GRB 020801

GRB020801: Imaging of Suggested OT Counterpart at the Magellan Observatory

M. Garcia and D. Rusin (CFA); N. Butler, A. Dullighan, G. Ricker, and 
R. Vanderspek (MIT)

write:

We have imaged the suggested optical counterpart of GRB020801 
(Kilmartin and Gilmore; GCN 1462
Loading...
 
 ), which was localized in the X-ray 
band by HETE, with the LDSS-2 instrument on Magellan 1 (Walter A. 
Baade Telescope), obtaining two broadband CCD images.  By comparing 
the Kilmartin-Gilmore object with the USNO A-2 stars in the field, we 
derive approximate magnitudes of 19.31 (03 Aug 2002, 02:01 UT) and 
19.61 (03 Aug 2002, 02:20 UT) for the object.  We estimate our 
magnitude conversion to R has a zero point rms error of 0.4 
magnitudes, and that our internal photometric errors have rms errors 
of 0.03 magnitudes.  The brightness of the Kilmartin-Gilmore object 
which we measure agrees well with that cited in GCN 1462
Loading...
 
 , but also 
indicates that the object is variable.  The lack of fading rules out 
this object as the GRB afterglow counterpart (as suggested by Fox and 
Price; GCN 1464
Loading...
 
 ); the fluctuations may indicate that it is a variable 
(dMe?) star.

This message may be cited.

Derek Fox (Caltech) and Paul Price (RSA/ANU) report:

"The OT candidate for GRB020801 (HETE Triggers 2177 and 2178) reported
by Kilmartin & Gilmore (GCN 1462
Loading...
 
 ) is detected in the Digitized Sky
Survey (POSS-II) N-emulsion (~I-band) image at a similar magnitude to
that seen in their finding chart.  Given the unfiltered nature of
their observations it seems likely that this represents a redetection
of the DSS source rather than a new source and candidate OT."

P. Kilmartin (p.kilmartin@phys.canterbury.ac.nz)
and A. Gilmore, Mount John Observatory, on behalf
of the AAVSO International GRB Network, report:

We have imaged the error circle of the long
GRB020801 (HETE trigger 2177/8) using the MJO 0.6m
telescope and ST-9E CCD.  Fifteen unfiltered 60-second
exposures, centered on UT 020802.383 (20hrs after the burst),
were taken and median combined, and with a limiting
magnitude of roughly R=20 based on USNO-A2.0.  Comparing against the
DSS, we find a new object with approximate R magnitude of 19.4,
located at

   21:02:37.34  -53:44:59.3  J2000

Frames taken 21min apart show no movement, and the
AAVSO web site indicates no known asteroid is in
this field of view.  We have continued imaging much of
the error circle, but have found nothing else that is not
on the DSS images.

We have placed a 5x5arcmin finding chart marking the
new object at:
  ftp://ftp.nofs.navy.mil/pub/outgoing/aah/grb/grb020801.jpg
The object appears extended on this finding chart, but
appears stellar on other later image sets.

The AAVSO would like to thank the Curry Foundation for supporting the
AAVSO International GRB Network.