GCN Circular 6330
Subject
GRB 070420: Swift detection of a burst with optical afterglow
Date
2007-04-20T06:56:57Z (17 years ago)
From
David Palmer at LANL <palmer@lanl.gov>
M. Stamatikos (NASA/ORAU), D. N. Burrows (PSU),
G. Cusumano (INAF-IASFPA), P. A. Evans (U Leicester),
C. Gronwall (PSU), V. Mangano (INAF-IASFPA),
C. B. Markwardt (GSFC/UMD), P. T. O'Brien (U Leicester),
D. M. Palmer (LANL), A. M. Parsons (GSFC), M. Perri (ASDC) and
G. Stratta (ASDC) report on behalf of the Swift Team:
At 06:18:13 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 070420 (trigger=276321). Swift slewed immediately to the burst.
The BAT on-board calculated location is
RA, Dec 121.253, -45.561 which is
RA(J2000) = 08h 05m 01s
Dec(J2000) = -45d 33' 38"
with an uncertainty of 3 arcmin (radius, 90% containment, including
systematic uncertainty). The BAT light curve showed a multiply-peaked
structure with a duration of at least 70 sec starting at T-50s.
The peak count rate was ~4000 counts/sec (15-350 keV), at ~7 sec
after the trigger.
XRT began observing the field at 06:19:52 UT, 99 seconds after the BAT
trigger. XRT found a bright, fading, previously uncatalogued X-ray source
in the field of view at the following coordinates:
RA(J2000) = 08h 04m 55.3s
Dec(J2000)= -45d 33' 23.2"
with an uncertainty of 4 arcseconds radius (90% containment). This is a
ground calculated position based on prompt downlinked data. This position
lies 62 arcseconds from the center of the BAT error circle.
UVOT took a finding chart exposure of 100 seconds with the White
(160-650 nm) filter starting 108 seconds after the BAT trigger. An
afterglow candidate has been found in the initial data products. The
2.7'x2.7' region for the list of sources generated on-board covers
100% of the XRT error circle. A source is detected at
RA(J2000) = 08h 04m 55.25s
Dec(J2000)= -45d 33' 21.0"
with an estimated uncertainty of +/-0.5 arcsec. This position is
2.0 arcsec from the XRT position. The estimated magnitude in the
White filter is 17.3. No correction has been made for the expected
extinction correspondingto E(B-V) of 0.52.