INTEGRAL and Swift/XRT observations of the source PKS 0208-512

S. Zhang¹, W. Collmar², D. F. Torres³, J.-M. Wang^1,4, M. Lang² and S.-N. Zhang¹

¹ Key Laboratory for Particle Astrophysics, Institute of High Energy Physics, Beijing 100049, PR China e-mail: szhang@mail.ihep.ac.cn
² Max-Planck-Institut für Extraterrestrische Physik, PO Box 1603, 85740 Garching, Germany
³ ICREA & Institut de Ciències de l'Espai (IEEC-CSIC), Campus UAB, Facultat de Ciències, Torre C5-parell, 2a planta, 08193 Barcelona, Spain
⁴ Theoretical Physics Center for Science Facilities (TPCSF), CAS, PR China

Received: 12 November 2009
Accepted: 9 February 2010

Abstract

Aims. 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.

Methods. The high energy X-ray and γ-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 γ-ray flare observed by Fermi/LAT.

Results. 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 γ-ray energies PKS 0208-512 shows a marginally significant (~3.2σ) 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.