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We present the results from an ESO/VLT campaign aimed at studying theafterglow properties of the short/hard gamma ray burst GRB 070707. Observationswere carried out at ten different epochs from ~0.5 to ~80 days after the event.The optical flux decayed steeply with a power-law decay index greater than 3,later levelling off at R~27.3 mag; this is likely the emission level of thehost galaxy, the faintest yet detected for a short GRB. Spectroscopicobservations did not reveal any line features/edges that could unambiguouslypinpoint the GRB redshift, but set a limit z < 3.6. In the range of allowedredshifts, the host has a low luminosity, comparable to that of long-durationGRBs. The existence of such faint host galaxies suggests caution whenassociating short GRBs with bright, offset galaxies, where the true host mightjust be too dim for detection. The steepness of the decay of the opticalafterglow of GRB 070707 challenges external shock models for the opticalafterglow of short/hard GRBs. We argue that this behaviour might results fromprolonged activity of the central engine or require alternative scenarios.

The short GRB070707 afterglow and its very faint host galaxy