INTEGRAL and Swift/XRT observations of the source PKS 0208-512
  The active galaxy PKS 0208-512, detected at lower energies by COMPTEL, has
been claimed to be a MeV blazar from EGRET. We report on the most recent
INTEGRAL observations of the blazar PKS 0208-512, which are supplemented by
Swift ToO observations. The high energy X-ray and gamma-ray emission of PKS
0208-512 during August - December 2008 has been studied using 682 ks of
INTEGRAL guest observer time and ~ 56 ks of Swift/XRT observations. These data
were collected during the decay of a gamma-ray flare observed by Fermi/LAT. At
X-ray energies (0.2 - 10 keV) PKS 0208-512 is significantly detected by
Swift/XRT, showing a power-law spectrum with a photon index of ~ 1.64. Its
X-ray luminosity varied by roughly 30% during one month. At hard X-/soft
gamma-ray energies PKS 0208-512 shows a marginally significant (~ 3.2 sigma)
emission in the 0.5-1 MeV band when combining all INTEGRAL/SPI data.
Non-detections at energies below and above this band by INTEGRAL/SPI may
indicate intrinsic excess emission. If this possible excess is produced by the
blazar, one possible explanation could be that its jet consists of an abundant
electron-positron plasma, which may lead to the emission of an annihilation
radiation feature. Assuming this scenario, we estimate physical parameters of
the jet of PKS 0208-512.
