The afterglow of GRB 070707 and a possible kilonova component

GRB 070707 was the first short gamma-ray burst (GRB) detected by INTEGRAL and the optical afterglow was attributed to the prolonged activity of the central engine in the literature. Here, we reanalyse the afterglow data and examine the physical origin of the emission. The redshift of this burst is uncertain and in this work we assume an association with a galaxy at the redshift of 0.2394 for a chance coincidence probability P-cc = 0.046. It is found that the sole forward shock radiation cannot well reproduce the data, while including a kilonova component similar to AT2017gfo is very helpful in reproducing the multiwavelength afterglow emission. The properties of the candidate host galaxy have been studied in detail; its high metallicity, low star formation rate, and old stellar population age are similar to the host galaxies of other GRBs associated with kilonovae. In view of the facts that a kilonova signal was identified in the first short GRB with detected optical emission (i.e. GRB 050709) and the first short GRB with gravitational wave detection (i.e. GRB 170817A), and now the identification of a kilonova signature in the first INTEGRAL short GRB strongly indicates that kilonovae are rather common among the neutron star merger events.