A Gamma-Ray Burst Remnant in Our Galaxy: HESS J1303-631

We present an investigation of the multiwavelength data on HESS J1303-631, an unidentified TeV source serendipitously discovered in the Galactic plane by the HESS collaboration. Our results strongly suggest the identification of this particular source as the remnant of a gamma-ray burst (GRB) that happened some few tens of thousands years ago in our Galaxy at a distance on the order of >~10 kpc from us. We show through detailed calculations of particle diffusion, interaction, and radiation processes of relativistic particles in the interstellar medium that it is possible for a GRB remnant (GRBR) to be a strong TeV emitter with no observable synchrotron emission. We predict spectral and spatial signatures that would unambiguously distinguish GRBRs from ordinary supernova remnants, including (1) large energy budgets inferred from their TeV emission, but at the same time (2) suppressed fluxes in the radio through GeV wave bands; (3) extended center-filled emission with an energy-dependent spatial profile; and (4) possible elongation in the direction of the past pair of GRB jets. While GRBRs can best be detected by ground-based gamma-ray detectors, the future GLAST mission will play a crucial role in confirming the predicted low level of GeV emission.