Letter to the Editor

Detection of variable VHE γ-ray emission from the extra-galactic γ-ray binary LMC P3

¹ Centre for Space Research, North-West University, Potchefstroom 2520, South Africa
² Universität Hamburg, Institut für Experimentalphysik, Luruper Chaussee 149, 22761 Hamburg, Germany
³ Max-Planck-Institut für Kernphysik, PO Box 103980, 69029 Heidelberg, Germany
⁴ Dublin Institute for Advanced Studies, 31 Fitzwilliam Place, Dublin 2, Ireland
⁵ National Academy of Sciences of the Republic of Armenia, Marshall Baghramian Avenue, 24, 0019 Yerevan, Armenia
⁶ Yerevan Physics Institute, 2 Alikhanian Brothers St., 375036 Yerevan, Armenia
⁷ Institut für Physik, Humboldt-Universität zu Berlin, Newtonstr. 15, 12489 Berlin, Germany
⁸ University of Namibia, Department of Physics, Private Bag 13301, Windhoek, Namibia
⁹ GRAPPA, Anton Pannekoek Institute for Astronomy, University of Amsterdam, Science Park 904, 1098 XH Amsterdam, The Netherlands
¹⁰ Department of Physics and Electrical Engineering, Linnaeus University, 351 95 Växjö, Sweden
¹¹ Institut für Theoretische Physik, Lehrstuhl IV: Weltraum und Astrophysik, Ruhr-Universität Bochum, 44780 Bochum, Germany
¹² GRAPPA, Anton Pannekoek Institute for Astronomy and Institute of High-Energy Physics, University of Amsterdam, Science Park 904, 1098 XH Amsterdam, The Netherlands
¹³ Institut für Astro- und Teilchenphysik, Leopold-Franzens-Universität Innsbruck, 6020 Innsbruck, Austria
¹⁴ School of Physical Sciences, University of Adelaide, Adelaide 5005, Australia
¹⁵ LUTH, Observatoire de Paris, PSL Research University, CNRS, Université Paris Diderot, 5 Place Jules Janssen, 92190 Meudon, France
¹⁶ Sorbonne Universités, UPMC Université Paris 06, Université Paris Diderot, Sorbonne Paris Cité, CNRS, Laboratoire de Physique Nucléaire et de Hautes Energies (LPNHE), 4 place Jussieu, 75252 Paris Cedex 5, France
¹⁷ Laboratoire Univers et Particules de Montpellier, Université Montpellier, CNRS/IN2P3, CC 72, Place Eugène Bataillon, 34095 Montpellier Cedex 5, France
¹⁸ IRFU, CEA, Université Paris-Saclay, 91191 Gif-sur-Yvette, France
¹⁹ Astronomical Observatory, The University of Warsaw, Al. Ujazdowskie 4, 00-478 Warsaw, Poland
²⁰ Aix Marseille Université, CNRS/IN2P3, CPPM, Marseille, France
²¹ Instytut Fizyki Ja̧drowej PAN, ul. Radzikowskiego 152, 31-342 Kraków, Poland
²² Funded by EU FP7 Marie Curie, Grant Agreement No. PIEF-GA-2012-332350
²³ School of Physics, University of the Witwatersrand, 1 Jan Smuts Avenue, Braamfontein, Johannesburg 2050, South Africa
²⁴ Laboratoire d’Annecy de Physique des Particules, Université Savoie Mont-Blanc, CNRS/IN2P3, 74941 Annecy-le-Vieux, France
²⁵ Landessternwarte, Universität Heidelberg, Königstuhl, 69117 Heidelberg, Germany
²⁶ Université Bordeaux, CNRS/IN2P3, Centre d’Études Nucléaires de Bordeaux Gradignan, 33175 Gradignan, France
²⁷ Oskar Klein Centre, Department of Physics, Stockholm University, Albanova University Center, 10691 Stockholm, Sweden
²⁸ Wallenberg Academy Fellow
²⁹ Institut für Astronomie und Astrophysik, Universität Tübingen, Sand 1, 72076 Tübingen, Germany
³⁰ Laboratoire Leprince-Ringuet, Ecole Polytechnique, CNRS/IN2P3, 91128 Palaiseau, France
³¹ APC, AstroParticule et Cosmologie, Université Paris Diderot, CNRS/IN2P3, CEA/Irfu, Observatoire de Paris, Sorbonne Paris Cité, 10, rue Alice Domon et Léonie Duquet, 75205 Paris Cedex 13, France
³² Univ. Grenoble Alpes, CNRS, IPAG, 38000 Grenoble, France
³³ Department of Physics and Astronomy, The University of Leicester, University Road, Leicester LE1 7RH, UK
³⁴ Nicolaus Copernicus Astronomical Center, Polish Academy of Sciences, ul. Bartycka 18, 00-716 Warsaw, Poland
³⁵ Institut für Physik und Astronomie, Universität Potsdam, Karl-Liebknecht-Strasse 24/25, 14476 Potsdam, Germany
³⁶ Friedrich-Alexander-Universität Erlangen-Nürnberg, Erlangen Centre for Astroparticle Physics, Erwin-Rommel-Str. 1, 91058 Erlangen, Germany
³⁷ DESY, 15738 Zeuthen, Germany
³⁸ Obserwatorium Astronomiczne, Uniwersytet Jagielloński, ul. Orla 171, 30-244 Kraków, Poland
³⁹ Centre for Astronomy, Faculty of Physics, Astronomy and Informatics, Nicolaus Copernicus University, Grudziadzka 5, 87-100 Torun, Poland
⁴⁰ Department of Physics, University of the Free State, PO Box 339, Bloemfontein 9300, South Africa
⁴¹ Heisenberg Fellow (DFG), ITA Universität Heidelberg, Germany
⁴² Department of Physics, Rikkyo University, 3-34-1 Nishi-Ikebukuro, Toshima-ku, Tokyo 171-8501, Japan
⁴³ Japan Aerospace Exploration Agency (JAXA), Institute of Space and Astronautical Science (ISAS), 3-1-1 Yoshinodai, Chuo-ku, Sagamihara, Kanagawa 229-8510, Japan
⁴⁴ Now at the School of Physics, The University of New South Wales, Sydney 2052, Australia
⁴⁵ Now at Instituto de Física de São Carlos, Universidade de São Paulo, Av. Trabalhador São-carlense, 400 – CEP 13566-590, São Carlos, SP, Brazil
⁴⁶ Now at Kavli Institute for Particle Astrophysics and Cosmology, Department of Physics and SLAC National Accelerator Laboratory, Stanford University, Stanford, CA 94305, USA

^★ Corresponding authors: H.E.S.S. Collaboration, e-mail: contact.hess@hess-experiment.eu

Received: 6 December 2017
Accepted: 4 January 2018

Abstract

Context. Recently, the high-energy (HE, 0.1–100 GeV) γ-ray emission from the object LMC P3 in the Large Magellanic Cloud (LMC) has been discovered to be modulated with a 10.3-day period, making it the first extra-galactic γ-ray binary.

Aim. This work aims at the detection of very-high-energy (VHE, >100 GeV) γ-ray emission and the search for modulation of the VHE signal with the orbital period of the binary system.

Methods. LMC P3 has been observed with the High Energy Stereoscopic System (H.E.S.S.); the acceptance-corrected exposure time is 100 h. The data set has been folded with the known orbital period of the system in order to test for variability of the emission.

Results. VHE γ-ray emission is detected with a statistical significance of 6.4 σ. The data clearly show variability which is phase-locked to the orbital period of the system. Periodicity cannot be deduced from the H.E.S.S. data set alone. The orbit-averaged luminosity in the 1–10 TeV energy range is (1.4 ± 0.2) × 1035 erg s⁻¹. A luminosity of (5 ± 1) × 1035 erg s⁻¹ is reached during 20% of the orbit. HE and VHE γ-ray emissions are anti-correlated. LMC P3 is the most luminous γ-ray binary known so far.