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GCN Circular 9646

GRB 090709A: P60 Observations
2009-07-10T06:31:02Z (15 years ago)
S. Bradley Cenko at Caltech <>
S. B. Cenko, J. S. Bloom, A. N. Morgan, and D. A. Perley (UC
Berkeley) report on behalf of a larger collaboration:

We have imaged the field of GRB090709A (Morris et al., GCN 9625) with the
automated Palomar 60-inch telescope.  Observations began at 7:40:26 UT on
9 July 2009 (~ 2 minutes after the burst trigger) and were taken in the
r', i', and z' filters.

We marginally detect a faint source at the location of the NIR afterglow
(Aoki et al., GCN 9634, Morgan et al., GCN 9635) in our first r' and z'
images.  However, nothing is detected at this location in subsequent
images or deeper coadditions at later times.  We therefore cannot
entirely rule out that these represent chance statistical fluctuations.

We report the following photometry and upper limits (referenced with
respected to the USNO-B1 catalog):

UT Midpoint     Exposure (s)    Filter          AB Mag
7:40:56         60              r'              21.7 +- 0.4
7:45:12         60              r'              > 21.4
8:08:57         600             r'              > 22.9
7:46:38         60              i'              > 21.0
8:11:59         480             i'              > 22.8
7:45:55         120             z'              20.5 +- 0.5
8:13:59         480             z'              > 21.5

The r' and z' detections, if real, would argue strongly in favor of a low
or moderate redshift origin with a large extinction column in the GRB host
galaxy (Butler, GCN 9639).  A combined fit of approximately co-eval
PAIRITEL (GCN 9635, Morgan et al.) and P60 photometry assuming moderate
redshift (z < 4) is consistent with a highly dust-extinguished (A_V > 2
mag) power-law spectral energy distribution.

A smoothed version of our first r' image can be found at:

The blue circle is the refined XRT localization (Osborne et al., GCN
9639), while the red circle is the location of the PAIRITEL NIR afterglow
(Morgan et al., GCN 9635).
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