On the Nature of the Discrete Gamma‐Ray Sources in the Vicinity of the Supernova Remnant G312.4−0.4

Abstract

We discuss the excess gamma-ray emission seen from point sources in the vicinity of the supernova remnant (SNR) G312.4-0.4 with the EGRET instrument on board the Compton Gamma Ray Observatory in the energy range of 100 MeV to 10 GeV. Two gamma-ray sources have been significantly detected. The best-fit position for the source 2EG J1412-6211, which was originally discovered by COS B (catalog name 2CG 311-01), is located approximately 17' southwest of the center of the supernova remnant G312.4-0.4. We find the gamma-ray flux level of this source to be relatively constant over a period of 4 yr. The origin of the gamma-ray emission with respect to a SNR-pulsar source is discussed. The best-fit position for the other source, 2EGS J1418-6049, lies 13 northeast of the center of G312.4-0.4. It has a variable flux level, with a spectrum extending up to a few GeV. We argue that 2EGS J1418-6049 is transient in nature and that its variability makes it unlikely to be associated with G312.4-0.4 or any other SNR or isolated pulsar. We suggest that this source may belong to a new class of unidentified Galactic sources which includes the EGRET source 2EG J0241+6119 (2CG 135+01).