Testing the Magnetar Model via Late Time Radio Observations of Two
  Macronova Candidates
  Compact binary mergers may have already been observed as they are the leading
model for short gamma-ray bursts (sGRBs). Radioactive decay within the ejecta
from these mergers is expected to produce an infra-red flare, dubbed macronova
(or kilonova), on a time scale of a week. Recently two such macronova
candidates were identified in followup observations of sGRBs, strengthening the
possibility that those indeed arise from mergers. The same ejecta will also
produce a long term (months to years) radio emission due to its interaction
with the surrounding ISM. In search for this emission, we observed the two
macronova candidates, GRB 130603B and GRB 060614 with the Jansky very large
array (VLA) and the Australia Telescope Compact Array (ATCA). Our observations
resulted in null-detections, putting strong upper limits on the kinetic energy
and mass of the ejecta. A possible outcome of a merger is a highly magnetized
neutron star (a magnetar), which has been suggested as the central engine for
GRBs. Such a magnetar will deposit a significant fraction of its energy into
the ejecta leading to a brighter radio flare. Our results, therefore, rule out
magnetars in these two events.
