TITLE:   GCN CIRCULAR
NUMBER:  19854
SUBJECT: GRB 160821B: VLA 5.0 GHz observations
DATE:    16/08/24 20:22:19 GMT
FROM:    Wen-fai Fong at U of Arizona  <wfong@email.arizona.edu>

W. Fong (University of Arizona), K. D. Alexander (Harvard), and T. Laskar
(NRAO/UC Berkeley) report:

"We observed the position of the short-duration GRB 160821B (Siegel et al.,
GCN 19833) with the Karl G. Jansky Very Large Array (VLA) beginning on 2016
Aug 22.088 UT (3.6 hr post-burst) at a mean frequency of 5.0 GHz. In 1 hour
of observations, we detect a faint radio source at the position:

RA(J2000) = 18:39:54.56
Dec(J2000) = 62:23:30.3

with an uncertainty of 0.3" in each coordinate. This position is consistent
with the position of the X-ray afterglow (Evans et al., GCN 19837), and
coincident with the position of the optical afterglow (Xu et al., GCN
19834; Levan et al., GCN 19846).

We measure a preliminary 5.0 GHz flux density of ~35 microJy. To assess
variability, we obtained an additional set of VLA observations starting at
26.5 hr after the burst. The source is no longer detected in these
observations to a 3-sigma limit of 18 microJy.

Due to the fading of the radio source, as well as the positional
coincidence with the X-ray and optical afterglows, we suggest this source
as the radio afterglow of GRB 160821B.

We thank the VLA staff for quickly executing these observations."