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Discovery of a non-blazar gamma-ray transient near the Galactic plane: GRO J1838-04

M. Tavani·R. Mukherjee·J. R. Mattox·J. Halpern·D. J. Thompson·G. Kanbach·W. Hermsen·S. N. Zhang·R. S. Foster
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Abstract

We report the discovery of a remarkable gamma-ray transient source near the Galactic plane, GRO J1838-04. This source was serendipitously discovered by EGRET in June 1995 with a peak intensity of 4 E(-6) ph/cm/cm/s (for photon energies larger than 100 MeV) and a 5.9 sigma significance. At that time, GRO J1838-04 was the second brightest gamma-ray source in the sky. A subsequent EGRET pointing in late September 1995 detected the source at a flux smaller than its peak value by a factor of 7. We determined that no radio-loud spectrally-flat blazar is within the error box of GRO J1838-04. We discuss the origin of the \ggg-ray transient source and show that interpretations in terms of AGNs or isolated pulsars are highly problematic. GRO J1838-04 provides strong evidence for the existence of a new class of variable gamma-ray sources.

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M. Tavani, R. Mukherjee, J. R. Mattox, J. Halpern, D. J. Thompson, G. Kanbach, W. Hermsen, S. N. Zhang, R. S. Foster. 1997-02-05. Discovery of a non-blazar gamma-ray transient near the Galactic plane: GRO J1838-04. https://doi.org/10.1086/310603

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