[vsnet-grb-info 10389] GRB 110328A / Swift J164449.3+573451: PTF Quiescent Optical Counterpart

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  11827
SUBJECT: GRB 110328A / Swift J164449.3+573451: PTF Quiescent Optical Counterpart
DATE:    11/03/28 21:23:00 GMT
FROM:    S. Bradley Cenko at Caltech  <cenko at srl.caltech.edu>

S. B. Cenko (UC Berkeley), P. E. Nugent (LBNL / UC Berkeley), Derek B. Fox
(Penn State), E. O. Ofek and M. M. Kasliwal (Caltech) report on behalf of
a larger collaboration:

As part of the Palomar Transient Factory, we have obtained pre-outburst
optical (R-band) imaging of the field of the high-energy transient source
GRB 110328A / Swift J164449.3+573451 (GCNs 11823, 11824) with the Palomar
48-inch Oschin Schmidt telescope over the time period from 2009 May to
2010 October.  In a stacked frame of all available data, we find a faint,
unresolved source at location (J2000.0):

  RA: 16:44:49.97     Dec: +57:34:59.7

The astrometric uncertainty associated with this position is ~ 150 mas
in each coordinate (based on the USNO-B1 catalog).  This is consistent
with the enhanced XRT position (GCN 11826), and is therefore likely to be
associated with the high-energy transient.  The detection of such a
relatively bright optical counterpart strongly disfavors a cosmological
long-duration GRB, and instead suggests that Swift J164449.3+573451 is
more likely a new Galactic transient source (GCN 11824, ATEL 3242).

In attempting to estimate the brightness of this object, we find that
nearby calibration stars from the USNO-B catalog are likely to be
inaccurate (resulting in limits significantly deeper than our system can
achieve).  Based on past observations of other fields, we estimate the
brightness of the counterpart to be R ~ 22, although we caution that
this estimate may suffer from significant uncertainty.