{
  "bibcode": "1999GCN...247....1S",
  "body": "Xiangdong Shi and Geza Gyuk (UC, San Diego):\n\nIn GCN#211,239 S. R. Kulkarni and D. A. Frail reported radio observations\nof GRB990123, which show a \"radio flare\" on Jan. 24. GRB990123 appears\notherwise to be radio-quiet as of yet (GCN#200,212,239).  We suggest the\npossibility that this \"flare\" resulted from the GRB external shock running\ninto a cloud off line-of-sight. This section of the shock was decelerated\nefficiently and its sychrotron frequency quickly fell into the range of\nradio waves. This inhomogeneity of the medium may explain the abruptness\nand shortness of the radio emission.  The \"flares\" in other wavelengths\nwere brief and might also have been buried in the main afterglow.\n\nWe speculate that the cloud may have been composed of prior ejecta from\nthe gamma-ray burst progenitor. If there are still other nearby clouds, it\nwill be interesting to see whether the \"flares\" recur.\n\nOne implication of this hypothesis, if it is true, is that the GRB990123\nis not likely to be strongly beamed (>10).  Its intrinsic energy output\nwould in turn be indeed huge.\n\nThis message is citable.",
  "circularId": 247,
  "createdOn": 918065837000,
  "email": "shi@maroonbell.ucsd.edu",
  "subject": "GRB990123, is the \"radio flare\" due to an inhomogeneous medium?",
  "submitter": "Xiangdong Shi at UCSD  <shi@maroonbell.ucsd.edu>",
  "eventId": "GRB 990123"
}