Aleksic, J. ; Alvarez, E. A. ; Antonelli, L. A. ; et al. ; - ASI Sponsor
Mar - 2012
DOI: 10.1088/0004-637X/748/1/46
ISSN : 0004-637X ;
journal : The Astrophysical Journal

Volume : 748 ; Issue : 46
type: Article Journal

We present the analysis of three years (2007-2009) of MAGIC observations of the BL Lac object PG 1553+113 at very high energies (VHEs). Adding the new data set to previous observations, this source becomes one of the best long-term followed sources at energies above 100 GeV. Power law fits of the individual years are compatible with a steady mean photon index 4.27 ± 0.14. In the last three years of data, the flux level above 150 GeV shows a marginal variability, in the range from 4% to 11% of the Crab Nebula flux. Simultaneous optical measurements confirm a modest variability. We also performed a temporal analysis of all available Fermi/LAT data of PG 1553+113 above 1GeV, which reveals a clear variability in the 2008–2009 sample. Finally, we present a combination of the mean spectrum measured at very high energies with archival data available for other wavelengths. The mean spectral energy distribution can be modeled with a one–zone SSC model, which gives the main physical parameters governing the VHE emission in the blazar jet.

keywords : BL Lacertae objects: individual: PG 1553+113,gamma rays: galaxies,radiation mechanisms: non-thermal