Issue |
A&A
Volume 503, Number 3, September I 2009
|
|
---|---|---|
Page(s) | 817 - 825 | |
Section | Galactic structure, stellar clusters, and populations | |
DOI | https://doi.org/10.1051/0004-6361/200811569 | |
Published online | 02 July 2009 |
Spectrum and variability of the Galactic center VHE γ-ray source HESS J1745–290
1
Max-Planck-Institut für Kernphysik, P.O. Box 103980, 69029 Heidelberg, Germany e-mail: Christopher.van.Eldik@mpi-hd.mpg.de
2
Dublin Institute for Advanced Studies, 5 Merrion Square, Dublin 2, Ireland
3
Yerevan Physics Institute, 2 Alikhanian Brothers St., 375036 Yerevan, Armenia
4
Universität Erlangen-Nürnberg, Physikalisches Institut, Erwin-Rommel-Str. 1, 91058 Erlangen, Germany
5
University of Durham, Department of Physics, South Road, Durham DH1 3LE, UK
6
Centre d'Etude Spatiale des Rayonnements, CNRS/UPS, 9 av. du Colonel Roche, BP 4346, 31029 Toulouse Cedex 4, France
7
Astroparticule et Cosmologie (APC), CNRS, Universite Paris 7 Denis Diderot, 10, rue Alice Domon et Leonie Duquet, 75205 Paris Cedex 13, UMR 7164 (CNRS, Université Paris VII, CEA, Observatoire de Paris) France
8
Landessternwarte, Universität Heidelberg, Königstuhl, 69117 Heidelberg, Germany
9
Institut für Physik, Humboldt-Universität zu Berlin, Newtonstr. 15, 12489 Berlin, Germany
10
LUTH, Observatoire de Paris, CNRS, Université Paris Diderot, 5 Place Jules Janssen, 92190 Meudon, France Obserwatorium Astronomiczne, Uniwersytet Ja
11
IRFU/DSM/CEA, CE Saclay, 91191 Gif-sur-Yvette, Cedex, France e-mail: matthieu.vivier@cea.fr
12
Nicolaus Copernicus Astronomical Center, ul. Bartycka 18, 00-716 Warsaw, Poland
13
Unit for Space Physics, North-West University, Potchefstroom 2520, South Africa
14
Laboratoire d'Astrophysique de Grenoble, INSU/CNRS, Université Joseph Fourier, BP 53, 38041 Grenoble Cedex 9, France
15
LPNHE, Université Pierre et Marie Curie Paris 6, Université Denis Diderot Paris 7, CNRS/IN2P3, 4 Place Jussieu, 75252, Paris Cedex 5, France
16
Laboratoire Leprince-Ringuet, Ecole Polytechnique, CNRS/IN2P3, 91128 Palaiseau, France
17
Laboratoire d'Annecy-le-Vieux de Physique des Particules, CNRS/IN2P3, 9 Chemin de Bellevue, BP 110, 74941 Annecy-le-Vieux Cedex, France
18
University of Namibia, Private Bag 13301, Windhoek, Namibia
19
Instytut Fizyki Jądrowej PAN, ul. Radzikowskiego 152, 31-342 Kraków, Poland
20
Laboratoire de Physique Théorique et Astroparticules, CNRS/IN2P3, Université Montpellier II, CC 70, Place Eugène Bataillon, 34095 Montpellier Cedex 5, France
21
Universität Hamburg, Institut für Experimentalphysik, Luruper Chaussee 149, 22761 Hamburg, Germany
22
School of Physics & Astronomy, University of Leeds, Leeds LS2 9JT, UK
23
Institut für Astronomie und Astrophysik, Universität Tübingen, Sand 1, 72076 Tübingen, Germany
24
Toruń Centre for Astronomy, Nicolaus Copernicus University, ul. Gagarina 11, 87-100 Toruń, Poland
25
Institute of Particle and Nuclear Physics, Charles University, V Holesovickach 2, 180 00 Prague 8, Czech Republic
26
European Associated Laboratory for Gamma-Ray Astronomy, jointly supported by CNRS and MPG
27
Obserwatorium Astronomiczne, Uniwersytet Jagielloński, ul. Orla 171, 30-244 Kraków, Poland
28
School of Chemistry & Physics, University of Adelaide, Adelaide 5005, Australia
29
Institut für Theoretische Physik, Lehrstuhl IV: Weltraum und Astrophysik, Ruhr-Universität Bochum, 44780 Bochum, Germany
Received:
22
December
2008
Accepted:
1
May
2009
Aims. A detailed study of the spectrum and variability of the source HESS J1745-290 in the Galactic Center (GC) region using new data from the H.E.S.S. array of Cherenkov telescopes is presented. Flaring activity and quasi periodic oscillations (QPO) of HESS J1745-290 are investigated.
Methods. The image analysis is performed with a combination of a semi-analytical shower model and the statistical moment-based Hillas technique. The spectrum and lightcurves of HESS J1745-290 are derived with a likelihood method based on a spectral shape hypothesis. Rayleigh tests and Fourier analysis of the H.E.S.S. GC signal are used to study the periodicity of the source.
Results. With a three-fold increase in statistics compared to previous work, a deviation from a simple power law spectrum is detected for the first time. The measured energy spectrum over the three years 2004, 2005 and 2006 of data taking is compatible with both a power law spectrum with an exponential cut-off and a broken power law spectrum. The curvature of the energy spectrum is likely to be intrinsic to the photon source, as opposed to effects of interstellar absorption. The power law spectrum with an exponential cut-off is characterized by a photon index of 2.10 ± 0.04 ± 0.10
and a cut-off energy at 15.7 ± 3.4
± 2.5
TeV. The broken power law spectrum exhibits spectral indices of 2.02 ± 0.08
± 0.10
and 2.63 ± 0.14
± 0.10
with a break energy at 2.57 ± 0.19
± 0.44
TeV. No significant flux variation is found. Increases in the γ-ray flux of HESS J1745-290 by at least a factor of two would be required for a 3σ detection of a flare with time scales of an hour. Investigation of possible QPO activity at periods claimed to be detected in X-rays does not show any periodicities in the H.E.S.S. signal.
Key words: Galaxy: center / gamma rays: observations / methods: data analysis
© ESO, 2009
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