GRB 990712
IAU Circular 7255:
G. Bakos, Space Telescope Science Institute (STScI) and
Konkoly Observatory; K. Sahu, STScI; and J. Menzies, South African
Astronomical Observatory (SAAO), on behalf of the PLANET
collaboration; and P. Vreeswijk, University of Amsterdam, and F.
Frontera, Istituto Tecnologie e Studio Radiazioni Extraterrestri,
CNR, Bologna, on behalf of the Amsterdam and BeppoSAX/Bologna GRB
follow-up teams, report: "The GRB 990712 WFC error circle (IAUC
7721) was observed with the 1-m SAAO telescope at Sutherland on
July 12, 13, and 14. An R image taken on July 12.87 UT
(integration time 900 s), when compared with the Digitized Sky
Survey (DSS) image, showed a source at R.A. = 22h31m53s.1, Decl. =
-73o24'29" (equinox 2000.0; positional uncertainty 1") that is
absent in the DSS image. Images taken during the following two
nights showed the source to fade, and this further supports the
identification. For photometric calibration, the standard stars
F203 and F209 were observed, and the resultant magnitudes for the
object are: July 12.87 (not 12.82 as the IAUC says!), R = 19.4;
13.74, R = 20.9; 13.76, I = 20.5; 14.76, R = 21.2; 14.77, V = 21.9.
A finding chart is available at
http://www.stsci.edu/~ksahu/grb990712.html."
The following image has a dimension of 5 x 4 arcmin. North is up
and East is to the left.
MAGNITUDES OF THE STARS IN THE FIELD
----------------------------------------------------
No. RA(2000) Dec(2000) V R I
----------------------------------------------------
1 22:31:50.65 -73:24:25.1 17.26 16.46 15.66
2 22:31:39.88 -73:25:10.0 17.05 16.71 16.31
3 22:31:49.57 -73:26:09.3 16.53 16.03 15.52
4 22:32:18.48 -73:24:10.7 15.98 15.33 14.67
----------------------------------------------------
GCN Circular #387:
Gaspar Bakos (STScI and Konkoly Observatory), Kailash Sahu (STScI) and
John Menzies (SAAO) observing on behalf of the PLANET collaboration, and
Paul Vreeswijk (Univ. Amsterdam) and Filippo Frontera (ITESE, CNR, Bologna)
on behalf of the Amsterdam/Beppo-SAX-Bologna GRB follow-up team report:
GRB 990712 WFC error circle (Frontera et al. GCN #385) was observed with the
1m telescope of the South African Astronomical Observatory at Sutherland
on July 12.87 UT in R filter with an integration time of 900 sec. Comparison
with the Digitized Sky Survey (DSS) image shows a relatively bright source
at RA (2000) = 22h 31m 53.1s Dec (2000) = -73d 24' 29" (with a positional
uncertainty of about 1 arcsec) which is absent in the DSS image. Based on
the red magnitudes of the USNO stars in the field, the estimated magnitude
of the new source is R = 17.85 +/- 0.2. Since the limiting magnitude of the
DSS image is at least 21, the new source is most likely the optical counterpart
of GRB 990712. Further observations are urged.
Note that the Magnitudes given in the GCN were based on the red-magnitudes
of the USNO stars in the field. Subsequent standard star observations
revealed that the USNO magnitudes were off by as much as 2 magnitudes
in a few cases. The magnitudes given in the IAU circular are based
on the standard star measurements, and hence are more accurate
(+/- ~0.1 magnitudes).
Kailash Sahu (ksahu@stsci.edu)
last modified: July 18 1999