| Circular_text |
TITLE: GCN CIRCULAR
NUMBER: 8182
SUBJECT: GRB 080905B: Swift detection of a burst with possible optical counterpart
DATE: 08/09/05 17:22:03 GMT
FROM: Jamie A. Kennea at PSU/Swift-XRT
M. C. Stroh (PSU), S. D. Barthelmy (GSFC),
W. H. Baumgartner (GSFC/UMBC), A. P. Beardmore (U Leicester),
D. N. Burrows (PSU), M. M. Chester (PSU), J. R. Cummings (NASA/UMBC),
P. A. Evans (U Leicester), N. Gehrels (NASA/GSFC),
S. T. Holland (CRESST/USRA/GSFC), S. Immler (CRESST/GSFC/UMD),
J. A. Kennea (PSU), H. A. Krimm (CRESST/GSFC/USRA),
F. E. Marshall (NASA/GSFC), P. T. O'Brien (U Leicester),
C. Pagani (PSU), K. L. Page (U Leicester), B. Preger (ASDC),
J. L. Racusin (PSU), T. Sakamoto (NASA/UMBC), P. Schady (MSSL-UCL),
R. L. C. Starling (U Leicester) and L. Vetere (PSU) report on behalf
of the Swift Team:
At 16:55:45 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 080905B (trigger=323898). Swift slewed immediately to the burst.
The BAT on-board calculated location is
RA, Dec 301.723, -62.571 which is
RA(J2000) = 20h 06m 53s
Dec(J2000) = -62d 34' 15"
with an uncertainty of 3 arcmin (radius, 90% containment, including
systematic uncertainty). The BAT light curve showed three well separated
peaks each about 10 seconds long with a total burst duration of about
90 sec. The peak count rate was ~2000 counts/sec (15-350 keV), at ~4 sec
after the trigger.
The XRT began observing the field at 16:57:28.6 UT, 103.2 seconds after
the BAT trigger. Using promptly downlinked data we find a bright,
uncatalogued X-ray source with an enhanced position: RA, Dec 301.74027,
-62.56347 which is equivalent to:
RA(J2000) = 20h 06m 57.66s
Dec(J2000) = -62d 33' 48.5"
with an uncertainty of 2.7 arcseconds (radius, 90% containment). This
location is 39 arcseconds from the BAT onboard position, within the BAT
error circle.
A power-law fit to a spectrum formed from promptly downlinked event
data gives a column density in excess of the Galactic value (3.49e+20
cm^-2, Kalberla et al. 2005), with an excess column of 1.7
(+1.47/-1.31) x 10^21 cm^-2 (90% confidence).
The initial flux in the 2.5 s image was 2.11e-09 erg cm^-2 s^-1 (0.2-10
keV).
UVOT took a finding chart exposure of 100 seconds with the White
(160-650 nm) filter starting 112 seconds after the BAT trigger.
The 2.7'x2.7' sub-image covers 100% of the XRT error circle. Inside
the XRT error circle is a 16th mag source that is starlike in the DSS,
but appears extended or double in the UVOT image and may be an
optical afterglow. A second finding chart in V does not allow us to
confirm or reject the candidate at this time. No correction has
been made for the expected extinction corresponding to E(B-V) of
0.05.
Burst Advocate for this burst is M. C. Stroh (stroh AT astroh.org).
Please contact the BA by email if you require additional information
regarding Swift followup of this burst. In extremely urgent cases, after
trying the Burst Advocate, you can contact the Swift PI by phone (see
Swift TOO web site for information: http://www.swift.psu.edu/too.html.)
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