{
  "bibcode": "2005GCN..3890....1C",
  "body": "G. Crew, G. Ricker, J-L. Atteia, N. Kawai, D. Lamb, and S. Woosley, on\nbehalf of the HETE Science Team;\n\nM. Arimoto, T. Donaghy, E. Fenimore, M. Galassi, C. Graziani,\nJ. Kotoku, M. Maetou, M. Matsuoka, Y. Nakagawa, T. Sakamoto, R. Sato,\nY. Shirasaki, M. Suzuki, T. Tamagawa, K. Tanaka, Y. Yamamoto,\nand A. Yoshida, on behalf of the HETE WXM Team;\n\nN. Butler, J. Doty, G. Prigozhin, R. Vanderspek, J. Villasenor,\nJ. G. Jernigan, A. Levine, G. Azzibrouck, J. Braga, R. Manchanda,\nand G. Pizzichini, on behalf of the HETE Operations and HETE\nOptical-SXC Teams;\n\nM. Boer, J-F Olive, J-P Dezalay, and K. Hurley, on behalf of the HETE\nFREGATE Team;\n\nreport:\n\nThe FREGATE instrument onboard HETE also detected the Swift burst GRB\n050824 (Campana, et al., GCN 3866) as an untriggered event (U11648)\nwith a significance of 6 sigma.  The direction to the burst source was\nabout 50 degrees from the instrument boresight, placing it outside the\nWXM and SXC fields-of-view.\n\nWe have analyzed the spectrum of the event.  A power-law (PL) fit to\nthe full FREGATE energy range (6-400 keV) yields a best-fit power-law\nindex of 2.35 +0.88/-0.48 (90% CL), consistent with the PL index\nreported by the Swift BAT team (Krimm et al., GCN 3871).  Assuming the\nbest-fit PL index, the value of the fluence ratio S(2-30)/S(30-400) is\n2.7.  GRB 050824 is thus an X-Ray Flash.\n\nA PL fit restricted to photons with energy above 20 keV yields a\nbest-fit PL index of 3.29 +2.50/-1.36 (90% CL).  This steepening of \nthe PL index suggests that the spectrum is representable by a Band\nmodel with a value of E_peak near or below the low end of the FREGATE\nenergy range, so that the PL fit to the full energy range represents \nan average of the contributions from the high- and low-energy parts of \nthe Band model.\n\nBecause of the low S/N of the event, a PL times exponential fit and a\nBand-function fit are not statistically preferred over the simple PL\nmodel.  Nonetheless, in order to constrain E_peak, we have performed a\n\"constrained-Band model\" analysis of the spectrum (see Sakamoto et al.,\nApJ 602, 875), and find E_peak < 12.7 keV (90% CL).\n\nFREGATE light curve data and plots will be available soon at the\nfollowing URL: http://space.mit.edu/HETE/Bursts/U11648.",
  "circularId": 3890,
  "createdOn": 1125117615000,
  "email": "carlo@oddjob.uchicago.edu",
  "subject": "GRB050824, HETE-2 Observation",
  "submitter": "Carlo Graziani at U.Chicago  <carlo@oddjob.uchicago.edu>",
  "eventId": "GRB 050824"
}