标题： INTEGRAL 和 Swift/XRT 对源 PKS 0208-512 的观测 显示英文标题

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

摘要： 活动星系PKS 0208-512，由COMPTEL在较低能量下探测到，曾被声称是EGRET的MeV耀星。我们报告了对耀星PKS 0208-512的最新INTEGRAL观测结果，这些观测结果补充了Swift ToO的观测。在2008年8月至12月期间，使用682 ks的INTEGRAL客座观察时间和约56 ks的Swift/XRT观测数据研究了PKS 0208-512的高能X射线和伽马射线辐射。这些数据是在Fermi/LAT观测到的伽马射线爆发衰减期间收集的。在X射线能量（0.2 - 10 keV）下，PKS 0208-512被Swift/XRT显著探测到，显示出光子指数约为1.64的幂律谱。其X射线光度在一个月内变化了大约30%。在硬X射线/软伽马射线能量下，当结合所有INTEGRAL/SPI数据时，PKS 0208-512在0.5-1 MeV波段显示出边缘显著（约3.2 sigma）的发射。INTEGRAL/SPI在该波段以下和以上能量的非探测可能表明固有过量发射。如果这种可能的过量是由耀星产生的，一种可能的解释是其喷流包含丰富的电子-正电子等离子体，这可能导致湮灭辐射特征的发射。假设这种情形，我们估算了PKS 0208-512喷流的物理参数。 显示英文摘要

摘要： 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.