GCN Circular 2236
Subject
GRB 030418: Second Epoch Optical Observations with Magellan
Date
2003-05-20T03:12:39Z (21 years ago)
From
George Ricker at MIT <grr@space.mit.edu>
GRB 030418: Second Epoch Optical Observations with Magellan
A. Dullighan, N. R. Butler, G. R. Ricker, J. L. Elliot, K. Clancy
(MIT), and D. Osip (Las Campanas Observatory)
report:
On 2003 April 25.00 UT, we observed the optical afterglow (Price et
al; GCN2148) of the HETE-localized GRB 030418 (Shirasaki et al;
GCN2210) with the Magellan 6.5 meter Clay telescope at Las Campanas
Observatory in Chile. Our observations consisted of two 400s R-Band
images, one 400s I-Band image, and one 400s V-Band image taken with
the MagIC instrument.
The afterglow declined in brightness with respect to our previous
measurements (Dullighan et al; GCN2168). The R band data is
consistent with a revised power law decay index = 1.2 +/- 0.1, when
the two data points from Price et al. (GCN2148 and GCN2150) are
included. The afterglow was still point-like, but very close to the
limiting magnitudes of the images. No evidence of a host galaxy is
observed. We can, however, place a limit on the redshift of the
afterglow of z<~5, due to the small V-R color difference we observe
(i.e., no evidence for a Lyman alpha break). Our second epoch results
were as follows:
UT t-t0 (days) Mag
2003-04-25.00 6.58 R=24.9 +/- 0.4
2003-04-25.01 6.59 I>24 (limiting magnitude)
2003-04-25.02 6.60 V=25.1 +/- 0.5
The magnitudes reported above are referenced to the photometry
reported by A. Henden (GCN2216). We have also recalibrated the
magnitudes we reported in GCN 2168 to A. Henden's photometry
(GCN2216). The errors in calculating relative magnitudes have now
been taken into account. Our revised first epoch results are as
follows:
UT t-t0 (days) Mag (Original) Mag (Revised)
2003-04-21.02 2.60 R=23.64 +/- 0.07 R=23.3 +/- 0.1
2003-04-21.03 2.61 I=22.60 +/- 0.05 I=23.0 +/- 0.1
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