{
  "bibcode": "1999GCN...234....1R",
  "body": "Search for Potential Images of GRB 990123\n\nR. Rutledge and S. R. Kulkarni (CIT) note: \n\nDjorgovski et al. (GCN #216) have suggested that GRB 990123 is lensed\nby a foreground galaxy identified by Odewahn et al. (GCN #201) and\npresumed to be at redshift 0.21 or 0.28 (Hjorth et al. GCN #219). The\nbasis of this argument is two fold: (1) the energetics of the GRB are\nreduced, as lensing would provide strong amplification, and (2) the\nforeground galaxy, due to its placement and likely mass, must result\nin some amount of lensing of a background object at the position of\nthe optical transient. \n\nA consequence of this lensing hypothesis is image splitting. The same\nburst would arrive at different times,  with the time difference\nproportional to the image separation (e.g., Turner et al. GCN #221).\nMotivated by these considerations we have looked into the BATSE\ncatalog to see if there are GRBs in the general vicinity of the\nlocation of GRB 990123 (Piro et al, GCN #199) and with close to\nidentical profile.  The two profiles need not be exactly identical\nsince microlensing combined with source expansion can lead to changes\nin profile.\n\nWithin a 4-sigma error radius consistent with the GRB 990123 OT\ntransient position, we find two double-peaked GRBs.  In one of these\n(GRB 970627, BATSE Trigger #6279), the peaks are similar in separation\nand peak-width ratio to GRB 990123, although the peak intensity ratio\nis different by about 60+/-20%.  In addition, there is excess emission\nin GRB 990123 following the two peaks, which is not observed from GRB\n970627.  However, based on the characteristics of intensity profiles,\nit is possible that GRB 970627 and GRB 990123 are lensed images of the\nsame GRB event.\n\nWe estimate that the chance probability of a similar profile GRB being\nconsistent in position is about 2%, based on the identification of 8\nsimilar GRB intensity profiles among the approximately 2000 GRBs in\nthe BATSE catalog. If we include in this statistic GRBs with a  more\ndissimilar intensity profile, the chance probability increases.  We\nfind 24 double-peaked GRBs (of 2000 in the BATSE Catalog) which are\ncomparable in peak separation (15-25 seconds) but are still dissimilar\nto GRB 990123, resulting in a chance probability of 6.4%.  A\ncomparison between the light curves of these two GRBs is available at\nhttp://www.srl.caltech.edu/personnel/rutledge/0123/bursts.html.\n\nIf GRB 970627 is indeed a lensed image of GRB 990123, then to explain\nthe very long time delay between the two images (1.5 years), the\npositional splitting must be several arcseconds in size and would most\ncertainly require multiple lenses or a cluster.\n\nThis message may be cited.",
  "circularId": 234,
  "createdOn": 917468864000,
  "email": "rutledge@srl.caltech.edu",
  "subject": "Search for Potential Images of GRB 990123",
  "submitter": "Robert Rutledge at Caltech  <rutledge@srl.caltech.edu>",
  "eventId": "GRB 990123"
}