{
  "bibcode": "1999GCN...243....1D",
  "body": "GRB 990123:  New Constraints on Possible Foreground Galaxies\n\nS. G. Djorgovski, S. R. Kulkarni, J. S. Bloom, C. Koresko, R. R. Gal, \nS. C. Odewahn (Caltech), M. A. Malkan, I. S. McLean (UCLA), H. I. Teplitz\n(GSFC), D. Koerner (U. Penn.), D. Kirkpatrick (IPAC), and D. A. Frail (NRAO), \nreport on behalf of the Caltech-UC-NRAO-CARA GRB collaboration:\n\nWe performed a new differential astrometry between the Palomar discovery \nimages of the optical transient (OT) associated with GRB 990123 (GCN 201, \nGCN 205) and the DPOSS F (red) plate containing the field.  The results \nindicate that the apparent foreground galaxy near the OT position (GCN 201, \nGCN 206, GCN 207) is offset by 2.4 arcsec to the N and 1.0 arcsec to the E \nof the OT, with the estimated errors of 0.13 arcsec (systematic) + 0.3 arcsec \n(random) in each coordinate.  As we noted before, at R ~ 21.5 mag this \nobject corresponds to approximately 2-sigma detection on the plate scan.\n\nWe detect no objects down to a limiting magnitude K ~ 23 in this location\nin the stack of deep K-band images obtained at the Keck-I telescope on 24 \nand 27 January 1999 UT (GCN 240).  The implied limiting color is so blue \nthat we can exclude even the most actively star-forming galaxies.  We thus\nconclude that the sky survey detection was spurious.  This is in a complete\nagreement with the findings by Yadigaroglu et al. (GCN 242) in the R band.\n\nThis leaves open the question of the identification of galaxies responsible\nfor the absorption systems at z = 0.286 and z = 0.210 reported by Hjorth\net al. (GCN 219), as well as the z = 1.60 absorption system itself (Kelson\net al., IAUC 7096; and GCN 219).\n\nUsing the best-fit R-band light curve power-law slope alpha = -1.13 +/- 0.03\n(GCN 208, GCN 240) normalized to the K-band detection from 24 January 1999,\nwe estimate the maximum allowed contribution to the observed K-band light\nin our measurements from 27 and 28 January 1999 UT from any underlying galaxy\n(either the host and/or the foreground absorbers).  We obtain K > 22 mag for\nany such objects.\n\nHowever, in our best-seeing (FWHM ~ 0.5 arcsec) images, from 27 January 1999 \nUT, we detect a faint, galaxy-like extension to the N of the OT, with an \napparent center about 0.5 arcsec from the OT itself.  Its rough estimated \nmagnitude is in the range of K ~ 22 to 23 mag, in agreement with the limits\nderived from the light curve analysis.\n\nPending an independent confirmation of this detection, this object may be\neither a foreground dwarf galaxy responsible for one of the absorption\nsystems reported by Hjorth et al., or a highly luminous host of the GRB\nitself (possibly responsible for the absorption system at z=1.6).\n\nWhile there is no clear observational evidence for a strong gravitational \nlensing of this burst, the possibility remains open, and the presence of \nforeground galaxies along the line of sight suggests that some lensing \nmagnification must be taking place (regardless of the extraordinary apparent \nenergetics of this burst).  Forthcoming observations from the Keck and the \nHST should clarify the situation.\n\nThis report is citeable.",
  "circularId": 243,
  "createdOn": 917882514000,
  "email": "george@oracle.caltech.edu",
  "subject": "GRB 990123:  New Constraints on Possible Foreground Galaxies",
  "submitter": "George Djorgovski at Caltech/Palomar  <george@oracle.caltech.edu>",
  "eventId": "GRB 990123"
}