EDP Sciences
Free access
Volume 386, Number 3, May II 2002
Page(s) 843 - 853
Section Extragalactic astronomy
DOI http://dx.doi.org/10.1051/0004-6361:20020267

A&A 386, 843-853 (2002)
DOI: 10.1051/0004-6361:20020267

COMPTEL observations of the gamma-ray blazar PKS 1622-297

S. Zhang1, 2, W. Collmar1, K. Bennett3, H. Bloemen4, W. Hermsen4, M. McConnell5, O. Reimer6, V. Schönfelder1, S. J. Wagner7 and O. R. Williams3

1  Max-Planck-Institut für extraterrestrische Physik, PO Box 1603, 85740 Garching, Germany
2  Laboratory of Cosmic Ray and High Energy Astrophysics, Institute of High Energy Physics, PO Box 918-3, Beijing 100039, China
3  Astrophysics Division, Space Science Department of ESA/ESTEC, 2200 AG Noordwijk, The Netherlands
4  SRON National Institute for Space Research, Sorbonnelaan 2, 3584 CA Utrecht, The Netherlands
5  University of New Hampshire, Institute for the Study of Earth, Oceans and Space, Durham NH 03824, USA
6  NASA/Goddard Space Flight Center, Greenbelt, MD 20771, USA
7  Landessternwarte Heidelberg, Königstuhl, 69117 Heidelberg, Germany

(Received 6 November 2001 / Accepted 19 February 2002)

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.

Key words: $\gamma$ rays: observations -- galaxies: active -- galaxies: quasars: individual: PKS 1622-297

Offprint request: S. Zhang, shz@mpe.mpg.de

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