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GCN Circular 10727

GRB 100418A: Keck imaging
2010-05-07T23:19:17Z (14 years ago)
Daniel Perley at U.C. Berkeley <>
D. A. Perley, S. B. Cenko, A. A. Miller, D. Poznanski, A. V. Filippenko, 
J. S. Bloom (UC Berkeley), and P. Nugent (LBNL) report:

We imaged the field of GRB 100418A (Marshall et al., GCN 10612) with the 
Low Resolution Imaging Spectrometer on the Keck I 10-m telescope during 
morning twilight on 2010-05-06 UT.  Two exposures of 380 seconds each 
were acquired in the g and R bands simultaneously.  The midpoint of the 
observation was 14:54 UT, 17.739 days after the GRB.

At the position of the afterglow and calibrating to 9 nearby unsaturated 
SDSS stars, we measure magnitudes of:

g = 22.67 � 0.07
R = 21.85 � 0.05

The g-band magnitude is marginally consistent with the SDSS magnitude 
(Malesani et al., GCN 10621) of g = 22.89 � 0.17, and suggests that the 
UVOT flattening (Marshall et al., GCN 10720) is primarily due to the 
host galaxy, not an associated supernova.  Our reported R-band magnitude 
is significantly brighter than the host, but this excess is consistent 
with an afterglow origin (Bikmaev et al., GCN 10726).  Additional 
follow-up observations will be necessary to comment on the presence (or 
absence) of a supernova counterpart.
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