NEW COMPTEL GAMMA-RAY SOURCE (GRO-J0516-609) NEAR PKS-0506-612 0522-611 - FIRST EVIDENCE FOR MEV BLAZARS/

We report evidence for a blazar-type AGN that is exceptionally bright at MeV energies. It is firmly detected by COMPTEL in the 1-10 MeV rang e, but we find only a weak similar to 3 sigma source in the EGRET arch ival data (>100 MeV), which is confirmed by the EGRET team. The source is now listed as one of the marginal detections in the latest EGRET c atalogue, being the weakest source in the whole list. It is located ab out 10 degrees from the LMC at l approximate to 270 degrees, b approxi mate to: -35 degrees. Within the 99% error region of this new COMPTEL source (GRO J0516-609), two potential AGN counterparts can be identifi ed. These are PKS 0506-612 and PKS 0522-611, separated by similar to 2 0, which are both compact, radio loud, flat-spectrum radio sources, li ke all AGNs detected at high-energy gamma-rays. The former is the pref erred counterpart by the weak EGRET detection, which has a smaller err or region. The source was in the COMPTEL field-of-view on three occasi ons during its Phase I sky survey, but it was detected only in the sec ond and third observation. This suggests a flux increase by a factor o f about two in the two-month period between the first and second viewi ng. Evidence for the weak EGRET source is also only found in the secon d and third observation. The radiated power per decade of energy (vF(v )) strongly peaks at similar to 3 MeV. If GRO J0516-609 is indeed a bl azar, it can probably be ruled out that the MeV gamma-rays are mainly due to Comptonization of an external radiation field. ''MeV blazars'' like GRO J0516-609 may be responsible for the observed MeV bump in the cosmic background spectrum.