GRB 080723

M. Stamatikos (NASA/ORAU), W. H. Baumgartner (GSFC/UMBC),
A. P. Beardmore (U Leicester), S. T. Holland (CRESST/USRA/GSFC),
S. D. Hunsberger (PSU), H. A. Krimm (CRESST/GSFC/USRA),
C. B. Markwardt (CRESST/GSFC/UMD), F. E. Marshall (NASA/GSFC),
K. L. Page (U Leicester), D. M. Palmer (LANL) and
T. N. Ukwatta (GSFC/GWU) report on behalf of the Swift Team:

At 04:19:24 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 080723 (trigger=317662).  Swift slewed immediately to the burst. 
The BAT on-board calculated location is 
RA, Dec 274.512, -6.923 which is 
   RA(J2000) = 18h 18m 03s
   Dec(J2000) = -06d 55' 20"
with an uncertainty of 3 arcmin (radius, 90% containment, including 
systematic uncertainty).  Because the BAT light curve has not been
received, we cannot comment on the burst profile at this time.  However,
there is a strong 8.4 sigma excess detected in the scaled map image, 
which strongly suggests a real gamma-ray burst occurred. 

The XRT began observing the field at 04:20:50.2 UT, 85.8 seconds after
the BAT trigger. Using promptly downlinked data we find a fading,
uncatalogued X-ray source with an enhanced position: RA, Dec 274.48985,
-6.89931 which is equivalent to:
   RA(J2000)  = 18h 17m 57.56s
   Dec(J2000) = -06d 53' 57.5"
with an uncertainty of 2.7 arcseconds (radius, 90% containment). This
location is 116 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 (3.94e+21
cm^-2, Kalberla et al. 2005), with an excess column of 5.7
(+6.36/-4.59) x 10^21 cm^-2 (90% confidence). 

UVOT took a finding chart exposure of 100 seconds with the White (160-650 nm)
filter starting 92 seconds after the BAT trigger. No afterglow candidate has
been found in the initial data products. The 2.7'x2.7' sub-image covers 0% of
the XRT error circle.  The 8'x8' region for the list of sources generated on-
board covers 100% of the BAT error circle. The list of sources is typically 
complete to about 18 mag.  No correction has been made for the large Galactic 
expected extinction corresponding to E(B-V) of 1.3 mag. 

Burst Advocate for this burst is M. Stamatikos (michael AT milkyway.gsfc.nasa.gov). 
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.)

A.P. Beardmore, P.A. Evans, M.R. Goad and J.P. Osborne (U. Leicester) 
report on behalf of the Swift-XRT team.

Using 5309 s of XRT Photon Counting mode data and 9 UVOT
images for GRB 080723, we find an astrometrically corrected X-ray
position (using the XRT-UVOT alignment and matching UVOT field sources
to the USNO-B1 catalogue): RA, Dec = 274.49035, -6.89952 which is equivalent
to:

RA (J2000): 18h 17m 57.68s
Dec (J2000): -06d 53' 58.3"

with an uncertainty of 1.7 arcsec (radius, 90% confidence).

This position may be improved as more data are received. The latest position
can be viewed at http://www.swift.ac.uk/xrt_positions. Position enhancement is
described by Goad et al. (2007, A&A, 476, 1401
http://www.swift.ac.uk/xrt_positions/Goad.pdf), the current algorithm is an
extension of this method.

This circular was automatically generated, and is an official product of the
Swift-XRT team.

M. Stamatikos (GSFC/ORAU), S. D. Barthelmy (GSFC), W. Baumgartner 
(GSFC/UMBC),
J. Cummings (GSFC/UMBC), E. Fenimore (LANL), N. Gehrels (GSFC),
H. Krimm (GSFC/USRA), C. Markwardt (GSFC/UMD), K. McLean (GSFC/UMD),
D. Palmer (LANL), A. Parsons (GSFC), T. Sakamoto (GSFC/UMBC),
G. Sato (ISAS), J. Tueller (GSFC), T. Ukwatta (GWU)
(i.e. the Swift-BAT team):

Using the data set from T-239 to T+963 sec from the recent telemetry 
downlink, we report further analysis of BAT GRB 080723 (trigger #317662)
(Stamatikos, et al., GCN Circ. 8000
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 ).  The BAT ground-calculated position is
RA, Dec = 274.461, -6.910 deg which is
    RA(J2000)  =  18h 17m 50.6s
    Dec(J2000) = -06d 54' 34.8"
with an uncertainty of 1.6 arcmin, (radius, sys+stat, 90% containment).
The burst was in the fully coded part of the BAT field of view.

The mask-weighted light curve showed a double-peaked structure, with the
first peak extending from T-1 sec to T+4 sec, and the second smaller 
peak from T+6 sec to T+20 sec. T90 (15-350 keV) is 17.3 +- 3.0 sec 
(estimated error including systematics).

The time-averaged spectrum from T-0.2 to T+18.7 sec is best fit by a 
simple power-law model.  The power law index of the time-averaged 
spectrum is 1.77 +- 0.21.  The fluence in the 15-150 keV band is
3.3 +- 0.4 x 10-7 erg/cm2. The 1-sec peak photon flux measured from 
T-0.13 sec in the 15-150 keV band is 0.9 +- 0.1 ph/cm2/sec.  All the 
quoted errors are at the 90% confidence level.

The results of the batgrbproduct analysis are available at
http://gcn.gsfc.nasa.gov/notices_s/317662/BA/