TITLE:   GCN GRB OBSERVATION REPORT
NUMBER:  1517
SUBJECT: Confirming no variability for GRB02081
DATE:    02/08/21 15:28:15 GMT
FROM:    Ingunn Burud at Space Telescope Science Inst  <burud@stsci.edu>

Andrew Levan, Ingunn Burud, Andy Fruchter, James Rhoads (STScI)
Maureen van den Berg, Jeroen Homan (Osservatorio Astronomico di Brera,
Itlay), Evert Rol (University of Amsterdam, Netherlands) and
Nial Tanvir (University of Hertfordshire, UK) on behalf of a larger
collaboration, report:

The error box of GRB 020819 was observed on August 19 at the JKT (La
Palma) beginning at 23.814, 8.9 hours after burst.  R band
observations in three epochs were obtained as described by Salamanca
et al (GCN 1512), these observations reach a limiting magnitude shown
below

Start time (UT)   Exp. Time     R_lim
23:32:30.117      2250          22.15
01:59:32.974      3000          22.30
05:04:11.925      1500          21.75

(The exposure time is shorter in the third epoch since one of the
frames was contaminated by a satellite track and was not used for
detailed analysis).

Comparison shows no new object brighter than the DSS-2 limit
in any exposure. Confirming the results of GCN 1506 and GCN
1509.

Combined images from each of the three epochs of observations were
subtracted using the method of Alard (Alard, 2000, A&AS, 144, 363).
The subtraction residuals were found to be of order 3% for
bright (though not saturated) objects. For fainter objects the
detection is limited by the noise in the image. With the exception of
the faintest objects the limit on the fading detection is ~0.1 mags.

We find that no objects in the frame exhibit variability beyond the
systematic errors for the entire period of the observation (5.365
hours).

We would like to thank L. Strolger for allowing us use his software
for image registration and subtraction.