TITLE: GCN CIRCULAR NUMBER: 9646 SUBJECT: GRB 090709A: P60 Observations DATE: 09/07/10 06:31:02 GMT FROM: 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: http://astro.berkeley.edu/~cenko/public/grb/grb090709/p60r.jpg 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).