Astronomy and Astrophysics – Astrophysics – Cosmology and Extragalactic Astrophysics
Scientific paper
2010-02-22
Astronomy and Astrophysics
Astrophysics
Cosmology and Extragalactic Astrophysics
accepted for publication in A&A
Scientific paper
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.
Collmar Werner
Lang Michael
Torres Diego F.
Wang Jian-Min
Zhang Shu
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