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Evidence for VHE gamma-ray emission from the distant BL Lac PG 1553+113

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journal contribution
posted on 24.10.2012, 08:53 by F. Aharonian, A. G. Akhperjanian, A. R. Bazer-Bachi, M. Beilicke, W. Benbow, D. Berge, K. Bernlohr, C. Boisson, O. Bolz, V. Borrel, I. Braun, J. Ripken, L. Rob, L. Rolland, G. Rowell, V. Sahakian, L. Sauge, S. Schlenker, R. Schlickeiser, C. Schuster, U. Schwanke, M. Siewert, H. Sol, D. Spangler, R. Steenkamp, C. Stegmann, G. Superina, J. P. Tavernet, R. Terrier, C. G. Theoret, M. Tluczykont, van Eldik C., G. Vasileiadis, C. Venter, P. Vincent, H. J. Volk, S. J. Wagner, M. Ward, F. Breitling, A. M. Brown, R. Buhler, S. Carrigan, P. M. Chadwick, L. M. Chounet, R. Cornils, L. Costamante, B. Degrange, H. J. Dickinson, A. Djannati-Atai, L. O. Drury, G. Dubus, K. Egberts, D. Emmanoulopoulos, P. Espigat, F. Feinstein, G. Fontaine, S. Funk, Y. A. Gallant, B. Giebels, J. F. Glicenstein, P. Goret, C. Hadjichristidis, D. Hauser, M. Hauser, G. Heinzelmann, G. Henri, G. Hermann, J. A. Hinton, W. Hofmann, M. Holleran, D. Horns, A. Jacholkowska, de Jager O. C., B. Khelifi, N. Komin, A. Konopelko, I. J. Latham, Le Gallou R., A. Lemiere, M. Lemoine-Goumard, T. Lohse, J. M. Martin, O. Martineau-Huynh, A. Marcowith, C. Masterson, T. J. L. McComb, de Naurois M., D. Nedbal, S. J. Nolan, A. Noutsos, K. J. Orford, J. L. Osborne, M. Ouchrif, M. Panter, G. Pelletier, S. Pita, G. Puhlhofer, M. Punch, B. C. Raubenheimer, M. Raue, S. M. Rayner, A. Reimer, O. Reimer
The high-frequency peaked BL Lac PG 1553+113 was observed in 2005 with the HESS stereoscopic array of imaging atmospheric-Cherenkov telescopes in Namibia. Using the HESS standard analysis, an excess was measured at the 4.0$\sigma$ level in these observations (7.6 hours live time). Three alternative, lower-threshold analyses yield >5$\sigma$ excesses. The observed integral flux above 200 GeV is $(4.8\pm1.3_{\rm stat}\pm1.0_{\rm syst})\times10^{-12}$ cm-2 s-1, and shows no evidence for variability. The measured energy spectrum is characterized by a very soft power law (photon index of $\Gamma=4.0\pm0.6$). Although the redshift of PG 1553+113 is unknown, there are strong indications that it is greater than z=0.25 and possibly larger than z=0.78. The observed spectrum is interpreted in the context of VHE $\gamma$-ray absorption by the Extragalactic Background Light, and is used to place an upper limit on the redshift of z<0.74.

History

Citation

Astronomy & Astrophysics, 2006, 448 (2), pp. L19-L23

Version

VoR (Version of Record)

Published in

Astronomy & Astrophysics

Publisher

EDP Sciences for European Southern Observatory (ESO)

issn

0004-6361

Copyright date

2006

Available date

24/10/2012

Publisher version

http://www.aanda.org/articles/aa/abs/2006/11/aahl143/aahl143.html

Language

en