{
  "bibcode": "2005GCN..3053....1N",
  "body": "HETE-2 Observations of GRB 050215b (=U11570): A Likely X-Ray Flash\n\nY. Nakagawa, G. Ricker, J-L. Atteia, N. Kawai, D. Lamb, and S. Woosley,\non behalf of the HETE Science Team;\n\nT. Donaghy, E. Fenimore, M. Galassi, C. Graziani, M. Matsuoka,\nT. Sakamoto, R. Sato, Y. Shirasaki, M. Suzuki, T. Tamagawa, Y. Urata,\nT. Yamazaki, Y. Yamamoto, and A. Yoshida, on behalf of the HETE WXM\nTeam;\n\nN. Butler, G. Crew, J. Doty, G. Prigozhin, R. Vanderspek,\nJ. Villasenor, J. G. Jernigan, A. Levine, G. Azzibrouck, J. Braga,\nR. Manchanda, and G. Pizzichini, on behalf of the HETE Operations and\nHETE Optical-SXC Teams;\n\nM. Boer, J-F Olive, J-P Dezalay, and K. Hurley, on behalf of the HETE\nFREGATE Team;\n\nreport:\n\nGRB 050215b (=U11570) occurred 36 degrees off the HETE boresight, and\ntherefore well within the FREGATE field of view but only at the very\nedge of the WXM field of view.  Consequently, the burst is seen in the\nFREGATE data but not in the WXM data.\n\nUsing a simple power-law model to fit the FREGATE spectral data, we\nfind a best-fit power-law index of beta = -2.2 (+0.4/-0.6).  Using a\nconstrained Band model (Sakamoto et al., ApJ, 602, 875, 2004) to fit\nthe data, we find a best-fit value for the peak energy of E_peak =\n17.6 keV; a 68% confidence region 4.8 keV < E_peak < 23.7 keV, a 95%\nupper bound E_peak < 30.3 keV, and a 99% upper bound E_peak < 35.7 keV.\nFinally, using a Band model with the low-energy power-law index alpha\nfixed at -1 to fit the data, we find fluences of S_x (2-30 keV) = 2.8\n(+3.3/-1.1) x 10-7 erg cm-2 and S_gamma (30-400 keV) = 1.7 (+2.5/-1.3)\nx 10-7 erg cm-2.  The best-fit value of S_x/S_gamma is therefore 1.65.\nTaken together, these results are strong evidence that GRB 050215b was\nan X-Ray Flash.\n\nWe note that a supernova component has not been definitively\nestablished in the afterglow of any X-Ray Flash and that any supernova\ncomponent in the afterglow of GRB 050215b would be expected to peak\nsoon.  We therefore encourage further observations of the afterglow of\nthis burst.\n\nThis message may be cited.",
  "circularId": 3053,
  "createdOn": 1109134902000,
  "email": "lamb@oddjob.uchicago.edu",
  "subject": "HETE-2 Observations of GRB 050215b (=U11570): A Likely X-Ray Flash",
  "submitter": "Don Lamb at U.Chicago  <lamb@oddjob.uchicago.edu>",
  "eventId": "GRB 050215B"
}