Gamma-ray Burst 050918

(All information courtesy of the instrument teams.)

Previous IAU Circulars

• none

• GCN notice #4002
  D. Gotz, S. Mereghetti (IASF, Milano), S. Shaw, N. Mowlavi, M. Beck, A. Neronov (ISDC, Versoix) and J. Borkowski (CAMK, Torun) on behalf of the IBAS Localization Team report:
  A 50 s long GRB has been detected by IBAS in IBIS/ISGRI data at 15:36:39 UT on September 18 2005. Its coordinates (J2000) are:

  RA:  267.6096 [degrees]
  DEC: -25.4141 [degrees]
    

  with an uncertainty of 2.8 arcmin (90% c.l. radius).
  No prompt IBAS Alert has been issued for this burst because its significance was below the threshold for automatic alert delivery.
  Its preliminary peak flux (20-200 keV, 1s integration time) is 0.7 ph (8E-08 erg)/cmsq/s. Its fluence (20-200 keV, 50 s integration time) is 2E-06 erg/cmsq.
  A plot of the light curve will be posted at http://ibas.mi.iasf.cnr.it/IBAS_Results.html
  This message can be cited.
• GCN notice #4006
  J. A. Kennea, D. N. Burrows, D. Grupe, P. Roming (PSU), J. Osborne (U. Leicester), S. T. Holland (GSFC/USRA) and N. Gehrels (GSFC) report on behalf of the Swift team:
  At September 20th 22:08 UT, Swift began a 10ks TOO observation of the Integral discovered burst GRB050918 (GCN 4002). Analysis of ground processed data from Swift/XRT reveals a previously uncatalogued faint X-ray point source inside the 2.8 arcminute Integral error circle, at the following coordinates:

  RA(J2000):   17:50:28.7,
  Dec(J2000): -25:24:41.2.
  

  The uncertainty on this position is estimated to be 7 arcseconds radius (90% containment). This position is 34 arcseconds from the center of the Integral error circle given in GCN 4002.
  There is no evidence of fading in this source, however as this observation occured more than 2 days after the burst this result is expected. Further observations will be required to determine if this source is the afterglow of GRB050918.
  A UVOT V-band image shows no new source, with respect to the DSS, inside the INTEGRAL 2.8 arcminute radius error circle. The 5-sigma limiting magnitude in a circular aperture with a radius of six arcseconds is V_lim=19.3.