COMPTEL Observations of the Gamma-Ray Blazar PKS 1622-297

Abstract

We report results of observations and analyses on the gamma-ray blazar PKS 1622-297, with emphasis on the COMPTEL data (0.75 - 30 MeV) collected between April 1991 and November 1997. PKS 1622-297 was detected as a source of gamma-rays by the EGRET experiment aboard CGRO in 1995 during a gamma-ray outburst at energies above 100 MeV lasting for five weeks. In this time period the blazar was significantly (~ 5.9 sigma) detected by COMPTEL at 10-30 MeV. At lower COMPTEL energies the detection is marginal, resulting in a hard MeV spectrum. The combined COMPTEL/EGRET energy spectrum shows a break at MeV energies. The broad-band spectrum (radio - gamma-rays) shows that the gamma-ray emission dominates the overall power output. On top of the 5-week gamma-ray outburst, EGRET detected a huge flare lasting for > 1 day. Enhanced MeV emission (10 - 30 MeV) is found near the time of this flare, suggesting a possible time delay with respect to the emission above 100 MeV. Outside the 5-week flaring period in 1995, we do not detect MeV emission from PKS 1622-297.