GRB 120817A

S. Immler (NASA/CRESST/GSFC) and B. P. Gompertz (U Leicester)
report on behalf of the Swift/UVOT team:

The Swift/UVOT began settled observations of the field of GRB 120817A
3115 s after the BAT trigger (Gompertz et al., GCN Circ. 13661
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 ).
No optical afterglow consistent with the XRT (Beardmore et al., GCN
13667
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 ) or the FTN positions (Guidorzi et al., GCN 13664
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 ) is detected
in the initial UVOT exposures. 

Preliminary 3-sigma upper limits using the UVOT photometric system
(Breeveld et al. 2011, AIP Conf. Proc. 1358, 373) for the first
finding chart (FC) exposure and subsequent exposures are:

Filter         T_start(s)   T_stop(s)      Exp(s)         Mag

white_FC          3115         3265          147         >19.4
white             3115         4496          344         >20.4
v                 3272        10816         1278         >20.2
b                 4092        17166          945         >21.1
u                 3887        22943         1904         >21.1
w1                3682        22294         2164         >20.3
m2                3476        21386         1838         >20.2
w2                4503         9902         1082         >20.0

The magnitudes in the table are not corrected for the Galactic extinction
due to the reddening of E(B-V) = 0.84 in the direction of the burst
(Schlegel et al. 1998).

J. Wren, W.T. Vestrand, P. Wozniak, and H. Davis,
of Los Alamos National Laboratory report:

A RAPTOR wide-field monitor located in Maui observed the location
of Swift trigger 531267 (Gompertz et al., GCN 13661
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 ) during the period
that the Swift BAT was observing gamma-ray emission.  The 10 s exposure
began at 06:49:38.0 UTC -- 4 s before the Swift trigger.  We detect no
new object at the location of the refined Swift XRT location
(Gompertz et al., GCN 13673
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 ) to a 3-sigma limiting magnitude of 10.3.
Our unfiltered images are calibrated to the Tycho-2 V-band.

B.P. Gompertz (U Leicester) reports on behalf of the Swift-XRT team:

We have analysed 9.7 ks of XRT data for GRB 120817A (Gompertz  et al.
GCN Circ. 13661
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 ), from 3.1 ks to 22.9 ks after the  BAT trigger. The
data are entirely in Photon Counting (PC) mode. The enhanced XRT
position for this burst was given by Beardmore et al. (GCN. Circ
13667).

The light curve can be modelled with  a power-law decay with a decay
index of alpha=0.70 (+/-0.18).

A spectrum formed from the PC mode data can be fitted with an absorbed
power-law with a photon spectral index of 2.0 (+0.4, -0.3). The
best-fitting absorption column is  5.9 (+2.6, -1.9) x 10^21 cm^-2, in
excess of the Galactic value of 2.9 x 10^21 cm^-2 (Kalberla et al.
2005). The counts to observed (unabsorbed) 0.3-10 keV flux conversion
factor deduced from this spectrum  is 4.8 x 10^-11 (8.9 x 10^-11) erg
cm^-2 count^-1. 

A summary of the PC-mode spectrum is thus:
Total column:	     5.9 (+2.6, -1.9) x 10^21 cm^-2
Galactic foreground: 2.9 x 10^21 cm^-2
Excess significance: 2.5 sigma
Photon index:	     2.0 (+0.4, -0.3)

The results of the XRT-team automatic analysis are available at
http://www.swift.ac.uk/xrt_products/00531267.

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

D. M. Palmer (LANL), S. D. Barthelmy (GSFC), W. H. Baumgartner (GSFC/UMBC),
J. R. Cummings (GSFC/UMBC), E. E. Fenimore (LANL), N. Gehrels (GSFC),
B.P. Gompertz (U Leicester), H. A. Krimm (GSFC/USRA), C. B. Markwardt (GSFC),
T. Sakamoto (GSFC/UMBC), G. Sato (ISAS), M. Stamatikos (OSU),
J. Tueller (GSFC), T. N. Ukwatta (MSU)
(i.e. the Swift-BAT team):
 

Using the data set from T-60 to T+243 sec from the recent telemetry downlink,
we report further analysis of BAT GRB 120817A (trigger #531267)
(Gompertz, et al., GCN Circ. 13661
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 ).  The BAT ground-calculated position is
RA, Dec = 250.692, -38.377 deg, which is 
   RA(J2000)  =  16h 42m 46.2s 
   Dec(J2000) = -38d 22' 36.8" 
with an uncertainty of 1.5 arcmin, (radius, sys+stat, 90% containment).
The partial coding was 85%.
 
The mask-weighted light curve shows two slighly overlapping peaks starting
at ~T-2 sec, peaking at ~T+0.0 and ~T+11 sec, with a tail ending at ~T+65 sec.
T90 (15-350 keV) is 28.2 +- 6.8 sec (estimated error including systematics).
 
The time-averaged spectrum from T-2.24 to T+30.77 sec is best fit by a simple
power-law model.  The power law index of the time-averaged spectrum is
1.97 +- 0.16.  The fluence in the 15-150 keV band is 6.9 +- 0.6 x 10^-7 erg/cm2.
The 1-sec peak photon flux measured from T-0.12 sec in the 15-150 keV band
is 0.8 +- 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/531267/BA/

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

Using 2321 s of XRT Photon Counting mode data and 5 UVOT
images for GRB 120817A, 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 = 250.68918, -38.35451 which is equivalent
to:

RA (J2000): 16h 42m 45.40s
Dec (J2000): -38d 21' 16.2"

with an uncertainty of 1.8 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) and Evans
et al. (2009, MNRAS, 397, 1177).

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

C. Guidorzi (U. Ferrara), C.G. Mundell, C.J. Mottram,
F. Virgili (LJMU), A. Gomboc (U. Ljubljana) report on
behalf of a larger collaboration:

The 2-m Faulkes Telescope North (FTN) automatically began observing
GRB 120817A (Gompertz et al. GCN Circ. 13661
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 ) on August 17 2012,
06:53:57 UT corresponding to 4.2 minutes post burst trigger
with BVRi' filters. Within the XRT error circle (Perri et al.
GCN Circ. 13662
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 ), close to a USNOB1 object we detect a faint,
uncatalogued, possibly fading source at the following position

R.A. = 16:42:45.92
Dec = -38:21:12.4   (J2000)

with an uncertainty of about 1".
The detection is marginal, with an estimated magnitude of
19.3 +/- 0.4 in the R band at a mean time of 17.4 minutes
(60 s exposure) calibrated against nearby USNOB-1 stars.

The 2-m Faulkes Telescope South (FTS) began observing at 77 min
post burst. In a stacked R-band frame we find marginal evidence
for fading, with R=19.8 +- 0.3 mag at a mean time of 105 min
(total exposure of 360 s). The nearby USNOB1 object is compatible
with being constant between the two observations.

The comparison between the FTN and FTS R-band images is available at
http://www.fe.infn.it/u/guidorzi/GRB120817A_XRT_FT_candidate.jpg

M. Perri (ASDC), G. Tagliaferri (INAF-OAB), P.A. Evans (U. Leicester),
J.P. Osborne (U. Leicester), D.N. Burrows (PSU) and J.A. Kennea (PSU)
report on behalf of the Swift-XRT team:

The XRT began observing the field of GRB 120817A at 07:41:33.5 UT,
3110.8 seconds after the BAT trigger. Using promptly downlinked data we
find an uncatalogued X-ray source located at RA, Dec 250.69098,
-38.35404 which is equivalent to:
   RA(J2000)  = 16h 42m 45.84s
   Dec(J2000) = -38d 21' 14.5"
with an uncertainty of 4.2 arcseconds (radius, 90% containment). This
location is 65 arcseconds from the BAT onboard position, within the BAT
error circle. This position may be improved as more data are received;
the latest position is available at http://www.swift.ac.uk/sper.  We
cannot determine whether the source is fading at the present time. 

A power-law fit to a spectrum formed from promptly downlinked event
data gives a column density consistent with the Galactic value of 2.88
x 10^21 cm^-2 (Kalberla et al. 2005).

B.P. Gompertz (U Leicester), P. A. Evans (U Leicester),
C. Guidorzi (U Ferrara), K. L. Page (U Leicester), D. M. Palmer (LANL)
and R. L. C. Starling (U Leicester) report on behalf of the Swift
Team:

At 06:49:42 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 120817A (trigger=531267).  Swift could not immediately slew
due to an Earth limb pointing constraint. 
The BAT on-board calculated location is 
RA, Dec 250.706, -38.340 which is 
   RA(J2000) = 16h 42m 49s
   Dec(J2000) = -38d 20' 25"
with an uncertainty of 3 arcmin (radius, 90% containment, including 
systematic uncertainty).  The BAT light curve showed a multiple-peaked
structure with a duration of about 25 sec.  The peak count rate
was ~1700 counts/sec (15-350 keV), at ~0 sec after the trigger. 

Due to an observing constraint, Swift will not slew until T0+50.1
minutes. There will be no XRT or UVOT data until this time. 

Burst Advocate for this burst is B.P. Gompertz (bpg6 AT le.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.)