COMPTEL observations of the γ-ray blazars 3C 454.3 and CTA 102 during the CGRO mission

¹ Laboratory for Particle Astrophysics, Institute of High Energy Physics, PO Box 918-3, Beijing 100049, PR China e-mail: szhang@mail.ihep.ac.cn
² Max-Planck-Institut für extraterrestrische Physik, Postfach 1613, 85741 Garching, Germany

Received: 8 June 2005
Accepted: 5 August 2005

Abstract

We have investigated the MeV behaviour of the γ-ray blazars 3C 454.3 and CTA 102 by analyzing all COMPTEL observations of this sky region during the complete CGRO mission. Both sources are detected by COMPTEL at the upper COMPTEL energies, although their flux estimates may be uncertain by possible minor contributions of nearby unidentified EGRET γ-ray sources. While CTA 102 was only detected at energies above 10 MeV during the early mission, 3C 454.3 is most significantly detected in the COMPTEL 3-10 MeV band in the sum of all data. Time-resolved analyses indicate a weak (near COMPTEL threshold) but likely steady 3-10 MeV emission over years, being independent of the observed time variability at energies above 100 MeV as observed by EGRET. This energy-dependent variability behaviour suggests different emission mechanisms at work in the two bands. Putting the COMPTEL fluxes in multifrequency perspective (radio to γ-rays) reveals for both sources the typical two-hump blazar spectrum, with a low-energy maximum around the IR and a high-energy maximum at MeV energies. The latter one dominates the energy output across the whole electro-magnetic spectrum. The results of our analyses are discussed in the framework of current blazar modeling.