GRB 110328A / Swift J164449.3+573451: PTF Quiescent Optical Counterpart
ATel #3243; S. B. Cenko (UC Berkeley), P. E. Nugent (LBNL / UC Berkeley), Derek B. Fox (Penn State), E. O. Ofek and M. M. Kasliwal (Caltech) on behalf of a larger collaboration:
on 28 Mar 2011; 21:37 UT
Credential Certification: S. Bradley Cenko (cenko@astro.berkeley.edu)
Subjects: Optical, Gamma-Ray Burst, Transient
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 (GCN #11823,GCN #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.
This message was also circulated as GCN #11827.