GRB 080915

S. R. Oates (UCL-MSSL), A. P. Beardmore (U Leicester),
J. R. Cummings (NASA/UMBC), P. A. Evans (U Leicester),
C. Gronwall (PSU), S. T. Holland (CRESST/USRA/GSFC),
J. A. Kennea (PSU), F. E. Marshall (NASA/GSFC),
K. L. Page (U Leicester), D. M. Palmer (LANL), A. M. Parsons (GSFC),
R. L. C. Starling (U Leicester) and T. N. Ukwatta (GSFC/GWU) report
on behalf of the Swift Team:

At 00:02:49 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 080915 (trigger=324744). The BAT on-board calculated location 
is RA, Dec 18.004, -76.014 which is 
   RA(J2000) = 01h 12m 01s
   Dec(J2000) = -76d 00' 51"
with an uncertainty of 3 arcmin (radius, 90% containment, including 
systematic uncertainty).  The BAT light curve showed a single-peaked
structure with a duration of about 20 sec.  The peak count rate
was ~700 counts/sec (15-350 keV), at ~2 sec after the trigger. 

Due to an observing constraint, Swift will not slew until 
T0+62.4 minutes. There will be no XRT or UVOT data until
this time. 

Burst Advocate for this burst is S. R. Oates (sro AT mssl.ucl.ac.uk). 
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.)

W. Rujopakarn (Steward), H. Swan (U Mich), T. Guver (U Arizona) report on
behalf of the ROTSE collaboration:

ROTSE-IIIc, located at the H.E.S.S. site at Mt. Gamsberg, Namibia,
responded to GRB 080915 (Swift trigger 324744; Oates et al., GCN 8227
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 ),
producing images beginning 11.2 s after the GCN notice time. An automated
response took the first image at 00:03:42.2 UT, 52.2 s after the burst,
under cloudy conditions. These observations were affected by the full
moon. We took 10 5-sec, and 1 20-sec exposures. These unfiltered images
are calibrated relative to USNO A2.0 (R). Imaging is on going.

Comparison to the DSS (second epoch) reveals no new sources within the
3-sigma Swift/BAT error circle. Individual images have limiting magnitudes
ranging from 14.0-14.3; we set the following specific limit.

start UT       end UT      t_exp(s)   mlim   t_start-tGRB(s)  Coadd?
--------------------------------------------------------------------
00:03:42.2   00:03:47.2         5     14.2           52.2       N

T. Ukwatta (GWU), 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),
S. R. Oates (UCL-MSSL), D. Palmer (LANL), A. Parsons (GSFC),
T. Sakamoto (GSFC/UMBC), G. Sato (ISAS), M. Stamatikos (GSFC/ORAU),
J. Tueller (GSFC)
(i.e. the Swift-BAT team):
 
Using the data set from T-239 to T+963 sec from recent telemetry downlinks,
we report further analysis of BAT GRB 080915 (trigger #324744)
(Oates, et al., GCN Circ. 8227
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 ).  The BAT ground-calculated position is
RA, Dec = 17.911, -76.042 deg, which is 
   RA(J2000)  =  01h 11m 38.5s 
   Dec(J2000) = -76d 02' 29.9" 
with an uncertainty of 2.4 arcmin, (radius, sys+stat, 90% containment).
The partial coding was 89%.
 
The mask-weighted light curve shows a single FRED-like peak starting
at ~T-5 sec, peaking at ~T+4 sec and ending at ~T+25 sec.
T90 (15-350 keV) is 14 +- 5 sec (estimated error including systematics).
 
The time-averaged spectrum from T-1.2 to T+16.2 sec is best fit by a simple
power-law model.  The power law index of the time-averaged spectrum is
1.64 +- 0.29.  The fluence in the 15-150 keV band is 2.3 +- 0.5 x 10^-7 erg/cm2.
The 1-sec peak photon flux measured from T+3.03 sec in the 15-150 keV band
is 0.5 +- 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/324744/BA/

P.A. Evans (U. Leicester) and S.R. Oates (MSSL/UCL)
report on behalf of the Swift-XRT team.

We have analysed 1.7 ks of XRT data on GRB080915 (Oates et al, GCN Circ
8227
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 ), beginning  4.9 ks after the GRB trigger. Swift did not slew
immediately to the burst due to an Earth limb constraint.

We find a faint, fading source with a mean count rate ~0.01 counts per
second at a position of RA, Dec=17.9473, -76.0204 degrees, which is
equivalent to:

RA (J2000):  01h 11m 47.35s
Dec (J2000): -76d 01' 13.4"

with an uncertainy of 6.5 arcsec (radius, 90% containment). This
position is 54 arcsec from the BAT position, within the BAT error
circle.

The light curve shows a power-law decay with an index of 0.94
(+1.19/-0.58); the large uncertainty arises because the light curve
contains only 2 points.

A spectrum formed from the PC data can be modelled with an absorbed
power-law. The absorption column is poorly constained, but consistent
with the Galactic value of 6.7 x 10^20 cm^-2 (Kalberla et al. 2005), and
the photon index is 2.3 (+2.6, -1.3).

If the light curve continues to decay at alpha=0.94 we predict a count
rate at T0+24 hrs of 0.0018  counts per second. This corresponds to an
observed (unabsorbed) 0.3-10 keV flux of 6.36 x 10^-14 (1.22 x 10^-13)
erg cm^-2 s^-1.

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

A. Breeveld (MSSL-UCL) and S.R. Oates (MSSL-UCL) report on behalf of the
Swift/UVOT team:

The Swift/UVOT observed the field of GRB 080915 (Oates et al., GCN Circ.
8227
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 ) with settled exposures starting 3872s after the trigger. We do not
find a source in any of the UVOT observations inside the XRT error
circle (Evans et al., GCN Circ. 8231
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 ). The 3-sigma upper limits in the
UVOT photometric system (Poole et al. 2008, MNRAS, 383, 627) for
detecting a source in the first white finding chart exposure and
subsequent co-added exposures are:

Filter          T_start T_stop  Exp     Mag (3-sigma UL)
                  (s)     (s)     (s)
=========================================================
white (FC)      3872    3972    98.2    > 19.9
white           5004    5204    196.6   > 20.5
v               3979    4179    196.6   > 18.8
v               9633    10539   885.1   > 19.7
b               4799    4999    196.6   > 19.6
u               4594    4794    196.6	> 19.1
uvw1            4389    4589    196.6	> 19.3
uvm2            4184    11087   731.3   > 20.4
uvw2            5210    5329    117.3	> 19.6

The values quoted above are not corrected for the expected Galactic
extinction corresponding to a reddening of E(B-V) = 0.049 mag in the
direction of the burst (Schlegel et al. 1998).

S. Covino, P. D'Avanzo, L.A. Antonelli, D. Malesani, D. Fugazza, L.  
Calzoletti,  S. Campana, G.  Chincarini, M.L. Conciatore, S. Cutini,  
V. D'Elia,  F. D'Alessio, F.  Fiore, P. Goldoni, D. Guetta,  C.  
Guidorzi, G.L. Israel, E. Maiorano, N. Masetti, A. Melandri, E.  
Meurs, L. Nicastro, E. Palazzi, E. Pian, S. Piranomonte, L.  Stella,  
G.  Stratta, G. Tagliaferri, G. Tosti, V.Testa, S.D. Vergani, F.  
Vitali report on behalf of the REM team:


The robotic 60-cm REM telescope located at La Silla (Chile) observed  
automatically the field of the GRB 080915 (Oates et al. GCN 8227
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 ) on  
Sep 15 starting from about 2 min after the GRB time for 30 min. In  
the XRT error circle (Evans et al. GCN 8231
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 ) we see no sources  
fainter than the 2MASS limits in the J, H and K bands.