{
  "bibcode": "2007GCN..7140....1P",
  "body": "D. A. Perley, J. S. Bloom, M. Modjaz, D. Poznanski (UC Berkeley) and C. \nC. Thoene (DARK) report:\n\nOn the night of 2007-07-18 we re-observed the field of GRB 070429B (GCN \n6358, Markwardt et al.), likely to be a short-hard burst (T90 = 0.5 +- \n0.1 s, GCN 6365, Tueller et al.) under photometric conditions using the \nKeck I telescope + LRIS, in g and R filters simultaneously for a total \nintegration of 930s(g) / 840s(R) under relatively poor seeing.  We \nfurther imaged the field using GMOS on Gemini-South on 2007-11-27 for \n1200s in r filter under excellent seeing.\n\nThe bright source reported by Cucchiara et al. (GCN 6368), designated \nobject \"A\" by Antonelli et al. (GCN 6372) and likely the host galaxy of \nthe GRB, is well-detected in R and r and weakly detected in g.  Using \nLandolt standard stars we measure an aperture magnitude for this object \n(in a 2.1\" radius aperture) of\n\ng = 24.79 +/- 0.14\nR = 23.24 +/- 0.05\n\nThis is consistent within errors with the magnitudes reported by \nCucchiara et al. and Antonelli et al. 4 and 5 hours after the burst, \nrespectively.  Image subtraction of the new Gemini imaging versus the \nearlier epoch (GCN 6368) reveals no variability to a limiting magnitude \nof R > 24.5, ruling out an afterglow contribution in the first epoch \n(4.84 hours after the burst) at this level.\n\nObject \"B\" is also detected in both filters, and also shows no evidence \nfor variability.\n\n\nOn the night of 2007-10-09 we performed longslit spectroscopy covering \nboth targets (\"A\" and \"B\") in two integrations of 1500s each, using Keck \nI + LRIS.\n\nThe trace of object \"A\" is faint and the spectrum is mostly featureless, \nbut a faint line signature is observed centered at 7098 Angstroms, with \na FWHM of 6 Angstroms.  The feature appears present in both exposures, \nthough this site is severely affected by a cosmic ray in one exposure. \nWe identify this feature as most likely being the [OII]3727 doublet. \nOther line identifications (H-alpha, H-beta, or [OIII]) are disfavored \ndue to the absence of corroborating lines that would be expected over \nour spectral range (3500-8900 Angstroms) in those cases.\n\nAssociation of this feature with [OII] indicates a redshift for this \nobject of z=0.904.  Calibrating relative to R-band photometry, we \nestimate a preliminary line flux of 3e-17 erg/s/cm^2, corresponding to \nan unextincted star formation rate (Kewley et al. 2002) of 0.7 M_sun/yr, \ncomparable to that observed in previous short burst hosts.  We note also \nthe red color of this galaxy.\n\nNo obvious trace or line features are observed for object B.",
  "circularId": 7140,
  "createdOn": 1196465117000,
  "email": "dperley@astro.berkeley.edu",
  "subject": "GRB 070429B: Probable host galaxy and redshift",
  "submitter": "Daniel Perley at U.C. Berkeley  <dperley@astro.berkeley.edu>",
  "eventId": "GRB 070429B"
}