{
  "bibcode": "2001GCN..1084....1R",
  "body": "Dramatic Increase in the Rate of X-ray Bursts Reported by HETE\n\nG. Ricker (MIT), on behalf of the HETE Team, reports:\n\nOver the past few weeks, the number of X-ray bursts (XRBs) reported \nby HETE has been gradually increasing, reaching ~10 per day during \nthe past 2-3 days. This seeming storm of XRBs is being produced by an \nensemble of ~10 distinct XRB sources, which are optimally placed in \nthe HETE field-of-view (FOV) for detectability.\n\nThis dramatic overall increase is due to two factors: 1) Improvements \nin the on-board detection algorithm, resulting from lowered trigger \nthresholds and increased numbers of trigger time scales being \nactivated; 2) Sco X-1 has moved out of the HETE instruments' FOV, \ngreatly reducing the overall background, thus improving the \ninstruments' burst detection efficiency.\n\n(NB: Despite the flurry of XRBs, soft gamma repeaters [SGR] and \ngamma-ray bursts [GRB] positions are now being, and will continue to \nbe, reported for events which trigger the high energy bands of the \nFREGATE instrument directly.)\n\nMany of the faint XRB detections are near threshold, and thus their \nonboard localization is unreliable. In order not to saturate rapid \nresponse telescopes and observing programs which primarily target \nSGRs and GRBs, these XRB events are being reported to the GCN with no \npositions. (In fact, reliable positions are subsequently established \nby the WXM ground software for a large fraction of these XRB events.) \nA  refined reporting algorithm, which will more clearly distinguish \nfainter, poorly-localized XRBs from brighter, well-localized XRBs \nwill be implemented in the near future. In the meantime, the XRB \n\"alert only\" reports will continue.  Beginning in late August, when \nthe Galactic Bulge Region moves out of HETE's FOV, we anticipate a \nprecipitous drop in the reported XRB rate.",
  "circularId": 1084,
  "createdOn": 996527165000,
  "email": "grr@space.mit.edu",
  "subject": "Dramatic Increase in the Rate of X-ray Bursts Reported by HETE",
  "submitter": "George Ricker at MIT  <grr@space.mit.edu>"
}