[vsnet-grb-info 563] GRB 021112: Variable Source in R-band search

[GCN Circulars <gcncirc@lheawww.gsfc.nasa.gov>]

TITLE:   GCN GRB OBSERVATION REPORT
NUMBER:  1696
SUBJECT: GRB 021112: Variable Source in R-band search
DATE:    02/11/18 22:49:28 GMT
FROM:    James Rhoads at STScI  <rhoads@stsci.edu>

L. Strolger, J. E. Rhoads, A. Fruchter, I. Burud (STScI); A. J. Levan
(Leicester), and J. J. Kavelaars (McMaster) report.

In follow-up to our observations reported in GCN 1684, additional
observations of the GRB 021112 error box (GCN 1682) were made using the
KPNO-4m + Mosaic I imager on UT 2002 November 13.2. Four R-band images
were obtained dithered to cover the entire HETE-2 error circle, for a
combined exposure time of 1680s. Further detailed analysis of the
field, including localized registration, PSF-matching, and subtraction
of the combined observations made Nov. 12.3 from the combined
observations made Nov. 13.2 have revealed a candidate optical transient
(OT) located just outside the HETE-2 90% error circle, at
	RA: 02:38:27.80 Dec: +48:33:18.4 (J2000.0)
Coordinates and offsets from neighboring stars were determined from
direct comparison to the DDS-2 (R-band). A source is visible at the
limit of the DDS-2 red plate at the position of the variable object.

PSF photometry performed on the candidate OT and 5 neighboring stars have
shown the object apparently brightened by 0.55 +/- 0.03 magnitudes between
the observations made on Nov. 12.3 and Nov 13.2.
Further information summarizing the discovery and analysis
can be found on http://www.stsci.edu/~fruchter/GRB/021112/ .

An approximate photometric zero point (based only on the typical throughput
for the camera) gives R=21.1 on Nov 12.3 and R=20.6 on Nov. 13.2.
Local reference star magnitudes are given on the above web page to
facilitate comparison with other data.

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