Multiwavelength observations of PKS 2255-282

Abstract

During high radio frequency active galactic nucleus monitoring, we observed a major millimeter wave outburst from PKS 2255-282 in 1997 and initiated a campaign for multifrequency radio monitoring and VLBI imaging of the source. In 1998 January the EGRET instrument on board the Compton Gamma Ray Observatory detected a bright high-energy γ-ray outburst from its direction. Thus, we had the unique opportunity to monitor the source in detail at various radio frequencies already before the detection of the γ-ray outburst. We also initiated multiwavelength follow-up observations. In this paper we present multiwavelength data for PKS 2255-282 before and after the γ-ray outburst. Further, based on the observations, we estimate some physical parameters for this source and discuss the various emission mechanisms possibly involved during this outburst.