3C 273 revisited : confirmation by COS-B of high energy gamma-ray emission.
Caraveo, P. A.; Bignami, G. F.; Hermsen, W.; Masnou, J. L.; Bennett, K.; Buccheri, R.; Kanbach, G.; Lichti, G. G.; Mayer-Hasselwander, H. A.; Paul, J. A.; Scarsi, L.; Swanenburg, B. N.; Wills, R. D.; Sacco, B.
Italy, Netherlands, Germany, France
Abstract
The results of a second observation in the Virgo region by the ESA COS-B satellite are presented. The presence of a high- energy (50-800 MeV) gamma-radiation source is confirmed, and its position is consistent with 3C273. The error box at the 90% confidence level containing the quasar is ∼2.5 square degrees, and the probability of a chance coincidence of the γ-ray source with 3C273 is approximately 10-3. No variation of the γ-ray fluxes between the two observations in July 76 and June 78 is observed within the ∼50% uncertainty. Spectral γ-ray data for the total 3C273 data set are presented and compared with low and high-energy X-ray contemporary measurements. Recent Einstein Observatory X-ray data on the short term variability of the central part of the QSO are used to show that, within reasonable assumptions, the photon-photon interaction excludes the γ-ray source from coinciding with the variable X-ray source, thus ruling out comptonisation models for the production of energetic photons.