Failed Gamma-Ray Bursts: Thermal UV/Soft X-ray Emission Accompanied by   Peculiar Afterglows
  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 UV/Soft X-ray band. The photospheric emission lasts for about one thousand seconds with luminosity about several times 10^46 erg/s. 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. 
M. Xu, S. Nagataki, Y.-F. Huang, and S.-H. Lee
astro-ph.HE