Content uploaded by Carmelo Pellegrino
Author content
All content in this area was uploaded by Carmelo Pellegrino on Jun 20, 2017
Content may be subject to copyright.
First combined search for neutrino point-sources in
the Southern Sky with the ANTARES and IceCube
neutrino telescopes
The ANTARES1and IceCube2Collaborations
1Complete list of authors on pages 2-4
2Complete list of authors on pages 5-7
A search for cosmic neutrino point-like sources using the ANTARES and IceCube neutrino tele-
scopes over the Southern Hemisphere is presented. The ANTARES data was collected between
January 2007 and December 2012, whereas the IceCube data ranges from April 2008 to May
2011. Clusters of muon neutrinos over the diffusely distributed background have been looked for
by means of an unbinned maximum likelihood maximisation. This method is used to search for
a localised excess of events over the whole Southern Sky assuming an E−2source spectrum. A
search over a pre-selected list of candidate sources has also been carried out for different source
assumptions: spectral indices of 2.0 and 2.5, and energy cutoffs of 1 PeV, 300 TeV and 100 TeV.
No significant excess over the expected background has been found, and upper limits for the
candidate sources are presented compared to the individual experiments.
Corresponding authors: Javier Barrios-Martí 1a∗
, Chad Finley2b
1javier.barrios@ific.uv.es
2cfinley@fysik.su.se
aInstituto de Física Corpuscular, IFIC (UV-CSIC), Parque Científico, C/Catedrático José
Beltrán 2, E-46980 Paterna, Spain
bOskar Klein Centre and Dept. of Physics, Stockholm University, SE-10691 Stockholm, Sweden
The 34th International Cosmic Ray Conference,
30 July- 6 August, 2015
The Hague, The Netherlands
∗Speaker.
c
Copyright owned by the author(s) under the terms of the Creative Commons Attribution-NonCommercial-ShareAlike Licence. http://pos.sissa.it/
arXiv:1511.05025v1 [astro-ph.HE] 16 Nov 2015
ANTARES-IceCube combined point-source search Javier Barrios-Martí 1a
The ANTARES Collaboration
S. Adrián-Martíneza, M. Agerong, A. Albertb, M. Andréc, G. Antone, M. Ardida, J.-J. Aubertg,
B. Bareth, J. Barrios-Martíi, S. Basaj, V. Berting, S. Biagik,l, R. Bormuthg,ak, M.C. Bouwhuisf, R.
Bruijnf,ac, J. Brunnerg, J. Bustog, A. Caponem,n, L. Carameteo, J. Carrg, T. Chiarusik, M. Circellar,
A. Coleiroh, R. Coniglionev, H. Costantinig, P. Coyleg, A. Creusoth, I. Dekeysers, A. Deschampsq,
G. De Bonism,n, C. Distefanov, C. Donzaudh,w, D. Dornicg, D. Drouhinb, A. Dumasp, T. Eberle,
D. Elsässery, A. Enzenhöfere, SK. Fehne, I. Felisa, P. Fermanim,n, L.A. Fuscok,l, S. Galatàh, P. Gayp,
S. Geißelsödere, K. Geyere, V. Giordanoz, A. Gleixnere, H. Glotinan , R. Gracia-Ruizh, K. Grafe,
S. Hallmanne, H. van Harenaa, A.J. Heijboer f, Y. Helloq, J.J. Hernández-Reyi, J. Hößle, J. Hofestädte,
C. Hugond, C.W Jamese, M. de Jong f, M. Kadlery, O. Kalekine, U. Katze, D. Kießlinge, P. Kooijmanf,ab,ac,
A. Kouchnerh, M. Kretery, I. Kreykenbohmad , V. Kulikovskiyd,ae, C. Lachaudh, D. Lefèvres,
E. Leonoraz,a f , S. Loucatosah, M. Marcelinj, A. Margiottak,l, A. Marinelliao,a p, J.A. Martínez-
Moraa, A. Mathieug, T. Michaelf, P. Migliozzit, A. Moussaam, L. Moscosoh,†, C. Muellery, E. Nezrij,
G.E. P˘
av˘
ala¸so, P. Payreg,†, C. Pellegrinok,l, C. Perrinam,n, P. Piattelliv, V. Popao, T. Pradierai,
C. Raccab, G. Riccobenev, K. Roensche, M. Saldañaa, D.F.E. Samtlebenf,ak, A. Sánchez-Losai,
M. Sanguinetid,al , P. Sapienzav, J. Schmide, J. Schnabele, F. Schüsslerah , T. Seitze, C. Siegere,
M. Spuriok,l, J.J.M. Steijgerf, Th. Stolarczykah, M. Taiutid,al , C. Tamburinis, A. Trovatov, M. Tselengidoue,
D. Turping, C. Tönnisi, B. Vallageah, C. Valléeg, V. Van Elewyckh, E. Visserf, D. Vivolot,u,
S. Wagnere, J. Wilmsad , J.D. Zornozai, J. Zúñigai
aInstitut d’Investigació per a la Gestió Integrada de les Zones Costaneres (IGIC) - Universitat
Politècnica de València. C/ Paranimf 1 , 46730 Gandia, Spain
bGRPHE -Université de Haute Alsace & Institut universitaire de technologie de Colmar, 34 rue du
Grillenbreit BP 50568 - 68008 Colmar, France
cTechnical University of Catalonia, Laboratory of Applied Bioacoustics, Rambla Exposició,08800
Vilanova i la Geltrú,Barcelona, Spain
dINFN - Sezione di Genova, Via Dodecaneso 33, 16146 Genova, Italy
eFriedrich-Alexander-Universität Erlangen-Nürnberg, Erlangen Centre for Astroparticle Physics,
Erwin-Rommel-Str. 1, 91058 Erlangen, Germany
fNikhef, Science Park, Amsterdam, The Netherlands
gAix Marseille Université, CNRS/IN2P3, CPPM UMR 7346, 13288, Marseille, France
hAPC, Université Paris Diderot, CNRS/IN2P3, CEA/IRFU, Observatoire de Paris, Sorbonne Paris
Cité, 75205 Paris, France
iIFIC - Instituto de Física Corpuscular, Parque Científico c/ Catedrático José Beltrán, 2 - E46980
Paterna, Valencia (Spain)
jLAM - Laboratoire d’Astrophysique de Marseille, Pôle de l’Étoile Site de Château-Gombert, rue
Frédéric Joliot-Curie 38, 13388 Marseille Cedex 13, France
kINFN - Sezione di Bologna, Viale Berti-Pichat 6/2, 40127 Bologna, Italy
lDipartimento di Fisica dell’Università, Viale Berti Pichat 6/2, 40127 Bologna, Italy
mINFN -Sezione di Roma, P.le Aldo Moro 2, 00185 Roma, Italy
nDipartimento di Fisica dell’Università La Sapienza, P.le Aldo Moro 2, 00185 Roma, Italy
oInstitute for Space Sciences, R-77125 Bucharest, M˘
agurele, Romania
2
ANTARES-IceCube combined point-source search Javier Barrios-Martí 1a
pLaboratoire de Physique Corpusculaire, Clermont Université, Université Blaise Pascal, CNRS/IN2P3,
BP 10448, F-63000 Clermont-Ferrand, France
qGéoazur, Université Nice Sophia-Antipolis, CNRS, IRD, Observatoire de la Côte d’Azur, Sophia
Antipolis, France
rINFN - Sezione di Bari, Via E. Orabona 4, 70126 Bari, Italy
sAix Marseille Université, CNRS/INSU, IRD, Mediterranean Institute of Oceanography (MIO),
UM 110, Marseille, France ; Université de Toulon, CNRS, IRD, Mediterranean Institute of Oceanog-
raphy (MIO), UM 110, La Garde, France
tINFN -Sezione di Napoli, Via Cintia 80126 Napoli, Italy
uDipartimento di Fisica dell’Università Federico II di Napoli, Via Cintia 80126, Napoli, Italy
vINFN - Laboratori Nazionali del Sud (LNS), Via S. Sofia 62, 95123 Catania, Italy
wUniv. Paris-Sud , 91405 Orsay Cedex, France
yInstitut für Theoretische Physik und Astrophysik, Universität Würzburg, Emil-Fischer Str. 31,
97074 Würzburg, Germany
zINFN - Sezione di Catania, Viale Andrea Doria 6, 95125 Catania, Italy
aaRoyal Netherlands Institute for Sea Research (NIOZ), Landsdiep 4,1797 SZ ’t Horntje (Texel),
The Netherlands
abUniversiteit Utrecht, Faculteit Betawetenschappen, Princetonplein 5, 3584 CC Utrecht, The Nether-
lands
acUniversiteit van Amsterdam, Instituut voor Hoge-Energie Fysica, Science Park 105, 1098 XG
Amsterdam, The Netherlands
ad Dr. Remeis-Sternwarte and ECAP, Universität Erlangen-Nürnberg, Sternwartstr. 7, 96049 Bam-
berg, Germany
aeMoscow State University,Skobeltsyn Institute of Nuclear Physics,Leninskie gory, 119991 Moscow,
Russia
a f Dipartimento di Fisica ed Astronomia dell’Università, Viale Andrea Doria 6, 95125 Catania, Italy
ahDirection des Sciences de la Matière - Institut de recherche sur les lois fondamentales de l’Univers
- Service de Physique des Particules, CEA Saclay, 91191 Gif-sur-Yvette Cedex, France
aiUniversité de Strasbourg, IPHC, 23 rue Becquerel 67087 Strasbourg, France CNRS, UMR7178,
67087 Strasbourg, France
akUniversiteit Leiden, Leids Instituut voor Onderzoek in Natuurkunde, 2333 CA Leiden, The
Netherlands
al Dipartimento di Fisica dell’Università, Via Dodecaneso 33, 16146 Genova, Italy
amUniversity Mohammed I, Laboratory of Physics of Matter and Radiations, B.P.717, Oujda 6000,
Morocco
an LSIS, Aix Marseille Université CNRS ENSAM LSIS UMR 7296 13397 Marseille, France ;
Université de Toulon CNRS LSIS UMR 7296 83957 La Garde, France ; Institut Universitaire de
France, 75005 Paris, France
aoINFN - Sezione di Pisa, Largo B. Pontecorvo 3, 56127 Pisa, Italy
ap Dipartimento di Fisica dell’Università, Largo B. Pontecorvo 3, 56127 Pisa, Italy
†Deceased
3
ANTARES-IceCube combined point-source search Javier Barrios-Martí 1a
Acknowledgment: The authors acknowledge the financial support of the funding agencies: Centre
National de la Recherche Scientifique (CNRS), Commissariat à l’énergie atomique et aux énergies
alternatives (CEA), Commission Européenne (FEDER fund and Marie Curie Program), Région
Île-de-France (DIM-ACAV) Région Alsace (contrat CPER), Région Provence-Alpes-Côte d’Azur,
Département du Var and Ville de La Seyne-sur-Mer, France; Bundesministerium für Bildung und
Forschung (BMBF), Germany; Istituto Nazionale di Fisica Nucleare (INFN), Italy; Stichting voor
Fundamenteel Onderzoek der Materie (FOM), Nederlandse organisatie voor Wetenschappelijk On-
derzoek (NWO), the Netherlands; Council of the President of the Russian Federation for young
scientists and leading scientific schools supporting grants, Russia; National Authority for Scien-
tific Research (ANCS), Romania; Ministerio de Economía y Competitividad (MINECO), Prome-
teo and Grisolía programs of Generalitat Valenciana and MultiDark, Spain; Agence de l’Oriental
and CNRST, Morocco. We also acknowledge the technical support of Ifremer, AIM and Foselev
Marine for the sea operation and the CC-IN2P3 for the computing facilities
4
ANTARES-IceCube combined point-source search Javier Barrios-Martí 1a
IceCube Collaboration
M. G. Aartsen2, K. Abraham32, M. Ackermann48, J. Adams15, J. A. Aguilar12, M. Ahlers29 ,
M. Ahrens39, D. Altmann23 , T. Anderson45 , M. Archinger30, C. Arguelles29, T. C. Arlen45 , J. Auffenberg1,
X. Bai37, S. W. Barwick26, V. Baum30, R. Bay7, J. J. Beatty17,18 , J. Becker Tjus10, K.-H. Becker47,
E. Beiser29, S. BenZvi29 , P. Berghaus48, D. Berley16, E. Bernardini48, A. Bernhard32, D. Z. Besson27,
G. Binder8,7, D. Bindig47, M. Bissok1, E. Blaufuss16 , J. Blumenthal1, D. J. Boersma46, C. Bohm39,
M. Börner20, F. Bos10, D. Bose41, S. Böser30 , O. Botner46, J. Braun29, L. Brayeur13, H.-P. Bretz48,
N. Buzinsky22, J. Casey5, M. Casier13 , E. Cheung16, D. Chirkin29, A. Christov24, B. Christy16,
K. Clark42, L. Classen23, S. Coenders32, D. F. Cowen45,44, A. H. Cruz Silva48, J. Daughhetee5,
J. C. Davis17, M. Day29, J. P. A. M. de André21, C. De Clercq13 , E. del Pino Rosendo30, H. Dembinski33 ,
S. De Ridder25, P. Desiati29, K. D. de Vries13, G. de Wasseige13, M. de With9, T. DeYoung21,
J. C. Díaz-Vélez29, V. di Lorenzo30, J. P. Dumm39, M. Dunkman45, R. Eagan45, B. Eberhardt30,
T. Ehrhardt30 , B. Eichmann10, S. Euler46, P. A. Evenson33, O. Fadiran29, S. Fahey29, A. R. Fazely6,
A. Fedynitch10, J. Feintzeig29 , J. Felde16, K. Filimonov7, C. Finley39, T. Fischer-Wasels47, S. Flis39,
C.-C. Fösig30, T. Fuchs20, T. K. Gaisser33, R. Gaior14, J. Gallagher28, L. Gerhardt8,7, K. Ghorbani29,
D. Gier1, L. Gladstone29, M. Glagla1, T. Glüsenkamp48, A. Goldschmidt8, G. Golup13, J. G. Gonzalez33 ,
D. Góra48, D. Grant22 , J. C. Groh45, A. Groß32, C. Ha8,7, C. Haack1, A. Haj Ismail25, A. Hallgren46,
F. Halzen29 , B. Hansmann1, K. Hanson29, D. Hebecker9, D. Heereman12, K. Helbing47 , R. Hellauer16,
D. Hellwig1, S. Hickford47, J. Hignight21 , G. C. Hill2, K. D. Hoffman16, R. Hoffmann47, K. Holzapfel32,
A. Homeier11, K. Hoshina29,a, F. Huang45 , M. Huber32, W. Huelsnitz16, P. O. Hulth39 , K. Hultqvist39,
S. In41, A. Ishihara14, E. Jacobi48, G. S. Japaridze4, K. Jero29, M. Jurkovic32, B. Kaminsky48,
A. Kappes23, T. Karg48, A. Karle29, M. Kauer29,34, A. Keivani45, J. L. Kelley29, J. Kemp1, A. Kheirandish29,
J. Kiryluk40, J. Kläs47, S. R. Klein8,7, G. Kohnen31, R. Koirala33, H. Kolanoski9, R. Konietz1,
A. Koob1, L. Köpke30, C. Kopper22, S. Kopper47, D. J. Koskinen19, M. Kowalski9,48, K. Krings32,
G. Kroll30, M. Kroll10 , J. Kunnen13, N. Kurahashi36, T. Kuwabara14, M. Labare25, J. L. Lanfranchi45 ,
M. J. Larson19, M. Lesiak-Bzdak40, M. Leuermann1, J. Leuner1, J. Lünemann30 , J. Madsen38,
G. Maggi13, K. B. M. Mahn21 , R. Maruyama34, K. Mase14 , H. S. Matis8, R. Maunu16, F. McNally29,
K. Meagher12, M. Medici19 , A. Meli25, T. Menne20 , G. Merino29, T. Meures12 , S. Miarecki8,7,
E. Middell48, E. Middlemas29, L. Mohrmann48, T. Montaruli24, R. Morse29, R. Nahnhauer48,
U. Naumann47, H. Niederhausen40, S. C. Nowicki22, D. R. Nygren8, A. Obertacke47, A. Olivas16,
A. Omairat47, A. O’Murchadha12 , T. Palczewski43, H. Pandya33, L. Paul1, J. A. Pepper43, C. Pérez de los Heros46 ,
C. Pfendner17, D. Pieloth20, E. Pinat12, J. Posselt47, P. B. Price7, G. T. Przybylski8, J. Pütz1,
M. Quinnan45, L. Rädel1, M. Rameez24, K. Rawlins3, P. Redl16, R. Reimann1, M. Relich14 ,
E. Resconi32, W. Rhode20, M. Richman36, S. Richter29, B. Riedel22, S. Robertson2, M. Rongen1,
C. Rott41, T. Ruhe20, D. Ryckbosch25, S. M. Saba10, L. Sabbatini29, H.-G. Sander30, A. Sandrock20,
J. Sandroos30, S. Sarkar19,35, K. Schatto30, F. Scheriau20, M. Schimp1, T. Schmidt16, M. Schmitz20,
S. Schoenen1, S. Schöneberg10, A. Schönwald48, L. Schulte11, D. Seckel33, S. Seunarine38, R. Shanidze48,
M. W. E. Smith45, D. Soldin47, G. M. Spiczak38, C. Spiering48, M. Stahlberg1, M. Stamatikos17,b,
T. Stanev33, N. A. Stanisha45, A. Stasik48, T. Stezelberger8, R. G. Stokstad8, A. Stößl48 , E. A. Strahler13,
R. Ström46, N. L. Strotjohann48 , G. W. Sullivan16, M. Sutherland17, H. Taavola46, I. Taboada5,
S. Ter-Antonyan6, A. Terliuk48 , G. Teši´
c45, S. Tilav33, P. A. Toale43, M. N. Tobin29, D. Tosi29,
M. Tselengidou23, A. Turcati32, E. Unger46 , M. Usner48, S. Vallecorsa24, J. Vandenbroucke29,
5
ANTARES-IceCube combined point-source search Javier Barrios-Martí 1a
N. van Eijndhoven13, S. Vanheule25, J. van Santen29, J. Veenkamp32, M. Vehring1, M. Voge11,
M. Vraeghe25, C. Walck39, M. Wallraff1, N. Wandkowsky29, Ch. Weaver22, C. Wendt29, S. Westerhoff29,
B. J. Whelan2, N. Whitehorn29, C. Wichary1, K. Wiebe30, C. H. Wiebusch1, L. Wille29, D. R. Williams43,
H. Wissing16, M. Wolf39, T. R. Wood22, K. Woschnagg7, D. L. Xu43, X. W. Xu6, Y. Xu40, J. P. Yanez48,
G. Yodh26, S. Yoshida14, M. Zoll39
1III. Physikalisches Institut, RWTH Aachen University, D-52056 Aachen, Germany
2School of Chemistry & Physics, University of Adelaide, Adelaide SA, 5005 Australia
3Dept. of Physics and Astronomy, University of Alaska Anchorage, 3211 Providence Dr., Anchor-
age, AK 99508, USA
4CTSPS, Clark-Atlanta University, Atlanta, GA 30314, USA
5School of Physics and Center for Relativistic Astrophysics, Georgia Institute of Technology, At-
lanta, GA 30332, USA
6Dept. of Physics, Southern University, Baton Rouge, LA 70813, USA
7Dept. of Physics, University of California, Berkeley, CA 94720, USA
8Lawrence Berkeley National Laboratory, Berkeley, CA 94720, USA
9Institut für Physik, Humboldt-Universität zu Berlin, D-12489 Berlin, Germany
10Fakultät für Physik & Astronomie, Ruhr-Universität Bochum, D-44780 Bochum, Germany
11Physikalisches Institut, Universität Bonn, Nussallee 12, D-53115 Bonn, Germany
12Université Libre de Bruxelles, Science Faculty CP230, B-1050 Brussels, Belgium
13Vrije Universiteit Brussel, Dienst ELEM, B-1050 Brussels, Belgium
14Dept. of Physics, Chiba University, Chiba 263-8522, Japan
15Dept. of Physics and Astronomy, University of Canterbury, Private Bag 4800, Christchurch, New
Zealand
16Dept. of Physics, University of Maryland, College Park, MD 20742, USA
17Dept. of Physics and Center for Cosmology and Astro-Particle Physics, Ohio State University,
Columbus, OH 43210, USA
18Dept. of Astronomy, Ohio State University, Columbus, OH 43210, USA
19Niels Bohr Institute, University of Copenhagen, DK-2100 Copenhagen, Denmark
20Dept. of Physics, TU Dortmund University, D-44221 Dortmund, Germany
21Dept. of Physics and Astronomy, Michigan State University, East Lansing, MI 48824, USA
22Dept. of Physics, University of Alberta, Edmonton, Alberta, Canada T6G 2E1
23Erlangen Centre for Astroparticle Physics, Friedrich-Alexander-Universität Erlangen-Nürnberg,
D-91058 Erlangen, Germany
24Département de physique nucléaire et corpusculaire, Université de Genève, CH-1211 Genève,
Switzerland
25Dept. of Physics and Astronomy, University of Gent, B-9000 Gent, Belgium
26Dept. of Physics and Astronomy, University of California, Irvine, CA 92697, USA
27Dept. of Physics and Astronomy, University of Kansas, Lawrence, KS 66045, USA
28Dept. of Astronomy, University of Wisconsin, Madison, WI 53706, USA
29Dept. of Physics and Wisconsin IceCube Particle Astrophysics Center, University of Wisconsin,
Madison, WI 53706, USA
30Institute of Physics, University of Mainz, Staudinger Weg 7, D-55099 Mainz, Germany
6
ANTARES-IceCube combined point-source search Javier Barrios-Martí 1a
31Université de Mons, 7000 Mons, Belgium
32Technische Universität München, D-85748 Garching, Germany
33Bartol Research Institute and Dept. of Physics and Astronomy, University of Delaware, Newark,
DE 19716, USA
34Dept. of Physics, Yale University, New Haven, CT 06520, USA
35Dept. of Physics, University of Oxford, 1 Keble Road, Oxford OX1 3NP, UK
36Dept. of Physics, Drexel University, 3141 Chestnut Street, Philadelphia, PA 19104, USA
37Physics Department, South Dakota School of Mines and Technology, Rapid City, SD 57701,
USA
38Dept. of Physics, University of Wisconsin, River Falls, WI 54022, USA
39Oskar Klein Centre and Dept. of Physics, Stockholm University, SE-10691 Stockholm, Sweden
40Dept. of Physics and Astronomy, Stony Brook University, Stony Brook, NY 11794-3800, USA
41Dept. of Physics, Sungkyunkwan University, Suwon 440-746, Korea
42Dept. of Physics, University of Toronto, Toronto, Ontario, Canada, M5S 1A7
43Dept. of Physics and Astronomy, University of Alabama, Tuscaloosa, AL 35487, USA
44Dept. of Astronomy and Astrophysics, Pennsylvania State University, University Park, PA 16802,
USA
45Dept. of Physics, Pennsylvania State University, University Park, PA 16802, USA
46Dept. of Physics and Astronomy, Uppsala University, Box 516, S-75120 Uppsala, Sweden
47Dept. of Physics, University of Wuppertal, D-42119 Wuppertal, Germany
48DESY, D-15735 Zeuthen, Germany
aEarthquake Research Institute, University of Tokyo, Bunkyo, Tokyo 113-0032, Japan
bNASA Goddard Space Flight Center, Greenbelt, MD 20771, USA
Acknowledgment: We acknowledge the support from the following agencies: U.S. National Sci-
ence Foundation-Office of Polar Programs, U.S. National Science Foundation-Physics Division,
University of Wisconsin Alumni Research Foundation, the Grid Laboratory Of Wisconsin (GLOW)
grid infrastructure at the University of Wisconsin - Madison, the Open Science Grid (OSG) grid in-
frastructure; U.S. Department of Energy, and National Energy Research Scientific Computing Cen-
ter, the Louisiana Optical Network Initiative (LONI) grid computing resources; Natural Sciences
and Engineering Research Council of Canada, WestGrid and Compute/Calcul Canada; Swedish
Research Council, Swedish Polar Research Secretariat, Swedish National Infrastructure for Com-
puting (SNIC), and Knut and Alice Wallenberg Foundation, Sweden; German Ministry for Educa-
tion and Research (BMBF), Deutsche Forschungsgemeinschaft (DFG), Helmholtz Alliance for As-
troparticle Physics (HAP), Research Department of Plasmas with Complex Interactions (Bochum),
Germany; Fund for Scientific Research (FNRS-FWO), FWO Odysseus programme, Flanders Insti-
tute to encourage scientific and technological research in industry (IWT), Belgian Federal Science
Policy Office (Belspo); University of Oxford, United Kingdom; Marsden Fund, New Zealand;
Australian Research Council; Japan Society for Promotion of Science (JSPS); the Swiss National
Science Foundation (SNSF), Switzerland; National Research Foundation of Korea (NRF); Danish
National Research Foundation, Denmark (DNRF)
7
ANTARES-IceCube combined point-source search Javier Barrios-Martí 1a
1. Introduction
Neutrinos offer unique insight into the Universe due to the fact that they interact only weakly.
This also implies that their detection is challenging. The field is presently led by the IceCube [1]
and ANTARES [2] experiments. IceCube is the first detector to reach the cubic-kilometer size pre-
dicted to be necessary to detect cosmic neutrino fluxes. Recently, IceCube has reported the crucial
discovery of a flux of neutrinos up to ∼PeV energies which cannot be explained by the background
of atmospheric muons and neutrinos [3,4]. Meanwhile the ANTARES experiment has proven the
feasibility of the Cherenkov telescope technique in sea water [5,6]. While its instrumented vol-
ume is significantly smaller than that of IceCube, its geographical location provides a better view
of the Southern sky for neutrino energies below 100 TeV. This provides better sensitivity to the
many predicted Galactic sources of neutrinos in this part of the sky. The complementarity of the
detectors for Southern sky sources allows for a gain in sensitivity by combining the analysis of data
from both experiments in a joint search for point sources. The improvement with this combination
depends on the actual details of the fluxes, in particular the energy spectrum and a possible energy
cut-off of the signal. The energy spectra are not yet known and predictions vary widely depending
on the source model.
2. Neutrino Data Samples
The data sample corresponds to all events from the Southern sky which were included in the
three-year IceCube point-source analysis [7] combined with the events in the latest ANTARES
point-source analysis [8]. The ANTARES sample corresponds to data recorded from 2007 January
29 to 2012 December 31. The total number of events in this sample amounts to 5516, of which 4136
are from the Southern Hemisphere. The estimated contamination of mis-reconstructed atmospheric
muons is of 10%. The IceCube data was recorded from 2008 April 5 to 2011 May 13, with a total
number of 146 018 events in the Southern Sky. In contrast to the ANTARES sample, these events
are predominantly atmospheric muons rather than atmospheric neutrinos, because the Earth cannot
be used as a neutrino filter for directions above the detector.
The fraction of expected source events needs to be calculated in order to estimate the relative
contribution of each sample in the likelihood. This quantity is defined as the ratio of the expected
number of signal events from the given sample to the expected number from all samples,
Cj(δ,dΦ/dEν) = Nj(δ,dΦ/dEν)
∑iNi(δ,dΦ/dEν),(2.1)
where the total number of expected events for the j-th sample, Nj, with a given source declination,
δ, and a given source spectrum, dΦ
dEν, can be calculated as
Njδ,dΦ
dEν=Zdt ZdEνAj
eff(Eν,δ)dΦ
dEν
.(2.2)
The time integration extends over the live time of each sample and Aj
eff(Eν,δ)indicates the
effective area of the corresponding detector layout jas a function of the neutrino energy, Eν, and
the declination of the source, δ. The declination of a given event is not directly related with the
8
ANTARES-IceCube combined point-source search Javier Barrios-Martí 1a
zenith direction in the ANTARES telescope, and therefore, the effective area for a given declination
changes at different times of the day. Steady, non time-dependent sources are assumed for this
analysis. Therefore, it is possible to integrate the zenith dependence for the considered period.
Since each detector layout has a different response depending on the neutrino energy and
declination, this relative fraction of source events needs to be calculated for different source spectra
and source declinations. Figure 1shows the relative fraction of signal events for an unbroken E−2
spectrum, which corresponds to the standard first order Fermi spectrum [9,10]. In this case, there
is a significant contribution from all samples over most of the Southern Sky, with the ANTARES
contribution being more significant for declinations closer to δ= –90◦, and IceCube for declinations
closer to 0◦.
Other source assumptions are also considered in this analysis. The relative fraction of source
events is also calculated for an unbroken E−2.5power-law spectrum, as suggested in recent IceCube
diffuse-flux searches [11], and for an E−2spectrum with an exponential square-root cut-off (dΦ
dE ∝
E−2exph−qE
Ecut−off i) for energy cut-offs of 100 TeV, 300 TeV and 1 PeV, since a square-root
dependence may be expected from Galactic sources [12]. Figure 2shows the relative fraction
of source events for these cases. Compared with an unbroken E−2spectrum, the contribution of
high energy neutrinos in all of these cases is lower, and therefore the relative contribution of the
ANTARES sample increases.
Figure 1: Relative fraction of signal events for each sample as a function of the source declination for the
case of an E−2energy spectrum. The orange, blue, and yellow shaded areas correspond respectively to the
IceCube 40, 59 and 79-string data samples, and the green shaded area indicates the ANTARES sample. The
relative fraction of signal events is used as part of the likelihood function calculation during the search.
3. Search method
An unbinned maximum likelihood ratio estimation has been performed to search for excesses
of events that could indicate cosmic neutrinos coming from a source. In order to estimate the
significance of a cluster of events, this likelihood takes into account the energy and directional
information of each event. The data sample to which an event belongs is also taken into account,
due to the differences in detector response. The likelihood, as a function of the total number of
fitted signal events, ns, can be expressed as
L(ns) =
4
∏
j=1
Nj
∏
i=1"nj
s
NjSj
i+ 1−nj
s
Nj!Bj
i#,(3.1)
9
ANTARES-IceCube combined point-source search Javier Barrios-Martí 1a
Figure 2: Relative fraction of signal events of each sample as a function of the source declination for
different energy spectra: E−2with energy cutoff Ecutoff of 1 PeV (top-left), 300 TeV (top-right), 100 TeV
(bottom-left); and E−2.5spectrum (bottom-right). The orange, blue and yellow shaded areas correspond
to the IceCube 40, 59 and 79-string data samples, respectively, and the green shaded area indicates the
ANTARES sample. The relative fraction is used as part of the likelihood function calculation during the
search.
where jindicates one of the four data samples (ANTARES, IC40, IC59 or IC79), iindicates an
event belonging to the j-th sample, Sj
iis the value of the signal probability distribution function
(PDF) for the i-th event in the j-th sample, Bj
iindicates the value of the background PDF, Njis
the total number of events in the j-th sample, and nj
sis the number of signal events fitted for in the
j−th sample. Since a given evaluation of the likelihood refers to a single source hypothesis at a
fixed sky location, the number of signal events nj
sthat is fitted for in each sample is related to the
total number of signal events nsby the relative contribution of each sample, nj
s=ns·Cj(δ,dΦ
dE ).
The signal and background PDFs for the IceCube and ANTARES samples have slightly dif-
ferent definitions. The signal PDF for ANTARES is defined as
SANT =1
2πσ2exp−∆Ψ(~xs)2
2σ2PANT
s(Nhits,σ),(3.2)
where ~xs= (αs,δs) indicates the source direction in equatorial coordinates, ∆Ψ(~xs)is the angular
distance of a given event to the source, σis the angular error estimate, and PANT
s(Nhits,σ)is the
probability for a signal event to be reconstructed with an angular error estimate of σand a number
of hits taken in the event reconstruction Nhits. The number of hits is a proxy for the energy of the
event [13].
The definition of the signal PDFs for the IceCube samples is similar,
SIC =1
2πσ2exp−∆ψ(~xs)2
2σ2PIC
s(E,σ|δ),(3.3)
10
ANTARES-IceCube combined point-source search Javier Barrios-Martí 1a
where the main difference lies in the use of the reconstructed energy, E, and the declination depen-
dence of the probability for a signal event to be reconstructed with a given σand E. Details about
the reconstructed energy proxy can be found in [7] and [14]. The declination dependence is needed
mainly because of the event selection cut on reconstructed energy, which is designed to reduce the
atmospheric muon background.
Background events are expected to be distributed uniformly in right ascension. The back-
ground PDFs are in fact obtained from the experimental data itself. The definitions of the PDFs
are:
BANT =BAN T (δ)
2πPANT
b(Nhits,σ),BIC =BIC(δ)
2πPIC
b(E,σ|δ),(3.4)
where B(δ) is the per-solid-angle rate of observed events as a function of the declination in the cor-
responding sample. PAN T
b(Nhits,σ)and PIC
b(E,σ|δ)characterize the distributions for background
event properties, in analogy with the definitions of PANT
sand PIC
sfor signal events given above.
The test statistic, TS, is determined from the likelihood (Eq. 3.1) as TS = logL(ˆns)−logL(ns=
0), where ˆnsis the value that maximizes the likelihood. The larger the TS, the lower the probability
(p-value) of the observation to be produced by the expected background. Simulations are performed
to obtain the distributions of the TS. The significance (specifically, the p-value) of an observation
is determined by the fraction of TS values which are larger or equal to the observed TS.
The TS is calculated as a preliminary step to obtain the post-trial p-values of a search. TS
distributions for the fixed-source, background-only hypotheses have been calculated in steps of 1◦
in declination from pseudo-data sets of randomized data. Because these distributions vary with
declination, the preliminary TS is turned into a "pre-trial p-value" by comparing the TS obtained
at the source location being examined to the background TS distribution for the corresponding
declination. Post-trial significance is then estimated with pseudo-data sets and according to the
type of search, as explained together with the results in Section 4.
Two different searches for point-like neutrino sources have been performed. In the candidate
list search, a possible excess of neutrino events is looked for at the location of 40 pre-selected
neutrino source candidates. Since the location of these sources is fixed (at known locations with
an uncertainty below the angular resolution of all samples) only the number of signal events nsis
a free parameter in the likelihood maximisation. These candidates correspond to all sources in the
Southern sky considered in the previous candidate-source list searches performed in the ANTARES
and IceCube point-source analyses [8] [7].
The second search is a “full sky” search, looking for a significant point-like excess anywhere
in the Southern sky. For this purpose, the likelihood is evaluated in steps of 1◦×1◦over the whole
scanned region. Since the angular resolution of both telescopes is smaller than the cell size, the
source position is taken as an additional free parameter of the likelihood to fit the best position
within the boundaries.
Both the full Southern sky and candidate-list searches have been performed using an E−2
source spectrum in the signal PDFs. The main virtue of the energy term in the PDFs is to add
power to distinguish signal neutrinos from the softer spectra of atmospheric neutrinos (∼E−3.7) and
atmospheric muons (∼E−3). Limits for the sources in the candidate list have also been calculated
for the source spectra mentioned in section 2.
11
ANTARES-IceCube combined point-source search Javier Barrios-Martí 1a
4. Results
No significant event clusters are found over the expected background. The most significant
cluster in the full-Southern sky search is located at equatorial coordinates α= 332.8◦,δ=–46.1◦,
with best-fit ˆns=7.9 and pre-trial p-value of 6.0×10−7. It’s found that 24% of pseudo-data sets
have a smaller p-value somewhere in the sky than is found in the real data; the post-trial significance
is thus 24% (0.7σin the one-sided sigma convention). The direction of this cluster is consistent
with the second most significant cluster in the previous ANTARES point-source analysis (but also
less significant).
Name δ(◦)α(◦)nspφ90CL
E−2φ90%CL
Ec=1PeV φ90C L
Ec=300TeV φ90CL
Ec=100TeV φ90CL
E−2.5
HESSJ1741-302 -30.2 -94.8 1.6 0.003 2.5E-08 7.5E-06 5.5E-08 7.2E-08 1.0E-07
3C279 -5.8 -166.0 1.1 0.05 3.1E-09 1.0E-06 6.5E-09 9.2E-09 6.7E-08
PKS0548-322 -32.3 87.7 0.9 0.07 1.6E-08 5.0E-06 3.8E-08 4.9E-08 1.4E-08
ESO139-G12 -59.9 -95.6 0.8 0.07 1.8E-08 3.9E-06 2.9E-08 3.7E-08 5.1E-08
HESSJ1023-575 -57.8 155.8 0.8 0.08 1.7E-08 3.5E-06 2.8E-08 3.5E-08 4.7E-08
RCW86 -62.5 -139.3 0.2 0.11 1.4E-08 4.4E-06 3.6E-09 4.0E-08 5.7E-08
Table 1: Pre-trial p-values, p, fitted number of source events, ns, and 90% C.L. flux limits, Φ90CL
νfor the
different source spectra for the 6 candidate sources with the lowest p-values. Units for the flux limits for the
E−2.5spectra, φ90CL
E−2.5, are given in GeV1.5cm−2s−1, whereas the rest are in GeV cm−2s−1. The sources are
sorted by their declination.
The results of the candidate source list search are presented in Table 1. No statistically sig-
nificant excess is found. The most significant excess for any object in the list corresponds to
HESS J1741-302 with a pre-trial p-value of 0.003. To account for trial factors, the search is per-
formed on the same list of sources using pseudo data-sets . 11% of randomized data sets have a
smaller p-value for some source than that found for the real data; the post-trial significance of the
source list search is thus 11% (1.2σin the one-sided sigma convention).
Table 1provides the pre-trial p-values, best-fit signal events nsand flux upper limits (under
different assumptions of the energy spectrum) for the six sources with the lowest p-value. Figure 3
shows the sensitivities and limits for this search (assuming an E−2spectrum) in comparison with
the previously published ANTARES and IceCube analyses of the same data. The point source sen-
sitivity in a substantial region of the sky, centered approximately at the declination of the Galactic
Center (δ=−30◦), can be seen to have improved by up to a factor of two. Similar gains in other
regions of the sky can be seen for different energy spectra in Figure 4.
5. Conclusion
We have presented the first combined point-source analysis of data from the ANTARES and
IceCube detectors. The combination of their different characteristics, in particular IceCube’s larger
size and ANTARES’ location in the Northern hemisphere, complement each other for Southern
sky searches. We have calculated the sensitivity to point sources and, with respect to an analysis of
either data set alone, found that up to a factor of two improvement is achieved in different regions
of the Southern sky, depending on the energy spectrum of the source. Two joint analyses of the data
sets have been performed: a search over the whole Southern sky for a point-like excess of neutrino
events, and a targeted analysis of 40 pre-selected candidate source objects. The largest excess in
12
ANTARES-IceCube combined point-source search Javier Barrios-Martí 1a
Figure 3: 90% CL sensitivities and limits (Neyman method) for the neutrino emission from point sources as
a function of source declination in the sky, for an assumed E−2energy spectrum of the source. Green points
indicate the actual limits on the candidate sources. The green line indicates the sensitivity of the combined
search. Blue and red curves/points indicate the published sensitivities/limits for the IceCube and ANTARES
analyses, respectively.
Figure 4: Point source sensitivities and limits for the following energy spectra: E−2with a square-root
exponential cut-off at E=1PeV (top left), E=300TeV (top right), E=100 TeV (bottom left) and E−2.5
unbroken power-law (bottom right). Green points indicate the actual limits on the candidate sources. The
green line indicates the sensitivity for the combined search. Blue and red curves/points indicate the sensitiv-
ities for the individual IceCube and ANTARES analyses, respectively.
13
ANTARES-IceCube combined point-source search Javier Barrios-Martí 1a
the Southern sky search has a post trial p-value of 0.24 (significance of 0.7σ). In the source list
search the candidate with the highest significance corresponds to HESS J1741-302, with a post-trial
p-value of 0.11 (significance of 1.2σ). Both of the results are compatible with the background-only
hypothesis and no significant excess is found. Flux upper limits for each of the source candidates
have been calculated for E−2and E−2.5power-law energy spectra, as well as for E−2spectra with
cut-offs at energies of 1PeV, 300 TeV, and 100 TeV. Because of their complementary nature, with
IceCube providing more sensitivity at higher energies and ANTARES at lower energies, a joint
analysis of future data sets will continue to provide the best point-source sensitivity in critical
overlap regions in the Southern sky, where neutrino emission from Galactic sources in particular
may be found.
References
[1] Achterberg, A., Ackermann, M., Adams, J., et al. (IceCube Collaboration) 2006, APh, 26, 155.
[2] Ageron M., Aguilar J. A., Samarai I. Al et al. (ANTARES Collaboration) 2011, Nucl. Instrum. Meth.,
A 656, 11.
[3] Aartsen, M. G., et al. (IceCube Collaboration) 2013c, Sci, 342, 1242856.
[4] Aartsen, M. G., et al. (IceCube Collaboration) 2013b, Phys. Rev. Lett.,113, 101101.
[5] Adrián-Martínez S., Samarai I.Al, Albert A. et al. (ANTARES Collaboration) 2012a, Phys. Lett. B,
714, 224.
[6] Adrián-Martínez S., Samarai I.Al, Albert A. et al. (ANTARES Collaboration) 2013b, Eur. Phys. J. C,
73, 2606.
[7] Aartsen M. G., Abbasi R., Abdou Y. et al. (IceCube Collaboration) 2013d, ApJ, 779, 132.
[8] Adrián-Martínez S., Albert A., André M., et al. (ANTARES Collaboration) 2014, ApJ, 786, L5.
[9] Krymskii G.F., 1997, Soviet Physics Doklady, 22, 327.
[10] Blandford, R.D. & Ostriker, J.P, 1978, ApJ, 221, L29.
[11] Aartsen M. G., Ackermann M., Adams J. et al. (IceCube Collaboration), 2015, Phys. Rev. D, 91,
022001.
[12] Kappes A., Hinton J., Stegmann C. & Aharonian F. A., 2007, ApJ, 656, 870.
[13] Adrián-Martínez S., Samarai I. Al., Albert A. et al. (ANTARES Collaboration), 2012, ApJ, 760, 53
[14] Abbasi R., Abdou Y., Abu-Zayyad T. et al. (IceCube Collaboration), 2011, ApJ, 732, 18
14