GRB 080802

W. H. Baumgartner (GSFC/UMBC), A. P. Beardmore (U Leicester),
M. M. Chester (PSU), C. B. Markwardt (CRESST/GSFC/UMD),
D. M. Palmer (LANL) and E. Troja (INAF-IASFPA) report on behalf of
the Swift Team:

At 15:12:21 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 080802 (trigger=318832).  Swift slewed immediately to the burst. 
The BAT on-board calculated location is 
RA, Dec 270.748, -32.333 which is 
   RA(J2000) = 18h 02m 60s
   Dec(J2000) = -32d 19' 59"
with an uncertainty of 3 arcmin (radius, 90% containment, including 
systematic uncertainty).  The BAT light curve showed a complex
structure with a duration of about 50 sec.  The peak count rate
was ~1000 counts/sec (15-350 keV), at ~2 sec after the trigger. 

The XRT began observing the field at 15:13:39.7 UT, 78 seconds
after the BAT trigger. Using promptly downlinked data we find a bright,
variable, uncatalogued X-ray source located at RA, Dec 270.72692,
-32.33395 which is equivalent to:
   RA(J2000)  = 18h 02m 54.46s
   Dec(J2000) = -32d 20' 02.2"
with an uncertainty of 3.1 arcseconds (radius, 90% containment). This is
1.1 arcminutes from the BAT position and within its error radius. 

A power-law fit to a spectrum formed from promptly downlinked event
data gives a column density in excess of the Galactic value (2.75e+21
cm^-2, Kalberla et al. 2005), with an excess column of 2.3
(+2.63/-2.21) x 10^21 cm^-2 (90% confidence). 

The initial flux in the 2.5 s image was 1.47e-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 86 seconds after the BAT trigger. No 
afterglow candidate is apparent in the initial data products. The 
2.7'x2.7' sub-image covers 25% of  the BAT error circle and 100% of 
the XRT error circle. The typical 3-sigma upper limit has been about 
 18.5 mag. The list of sources is typically complete to about 18 mag. 
 No  correction has been made for the expected extinction, which at
this location is large and uncertain. 

Because this source is near the Galactic center, this event may
be a local transient rather than a cosmological GRB.  However,
no known sources are found at the XRT position in either 
SIMBAD or NED. 

No BAT_POSITION notice was available due to a TDRSS hand-over
at the time of the burst.

H. Krimm (GSFC/USRA), S. D. Barthelmy (GSFC), W. Baumgartner (GSFC/UMBC),
J. Cummings (GSFC/UMBC), E. Fenimore (LANL), N. Gehrels (GSFC),
C. Markwardt (GSFC/UMD), K. McLean (GSFC/UMD), D. Palmer (LANL),
A. Parsons (GSFC), T. Sakamoto (GSFC/UMBC), G. Sato (ISAS),
M. Stamatikos (GSFC/ORAU), J. Tueller (GSFC), T. Ukwatta (GWU)
(i.e. the Swift-BAT team):
 
Using the data set from T-239 to T+388 sec from the recent telemetry downlink,
we report further analysis of BAT GRB 080802 (trigger #318832)
(Baumgartner, et al., GCN Circ. 8051
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 ).  The BAT ground-calculated position is
RA, Dec = 270.729, -32.329 deg which is 
   RA(J2000)  =  18h 02m 55.0s 
   Dec(J2000) = -32d 19' 45.6" 
with an uncertainty of 1.6 arcmin, (radius, sys+stat, 90% containment).
The partial coding was 100%.
 
The mask-weighted light curve shows several overlapping peaks starting
at ~T-40 sec and ending at ~T+180.  T90 (15-350 keV) is 176 +- 50 sec
(estimated error including systematics).
 
The time-averaged spectrum from T-31.1 to T+176.9 sec is best fit by a simple
power-law model.  The power law index of the time-averaged spectrum is
1.76 +- 0.19.  The fluence in the 15-150 keV band is 1.3 +- 0.2 x 10^-6 erg/cm2.
The 1-sec peak photon flux measured from T-7.56 sec in the 15-150 keV band
is 0.3 +- 0.0 ph/cm2/sec.  All the quoted errors are at the 90% confidence
level. 

Given the Galactic lon,lat being in the bulge, we can not rule out
a non-GRB source for this trigger.  All other factors point to a GRB.
 
The results of the batgrbproduct analysis are available at
http://gcn.gsfc.nasa.gov/notices_s/318832/BA/

Adria C. Updike (Clemson U), James Neff (College of Charleston), and
Dieter H. Hartmann (Clemson U) report:

We observed the field of GRB 080802 (GCN 8051
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 , Baumgartner et al.) using
the 0.5m UVI (University of the Virgin Islands) telescope at St. Thomas
for 5 minutes in the R band, beginning 00:12 UT (~9 hours after the
trigger).  We detect no new sources within the XRT error circle to a
limiting magnitude of R ~ 18.5 as calibrated against the USNO B1.0
catalog.  Further observations we hampered by cloud cover.

This message may be cited.

M.C. Stroh (PSU) reports on behalf of the Swift-XRT team:

We have analyzed the first two orbits of Swift-XRT data obtained for  
GRB 080802 (Baumgartner et al., GCN Circ. 8051
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 ), totaling 81s of  
Windowed Timing and 2.4ks of Photon Counting data.

The X-ray light-curve begins with a single flare that peaks to ~40 cts/ 
s near T+100 seconds. The rest of the light-curve can be fit by a  
single broken power-law with an initial decay index of 2.91 +/- 0.33,  
second decay index of -0.51 +/- 0.25 and a break near T+1000s. Since  
the second decay index indicates brightening, we cannot accurately  
predict counting rates at T+24 or T+48 hours.

The spectrum from the Windowed Timing data can be fit with a power-law  
in excess of the Galactic value (2.75e21 cm-2, Kalberla et al. 2005),  
with a column density of 4.8 (+2.0/-1.7)e21 cm^-2 and a photon index  
of 1.40 (+0.24/-0.22). The observed (unabsorbed) 0.3-10 keV flux is  
4.78e-10 (4.95e-10) ergs/cm^2/s.

This is an official product of the Swift-XRT team.

P. Schady (MSSL-UCL) and W.H. Baumgartner (GSFC/UMBC) report on behalf of 
the Swift/UVOT team:

The Swift/UVOT observed the field of GRB 080802 starting 87 s after the 
BAT trigger (Baumgartner et al., GCN Circ. 8051
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 ).  We do not find a source 
in any of the UVOT observations inside the XRT error circle (Baumgartner 
et al., GCN Circ. 8051
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 ). The 3-sigma upper limits for detecting a source 
in the first white and v finding charts (FC) exposure and co-added frames 
are:

Filter          T_start T_stop  Exp     Mag (3-sigma UL)
                 (s)     (s)     (s)
=========================================================
white (FC)      87      186     100     > 20.0
white           4803    5002    200     > 20.4
v (FC)          193     406     213     > 18.7
v               5214    5413    200     > 18.7
b               4598    6189    356     > 20.1
u               4393    6028    400     > 19.9
uvw1            4188    5822    400     > 19.8
uvm2            3983    5618    400     > 19.7
uvw2            5009    5208    200     > 19.5

The values quoted above are not corrected for the expected Galactic 
extinction corresponding to a reddening of E(B-V) = 0.80 mag in the 
direction of the burst (Schlegel et al. 1998).