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GCN Circular 1757

Subject
GRB021211: Measurement of Early Time Afterglow
Date
2002-12-14T03:51:40Z (21 years ago)
From
Tom Vestrand at LANL <vestrand@lanl.gov>
P. Wozniak, W.T. Vestrand, D. Starr, J. Wren, K. Borozdin, S. Brumby, D.
Casperson, M. Galassi, K. McGowan and R. White report:

One of our RAPTOR (RAPid Telescopes for Optical Response) telescopes at
the Los Alamos National Laboratory responded to HETE trigger 2493 in
real-time. Our imaging of the burst location began at 11:19:38.9 UT,
64.9 seconds after the GRB time. The first image, a 60-second exposure,
shows an optical transient (OT) at the position identified by Fox and Price
(GCN 1731). The OT signal was slightly blended with a nearby star. To correct
for the blending we used difference image photometry with reference images
obtained after the OT faded below our detection limit. Correlating our
unfiltered magnitude with the USNO photometry reported by Henden (GCN 1753)
we derive a Rc magnitude of 14.06+/-0.08. Assuming an afterglow flux decay with
power-law index alpha=-1.6, the flux-weighted image time is 89.7 seconds
after the GRB time. Our measurements are consistent with the suggestion by
Chornock et al. (GCN 1754) that the early afterglow was fading more
rapidly than the late afterglow.

An animation that compares the detection image with an image taken after
the object faded below our detection limit will be posted on the
RAPTOR website at: www.raptor.lanl.gov

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