GRB 990510 Observations at the Danish 1.54m on La Silla
GRB 990510 Optical Observations (GCN Circular #320)
J. Hjorth (Copenhagen), I. Burud (Liege), A. Pizzella (ESO Chile),
H. Pedersen (Copenhagen), A. O. Jaunsen (Oslo), B. Lindgren (Copenhagen)
"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/ ."
(see also GCN circulars)
Combined 5700 sec image (seeing FWHM 1.47").
Results of deconvolutions. Top panels are the original image (FWHM=1.47").
The middle panels
are the deconvolved images (FWHM=0.39"). The bottom panels are the residuals
without point sources. The left panel assumes that the object 2.1" south
of the OT is a point source. The right panel treats it as a part of
Blow-up of the deconvolved area with no assumptions about the
object 2.1" south of the OT.