Detection of Very-High Energy Gamma-Rays from the BL Lac Object PG 1553+113 with the MAGIC Telescope

TL;DR

The MAGIC telescope detected very-high energy gamma-ray emission from the BL Lac object PG 1553+113, providing spectral data and redshift constraints despite the absence of direct measurements.

Contribution

First detection of VHE gamma rays from PG 1553+113 with spectral analysis and redshift upper limits based on gamma-ray observations.

Findings

Significant gamma-ray detection with 8.8 sigma significance.

Spectral index of -4.2+-0.3 in the 90 GeV to 500 GeV range.

Redshift upper limits of z=0.74 and z=0.56 from spectral modeling.

Abstract

The MAGIC telescope has observed very-high energy gamma-ray emission from the BL Lac object PG 1553+113 in 2005 and 2006 at an overall significance is 8.8 sigma. The light curve shows no significant flux variations on a daily timescale. The flux level during 2005 was, however, significantly higher as compared to 2006. The differential energy spectrum between approx. 90 GeV and 500 GeV is well described by a power law with a spectral index of -4.2+-0.3. The photon energy spectrum and spectral modeling allow to pose upper limits of z=0.74 and z=0.56, respectively, on the yet undetermined redshift of PG 1553+113. Recent VLT observations of this blazar show featureless spectra in the near-IR, thus no direct redshift could be determined from these measurements.