronomy, University of Delaware, Newark, DE 19716,
USA  K. Tollefson Dept. of Physics and Astronomy, Michigan State University,
East Lansing, MI 48824, USA  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  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  M. Unland Elorrieta  Institut für Kernphysik, Westfälische Wilhelms-
Universität Münster, D-48149 Münster, Germany  K. Upshaw  Dept. of Physics,
Southern University, Baton Rouge, LA 70813, USA  N. Valtonen-Mattila  Dept. of
Physics and Astronomy, Uppsala University, Box 516, S-75120 Uppsala, Sweden
J. Vandenbroucke 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  J.
Veitch-Michaelis  Dept. of Physics and Wisconsin IceCube Particle Astrophysics
Center, University of Wisconsin–Madison, Madison, WI 53706, USA  S. Verpoest
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  W. Wang  Dept. of Physics and Wisconsin IceCube Particle
Astrophysics Center, University of Wisconsin–Madison, Madison, WI 53706, USA
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  P. Weigel  Dept. of Physics, Massachusetts Institute of Technology,
Cambridge, MA 02139, USA  A. Weindl  Karlsruhe Institute of Technology,
Institute for Astroparticle Physics, D-76021 Karlsruhe, Germany  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  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  C. H. Wiebusch
III. Physikalisches Institut, RWTH Aachen University, D-52056 Aachen, Germany
N. Willey  Dept. of Physics and Astronomy, Michigan State University, East
Lansing, MI 48824, USA  D. R. Williams  Dept. of Physics and Astronomy,
University of Alabama, Tuscaloosa, AL 35487, USA  M. Wolf Dept. of Physics and
Wisconsin IceCube Particle Astrophysics Center, University of
Wisconsin–Madison, Madison, WI 53706, 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  J. P. Yanez  Dept. of
Physics, University of Alberta, Edmonton, Alberta, Canada T6G 2E1  E. Yildizci
Dept. of Physics and Wisconsin IceCube Particle Astrophysics Center,
University of Wisconsin–Madison, Madison, WI 53706, USA  S. Yoshida Dept. of
Physics and The International Center for Hadron Astrophysics, Chiba
University, Chiba 263-8522, Japan  S. Yu  Dept. of Physics and Astronomy,
Michigan State University, East Lansing, MI 48824, USA  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  P. Zhelnin
Department of Physics and Laboratory for Particle Physics and Cosmology,
Harvard University, Cambridge, MA 02138, USA

###### Abstract

The origin of astrophysical neutrinos has yet to be determined. The IceCube
Neutrino Observatory has observed astrophysical neutrinos but has not yet
identified their sources. Blazars are promising source candidates, but
previous searches for neutrino emission from populations of blazars detected
in $\gtrsim$ GeV gamma-rays have not observed any significant neutrino excess.
Recent findings in multi-messenger astronomy indicate that high-energy
photons, co-produced with high-energy neutrinos, are likely to be absorbed and
reemitted at lower energies. Thus, lower-energy photons may be better
indicators of TeV-PeV neutrino production. This paper presents the first time-
integrated stacking search for astrophysical neutrino emission from MeV-
detected blazars in the first Fermi-LAT low energy catalog (1FLE) using ten
years of IceCube muon-neutrino data. The results of this analysis are found to
be consistent with a background-only hypothesis. Assuming an E-2 neutrino
spectrum and proportionality between the blazars’ MeV gamma-ray fluxes and
TeV-PeV neutrino flux, the upper limit on the 1FLE blazar energy-scaled
neutrino flux is determined to be $1.64\times 10^{-12}$ TeV cm-2 s-1 at 90%
confidence level. This upper limit is approximately $1\%$ of IceCube’s diffuse
muon-neutrino flux measurement.

##  1 Introduction

High-energy cosmic rays have been observed arriving at Earth (Zyla et al.,
2020; Abreu et al., 2021; Abbasi et al., 2016), but their origins have yet to
be determined. The observation of these particles with PeV and higher energies
implies the existence of powerful astrophysical particle accelerators;
however, the nature and locations of these objects remains uncertain. Charged
particles with energies smaller than $\sim 10^{19}$ eV traveling through the
Universe are deflected by interstellar and intergalactic magnetic fields
(Arámburo-García et al., 2021), thereby making localization of cosmic ray
sources difficult.

In contrast to charged particles, photons and neutrinos travel along a
straight path from their sources making them useful messengers for observing
cosmic ray accelerators. Unlike photons which can be produced by leptonic or
hadronic processes, production of a large neutrino flux requires the presence
of a hadronic component. Therefore, the emission of neutrinos is generally
considered a strong sign of cosmic ray acceleration. Additionally, photon
attenuation probability increases rapidly with energy $\gtrsim$ 30 GeV over
cosmic distances (Ajello et al., 2017). On the other hand, the neutrino’s
small interaction cross-section allows it to travel great distances without
absorption making them effective at probing distances that photons cannot.

These same properties necessitate a large detector volume to effectively
observe neutrinos, especially those of astrophysical origin which have a
relatively small flux compared to solar and atmospheric neutrinos. The IceCube
Neutrino Observatory (hereafter, IceCube) is a cubic-kilometer Cherenkov light
detector located at the geographic South Pole (Aartsen et al., 2017a). In
2013, IceCube discovered the existence of a flux of high-energy, astrophysical
neutrinos (Aartsen et al., 2013). No sources of these astrophysical neutrinos
have yet been definitively discovered.

Active galactic nuclei (AGN) are highly energetic objects which have long been
theorized to be potential sites for particle acceleration and neutrino
production (Halzen & Zas, 1997). Accretion of surrounding matter onto a super-
massive black hole creates an ideal environment for acceleration and
interaction of cosmic particles. In some AGN, particles may additionally be
accelerated along a narrow, relativistic jet. Four AGN make up the most
significant combined group of sources in an analysis of 10 years of IceCube
data (Aartsen et al., 2020a); among these are the Seyfert and starburst galaxy
NGC 1068 and blazar TXS 0506+056.

This blazar, TXS 0506+056, is the first object to show evidence for
astrophysical neutrino emission (Aartsen et al., 2018a, b). Blazars are AGN
which have a relativistic jet directed toward Earth, providing a potentially
greater observed flux of accelerated particles (Urry & Padovani, 1995).
Current observations of blazars are unable to distinguish between leptonic,
hadronic, and mixed emission scenarios (Cerruti et al., 2019; Böttcher et al.,
2013). When a hadronic component is included, a neutrino counterpart is
expected alongside photon production; hence, detections of neutrinos from
blazars can help characterize their makeup.

Previous IceCube analyses (Aartsen et al., 2017b; Huber, 2019), though, have
not found significant astrophysical neutrino emission from blazars in the 2
year Fermi-LAT AGN catalog (2LAC) (Ackermann et al., 2011) and the Fermi-LAT
third high energy source catalog (3FHL) (Ajello et al., 2017). Recent
theoretical hypotheses (Murase et al., 2016) suggest that photons produced
alongside astrophysical neutrinos in cosmic accelerators will be more
effectively observed at reduced energies due to processes which attenuate
high-energy photons. At the source, high-energy gamma-rays are unlikely to
escape their environment without being absorbed, for example by pair-
production with other gamma-rays, inverse Compton scattering, or synchrotron
cooling (Mannheim et al., 1991, 2000). Photons that do escape their source
with $\gtrsim$ GeV energies have a high probability of cascading to lower
energies via interaction with extragalactic background light and the cosmic
microwave background as they travel from their source (Berezinskii & Smirnov,
1975). These processes lead not only to an increased observed electromagnetic
flux at MeV energies but also to the possibility for some neutrino sources to
be unobserved in the GeV-TeV energy range (Murase et al., 2016). In addition,
blazar spectral energy distributions tend to peak in the MeV regime,
especially for the most luminous objects (Fossati et al., 1998; Gao et al.,
2017; Ojha et al., 2019). For these reasons, MeV photons could be more
effective indicators of TeV-PeV neutrinos.

##  2 Sources

This analysis searches for correlation between IceCube neutrinos and 137
blazars in the first catalog of Fermi-LAT sources detected below 100 MeV
(1FLE) (Principe et al., 2018). These blazars are mapped in equatorial
coordinates in Figure 1 with marker sizes proportional to each blazar’s
respective 30-100 MeV photon energy flux. The Large Area Telescope (LAT) on
board the Fermi Gamma-ray Space Telescope (Fermi) observes the Universe in
gamma-rays of energies from 20 MeV to over 300 GeV, its most sensitive
energies falling in the GeV band (Atwood et al., 2009). The 1FLE catalog was
created using a wavelet transform method to localize sources and fit for
fluxes which is described in detail in Principe et al. (2018). The blazars
used in this analysis are classified as either flat-spectrum radio quasars
(FSRQs) or BL Lacertae objects (BL Lacs). These classifications are obtained
from each blazar’s respective source association in the 10-year Fermi-LAT data
release (4FGL-DR2) (Abdollahi et al., 2020) in order to have the most updated
identification. It is important to note, however, that blazars are not split
into separate classifications for use in this analysis. While there are
blazars shared between the 1FLE catalog and the catalogs used in previous
IceCube blazar stacking analyses (2LAC and 3FHL), the number of sources and
the photon flux energy range differentiate this analysis from previous,
similar ones. A brief overview of these quantities in this analysis and those
previously mentioned is presented in Table 1.

Figure 1: Sky map showing locations of 1FLE blazars used as sources in this
analysis in equatorial coordinates. The marker size for each blazar is
proportional to its MeV gamma-ray flux. Also shown are the Galactic center
(black cross) and Galactic plane (red line) for reference. Note that despite
some sources’ proximity to the Galactic plane, all blazars are extragalactic.

The 30-100 MeV photon energy range of the 1FLE catalog is below the peak
sensitivity of the Fermi-LAT instrument. In general, this leads to a lower
precision on measured quantities. For instance, the 1FLE catalog localizes
sources within error radii of about $0.25^{\circ}$ (Principe et al., 2018). In
comparison, 4FGL sources, which are localized using photons where Fermi-LAT is
more sensitive above 100 MeV, have error radii that tend to be around
$0.05^{\circ}$ (varying up to about $0.5^{\circ}$ and down to about
$0.005^{\circ}$) (Abdollahi et al., 2020). Despite these greater uncertainties
in the 1FLE catalog, the locations of the blazars do not vary greatly from
their 4FGL associations. Additionally, the 1FLE source detection methods are
designed to detect faint sources while also limiting source confusion (see
Principe et al. (2018) for full explanation). This specific focus of the 1FLE
catalog on detection efficiency in the 30-100 MeV photon energy range makes it
a good choice for this analysis. Of further importance is the fact that the
source localization errors are still smaller or similar to the IceCube
pointing resolution, so they do not contribute significant error when
correlating with IceCube events. All this considered, without instruments that
are sensitive to the MeV range of the electromagnetic spectrum, the 1FLE
catalog acts as an important bridge over previously unexplored energies. A
full list of source blazars used in this analysis and relevant quantities can
be found in Appendix A.

##  3 Data

The IceCube detector (Aartsen et al., 2017a) consists of 5160 digital optical
modules (DOMs) arranged in a cubic kilometer array of Antarctic ice. The main
component of each DOM is a photo-multiplier tube which collects the light
created by relativistic particles traveling through the ice. These particles
are produced as byproducts of neutrino interactions and emit Cherenkov
radiation when traveling faster than the local speed of light through the ice.
IceCube can detect all flavors of neutrinos, but no distinction can be made
between neutrino ($\nu$) and anti-neutrino ($\bar{\nu}$) except in rare cases
such as the Glashow resonance (IceCube Collaboration et al., 2021). IceCube
observes two main event topologies at energies $>100$ GeV: cascades and
tracks. Cascade events appear as a near-spherical propagation of light
resulting from neutral-current (NC) neutrino interactions of all flavors or
from charged-current (CC) interactions of electron- and tau-neutrinos
($\nu_{e}\bar{\nu}_{e}$ and $\nu_{\tau}\bar{\nu}_{\tau}$, respectively). At
energies greater than a few hundred TeV, the CC $\nu_{\tau}\bar{\nu}_{\tau}$
interaction can produce a double-cascade light signature as the resulting tau
particle travels a distance resolvable by IceCube (Aartsen et al., 2016). The
data used in this analysis are track events. The track topology mostly results
from the CC interactions of muon-neutrinos ($\nu_{\mu}+\bar{\nu}_{\mu}$); the
muon produced in these interactions travels of order several kilometers
through the Antarctic ice as it loses energy, thereby depositing light in a
linear pattern. This allows for tracks to be reconstructed with angular
resolution of $\lesssim 1^{\circ}$ for neutrinos with energies $\gtrsim$ 1 TeV
(Aartsen et al., 2020a). This angular resolution is smaller than that of
cascade events which makes track events favored for point source searches.

The dataset used to perform this analysis contains 1134451 IceCube track
events collected between April 6, 2008 and July 8, 2018 from the entire sky.
As the estimated angular uncertainty for each individual event does not
include systematic uncertainties, a minimum angular uncertainty of
$0.2^{\circ}$ is applied (Aartsen et al., 2020a). A majority of this dataset
is background events created by atmospheric neutrinos and muons resulting from
cosmic ray interactions with Earth’s atmosphere. Significant reduction of this
background is achieved in the Northern hemisphere due to shielding from muons
by the Earth. Further details about the dataset and event selection methods
may be found in Abbasi et al. (2021).

##  4 Analysis methods

This analysis uses a well-defined (Aartsen et al., 2017b, 2020b; Braun et al.,
2008) unbinned, maximum likelihood method which makes use of location and
energy information to determine possible correlation between IceCube neutrinos
and 1FLE blazars. It is a stacked search which looks for cumulative neutrino
emission from the source list as a whole, rather than individually. This time-
independent analysis assumes steady emission from the sources as opposed to
searching for transient emission. The likelihood, $\mathcal{L}$—which is a
function of two free variables, the number of signal events, $n_{s}$, and the
neutrino spectral index, $\gamma$—is defined in Equation 1. This likelihood
can then be maximized to obtain a best-fit $n_{s}$ and $\gamma$.

$\mathcal{L}(n_{s},\gamma)=\prod_{i}^{N}\left(\frac{n_{s}}{N}S_{i}+\left(1-\frac{n_{s}}{N}\right)B_{i}\right)$
(1)

The value $N$ is the total number of events in the data sample. The likelihood
consists of two PDFs for each event, $i$: one for signal, $S_{i}$, and one for
background, $B_{i}$. The PDFs each consist of a spatial and an energy factor
which correlate each event with a source.

As this is a stacked search, $S_{i}$ is the weighted sum over every source $j$
such that $S_{i}=\sum_{j}^{M}w_{j}R_{j}S_{i}^{j}$ for $M$ total sources. The
weight of each source consists of a detector acceptance weight, $R_{j}$, based
on the effective area at the source location and a source weighting scheme,
$w_{j}$, based on a chosen emission hypothesis. These weights are normalized
such that $\sum_{j}^{M}w_{j}R_{j}=1$; for more details see Aartsen et al.
(2020b). The two source weighting schemes chosen for use in this analysis are
equally-weighted sources (referred to as equal weights), and sources weighted
by their integrated photon energy fluxes in the 30-100 MeV range (referred to
as flux weights).

Table 1: Comparison of IceCube blazar stacking analyses.

Analysis | Source Catalog | Total Number of Blazars | Flux Weight Energy Range
---|---|---|---
|  |  | (GeV)
Aartsen et al. (2017b) | 2LAC | 862 | 0.1 - 100
Huber (2019) | 3FHL | 1301 | —
This work | 1FLE | 137 | 0.03 - 0.1

Note. — Overview of two blazar stacking analyses is shown in addition to this
work. In comparison to the 137 1FLE blazars studied in this analysis, 862
blazars from the 2LAC (Ackermann et al., 2011) catalog were analyzed with flux
weights in the 0.1 - 100 GeV energy range, and 1301 blazars from the 3FHL
(Ajello et al., 2017) catalog were analyzed without flux weights.

A test statistic (TS) is then constructed, as in Equation 2, to compare the
best-fit signal hypothesis to a background-only hypothesis that is
characterized by having zero signal events. This TS is used to determine the
significance of the correlation in the form of a p-value, defined as the
probability that the observed TS is a result of background fluctuations.

$\text{TS}=-2\log\left(\frac{\mathcal{L}(n_{s}=0)}{\mathcal{L}(n_{s},\gamma)}\right)$
(2)

As mentioned in Section 3, the data sample is background-dominated. IceCube’s
location at the geographic South Pole leads to a declination-dependent
detector acceptance and event rate. Therefore, a model-independent background
estimation is obtained by randomizing the right ascension of data events. This
background estimation is repeated many times to create a distribution to which
the observed TS may be compared in order to determine the p-value.

##  5 Results

The best-fit number of signal events for both source weighting hypotheses is
found to be zero, hence our observations are consistent with the background-
only hypothesis. Upper limits (ULs) are set on the energy-scaled neutrino flux
($E^{2}dN/dE$) for various, assumed neutrino spectral indices and do not
include systematic uncertainties. Such systematic uncertainties arise from DOM
efficiency, absorption or scattering of photons in the ice, and photo-nuclear
interaction models; the total systematic uncertainty on neutrino fluxes is
approximately 11% (Aartsen et al., 2017). The results of this analysis are
summarized in Table 2. Additionally, Figure 2 shows differential ULs on
energy-scaled neutrino flux for an $E^{-2}$ neutrino spectrum in bins of
energy. The range of energies shown in the figure is that which contributes
90% of the integrated sensitivity for each weighting scheme.

Table 2: Stacking analysis results for 1FLE blazars.

Weighting | TS | ns | Energy-scaled Neutrino Flux UL (TeV cm-2 s-1 at $1$ TeV)
---|---|---|---
Scheme |  |  | $\gamma=2.0$ | $\gamma=2.37$ | $\gamma=2.5$ | $\gamma=3.0$
Equal | 0 | 0 | $2.27\times 10^{-12}$ | $1.48\times 10^{-11}$ | $2.48\times 10^{-11}$ | $9.72\times 10^{-11}$
Flux | 0 | 0 | $1.64\times 10^{-12}$ | $9.98\times 10^{-12}$ | $1.65\times 10^{-11}$ | $6.07\times 10^{-11}$

Note. — The 90% confidence level upper limits on stacked, energy-scaled
neutrino ($\nu_{\mu}+\bar{\nu}_{\mu}$) flux are shown for several assumed
spectral indices at a reference energy of 1 TeV, along with the best-fit TS
and ns, for each weighting scheme. These upper limits do not include
systematic uncertainties.

Figure 2: 90% confidence level upper limits on energy-scaled neutrino
($\nu_{\mu}+\bar{\nu}_{\mu}$) flux from 1FLE blazars in four differential bins
per decade of energy. These limits correspond to an E-2 neutrino spectrum
within each energy bin and do not include systematic uncertainties. The
overall energy range is that which contributed 90% of the total sensitivity
for each respective weighting scheme.

Figure 3 compares the UL of this analysis under the flux-weighted source
hypothesis to the astrophysical, all-sky diffuse $\nu_{\mu}+\bar{\nu}_{\mu}$
flux from Abbasi et al. (2022). The UL of the analysis presented in this paper
is on the per-flavor neutrino flux which for a track dataset, such as the one
used here, can be closely approximated as a $\nu_{\mu}+\bar{\nu}_{\mu}$ flux.
The spectral index of the UL shown in Figure 3 is chosen to be 2.37 to match
the best-fit spectral index of the compared diffuse measurement. By extending
this limit to lower energies, it is also naively compared to the sum of 30-100
MeV photon energy fluxes from the 1FLE blazars used in this analysis. At
around this spectral index and smaller, the hadronic component of the MeV
gamma-ray flux may be constrained by the neutrino flux ULs presented here. The
specifics of this constraint and its viability are dependent on the choice of
blazar flux model but are beyond the scope of this paper.

Figure 3: 90% confidence level upper limit on energy-scaled neutrino
($\nu_{\mu}+\bar{\nu}_{\mu}$) flux from 1FLE blazars assuming a simple power-
law (orange) which is 1.0% of the diffuse flux measurement from Abbasi et al.
(2022) (blue, shown as a 68% confidence level band). This upper limit does not
include systematic uncertainties. The spectral index shown here,
$\gamma=2.37$, is the best-fit of this diffuse measurement. The solid orange
line shows the limit within the energy range which contributes 90% of the
total sensitivity. The dashed line extrapolates this limit to lower energies.
The green line shows the sum of integrated gamma-ray fluxes between 30 and 100
MeV for 1FLE blazars which are used as source weights in obtaining the shown
upper limit. Considering the relationship between this total flux and the
limit from this analysis in the 30-100 MeV range, in conjunction with a gamma-
ray model, could offer insight into the contribution of hadronic interactions
to the observed blazar flux distribution.

##  6 Conclusions

A stacking analysis searching for astrophysical neutrino production from 137
blazars in the Fermi-LAT 1FLE catalog using 10 years of IceCube muon-neutrino
data was presented. Observations were found, via the described methods, to be
consistent with the background-only hypothesis for both equal and flux source
weighting schemes. Upper limits were set on the energy-scaled neutrino flux
from these blazars for both source weightings and various assumed spectral
indices. Under the flux weighting scheme and for a spectral index of $2.37$,
the UL from this analysis is approximately 0.86 - 1.2% of the diffuse
$\nu_{\mu}+\bar{\nu}_{\mu}$ flux measurement.

It should be noted that this analysis contains limitations which result from
the 1FLE catalog lying outside of Fermi-LAT’s most sensitive energy range. The
localization and flux precisions are worse than those in the most sensitive
energies of this instrument, but are not accounted for with the methods of
this analysis. Nevertheless, this analysis is a first search for astrophysical
neutrino emission from 30-100 MeV gamma-ray-detected blazars and should lend
itself as motivation for future studies into the low-energy gamma-ray band.
Future electromagnetic observations in the MeV band will provide a larger
number of sources with higher precision allowing for an updated analysis
similar to the one presented here to be performed. For example, AMEGO-X
(Fleischhack, 2021) and e-ASTROGAM (De Angelis et al., 2018) plan to offer
much improved sensitivities in the MeV energy range and even down to a few
hundred keV. Future analyses will also benefit from additional neutrino
observations from upcoming improvements to neutrino observational
capabilities, such as with IceCube-Gen2 (Aartsen et al., 2021).

## Acknowledgements

The IceCube collaboration acknowledges the significant contributions to this
manuscript from Michael A. Campana. USA – U.S. National Science Foundation-
Office of Polar Programs, U.S. National Science Foundation-Physics Division,
U.S. National Science Foundation-EPSCoR, 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.

##  Appendix A Source List

Table 3: List of blazars from the 1FLE catalog which are used in this
analysis.

Name | 4FGL Association | Class | Right Ascension | Declination | 30-100 MeV Energy Flux | Redshifta
---|---|---|---|---|---|---
|  |  | (∘) | (∘) | ($10^{-12}$ erg cm-2 s-1) |
1FLE J0003+2114 | 4FGL J0001.5+2113 | fsrq | 0.8 | 21.2 | 8.2 $\pm$ 2.7 | 1.11
1FLE J0036-4236 | 4FGL J0030.3-4224 | fsrq | 9.2 | -42.6 | 8.3 $\pm$ 2.8 | 0.5
1FLE J0109+0136 | 4FGL J0108.6+0134 | fsrq | 17.3 | 1.6 | 34 $\pm$ 10 | 2.1
1FLE J0105+6233 | 4FGL J0109.7+6133 | fsrq | 16.5 | 62.6 | 35 $\pm$ 10 | 0.78
1FLE J0111+3207 | 4FGL J0112.8+3208 | fsrq | 18.0 | 32.1 | 10.5 $\pm$ 3.5 | 0.6
1FLE J0117+2420 | 4FGL J0115.8+2519 | bll | 19.4 | 24.3 | 10.4 $\pm$ 3.4 | 0.36
1FLE J0119-2300 | 4FGL J0118.9-2141 | fsrq | 19.8 | -23.0 | 8.5 $\pm$ 2.8 | 1.16
1FLE J0136+4752 | 4FGL J0137.0+4751 | fsrq | 24.2 | 47.9 | 13.8 $\pm$ 4.6 | 0.86
1FLE J0144-2728 | 4FGL J0145.0-2732 | fsrq | 26.2 | -27.5 | 8.4 $\pm$ 2.8 | 1.15
1FLE J0206-1705 | 4FGL J0205.0-1700 | fsrq | 31.6 | -17.1 | 7.8 $\pm$ 2.6 | 1.74
1FLE J0213-5047 | 4FGL J0210.7-5101 | fsrq | 33.4 | -50.8 | 19.1 $\pm$ 5.8 | 1.0
1FLE J0215+1034 | 4FGL J0211.2+1051 | bll | 33.8 | 10.6 | 7.4 $\pm$ 2.4 | –
1FLE J0221+7403 | 4FGL J0217.4+7352 | fsrq | 35.4 | 74.1 | 18.9 $\pm$ 5.7 | 2.37
1FLE J0213+0107 | 4FGL J0217.8+0144 | fsrq | 33.3 | 1.1 | 5.8 $\pm$ 1.9 | 1.72
1FLE J0221+3604 | 4FGL J0221.1+3556 | fsrq | 35.4 | 36.1 | 26.3 $\pm$ 7.9 | 0.94
1FLE J0219+4256 | 4FGL J0222.6+4302 | bll | 34.8 | 42.9 | 28.2 $\pm$ 8.5 | 0.44
1FLE J0238+2900 | 4FGL J0237.8+2848 | fsrq | 39.6 | 29.0 | 29.4 $\pm$ 8.9 | 1.21
1FLE J0238+1638 | 4FGL J0238.6+1637 | bll | 39.5 | 16.6 | 17.3 $\pm$ 5.2 | 0.94
1FLE J0246-4621 | 4FGL J0245.9-4650 | fsrq | 41.7 | -46.4 | 13.6 $\pm$ 4.5 | 1.38
1FLE J0254-2221 | 4FGL J0252.8-2219 | fsrq | 43.6 | -22.4 | 13.8 $\pm$ 4.6 | 1.43
1FLE J0309+1002 | 4FGL J0309.0+1029 | fsrq | 47.5 | 10.0 | 6.6 $\pm$ 2.2 | 0.86
1FLE J0304-6121 | 4FGL J0309.9-6058 | fsrq | 46.1 | -61.4 | 14.3 $\pm$ 4.7 | 1.48
1FLE J0325+2204 | 4FGL J0325.7+2225 | fsrq | 51.5 | 22.1 | 11.0 $\pm$ 3.7 | 2.07
1FLE J0329-3724 | 4FGL J0334.2-3725 | bll | 52.3 | -37.4 | 13.4 $\pm$ 4.4 | –
1FLE J0331-3909 | 4FGL J0334.2-4008 | bll | 52.9 | -39.2 | 7.8 $\pm$ 2.6 | 1.36
1FLE J0339-0133 | 4FGL J0339.5-0146 | fsrq | 54.8 | -1.6 | 13.9 $\pm$ 4.6 | 0.85
1FLE J0349-2045 | 4FGL J0349.8-2103 | fsrq | 57.4 | -20.8 | 7.2 $\pm$ 2.4 | 2.94
1FLE J0403-3554 | 4FGL J0403.9-3605 | fsrq | 60.8 | -35.9 | 40.8 $\pm$ 9.1 | 1.42
1FLE J0424-0042 | 4FGL J0423.3-0120 | fsrq | 66.1 | -0.7 | 7.6 $\pm$ 2.5 | 0.92
1FLE J0443-0024 | 4FGL J0442.6-0017 | fsrq | 71.0 | -0.4 | 7.6 $\pm$ 2.5 | 0.84
1FLE J0448-4535 | 4FGL J0455.7-4617 | fsrq | 72.2 | -45.6 | 14.6 $\pm$ 4.8 | 0.86
1FLE J0456-2322 | 4FGL J0457.0-2324 | fsrq | 74.2 | -23.4 | 30.3 $\pm$ 9.1 | 1.0
1FLE J0500-0209 | 4FGL J0501.2-0158 | fsrq | 75.2 | -2.2 | 10.1 $\pm$ 3.3 | 2.29
1FLE J0506+0528 b | 4FGL J0509.4+0542 | bll | 76.7 | 5.5 | 16.9 $\pm$ 5.6 | –
1FLE J0531+0707 | 4FGL J0532.6+0732 | fsrq | 82.8 | 7.1 | 8.0 $\pm$ 2.6 | 1.25
1FLE J0538-4438 | 4FGL J0538.8-4405 | bll | 84.5 | -44.6 | 32.7 $\pm$ 9.9 | 0.89
1FLE J0649+4529 | 4FGL J0654.4+4514 | fsrq | 102.4 | 45.5 | 12.8 $\pm$ 4.2 | 0.93
1FLE J0721+7121 | 4FGL J0721.9+7120 | bll | 110.4 | 71.4 | 46 $\pm$ 10 | 0.13
1FLE J0729-1230 | 4FGL J0730.3-1141 | fsrq | 112.4 | -12.5 | 22.9 $\pm$ 6.9 | 1.59
1FLE J0738+0133 | 4FGL J0739.2+0137 | fsrq | 114.5 | 1.6 | 15.9 $\pm$ 5.3 | 0.19
1FLE J0805-0743 | 4FGL J0808.2-0751 | fsrq | 121.4 | -7.7 | 12.5 $\pm$ 4.1 | 1.84
1FLE J0818+4202 | 4FGL J0818.2+4222 | bll | 124.7 | 42.0 | 14.5 $\pm$ 4.8 | 0.53
1FLE J0823-2228 | 4FGL J0825.9-2230 | bll | 125.9 | -22.5 | 13.1 $\pm$ 4.3 | 0.91
1FLE J0827+2440 | 4FGL J0830.8+2410 | fsrq | 126.8 | 24.7 | 11.4 $\pm$ 3.8 | 0.94
1FLE J0841+7056 | 4FGL J0841.3+7053 | fsrq | 130.4 | 70.9 | 54 $\pm$ 12 | 2.22
1FLE J0852-1149 | 4FGL J0850.1-1212 | fsrq | 133.2 | -11.8 | 7.3 $\pm$ 2.4 | 0.57
1FLE J0855+2014 | 4FGL J0854.8+2006 | bll | 134.0 | 20.2 | 13.4 $\pm$ 4.4 | 0.31
1FLE J0910+0159 | 4FGL J0909.1+0121 | fsrq | 137.6 | 2.0 | 5.9 $\pm$ 2.0 | 1.02
1FLE J0921+4425 | 4FGL J0920.9+4441 | fsrq | 140.4 | 44.4 | 15.2 $\pm$ 5.0 | 2.19
1FLE J0957+5503 | 4FGL J0957.6+5523 | fsrq | 149.3 | 55.1 | 8.8 $\pm$ 2.9 | 0.9
1FLE J1005-2205 | 4FGL J1006.7-2159 | fsrq | 151.3 | -22.1 | 7.6 $\pm$ 2.5 | 0.33
1FLE J1008-3201 | 4FGL J1008.8-3139 | bll | 152.0 | -32.0 | 7.7 $\pm$ 2.5 | –
1FLE J1011+2442 | 4FGL J1012.7+2439 | fsrq | 152.8 | 24.7 | 6.6 $\pm$ 2.2 | 1.8
1FLE J1031+6001 | 4FGL J1031.6+6019 | fsrq | 158.0 | 60.0 | 17.7 $\pm$ 5.3 | 1.23
1FLE J1030+3811 | 4FGL J1032.6+3737 | bll | 157.6 | 38.2 | 7.0 $\pm$ 2.3 | –
1FLE J1047+7131 | 4FGL J1048.4+7143 | fsrq | 161.9 | 71.5 | 51 $\pm$ 11 | 1.15
1FLE J1049+2227 | 4FGL J1054.5+2211 | bll | 162.3 | 22.5 | 6.2 $\pm$ 2.1 | –
1FLE J1059+0208 | 4FGL J1058.4+0133 | bll | 164.9 | 2.1 | 13.2 $\pm$ 4.4 | 0.89
1FLE J1100+8117 | 4FGL J1058.5+8115 | fsrq | 165.1 | 81.3 | 17.7 $\pm$ 5.3 | 0.71
1FLE J1105+3807 | 4FGL J1104.4+3812 | bll | 166.3 | 38.1 | 24.4 $\pm$ 7.4 | 0.03
1FLE J1118-0558 | 4FGL J1121.4-0553 | fsrq | 169.7 | -6.0 | 6.1 $\pm$ 2.0 | 1.3
1FLE J1125-1907 | 4FGL J1127.0-1857 | fsrq | 171.4 | -19.1 | 17.7 $\pm$ 5.3 | 1.05
1FLE J1125+3639 | 4FGL J1127.8+3618 | fsrq | 171.4 | 36.7 | 13.1 $\pm$ 4.3 | 0.88
1FLE J1138+3832 | 4FGL J1131.0+3815 | fsrq | 174.7 | 38.5 | 13.4 $\pm$ 4.4 | 1.73
1FLE J1145+4001 | 4FGL J1146.9+3958 | fsrq | 176.5 | 40.0 | 21.6 $\pm$ 6.5 | 1.09
1FLE J1148-3800 | 4FGL J1147.0-3812 | bll | 177.0 | -38.0 | 7.2 $\pm$ 2.4 | 1.05
1FLE J1147+4836 | 4FGL J1153.4+4931 | fsrq | 176.9 | 48.6 | 7.8 $\pm$ 2.6 | 0.33
1FLE J1201+2934 | 4FGL J1159.5+2914 | fsrq | 180.3 | 29.6 | 15.4 $\pm$ 5.1 | 0.72
1FLE J1206+5421 | 4FGL J1208.9+5441 | fsrq | 181.6 | 54.4 | 10.1 $\pm$ 3.4 | 1.34
1FLE J1219+2943 | 4FGL J1217.9+3007 | bll | 184.9 | 29.7 | 11.9 $\pm$ 3.9 | 0.13
1FLE J1216+5019 | 4FGL J1223.9+5000 | fsrq | 184.1 | 50.3 | 8.4 $\pm$ 2.8 | 1.07
1FLE J1224+2118 | 4FGL J1224.9+2122 | fsrq | 186.2 | 21.3 | 56 $\pm$ 13 | 0.44
1FLE J1227+0218 | 4FGL J1229.0+0202 | fsrq | 187.0 | 2.3 | 65 $\pm$ 14 | 0.16
1FLE J1247-2541 | 4FGL J1246.7-2548 | fsrq | 191.8 | -25.7 | 20.5 $\pm$ 6.2 | 0.64
1FLE J1256-0545 | 4FGL J1256.1-0547 | fsrq | 194.0 | -5.8 | 63 $\pm$ 14 | 0.54
1FLE J1256-2314 | 4FGL J1258.8-2219 | fsrq | 194.1 | -23.2 | 13.4 $\pm$ 4.4 | 1.3
1FLE J1309+3302 | 4FGL J1310.5+3221 | fsrq | 197.4 | 33.0 | 12.5 $\pm$ 4.1 | 1.0
1FLE J1324+2247 | 4FGL J1321.1+2216 | fsrq | 201.1 | 22.8 | 6.0 $\pm$ 2.0 | 0.94
1FLE J1332-0518 | 4FGL J1332.0-0509 | fsrq | 203.2 | -5.3 | 15.2 $\pm$ 5.0 | 2.15
1FLE J1333-1250 | 4FGL J1332.6-1256 | fsrq | 203.4 | -12.8 | 16.0 $\pm$ 5.3 | 1.5
1FLE J1342+6530 | 4FGL J1338.0+6534 | fsrq | 205.6 | 65.5 | 8.7 $\pm$ 2.9 | 0.95
1FLE J1344+4456 | 4FGL J1345.5+4453 | fsrq | 206.2 | 44.9 | 27.3 $\pm$ 8.2 | 2.53
1FLE J1416-0818 | 4FGL J1419.4-0838 | fsrq | 214.1 | -8.3 | 6.4 $\pm$ 2.1 | –
1FLE J1427-4205 | 4FGL J1427.9-4206 | fsrq | 217.0 | -42.1 | 77 $\pm$ 17 | 1.55
1FLE J1436+2409 | 4FGL J1436.9+2321 | fsrq | 219.2 | 24.2 | 14.3 $\pm$ 4.8 | 1.54
1FLE J1456-3612 | 4FGL J1457.4-3539 | fsrq | 224.2 | -36.2 | 12.7 $\pm$ 4.2 | 1.42
1FLE J1503+1033 | 4FGL J1504.4+1029 | fsrq | 225.9 | 10.6 | 31.7 $\pm$ 9.6 | 1.84
1FLE J1512-0913 | 4FGL J1512.8-0906 | fsrq | 228.2 | -9.2 | 156 $\pm$ 32 | 0.36
1FLE J1518-2422 | 4FGL J1517.7-2422 | bll | 229.7 | -24.4 | 14.7 $\pm$ 4.9 | 0.05
1FLE J1522+3147 | 4FGL J1522.1+3144 | fsrq | 230.6 | 31.8 | 56 $\pm$ 12 | 1.49
1FLE J1518-2650 | 4FGL J1522.6-2730 | bll | 229.5 | -26.8 | 10.3 $\pm$ 3.4 | 1.29
1FLE J1559+1149 | 4FGL J1555.7+1111 | bll | 239.9 | 11.8 | 7.8 $\pm$ 2.7 | –
1FLE J1603+5734 | 4FGL J1604.6+5714 | fsrq | 240.8 | 57.6 | 12.2 $\pm$ 4.1 | 0.72
1FLE J1626-7732 | 4FGL J1617.9-7718 | fsrq | 246.7 | -77.5 | 12.7 $\pm$ 4.2 | 1.71
1FLE J1625-2510 | 4FGL J1625.7-2527 | fsrq | 246.4 | -25.2 | 38 $\pm$ 12 | 0.79
1FLE J1625-2926 | 4FGL J1626.0-2950 | fsrq | 246.4 | -29.4 | 12.1 $\pm$ 4.0 | 0.82
1FLE J1636+3831 | 4FGL J1635.2+3808 | fsrq | 249.1 | 38.5 | 73 $\pm$ 16 | 1.81
1FLE J1703+6815 | 4FGL J1700.0+6830 | fsrq | 255.8 | 68.3 | 14.1 $\pm$ 4.8 | 0.3
1FLE J1720+0916 | 4FGL J1722.7+1014 | fsrq | 260.1 | 9.3 | 8.0 $\pm$ 2.7 | 0.73
1FLE J1739+5134 | 4FGL J1740.5+5211 | fsrq | 264.8 | 51.6 | 11.7 $\pm$ 3.9 | 1.38
1FLE J1735+7015 | 4FGL J1748.6+7005 | bll | 263.9 | 70.3 | 16.6 $\pm$ 5.5 | 0.77
1FLE J1753+7815 | 4FGL J1800.6+7828 | bll | 268.4 | 78.3 | 20.4 $\pm$ 6.2 | 0.68
1FLE J1827+6859 | 4FGL J1823.5+6858 | bll | 276.9 | 69.0 | 23.3 $\pm$ 7.0 | –
1FLE J1831-5805 | 4FGL J1832.6-5658 | bll | 277.9 | -58.1 | 21.2 $\pm$ 6.4 | –
1FLE J1834-2116 | 4FGL J1833.6-2103 | fsrq | 278.6 | -21.3 | 23.4 $\pm$ 7.1 | 2.51
1FLE J1838+6812 | 4FGL J1842.3+6810 | fsrq | 279.6 | 68.2 | 20.8 $\pm$ 6.3 | 0.47
1FLE J1845+3238 | 4FGL J1848.4+3217 | fsrq | 281.3 | 32.6 | 16.5 $\pm$ 5.5 | 0.8
1FLE J1914-2017 | 4FGL J1911.2-2006 | fsrq | 288.5 | -20.3 | 14.2 $\pm$ 4.7 | 1.12
1FLE J1938-6215 | 4FGL J1941.3-6210 | bll | 294.5 | -62.3 | 17.5 $\pm$ 5.3 | –
1FLE J1958-3919 | 4FGL J1958.0-3845 | fsrq | 299.6 | -39.3 | 16.1 $\pm$ 5.3 | 0.63
1FLE J2001+6556 | 4FGL J2007.2+6607 | fsrq | 300.3 | 65.9 | 14.1 $\pm$ 4.7 | 1.32
1FLE J2028+7651 | 4FGL J2022.5+7612 | bll | 307.2 | 76.9 | 16.4 $\pm$ 5.4 | 0.59
1FLE J2027-0805 | 4FGL J2025.6-0735 | fsrq | 306.8 | -8.1 | 21.1 $\pm$ 6.4 | 1.39
1FLE J2035+1102 | 4FGL J2035.4+1056 | fsrq | 308.8 | 11.0 | 17.6 $\pm$ 5.3 | 0.6
1FLE J2039+5042 | 4FGL J2038.7+5117 | fsrq | 309.9 | 50.7 | 21.5 $\pm$ 6.5 | 1.69
1FLE J2056-4724 | 4FGL J2056.2-4714 | fsrq | 314.2 | -47.4 | 31.3 $\pm$ 9.4 | 1.49
1FLE J2120-4549 | 4FGL J2126.3-4605 | fsrq | 320.2 | -45.8 | 9.8 $\pm$ 3.3 | 1.67
1FLE J2144+1751 | 4FGL J2143.5+1743 | fsrq | 326.2 | 17.9 | 22.1 $\pm$ 6.7 | 0.21
1FLE J2141-7616 | 4FGL J2147.3-7536 | fsrq | 325.4 | -76.3 | 19.9 $\pm$ 6.0 | 1.14
1FLE J2155-3018 | 4FGL J2151.8-3027 | fsrq | 328.9 | -30.3 | 39 $\pm$ 12 | 2.35
1FLE J2209-8335 | 4FGL J2201.5-8339 | fsrq | 332.4 | -83.6 | 11.5 $\pm$ 3.8 | 1.86
1FLE J2156+5102 | 4FGL J2201.8+5048 | fsrq | 329.2 | 51.0 | 27.5 $\pm$ 8.3 | 1.9
1FLE J2203+4214 | 4FGL J2202.7+4216 | bll | 330.8 | 42.2 | 57 $\pm$ 13 | 0.07
1FLE J2227-0838 | 4FGL J2229.7-0832 | fsrq | 337.0 | -8.6 | 18.7 $\pm$ 5.6 | 1.56
1FLE J2231+1132 | 4FGL J2232.6+1143 | fsrq | 337.9 | 11.5 | 69 $\pm$ 15 | 1.04
1FLE J2232-4923 | 4FGL J2235.3-4836 | fsrq | 338.0 | -49.4 | 6.8 $\pm$ 2.3 | 0.51
1FLE J2236+2807 | 4FGL J2236.3+2828 | fsrq | 339.2 | 28.1 | 9.2 $\pm$ 3.0 | 0.79
1FLE J2240-1340 | 4FGL J2236.5-1433 | bll | 340.1 | -13.7 | 8.3 $\pm$ 2.7 | –
1FLE J2251+4034 | 4FGL J2244.2+4057 | fsrq | 342.8 | 40.6 | 9.8 $\pm$ 3.3 | 1.17
1FLE J2256-2750 | 4FGL J2250.7-2806 | bll | 344.1 | -27.8 | 22.4 $\pm$ 6.8 | 0.52
1FLE J2254+1617 | 4FGL J2253.9+1609 | fsrq | 343.6 | 16.3 | 273 $\pm$ 56 | 0.86
1FLE J2311+3404 | 4FGL J2311.0+3425 | fsrq | 348.0 | 34.1 | 13.3 $\pm$ 4.4 | 1.82
1FLE J2320-0409 | 4FGL J2323.5-0317 | fsrq | 350.0 | -4.2 | 8.6 $\pm$ 2.9 | 1.39
1FLE J2329+0858 | 4FGL J2327.5+0939 | fsrq | 352.5 | 9.0 | 10.6 $\pm$ 3.5 | 1.84
1FLE J2330-4033 | 4FGL J2328.3-4036 | fsrq | 352.5 | -40.6 | 7.7 $\pm$ 2.6 | –
1FLE J2329-4929 | 4FGL J2329.3-4955 | fsrq | 352.4 | -49.5 | 37 $\pm$ 11 | 0.52
1FLE J2345-1611 | 4FGL J2345.2-1555 | fsrq | 356.5 | -16.2 | 15.7 $\pm$ 5.2 | 0.62

Note. — The provided uncertainties on the energy flux measurements are
$1\sigma$ errors. Classifications are obtained from the blazars’ associations
in the 4FGL-DR2 catalog. All other quantities obtained from the 1FLE catalog.

aRedshift in the 1FLE catalog is obtained from the sources’ associations in
the Fermi-LAT 3LAC catalog. A redshift of “–” indicates no association or no
redshift information.

bThis is the same blazar discussed in Section 1, TXS 0506+056.

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