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GCN Circular 3190

Subject
GRB 050408: ROTSE-III Optical Limits
Date
2005-04-08T18:53:32Z (19 years ago)
From
Don Smith at U michigan <dasmith@rotse2.physics.lsa.umich.edu>
GRB 050408: ROTSE-III Optical Limits

D.A. Smith, S.A. Yost, & E.S. Rykoff (U of Michigan) report on behalf of the
ROTSE collaboration:

ROTSE-IIIa, located at Siding Spring Observatory, Australia, responded to GRB
050408 (HETE trigger 3711).  An automated response produced images beginning at
16:23:09.4 UT, 18.5 s after the trigger time and 6.6 s after the alert was
distributed.  The first few images were therefore recorded while the burst was
still active at high energies (Sakamoto et al., GCN Circ. #3189).  The
telescope took 10 5-sec, 10 20-sec, and a series of 60-sec eposures. These
unfiltered images are calibrated relative to USNO A2.0 (R). The ROTSE-III
images show strong and increasing degredation from clouds.  After the 20th
image (~7.7 min after the trigger time), clouds became opaque enough to render
many images useless.

Comparison to the DSS (second epoch) reveals no new sources within the 3-sigma
SXC error circle. Individual images have limiting magnitudes ranging from
14.7-16.9. In particular, we set a limit of magnitude 14.7 in the first 5 s
exposure. Coadding the first ten images yields a limiting magnitude of 15.1,
and coadding the 20-s images (165.5-522.5 s after the trigger time) yields a
limiting magnitude of 17.8.
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