{
  "bibcode": "2007GCN..6980....1B",
  "body": "J. S. Bloom (UC Berkeley), J. X. Prochaska (UCO/Lick), D. A. Perley  \n(UC Berkeley), H.-W. Chen (U Chicago), D. L. Starr (UC Berkeley &  \nLCOGT), M. Modjaz, D. Poznanski (UC Berkeley) report:\n\n\"We observed the field of GRB 071021 (Sakamoto et al. GCN 6958) with  \nPAIRITEL (*) starting at 2007-10-22 04:53 UT in high wind and poor  \nseeing conditions at Mt Hopkins, Arizona. In the first 1340 second  \nstack, the IR source noted by Castro-Tirado et al. (GCN 6968/6971) is  \nnot detected to J=18.35 mag, H=16.87 mag, Ks=16.43 (2.5 sigma upper  \nlimit). This is not particularly constraining in light of the deep  \nSubaru imaging (Terada et al. GCN 6976) at a similar epoch.\n\n  We note that despite the z-band detection (Malesani et al. GCN  \n#6972) the very high-redshift hypothesis of Sakamoto et al. (GCN  \n6967) is not yet ruled out. In particular, in high z QSO spectra  \nthere can be some transmitted flux (in the z-band filter  \ntransmission) through the Lyman-alpha forest between ~8000 Ang and  \n8500 Ang (see, e.g., Fan et al. 2006 **) for z > 6.3 sources. So long  \nas the redshifted Lyman limit at the redshift of the emitting source  \nis blueward of ~8500 Ang, this light would not be entirely  \nsuppressed. This consideration yields an upper limit:\n\n                         (1 + z_GRB)*912 Ang < 8500 Ang\n                                     z_GRB <~ 8.3\n\n  At such redshifts, say z_GRB = 8, all reported long-wavelength  \nobservations to-date would be naturally accommodated:\n\n  - the deep non-detections at R and i-band (Berger & Covarrubias,  \nGCNs 6973,6974), being blueward of 912*[1+z_GRB])\n   - the faint detection at z-band (GCN 6972) due transmitted flux  \nbetween 912*[1+z_GRB] = 8200 and 8500 Ang is allowed (as above)\n   - the afterglow detections at H and K (GCN 6968; Terada et al. GCN  \n6976)\n   - the apparent faintness of J-band flux (GCN 6968) relative to H  \nand K given the Gunn-Peterson trough would extend to (1 + z_GRB)*1216  \nAng =~ 1.1 micron.\n\n  All of this assumes that the z-band source is not a foreground  \ngalaxy (in which case a higher-z GRB suggested by Castro-Tirado et  \nal. is allowed).  If indeed the GRB originated from z > 7, we would  \nexpect to see what would resemble emission lines between lam_obs =  \n912*[1+z_GRB] and ~8500 Ang, motivating the utility of *optical*  \nspectroscopy of this source. Even without spectroscopy, when final  \nmagnitudes are reported along with filter transmission curves, a full  \nSED should be illuminating.\"\n\nThis message may be cited.\n\n(*)  http://pairitel.org\n(**) http://www.journals.uchicago.edu/AJ/journal/issues/ \nv132n1/205115/205115.web.pdf",
  "circularId": 6980,
  "createdOn": 1193119513000,
  "email": "jbloom@astron.berkeley.edu",
  "subject": "GRB 071021: (Relatively shallow) IR non-detections; motivation for optical spectroscopy",
  "submitter": "Josh Bloom at UC Berkeley  <jbloom@astron.berkeley.edu>",
  "eventId": "GRB 071021"
}