NASA SWIFT: GRB 060418: Swift detection of a burst with bright x-ray and optical afterglow
TITLE: GCN GRB OBSERVATION REPORT
NUMBER: 4966
SUBJECT: GRB 060418: Swift detection of a burst with bright x-ray and optical afterglow
DATE: 06/04/18 03:23:03 GMT
FROM: Scott Barthelmy at NASA/GSFC Scott@lheamail.gsfc.nasa.gov
A. D. Falcone (PSU), S. D. Barthelmy (GSFC), D. N. Burrows (PSU), J. R. Cummings (NASA/ORAU), N. Gehrels (NASA/GSFC), S. D. Hunsberger (PSU), J. A. Kennea (PSU) and D. M. Palmer (LANL) report on behalf of the Swift Team:
At 03:06:08 UT, the Swift Burst Alert Telescope (BAT) triggered and located GRB 060418 (trigger=205851). Swift slewed immediately to the burst. The BAT on-board calculated location is RA,Dec 236.420, -3.643 {15h 45m 41s, -03d 38′ 35″} (J2000) with an uncertainty of 3 arcmin (radius, 90% containment, including systematic uncertainty). The BAT light curve shows a broad smooth peak starting at T-8 sec. It decays almost to background, and then a bright peak at T+27 sec (FWHM ~3 sec). There is possibly emission at T+130 sec. The peak count rate was ~6000 counts/sec (15-350 keV), at ~27 sec after the trigger.
The XRT began observing the field at 03:07:26 UT, 78 seconds after the BAT trigger. XRT found a bright, variable, uncatalogued X-ray source located at RA(J2000) = 15h 45m 42.8s, Dec(J2000) = -03d 38′ 26.1″, with an estimated uncertainty of 5.8 arcseconds (90% confidence radius). This location is 32 arcseconds from the BAT on-board position, within the BAT error circle. The initial flux in the 0.1s image was 1.6e-08 erg/cm2/s (0.2-10 keV).
UVOT took a finding chart exposure of 100 seconds with the White (160-650 nm) filter starting 88 seconds after the BAT trigger. There is a candidate afterglow in the rapidly available 2.7’x2.7′ sub-image at (RA,DEC) (J2000) of (236.4275,-3.6389) or (15h45m42.60s,-03o38’20.0″) with a 1-sigma error radius of about 0.5 arc sec. This position is 7.2 arc sec. from the center of the XRT error circle. The estimated V magnitude is 14.5 with a 1-sigma error of about 0.5 mag. No correction has been made for the expected extinction corresponding to E(B-V) of 0.22.
