{
  "bibcode": "2005GCN..3935....1P",
  "body": "A. Parsons (GSFC),  C. Sarazin (U. Virginia), L. Barbier (GSFC),\nS. Barthelmy (GSFC), J. Cummings (GSFC/NRC), D. Hullinger (GSFC/UMD),\nE. Fenimore (LANL), N. Gehrels (GSFC), H. Krimm (GSFC/USRA),\nC. Markwardt (GSFC/UMD), F. Marshall (GSFC), D. Palmer (LANL),\nT. Sakamoto (GSFC/NRC), G. Sato (ISAS), T. Takahashi (ISAS),\nJ. Tueller (GSFC) on behalf of the Swift-BAT team:\n\nUsing the data set from T-60 to T+120 sec from the recent telemetry\ndownlink, we report further analysis of Swift-BAT GRB 050906\n(trigger #153866)  (Krimm, et al., GCN 3926).  The refined BAT ground position\nis (RA,Dec) = 52.841,-14.652 {+03h 31m 22s,  -14d 39' 00\"} [deg; J2000]\n+- 2.6 arcmin, (90% containment).  This is 2.7 arcmin from the position\nreported in Krimm et al. 2005, GCN 3926. The partial coding was 77%.\n\nThe mask weighted light curve shows a small excess mostly in the\n25-100 keV energy range.  This a short burst of duration T90 (15-350 keV)\n128 +- 16 milliseconds. (estimated error including systematics).\n\nThe power law index of the time-averaged spectrum fit over T+0 to T+0.128 sec\nis 1.91 +- 0.42.   The fluence in the 15-150 keV band is (5.9 +/- \n3.2) x 10^-8 erg/cm2.\nThe 1-s peak photon flux measured from T0 in the 15-150 keV\nband is (0.22 +/- 0.11) ph/cm2/s.  All the quoted errors are at the 90%\nconfidence level.\n\nThe BAT error circle includes the relatively bright, nearby galaxy\nIC 328 (Levan & Tanvir GCN 3927).  The 2MASS K magnitude of this galaxy\nis K20 = 11.51.  The density of galaxies this bright on the sky is\nabout 1 per square deg (Kochanek, C. S., et al. 2001, ApJ, 560, 566).\nThus, the probability of finding a galaxy this bright in the BAT 3 arcmin\nerror circle is about 0.008.  The redshift of IC 328 is 0.0308\n(da Costa, L. N., et al. 1998, AJ, 116, 1), giving a luminosity distance\nof dL = 133 Mpc for the WMAP cosmology.  At this distance, the galaxy\nluminosity is ~10^11 Lsun(K), which is slightly greater than L*.\nThe number density of galaxies at least this luminous is ~0.0006/Mpc^3.\nThus, the probability of finding a galaxy at least this luminous at a\nredshift as small as that of IC 328 within 3 arcmin of the BAT position\nis about 0.001.\n\nIC 328 appears to be a spiral galaxy, and is quite blue (U-B = -0.6;\nCoziol, R. et al., 1994, AJ, 108, 405).  With these colors, it is\nlikely to have active star formation.  Thus, this host is quite different\nthan the hosts of the two short-hard bursts GRB 050509b and GRB 050724,\nwhich appear to have occurred in or near red elliptical galaxies.\n\nIt is possible that this GRB was caused by an SGR superflare in IC 328\n  (Levan & Tanvir GCN 3927, Palmer, D.M., et al. 2005, Nature, 434, 1107;\nHurley, K. et al. 2005, Nature, 434, 1098), although an underluminous\ncollapsar or NS-NS merger can not be ruled out.",
  "circularId": 3935,
  "createdOn": 1126043041000,
  "email": "krimm@milkyway.gsfc.nasa.gov",
  "subject": "GRB 050906:  Swift-BAT refined analysis",
  "submitter": "Hans Krimm at NASA-GSFC  <krimm@milkyway.gsfc.nasa.gov>",
  "eventId": "GRB 050906"
}