{
  "bibcode": "2010GCN.10612....1M",
  "body": "F. E. Marshall (NASA/GSFC), A. P. Beardmore (U Leicester),\nJ. M. Gelbord (PSU), S. T. Holland (CRESST/USRA/GSFC),\nE. A. Hoversten (PSU), J. A. Kennea (PSU),\nO. M. Littlejohns (U Leicester), C. B. Markwardt (CRESST/GSFC/UMD),\nP. T. O'Brien (U Leicester), C. Pagani (U Leicester),\nK. L. Page (U Leicester), D. M. Palmer (LANL),\nA. Rowlinson (U Leicester), M. C. Stroh (PSU),\nT. N. Ukwatta (GSFC/GWU) and L. Vetere (PSU) report on behalf of the\nSwift Team:\n\nAt 21:10:08 UT, the Swift Burst Alert Telescope (BAT) triggered and\nlocated GRB 100418A (trigger=419797).  Swift slewed immediately to the burst. \nThe BAT on-board calculated location is \nRA, Dec 256.376, +11.464 which is \n   RA(J2000) = 17h 05m 30s\n   Dec(J2000) = +11d 27' 50\"\nwith an uncertainty of 3 arcmin (radius, 90% containment, including \nsystematic uncertainty).  The BAT light curve showed a single-peaked\nstructure with a duration of about 4 sec.  The peak count rate\nwas ~700 counts/sec (15-350 keV), at ~0 sec after the trigger. \n\nThe XRT began observing the field at 21:11:27.1 UT, 79.1 seconds after\nthe BAT trigger. Using promptly downlinked data we find a bright,\nfading, uncatalogued X-ray source with an enhanced position: RA, Dec\n256.3635, 11.4619 which is equivalent to:\n   RA(J2000)  = 17h 05m 27.24s\n   Dec(J2000) = +11d 27' 42.7\"\nwith an uncertainty of 3.1 arcseconds (radius, 90% containment). This\nlocation is 44 arcseconds from the BAT onboard position, within the BAT\nerror circle. This position may be improved as more data are received;\nthe latest position is available at http://www.swift.ac.uk/sper. \n\nA power-law fit to a spectrum formed from promptly downlinked event\ndata gives a column density consistent with the Galactic value of\n4.78e+20 cm^-2 (Kalberla et al. 2005). \n\nThe initial flux in the 2.5 s image was 1.27e-09 erg cm^-2 s^-1 (0.2-10\nkeV). \n\nUVOT took a finding chart exposure of 150 seconds with the White   \nfilter  starting 87 seconds after the BAT trigger. A possible   \nafterglow candidate has  been found in the initial data products at   \nthe location of the XRT afterglow.  The preliminary UVOT position is  \n\n   \n    RA(J2000.0) =  17:05:26.96  =  256.36233 (deg)   \n   Dec(J2000.0) = +11:27:41.9   =  +11.46164 (deg)\n\nwith an  estimated uncertainty of 1.0 arcsec (radius, 90% confidence,  \nstatistical + systematic).  The estimated white magnitude is  20.7 +/-\n0.3.  No correction has  been made for the expected extinction  \ncorresponding to E(B-V) of   0.07. \n\nBurst Advocate for this burst is F. E. Marshall (marshall AT milkyway.gsfc.nasa.gov). \nPlease contact the BA by email if you require additional information\nregarding Swift followup of this burst. In extremely urgent cases, after\ntrying the Burst Advocate, you can contact the Swift PI by phone (see\nSwift TOO web site for information: http://www.swift.psu.edu/too.html.)",
  "circularId": 10612,
  "createdOn": 1271626078000,
  "email": "palmer@lanl.gov",
  "subject": "GRB 100418A: Swift detection of a burst with a possible optical afterglow",
  "submitter": "David Palmer at LANL  <palmer@lanl.gov>",
  "eventId": "GRB 100418A"
}