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THE ASTRONOMER Electronic Circular No 2432      2008 Mar 19 14.38UT
Ed:Guy M Hurst, 16,Westminster Close, Kempshott Rise,  Basingstoke,
Hants, RG22 4PP,England.Telephone/FAX(01256)471074Int:+441256471074
INTERNET: GUY@TAHQ.DEMON.CO.UK      Backup: gmh@wdcc1.bnsc.rl.ac.uk
WORLD WIDE WEB                         http://www.theastronomer.org
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GRB 080319B: BRIGHT OPTICAL COUNTERPART
David Palmer at LANL and others report on GCN Circular 7427 the 
detection of an intense burst by SWIFT together with a bright optical 
counterpart.
At 06:12:49 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 080319B (trigger=306757).  Swift slewed immediately to the 
burst. The BAT on-board calculated location is:
RA 14h 31m 42s DEC +36 18'10" (2000) with an uncertainty of 3 arcmin.
The BAT light curve showed one bright but complex peak with a duration 
of about 50 sec, with an extended tail. The peak count rate was ~70,000 
counts/sec (15-350 keV), at ~20 sec after the trigger.
The XRT began observing the field at 06:13:49.7 UT, 60.5 seconds after 
the BAT trigger. XRT found a very bright fading, uncatalogued X-ray 
source located at:
RA 14h 31m 40.7s DEC +36 18' 14.7" (2000)
with an uncertainty of 4.7 arcseconds.
UVOT took a finding chart exposure of 400 seconds with the V filter 
starting 175 seconds after the BAT trigger. There is a candidate
afterglow in the rapidly available 2.7'x2.7' sub-image. This position is 
consistent with the XRT error circle, but the source is so bright that a 
precise UVOT position is not possible due to saturation effects. The 
estimated magnitude is 11.5 with a 1-sigma error of about 0.5 mag.

Grzegorz Wrochna at Soltan Inst.for Nuclear Studies reports on GCN 
Circular 7439 that "Pi of the Sky" apparatus located at Las Campanas 
Observatory imaged the region of GRB 080319b before,
during and after the GRB with 10s exposures (IR-cut filter only). We 
observe optical emission at the position given by Swift XRT.
    start -   end     comment
6:12:33 - 6:12:43   not visible (>12 mag)
6:12:47 - 6:12:57   visible (~10 mag)
6:13:01 - 6:13:11   max. brightness (~6 mag)

Stefano Covino at Brera Astronomical Observatory relays on GCN 7446:
We started a refined analysis of the REM observations of GRB 080319B. As 
already reported by Cwiok et al. the optical counterpart of this GRB was 
exceptionally bright at early time. We measured, about 1 min after the 
burst, R~6.4 assuming R=11.20 for the USNO star at coordinates RA,DEC = 
14:31:23.61, 36:21:56.5. The source was already almost 2 mag fainter 
half a minute later. In the H band the source was H~5 around the same 
epoch.

Editor: The service providers of GCN apologise that the huge volume of 
notices this morning seriously delayed the news which reached TAHQ 
around 14h00mUT, hence the delay in the issue of this circular.

Guy M Hurst