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2012 (English)In: Astrophysical Journal, ISSN 0004-637X, E-ISSN 1538-4357, Vol. 748, no 1, 46- p.Article in journal (Refereed) Published
Abstract [en]

We present the results of five years (2005-2009) of MAGIC observations of the BL Lac object PG 1553+113 at very high energies (VHEs; E > 100 GeV). Power-law fits of the individual years are compatible with a steady mean photon index Gamma = 4.27 +/- 0.14. In the last three years of data, the flux level above 150 GeV shows a clear variability (probability of constant flux < 0.001%). The flux variations are modest, lying in the range from 4% to 11% of the Crab Nebula flux. Simultaneous optical data also show only modest variability that seems to be correlated with VHE gamma-ray variability. We also performed a temporal analysis of (all available) simultaneous Fermi/Large Area Telescope data of PG 1553+113 above 1 GeV, which reveals hints of variability in the 2008-2009 sample. Finally, we present a combination of the mean spectrum measured at VHEs with archival data available for other wavelengths. The mean spectral energy distribution can be modeled with a one-zone synchrotron self-Compton model, which gives the main physical parameters governing the VHE emission in the blazar jet.

Place, publisher, year, edition, pages
2012. Vol. 748, no 1, 46- p.
Keyword [en]
BL Lacertae objects: individual (PG 1553+113), gamma rays: galaxies, radiation mechanisms: non-thermal
National Category
Astronomy, Astrophysics and Cosmology
URN: urn:nbn:se:su:diva-76153DOI: 10.1088/0004-637X/748/1/46ISI: 000301347500046OAI: diva2:525882
158Available from: 2012-05-09 Created: 2012-05-09 Last updated: 2012-05-09Bibliographically approved

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Larsson, Stefan
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