{
  "bibcode": "1999GCN...238....1N",
  "body": "R. J. Nemiroff (Michigan Tech.), \nG. F. Marani (NRC/NASA), J. T. Bonnell (USRA/NASA),\nJ. P. Norris (NASA/GSFC), and C. A. Meegan (NASA/MSFC) report:\n\nThere is, as yet, no primary indication that GRB 990123 has undergone\nany type of strong gravitational lensing.\n\nWeak lensing:  Most sources at z>1.6 will be either gravitationally\namplified or (more likely) de-amplified by >5% by inhomogeneities in\nthe gravitational field between the observer and the source (see, for\nexample, Holz et al. astro-ph/9804271).\n\nStrong Lensing:\n\nGalaxy lensing: There is, as yet, no primary indication that GRB 990123\nis one of multiple macro-images created by an intervening galaxy lens.\nIn comparison with QSOs, it is not unusual for single image QSOs to be\nfound within 3 arcseconds of a low mass galaxy (e.g. Claeskens & Surdej\n1998, A&A 335, 69) or for a single image QSO to have absorption lines.\n\nAs GRB 990123 was the brightest event ever detected with a measured\ncosmological redshift, its macrolensing probability is high relative to\nother GRBs and afterglows, but still, quite possibly, low in absolute\nterms.  The foreground galaxy near GRB 990123 is intriguing but not yet\ndefining.  The \"probability\" now all hinges on the unknown masses and\nmass distributions internal to foreground galaxies.\n\nNo other BATSE triggered GRB has been found that is consistent with a\nlensing interpretation.  Twenty-three BATSE GRBS have occurred in the\npast three years within a 3-sigma error contour of GRB 990123.  The\nclosest two in light curve shape were judged to be BATSE triggers 6279\nand 6698.  A preliminary visual inspection reveals none of them is a\nclose light-curve match to GRB 990123.\n\nMillilensing: There is, as yet, no primary indication that GRB 990123\nhas undergone significant amplification by a compact mass on the\nglobular-cluster scale.  The two main peaks in the GRB light curve do\nnot appear to be co-added replicas of a single light curve seperated by\nmajor peak are significantly different (> 5 sigma,  preliminary\nanalysis) in BATSE channels 1 and 4.  Similarly, the ratios in peak\nflux between the first major peak and the last peak are also\nsignificantly different (> 5 sigma, preliminary analysis).\n\nMicrolensing: There is, as yet, no primary indication that GRB 990123\nhas undergone significant light curve distortion due to microlensing by\ncompact masses on the stellar mass scale.  Microlensing at low optical\ndepths would create images separated in time by only microseconds\n(Nemiroff 1994, ApJ 432, 478; Nemiroff 1998, ApJ 494, L173) to\nmilliseconds (Williams & Wijers 1997, MNRAS 286, L11), generally below\nminimum time scale of BATSE GRB resolution (64-ms).\n\nWe encourage, however, continued attempts to recover secondary images\nfrom any GRB or afterglow, including GRB 990123.",
  "circularId": 238,
  "createdOn": 917559338000,
  "email": "nemiroff@mtu.edu",
  "subject": "GRB990123, Preliminary Lens Search Results",
  "submitter": "Robert Nemiroff at Michigan Tech.  <nemiroff@mtu.edu>",
  "eventId": "GRB 990123"
}