Radio follow-up of gravitational wave triggers during Advanced LIGO O1
  We present radio follow-up observations carried out with the Karl G. Jansky
Very Large Array during the first observing run (O1) of the Advanced Laser
Interferometer Gravitational-wave Observatory (LIGO). A total of three
gravitational wave triggers were followed up during the ~4 months of O1, from
September 2015 to January 2016. Two of these triggers, GW150914 and GW151226,
are binary black hole merger events of high significance. A third trigger,
G194575, was subsequently declared as an event of no interest (i.e., a false
alarm). Our observations targeted selected optical transients identified by the
intermediate Palomar Transient Factory (iPTF) in the Advanced LIGO error
regions of the three triggers, and a limited region of the gravitational wave
localization area of G194575 not accessible to optical telescopes due to Sun
constraints, where a possible high-energy transient was identified. No
plausible radio counterparts to GW150914 and GW151226 were found, in agreement
with expectations for binary black hole mergers. We show that combining optical
and radio observations is key to identifying contaminating radio sources that
may be found in the follow-up of gravitational wave triggers, such as emission
associated to star formation and AGN. We discuss our results in the context of
the theoretical predictions for radio counterparts to gravitational wave
transients, and describe our future plans for the radio follow-up of Advanced
LIGO (and Virgo) triggers.
