Extended VHE γ-ray emission towards SGR1806−20, LBV 1806−20, and stellar cluster Cl* 1806−20

¹ Centre for Space Research, North-West University, 2520 Potchefstroom, 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, Republic of 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, 13301 Private Bag, 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 Chemistry & Physics, University of Adelaide, 5005 Adelaide, 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 DSM/Irfu, CEA Saclay, 91191 Gif-Sur-Yvette Cedex, France
¹⁹ Astronomical Observatory, The University of Warsaw, Al. Ujazdowskie 4, 00-478 Warsaw, Poland
²⁰ Aix Marseille Université, CNRS/IN2P3, CPPM UMR 7346, 13288 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, 2050 Johannesburg, South Africa
²⁴ Laboratoire d’Annecy-le-Vieux 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 Institut für Astronomie und Astrophysik, Universität Tübingen, Sand 1, 72076 Tübingen, Germany
²⁹ Laboratoire Leprince-Ringuet, Ecole Polytechnique, CNRS/IN2P3, 91128 Palaiseau, France
³⁰ 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
³¹ Univ. Grenoble Alpes, IPAG, CNRS, IPAG, 38000 Grenoble, France
³² Department of Physics and Astronomy, The University of Leicester, University Road, Leicester, LE1 7RH, UK
³³ Nicolaus Copernicus Astronomical Center, ul. Bartycka 18, 00-716 Warsaw, Poland
³⁴ Institut für Physik und Astronomie, Universität Potsdam, Karl-Liebknecht-Strasse 24/25, 14476 Potsdam, Germany
³⁵ Universität Erlangen-Nürnberg, Physikalisches Institut, Erwin-Rommel-Str. 1, 91058 Erlangen, Germany
³⁶ DESY, 15738 Zeuthen, Germany
³⁷ Obserwatorium Astronomiczne, UniwersytetJagielloński, ul. Orla 171, 30-244 Kraków, Poland
³⁸ Centre for Astronomy, Faculty of Physics, Astronomy and Informatics, Nicolaus Copernicus University, Grudziadzka 5, 87-100 Torun, Poland
³⁹ Department of Physics, University of the Free State, PO Box 339, 9300 Bloemfontein, South Africa
⁴⁰ Heisenberg Fellow (DFG), ITA UniversitätHeidelberg, Germany
⁴¹ GRAPPA, Institute of High-Energy Physics, University of Amsterdam, Science Park 904, 1098 XH Amsterdam, The Netherlands

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

Received: 12 April 2016
Accepted: 11 May 2016

Abstract

Using the High Energy Spectroscopic System (H.E.S.S.) telescopes we have discovered a steady and extended very high-energy (VHE) γ-ray source towards the luminous blue variable candidate LBV 1806−20, massive stellar cluster Cl* 1806−20, and magnetar SGR 1806−20. The new VHE source, HESS J1808−204, was detected at a statistical significance of >6σ (post-trial) with a photon flux normalisation (2.9 ± 0.4_stat ± 0.5_sys) × 10⁻¹³ ph cm⁻² s⁻¹ TeV⁻¹ at 1 TeV and a power-law photon index of 2.3 ± 0.2_stat ± 0.3_sys. The luminosity of this source (0.2 to 10 TeV; scaled to distance d = 8.7 kpc) is L_VHE ~ 1.6 × 10³⁴(d/8.7 kpc)² erg s⁻¹. The VHE γ-ray emission is extended and is well fit by a single Gaussian with statistical standard deviation of 0.095° ± 0.015°. This extension is similar to that of the synchrotron radio nebula G10.0−0.3, which is thought to be powered by LBV 1806−20. The VHE γ-ray luminosity could be provided by the stellar wind luminosity of LBV 1806−20 by itself and/or the massive star members of Cl* 1806−20. Alternatively, magnetic dissipation (e.g. via reconnection) from SGR 1806−20 can potentially account for the VHE luminosity. The origin and hadronic and/or leptonic nature of the accelerated particles responsible for HESS J1808−204 is not yet clear. If associated with SGR 1806−20, the potentially young age of the magnetar (650 yr) can be used to infer the transport limits of these particles to match the VHE source size. This discovery provides new interest in the potential for high-energy particle acceleration from magnetars, massive stars, and/or stellar clusters.