{
  "bibcode": "2009GCN..9601....1P",
  "body": "D. A. Perley, S. B. Cenko, and J. S. Bloom (UC Berkeley) report:\n\nWe imaged the field of dark gamma-ray burst GRB 090404 (Ziaeepour et \nal., GCN 9086) using the Keck I telescope (+LRIS) on the night of \n2009-06-25 (UT) for 1670 seconds in g-band and 1560 seconds in I-band \nunder excellent (0.5 arcsecond) seeing and photometric conditions.\n\nThe object outside the XRT error circle mentioned by Malesani et al. \n(GCN 9093, GCN 9095) is clearly detected as an extended source, likely a \nmoderate-redshift galaxy (hereafter \"G1\").  A second, slightly fainter \nextended source (\"G2\") is also detected 3.5 arcseconds to its northeast, \nand the two sources appear to be connected by faint emission, perhaps a \ntidal bridge.  Both sources are marginally detected in Sloan Digital Sky \nSurvey archival images (see also GCN 9096).\n\nAdditional faint, extended emission is detected just west of the \nbrighter galaxy G1.  The emission appears to be spread over several \narcminutes in the g-band image, with an obvious \"knot\" located 1 \narcsecond northeast of the millimeter afterglow position reported by \nCatro-Tirado et al. (GCN 9100).  The extended region itself passes \ndirectly through the millimeter position.  A false-color image of the \nfield, with the millimeter and enhanced XRT positions \n(http://www.swift.ac.uk/xrt_positions/00348428/image.php) superimposed, \nis posted to: http://lyra.berkeley.edu/~dperley/090404/090404_gI.png\n\nWe hypothesize that the extended emission may be a tidal tail extending \nfrom G1 as a result of interaction with its northeastern neighbor. \nAlternatively, the extended region may represent a very faint background \nhost galaxy.  Aperture photometry at the location of the millimeter \nafterglow gives a magnitude of g = 27.3 +/- 0.2.\n\nWe encourage spectroscopy of the two bright galaxies G1 and G2 to \ndetermine their redshifts.",
  "circularId": 9601,
  "createdOn": 1246516416000,
  "email": "dperley@astro.berkeley.edu",
  "subject": "GRB 090404: Deep optical imaging and possible host association",
  "submitter": "Daniel Perley at U.C. Berkeley  <dperley@astro.berkeley.edu>",
  "eventId": "GRB 090404"
}