Discovery and follow-up studies of the extended, off-plane, VHE gamma-ray source HESS J1507-622

¹ Max-Planck-Institut für Kernphysik, PO Box 103980, 69029 Heidelberg, Germany
e-mail: omar.tibolla@astro.uni-wuerzburg.de
² Yerevan Physics Institute, 2 Alikhanian Brothers St., 375036 Yerevan, Armenia
³ Centre d’Étude Spatiale des Rayonnements, CNRS/UPS, 9 Av. du Colonel Roche, BP 4346, 31029 Toulouse Cedex 4, France
⁴ Universität Hamburg, Institut für Experimentalphysik, Luruper Chaussee 149, 22761 Hamburg, Germany
⁵ Institut für Physik, Humboldt-Universität zu Berlin, Newtonstr. 15, 12489 Berlin, Germany
⁶ LUTH, Observatoire de Paris, CNRS, Université Paris Diderot, 5 place Jules Janssen, 92190 Meudon, France
⁷ IRFU/DSM/CEA, CE Saclay, 91191 Gif-sur-Yvette, Cedex, France
⁸ University of Durham, Department of Physics, South Road, Durham DH1 3LE, UK
⁹ Unit for Space Physics, North-West University, Potchefstroom 2520, South Africa
¹⁰ Laboratoire Leprince-Ringuet, École Polytechnique, CNRS/IN2P3, 91128 Palaiseau, France
¹¹ Laboratoire d’Annecy-le-Vieux de Physique des Particules, Université de Savoie, CNRS/IN2P3, 74941 Annecy-le-Vieux, France
¹² Astroparticule et Cosmologie (APC), CNRS, Université Paris 7 Denis Diderot, 10 rue Alice Domon et Léonie Duquet, 75205 Paris Cedex 13, France
¹³ Dublin Institute for Advanced Studies, 5 Merrion Square, Dublin 2, Ireland
¹⁴ Landessternwarte, Universität Heidelberg, Königstuhl, 69117 Heidelberg, Germany
¹⁵ Laboratoire de Physique Théorique et Astroparticules, Université Montpellier 2, CNRS/IN2P3, CC 70, Place Eugène Bataillon, 34095 Montpellier Cedex 5, France
¹⁶ Universität Erlangen-Nürnberg, Physikalisches Institut, Erwin-Rommel-Str. 1, 91058 Erlangen, Germany
¹⁷ Laboratoire d’Astrophysique de Grenoble, INSU/CNRS, Université Joseph Fourier, BP 53, 38041 Grenoble Cedex 9, France
¹⁸ Institut für Astronomie und Astrophysik, Universität Tübingen, Sand 1, 72076 Tübingen, Germany
¹⁹ LPNHE, Université Pierre et Marie Curie Paris 6, Université Denis Diderot Paris 7, CNRS/IN2P3, 4 place Jussieu, 75252 Paris Cedex 5, France
²⁰ Charles University, Faculty of Mathematics and Physics, Institute of Particle and Nuclear Physics, V Holešovičkách 2, 180 00, Prague 8, Czech Republic
²¹ Institut für Theoretische Physik, Lehrstuhl IV: Weltraum und Astrophysik, Ruhr-Universität Bochum, 44780 Bochum, Germany
²² University of Namibia, Private Bag 13301, Windhoek, Namibia
²³ Obserwatorium Astronomiczne, Uniwersytet Jagielloński, ul. Orla 171, 30-244 Kraków, Poland
²⁴ Nicolaus Copernicus Astronomical Center, ul. Bartycka 18, 00-716 Warsaw, Poland
²⁵ School of Physics & Astronomy, University of Leeds, Leeds LS2 9JT, UK
²⁶ School of Chemistry & Physics, University of Adelaide, Adelaide 5005, Australia
²⁷ Toruń Centre for Astronomy, Nicolaus Copernicus University, ul. Gagarina 11, 87-100 Toruń, Poland
²⁸ Instytut Fizyki Ja¸drowej PAN, ul. Radzikowskiego 152, 31-342 Kraków, Poland
²⁹ European Associated Laboratory for Gamma-Ray Astronomy, jointly supported by CNRS and MPG, Germany
³⁰ StanfordUniversity, HEPL & KIPAC, Stanford, CA 94305-4085, USA

Received: 10 June 2010
Accepted: 7 October 2010

Abstract

Context. The detection of gamma-rays in the very-high-energy (VHE) range (100 GeV−100 TeV) offers the possibility of studying the parent population of ultrarelativistic particles found in astrophysical sources, so it is useful for understanding the underlying astrophysical processes in nonthermal sources.

Aims. The discovery of the VHE gamma-ray source HESS J1507-622 is reported and possibilities regarding its nature are investigated.

Methods. The H.E.S.S. array of imaging atmospheric Cherenkov telescopes (IACTs) has a high sensitivity compared with previous instruments (~1% of the Crab flux in 25 h observation time for a 5σ point-source detection) and has a large field of view (~5° in diameter). HESS J1507-622 was discovered within the ongoing H.E.S.S. survey of the inner Galaxy, and the source was also studied by means of dedicated multiwavelength observations.

Results. A Galactic gamma-ray source, HESS J1507-622, located  ~3.5° from the Galactic plane was detected with a statistical significance  >9σ. Its energy spectrum is well fitted by a power law with spectral index Γ = 2.24  ±  0.16_stat  ±  0.20_sys and a flux above 1 TeV of (1.5 ± 0.4_stat ± 0.3_sys)  ×  10^-12 cm^-2 s^-1. Possible interpretations (considering both hadronic and leptonic models) of the VHE gamma-ray emission are discussed in the absence of an obvious counterpart.