Failed gamma-ray bursts: Thermal ultraviolet/soft X-ray emission accompanied by peculiar afterglows

Abstract

We show that the photospheres of "failed" gamma-ray bursts (GRBs), whose bulk Lorentz factors are much lower than 100, can be outside of internal shocks. The resulting radiation from the photospheres is thermal and bright in the UV/soft X-ray band. The photospheric emission lasts for about 1000 s with a luminosity about several times 1046 ergs-1. These events can be observed by current and future satellites. It is also shown that the afterglows of failed GRBs are peculiar at the early stage, which makes it possible to distinguish failed GRBs from ordinary GRBs and beaming-induced orphan afterglows. © 2012. The American Astronomical Society. All rights reserved.