GCN Circular 8075
Subject
GRB 080804: GROND observations
Date
2008-08-06T07:58:12Z (16 years ago)
From
Thomas Kruehler at MPE/MPI <kruehler@mpe.mpg.de>
T. Kruehler, F. Schrey, J. Greiner, A. Yoldas, C. Clemens, S. McBreen
(all MPE Garching),
A. Kupcu Yoldas (ESO) and G. Szokoly (Eoetvoes Univ., Budapest) report on
behalf of the GROND team:
GROND (Greiner et al. 2008, PASP 120, 405), mounted at the 2.2m ESO/MPI
telescope at La Silla Observatory (Chile), started observations of the
field of GRB 080804 (Racusin et al. 2008, GCN #8057) in g'r'i'z'JHK at
23:26 UT, 16 min after the burst. We clearly detect the optical
afterglow (Rujopakarn & Rykoff 2008, GCN #8056) in all filters at a
position consistent with UVOT (Racusin et al. 2008, GCN #8057) and the
Faulkes Telescope South (Guidorzi & Steele, GCN #8064). Observations
continued for 65 min and were resumed at 06:30 UT for 30 min.
Assuming the USNO-B1 star at RA(J2000)=328.6627, DEC(J2000)=-53.18288
having R2=18.08 mag, we measure the following r' magnitudes, not
corrected for the expected Galactic foreground extinction corresponding
to a reddening of E_(B-V)=0.02 (Schlegel et al. 1998):
Filter T_mid Exposure Brightness
(s) (s) (mag)
-----------------------------------------
r' 1160 67 18.09 +- 0.03
r' 1565 67 18.37 +- 0.03
r' 1996 115 18.66 +- 0.02
r' 2768 115 18.96 +- 0.02
r' 3672 375 19.25 +- 0.02
r' 26112 375 21.02 +- 0.04
The reported magnitudes are a subset of the complete observation
consisting of 24 individual frames. The total r band light curve is well
fitted by power law with index of 0.87 +- 0.03 between 0.32 h and 7.63 h
post burst. This decline is consistent with the Faulkes Telescope South
detection (Guidorzi & Steele, GCN #8064) at 14.235 h post burst.
Assuming the optical light curve continues the decline with the same
power law index, we predict r' band magnitudes of 22.7 at 2 days and
23.4 at 4 days post burst.
The broad band SED from g' to K can be fitted by a power law with index
0.8 +- 0.1 (statistical) +-0.1 (systematic), where the latter is due to
the lack of photometric calibration.