GCN Circular 320

GRB 990510 Optical Observations 


J. Hjorth (Copenhagen), I. Burud (Liege), A. Pizzella (ESO Chile), 
H. Pedersen (Copenhagen), A. O. Jaunsen (Oslo), B. Lindgren (Copenhagen)
report: 


"Thirty-one 300-sec R-band images of the optical transient (OT) related to 
GRB 990510 (GCN #310, 312, 313) were obtained with the DFOSC at the Danish 
1.54-m telescope on La Silla between 11.14 May and 11.37 May 1999 UT.  The 
seeing FWHM ranged from 1.2" to 1.6". An astrometric plate solution (USNO-A2.0) 
yielded the OT coordinates RA = 13:38:07.11, Dec = -80:29:48.2 (J2000) with an 
uncertainty of +- 0.44". Photometry was carried out using the deconvolution 
code described by Magain, Courbin & Sohy (ApJ, 494, 452, 1998). Simultaneous 
deconvolution of the 31 images resulted in a light curve with an rms scatter 
of 0.016 mag. The lightcurve is consistent with a power law decay with index 
-1.27 in this small interval. The combined lightcurve including data from 
Axelrod et al. (GCN #315), Galama et al. (GCN #313) and Pietrzynski & Udalski 
(GCN #316) is inconsistent with a single power law. Our results thus confirm 
the steepening of the light curve noted by Stanek et al. (GCN #318). The faint 
object 2.05" south and 0.56" east of the OT is clearly seen on the deconvolved 
image. The object does not appear extended towards the OT. Images, deconvolved 
images and light curves are posted at http://www.astro.ku.dk/~jens/grb990510/ ."