GeV photons from up-scattering of supernova shock breakout X-rays by an outside GRB jet

Shock breakout X-ray emission has been reported for the first time from a supernova connected with a gamma-ray burst, namely GRB060218/SN2006aj. The gamma-ray emission and the power-law decaying X-ray afterglow are ascribed to a highly relativistic jet, while the thermal soft X-rays are thought to be produced when the radiation-dominated shock breaks from the optically thick stellar wind. We study the inverse Compton emission of the breakout thermal soft X-rays scattered by relativistic electrons in the jet forward shock, which is is expected to be at larger radii than the breakout shock. This IC emission produces sub-GeV to GeV photons, which may be detectable by GLAST. The detection of such GeV photons simultaneously with the supernova shock breakout emission would give evidence for the presence of a GRB jet ahead of the shock while the shock is breaking out. The anisotropic scattering between the X-rays and relativistic electrons may lead to large angle emission outside of the jet opening angle. This has implications for the detection of GeV photons from burstless type Ib/c hypernova shock breakout, which due to its more isotropic emission might be observed with wide-field X-ray cameras such as LOBSTER. Subject headings: gamma rays: bursts— supernovae: general –radiation mechanisms: non-thermal Department of Astronomy and Astrophysics, Pennsylvania State University, University Park, PA 16802, USA Department of Astronomy, Nanjing University, Nanjing 210093, China Center for Gravitational Wave Physics and Department of Physics, Pennsylvania State University, University Park, PA 16802, USA