The Needle in the 100 deg2 Haystack: Uncovering Afterglows of Fermi GRBs
  with the Palomar Transient Factory
  The Fermi Gamma-ray Space Telescope has greatly expanded the number and
energy window of observations of gamma-ray bursts (GRBs). However, the coarse
localizations of tens to a hundred square degrees provided by the Fermi GRB
Monitor instrument have posed a formidable obstacle to locating the bursts'
host galaxies, measuring their redshifts, and tracking their panchromatic
afterglows. We have built a target-of-opportunity mode for the intermediate
Palomar Transient Factory in order to perform targeted searches for Fermi
afterglows. Here, we present the results of one year of this program: 8
afterglow discoveries out of 35 searches. Two of the bursts with detected
afterglows (GRBs 130702A and 140606B) were at low redshift (z=0.145 and 0.384
respectively) and had spectroscopically confirmed broad-line Type Ic
supernovae. We present our broadband follow-up including spectroscopy as well
as X-ray, UV, optical, millimeter, and radio observations. We study possible
selection effects in the context of the total Fermi and Swift GRB samples. We
identify one new outlier on the Amati relation. We find that two bursts are
consistent with a mildly relativistic shock breaking out from the progenitor
star, rather than the ultra-relativistic internal shock mechanism that powers
standard cosmological bursts. Finally, in the context of the Zwicky Transient
Facility, we discuss how we will continue to expand this effort to find optical
counterparts of binary neutron star mergers that may soon be detected by
Advanced LIGO and Virgo.
