DO ALL SHORT GRBs HAVE AN ASSOCIATED HOST GALAXY? THE CASE OF GRB 070707

Abstract

We present optical observations of the short GRB 070707, discovered by INTEGRAL. The afterglow light-curve shows a very steep decay after ≈ 2 days from the trigger, which cannot be accounted for by jetted or high latitude emission. Thanks to very deep ESO–VLT observations, we detect a very faint host galaxy with R = 27.3 ± 0.13. This result confirms that short GRBs can be associated with very faint galaxies, and suggests that some associations with bright objects in the close vicinity of other short GRBs should be treated with caution.