PG 1553+113: FIVE YEARS OF OBSERVATIONS WITH MAGIC

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.