dc.contributor.author Aharonian, F. en_US dc.contributor.author Büsching, I. en_US dc.contributor.author Davids, I.D. en_US dc.contributor.author De Jager, O.C. en_US dc.contributor.author Holleran, M. en_US dc.contributor.author Raubenheimer, B.C. en_US dc.contributor.author Venter, C. dc.date.accessioned 2010-08-04T15:37:46Z dc.date.available 2010-08-04T15:37:46Z dc.date.issued 2009 en_US dc.identifier.citation Aharonian, 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.issn 0004-6361 dc.identifier.issn 1432-0746 (Online) dc.identifier.uri http://hdl.handle.net/10394/3541 dc.identifier.uri https://doi.org/10.1051/0004-6361/200811569 dc.description.abstract 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 $\pm$ 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.uri http://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.publisher EDP Sciences dc.subject Galaxy: center dc.subject Gamma rays: observations dc.subject Methods: data analysis dc.title Spectrum and variability of the Galactic center VHE y-ray source HESS J1745-290 en_US dc.contributor.researchID 12006653 - Venter, Christo dc.contributor.researchID 10179240 - Raubenheimer, Barend Christoffel dc.contributor.researchID 10859748 - Holleran, Mathew dc.contributor.researchID 10065857 - De Jager, Ocker Cornelis dc.contributor.researchID 13146629 - Davids, Isak Delberth dc.contributor.researchID 13235176 - Büsching, Ingo
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