COMPTEL detection of the high-energy γ-ray source 2CG 135+01.


We present an analysis of COMPTEL observations made between November 1991 and May 1994 of 2CG 135+01, a bright γ-ray source located near the Galactic plane. At energies above 1MeV, an excess consistent with the position of 2CG 135+01 is detected in the sum of the observations, at flux levels which are a factor of 10-100 below those published in the past. The detection significance of this excess, when the possible presence of underlying Galactic diffuse emission is neglected, is 6.6σ for 3degrees of freedom. The differential photon spectrum in the 1-30MeV energy range can be described by a power law with a spectral index of 1.95^+0.2^_-0.3_. Due to the uncertainties involved in modelling the Galactic-disk diffuse emission underneath the source, the absolute flux levels must be considered uncertain by a factor of two. They are consistent with the extrapolation of the time-averaged spectrum of 2CG 135+01 measured with EGRET, thereby strengthening the identification. No significant temporal correlation between the γ-ray emission and the monitored radio emission of the possible counterpart radio source GT 0236+610 (showing a 26.5day modulation) is found.


Space Science Center, Physics

Publication Date


Journal Title

Astronomy and Astrophysics


Springer Netherlands

Document Type



c European Southern Observatory