GCN Circular 87

GRB 980519 Optical Observations

J. S. Bloom, S. G. Djorgovski, R. R. Gal, S. R. Kulkarni, and
A. Kelly, on behalf of the Caltech GRB Collaboration, report:
 
"We obtained CCD images of the field of GRB 980519 using COSMIC on the
Palomar Observatory 200-inch on UT May 20.  In particular, we imaged the
GRB field for 500 s (Cousins R) and 600 s (Gunn i). We photometrically
calibrated our Gunn i-band and Cousins R-band images against standard
Landolt 1992 (AJ 104, 340) stars (in SA 113).  We accounted for atmosphere
extinction and included a color correction term in the fit to account for
the fact that Landolt reports magnitudes in a different R and I band
system. Derived magnitudes of the following 10 secondary stars are thus in
the Londolt RI system (we kept the naming the convention of Jansen et al.
GCN 78
Not found
 
 
): 
 
Object   RA          DEC       I_landolt err    R_landolt err 
  A   23:22:20.0  +77:15:52   17.34 +/- 0.05   17.94 +/- 0.05
  B         29.6         44   18.64 +/- 0.05   19.41 +/- 0.05
  C         28.7         26   17.57 +/- 0.05   18.10 +/- 0.05
  E         20.6         24   18.85 +/- 0.05   20.19 +/- 0.06
  F         31.8         45   18.48 +/- 0.05   19.91 +/- 0.06
  G         33.2  +77:14:59   17.25 +/- 0.05   19.02 +/- 0.05
  H         20.7      14:55   18.13 +/- 0.05   19.44 +/- 0.05
  I         09.2  +77:15:51   19.27 +/- 0.06   19.80 +/- 0.06
  J         07.6  +77:16:01   19.05 +/- 0.06   20.08 +/- 0.06
  L         35.0      16:15   18.57 +/- 0.05   19.21 +/- 0.05
 
Uncertainty in optimum aperture size for each star is the dominate source
of statistical error. There is an overall zero-point systematic error (not
included above) in each band which amounts to 0.150 mag (I) and 0.151 (R).
The approximate RA and DEC are measured in J2000 from the Digital Sky
Survey (DSS).
 
We note our derivation for A,B, and C magnitudes are highly discrepant
from that of Jansen et al. GCN #78, but agree quite well with that of Kemp
and Halpern (GCN #80) and Diercks et al. (GCN #82).  At the time of
observations we find the OT has magnitudes of May 20.43 UT, I_landolt =
20.86 +/- 0.11; May 20.48 UT, R_landolt = 21.57 +/- 0.09.
 
A finding chart with the secondary stars noted may be found at
http://astro.caltech.edu/~jsb/grb980519.ps
 
This message may be cited."