GCN Circular 142
Subject
GRB980703 optical observations
Date
1998-07-09T13:14:21Z (26 years ago)
From
Holger Pedersen at Copenhagen U Obs <holger@astro.ku.dk>
H.Pedersen, Copenhagen University Observatory,
H.Korhonen, Nordic Optical Telescope, La Palma,
A.O.Jaunsen, Institute for Theoretical Astrophysics, Oslo,
I.Ilyin & R.Duemmler, University of Oulu, and
F.Frontera, Inst.TeSTRE, Bologna (on behalf of the BeppoSAX team), report:
On July 4, 5, 6, and 7 we obtained R band images (600 sec each, seeing
0.75"-1.0" FWHM) of the GRB980703-field using the 2.56-m Nordic Optical
Telescope. The field-of-view was 3' x 3' and all images were acquired under
good photometric conditions.
Images taken during the first three nights were centered on the position
initially reported from RXTE by Levine et al. (IAUC 6966) and missed the
radio- and optical transient (Frail et al., GCN #128) by ~8 arcsec.
Intercomparing these images we found one variable star. Its position is
R.A. 23:59:03.7, Dec. +08:33:51.3 (J2000). An approximate R-band zero-point
is determined from the USNO catalogue entry U0975_21757527 (a star 15" SW
of the OT), which has R=16.5. This gives the following photometry for the
new variable:
UT Var
1998 July 04.101 R= 21.0 +/- 0.2
04.149 R= 21.1 +/- 0.2
04.194 R= 21.6 +/- 0.2
05.086 R= 21.5 +/- 0.2
05.146 R= 21.2 +/- 0.2
05.195 R= 21.1 +/- 0.2
06.188 R= 21.1 +/- 0.2
An image centered on the RT/OT was taken on July 7. For the OT we find the
following R-band magnitude (using the already mentioned standard star):
1998 July 07.163 R= 22.45 +/- 0.2
The errors reflect a conservative estimate of the uncertainty in the
determination of the zero-point.
Our result is consistent with a power-law decline as reported by Bloom et al.
(GCN #136) when comparing to other reported R-band values.
Further information can be found on http://vega.uio.no/~ajaunsen/grb980703
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