Evidence that Gamma-ray Burst 130702A Exploded in a Dwarf Satellite of a
  Massive Galaxy
  GRB 130702A is a nearby long-duration gamma-ray burst (LGRB) discovered by
the Fermi satellite whose associated afterglow was detected by the Palomar
Transient Factory. Subsequent photometric and spectroscopic monitoring has
identified a coincident broad-lined Type Ic supernova (SN), and nebular
emission detected near the explosion site is consistent with a redshift of
z=0.145. The SN-GRB exploded at an offset of ~7.6" from the center of an
inclined r=18.1 mag red disk-dominated galaxy, and ~0.6" from the center of a
much fainter r=23 mag object. We obtained Keck-II DEIMOS spectra of the two
objects and find a 2{\sigma} upper limit on their line-of-sight velocity offset
of ~<60 km/s. If we project the SN-GRB coordinates onto the plane of the
inclined massive disk galaxy, the explosion would have a ~61+-10 kpc offset, or
~6 times the galaxy's half-light radius. This large estimated nuclear offset
suggests that the faint source is not a star-forming region of the massive red
galaxy but is instead a dwarf galaxy. The star-formation rate of the dwarf
galaxy is ~0.05 solar masses per year, and we place an upper limit on its
oxygen abundance of 12 + log(O/H) < 8.16 dex. The identification of an LGRB in
a dwarf satellite of a massive, metal-rich primary galaxy suggests that recent
detections of LGRBs spatially coincident with metal-rich galaxies may be, in
some cases, superpositions.
