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GCN Circular 486

GRB991216, optical observations
1999-12-18T05:45:34Z (24 years ago)
KPNO 0.9m group at KPNO <>
Chris Dolan (U. Wisconsin), Ian Dell'Antonio (KPNO/Brown U.), Buell
Jannuzi (NOAO/KPNO), and James Rhoads (STScI) report on behalf of the
KPNO GRB follow-up team:

"We report observations of the optical transient reported by Uglesich et al.
(GCN #472) probably corresponding to the gamma-ray bright burst GRB 991216 
(Kippen et al., GCN #463). We note that numerous independent confirming 
observations have now been reported starting with those of Henden 
et al. (GCN #473).

Our observations consist of six 180 second R-band exposures taken in
two groups of three with the KPNO 0.9m telescope and Mosaic camera on
December 17, 1999 UT.  Photometric calibration was performed using
observations of Landolt stars in SA93, SA97, and SA98 over a range of
airmasses from 1.1 to 2.0 to estimate the photometric zeropoints
(referenced to airmass=0; the extinction coefficient was measured
to be 0.085 mag/airmass in R for the night)
of the images with an accuracy of about  +- 0.03 mag 
(based on uncertainties in the flatfielding). 
This systematic uncertainty is in addition to our measurement 
uncertainty listed below.  Our reported coordinates of the 
optical transient were astrometrically calibrated to the USNO-A2 
catalog using approximately 6500 star positions, and should be 
accurate to better than +-0.15 arcsec.

R-band observations from the KPNO 0.9m+Mosaic:

 RA  (J2000)    DEC        UT_start on    Exp  Mag  Error(statistical)
                           Dec. 17, 1999
05:09:31.29  +11:17:07.5    03:33:13     180s 18.63   0.02
05:09:31.29  +11:17:07.5    03:38:50     180s 18.64   0.02
05:09:31.28  +11:17:07.5    03:44:38     180s 18.64   0.07*
05:09:31.27  +11:17:07.6    10:44:24     180s 19.25   0.03
05:09:31.29  +11:17:07.5    10:50:06     180s 19.23   0.08*
05:09:31.28  +11:17:07.5    10:55:49     180s 19.28   0.03

* near edge of chip boundary, measurement is more uncertain.

The inferred power-law decay index is -1.2, consistent with that
found by Uglesich et al.

Henden et al. (GCN #463) reported photometry relative to a
star at 05:09:39.30  +11:16:59.5 (J2000)
In our observations this star had a R magnitude of 15.187 +- 0.004 

Similarly, our measured R magnitudes for the stars measured by
Jha et al. (GCN #476) are:
  RA (J2000)    DEC(J2000)   R mag
05:09:29.799   +11:17:08.47  15.36+-0.01
05:09:32.132   +11:17:23.75  19.45+-0.03

This message can be cited."
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