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GCN Circular 8965

Subject
GRB 090308: Gemini GMOS Observations
Date
2009-03-10T05:31:26Z (15 years ago)
From
S. Bradley Cenko at Caltech <cenko@srl.caltech.edu>
S. B. Cenko, A. N. Morgan, D. A. Perley, N. R. Butler, and J. S. Bloom (UC
Berkeley) report on behalf of a larger collaboration:

We have imaged the field of GRB090308 (Evans et al.; GCN 8948) with GMOS
mounted on the Gemini South telescope beginning at approximately 1:38 UT
on the night of 9 March 2009 (~ 7.6 hours after the burst).  Images were
taken in the g', r', i', and z' filters for a total of 300 s in each band.

We find no significant sources inside the revised XRT error circle (Evans
et al.; GCN 8956) to the following limits: g' > 23.8; r' > 24.2; i' >
23.6; z' > 22.5. These limits were calculated using reference stars from
the USNO-B1 catalog and applying the filter transformations of Jordi,
Grebel, and Ammon (A&A 460, 2009).

We do, however, note the presence of an extremely red point source located
several arcseconds southwest of the refined XRT position, and immediately
outside the X-ray position provided by Butler (AJ 133, 2007; see
http://astro.berkeley.edu/~nat/swift/xrt_pos.html).  The coordinates of
this source are (J2000.0):

	RA: 12:13:59.89
	Dec: -48:49:03.5

This object is detected only in the r', i', and z' filters with
approximate magnitudes: r' = 23.6; i' = 21.6; z' = 20.2 (uncorrected for
Galactic extinction).  While we consider the association unlikely, further
observations are required to determine if this is the afterglow of
GRB090308.

We wish to thank the staff at Gemini Observatory for undertaking these
observations.
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