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dc.contributor.authorAharonian, F.en_US
dc.contributor.authorBüsching, I.en_US
dc.contributor.authorDavids, I.D.en_US
dc.contributor.authorDe Jager, O.C.en_US
dc.contributor.authorHolleran, M.en_US
dc.contributor.authorRaubenheimer, B.C.en_US
dc.contributor.authorVenter, C.
dc.date.accessioned2010-08-04T15:37:46Z
dc.date.available2010-08-04T15:37:46Z
dc.date.issued2009en_US
dc.identifier.citationAharonian, F. et al. 2009. Spectrum and variability of the Galactic center VHE y-ray source HESS J1745-290. Astronomy and astrophysics, 503(3):817-825. [https://doi.org/10.1051/0004-6361/200811569 ]en_US
dc.identifier.issn0004-6361
dc.identifier.issn1432-0746 (Online)
dc.identifier.urihttp://hdl.handle.net/10394/3541
dc.identifier.urihttps://doi.org/10.1051/0004-6361/200811569
dc.description.abstractAims. 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 $\pm$ 0.04 $_{{\rm stat}}$ $\pm$ 0.10 $_{{\rm syst}}$ and a cut-off energy at 15.7 $\pm$ 3.4 $_{{\rm stat}}$ $\pm$ 2.5 $_{{\rm syst}}$ TeV. The broken power law spectrum exhibits spectral indices of 2.02 $\pm$ 0.08 $_{{\rm stat}}$ $\pm$ 0.10 $_{{\rm syst}}$ and 2.63 $\pm$ 0.14 $_{{\rm stat}}$ $\pm$ 0.10 $_{{\rm syst}}$ with a break energy at 2.57 $\pm$ 0.19 $_{{\rm stat}}$ $\pm$ 0.44 $_{{\rm syst}}$ TeV. No significant flux variation is found. Increases in the $\gamma $-ray flux of HESS J1745-290 by at least a factor of two would be required for a 3$\sigma $ 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
dc.description.urihttp://www.aanda.org/index.php?option=com_article&access=standard&Itemid=129&url=/articles/aa/full_html/2009/33/aa11569-08/aa11569-08.html
dc.publisherEDP Sciences
dc.subjectGalaxy: center
dc.subjectGamma rays: observations
dc.subjectMethods: data analysis
dc.titleSpectrum and variability of the Galactic center VHE y-ray source HESS J1745-290en_US
dc.contributor.researchID12006653 - Venter, Christo
dc.contributor.researchID10179240 - Raubenheimer, Barend Christoffel
dc.contributor.researchID10859748 - Holleran, Mathew
dc.contributor.researchID10065857 - De Jager, Ocker Cornelis
dc.contributor.researchID13146629 - Davids, Isak Delberth
dc.contributor.researchID13235176 - Büsching, Ingo


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