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EP: Extraterrestrische Physik

EP 17: Astrophysik 1

EP 17.13: Vortrag

Donnerstag, 20. März 1997, 17:00–17:15, 302

COMPTEL Observations of the Gamma-ray Blazar PKS 0528+134 — •Werner Collmar — MPE, Postfach 1603, 85740 Garching

The COMPTEL experiment aboard the Compton Gamma-Ray Observatory (CGRO) has detected soft gamma-radiation (0.75 - 30 MeV) from 8 so-called ’Gamma-ray blazars’. One of them is the radio-loud quasar PKS 0528+134. During several observational periods between April ’91 and October ’94 COMPTEL has collected about 17 weeks of observation time on the galactic anticenter region where PKS 0528+134 is located. The quasar was detected by COMPTEL several times. Detections and non-detections indicate a time-variable MeV-flux. The time-average MeV-spectrum is well represented by a power-law shape with a photon index of -1.9. Subdividing the COMPTEL observations into gamma-ray ’low’ and ’high’ states as observed by the EGRET experiment on CGRO at energies above 100 MeV reveals different COMPTEL spectra: a soft and a hard spectrum for the ’low’ and ’high’ state, respectively. Combining the simultaneously measured COMPTEL and EGRET spectra indicate a bivalent spectral behaviour as well: while during ’high’ states a spectral break around 10 MeV is obvious, is the ’low’ state spectrum consistent with a simple power-law model. The results of the COMPTEL observations will be presented and their implications on blazar emission models will be discussed.