Discovery of a Nonblazar Gamma-Ray Transient Source Near the Galactic Plane: GRO J1838-04
Abstract
We report the discovery of a remarkable γ-ray transient source near the Galactic plane, GRO J1838-04. This source was serendipitously discovered by EGRET in 1995 June with a peak intensity of ~(4 +/- 1) × 10-6 photons cm-2 s-1 (for photon energies larger than 100 MeV) and a 5.9 σ significance. At that time, GRO J1838-04 was the second brightest γ-ray source in the sky. A subsequent EGRET pointing in 1995 late September detected the source at a flux smaller than its peak value by a factor of ~7. We determine that no radio-loud spectrally flat blazar is within the error box of GRO J1838-04. We discuss the origin of the γ-ray transient source and show that interpretations in terms of active galactic nuclei or isolated pulsars are highly problematic. GRO J1838-04 provides strong evidence for the existence of a new class of variable γ-ray sources.
- Publication:
-
The Astrophysical Journal
- Pub Date:
- April 1997
- DOI:
- 10.1086/310603
- arXiv:
- arXiv:astro-ph/9702053
- Bibcode:
- 1997ApJ...479L.109T
- Keywords:
-
- GAMMA RAYS: OBSERVATIONS;
- GALAXIES: ACTIVE;
- STARS: NEUTRON;
- Galaxies: Active;
- Gamma Rays: Observations;
- Stars: Neutron;
- Astrophysics
- E-Print:
- 15 pages, 4 postscript files with figures Accepted for publication in Astrophys. J. Letters, Feb. 3, 1997