2. PKS 0528+134
PKS 0528+134 () is one of the most distant quasar detected by EGRET in the -ray band. Located in the galactic anticenter region, it is heavily absorbed, although the estimates of are very uncertain (ranging from 2.3 to 5). Thus PKS 0528+134 is faint in the optical, with a typical average magnitude of 19.5 in the V band. It is a strong and flat radio source, with detected superluminal motion (4-6 for km s-1 Mpc-1, Pohl et al. 1996; Britzen et al. 1996). Close to Geminga and the Crab, it was frequently observed by EGRET, and seen flaring in March 1993, when the -ray flux was about 6 times brighter than average (Hunter et al. 1993; Mukherjee et al. 1996). Flux changes in the -band are accompanied by spectral variations in the sense that the spectrum is harder when brighter (Sambruna et al. 1997; Mukherjee et al. 1997a, 1997b). It is also one of the few extragalactic sources detected by COMPTEL (Collmar et al. 1997; Böttcher & Collmar 1998). The combined COMPTEL and EGRET observations show that the peak of the high energy emission occurs in the MeV band, at least in the flaring state.
© European Southern Observatory (ESO) 1999
Online publication: July 16, 1999