Vol 23, No 2

Possible Origin of a Newly Discovered GeV Gamma-Ray Source Fermi J1242.5+3236

Xiu-Rong Mo, Ming-Hong Luo, Hong-Bin Tan, Qing-Wen Tang and Ruo-Yu Liu


Based on the first 13.4 yr of Fermi science data in the energy range from 300 MeV to 500 GeV, we discovered a bright GeV gamma-ray source with a 5.64σ detection, named Fermi J1242.5+3236, which has an offset of about 0.º0996 from a nearby star-forming galaxy NGC 4631. When using the 12 yr' data, the detection significance of Fermi J1242.5+3236 is about 4.72σ. Fermi J1242.5+3236 is a steady point source without significant temporal variability and has a hard gamma-ray photon index of about −1.60 ± 0.24. The spatial offset and the hard gamma-ray spectrum disfavor this source as the diffuse gamma-ray emission from this galaxy. This new source might have a possible origin of an unidentified background blazar, which is more likely a high-synchrotron-peaked blazar for its hard gamma-ray photon index. A follow-up optical observation would help distinguish origin of Fermi J1242.5+3236.


galaxies: starburst – galaxies: star formation – gamma-rays: galaxies – galaxies: active

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