GCN Circular 2879
Subject
GRB 041218: R-band optical observations
Event
Date
2004-12-19T21:27:17Z (21 years ago)
From
Daniele Malesani at SISSA-ISAS,Trieste,Italy <malesani@sissa.it>
Paolo D'Avanzo, Stefano Ciroi, Daniele Malesani, Stefano Covino,
Vincenzo Testa, and Angelo Antonelli, report on behalf of a larger
Italian collaboration:
"We observed the field of GRB041218 (Mereghetti et al., GCN 2858)
starting about 6 hours after the trigger. Observations were performed
with the 182cm Copernicus telescope equipped with the AFOSC instrument,
at the Asiago Observatory (Northern Italy). Weather conditions were not
optimal, with a seeing of 3". We detected the optical afterglow in the R
filter (Torii, GCN 2860; Gorosabel et al., GCN 2861), with the following
magnitudes (based on the calibration provided by Henden, GCN 2869):
UT (mean) t-t0* mag error
-------------------------------
Dec 18.912 6.1 h 21.37 0.15
Dec 19.061 9.7 h 22.41 0.46
t0 = Dec 18.6565 UT (burst explosion time).
In the last epoch, the object is barely visible, but clearly faded since
the first epoch. Our results are consistent with those reported by Greco
et al. (GCN 2863), Halpern & Tuttle (GCN 2873) and Monfardini et al.
(GCN 2878). Using all the available data, the decay index is alpha ~ 1.4
(F=K*t^-alpha) from ~2 to ~13 hours after the GRB. When comparing with
the earliest measurement from Torii (GCN 2860), a steepening in the
light curve is apparent.
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