GRB 130812A

V. D'Elia (ASDC), S. D. Barthelmy (GSFC), D. N. Burrows (PSU),
N. Gehrels (NASA/GSFC), J. A. Kennea (PSU), N. P. M. Kuin (UCL-MSSL),
V. Mangano (PSU), C. B. Markwardt (NASA/GSFC) and M. H. Siegel (PSU)
report on behalf of the Swift Team:

At 22:22:52 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 130812A (trigger=566228).  Swift slewed immediately to the burst. 
The BAT on-board calculated location is 
RA, Dec 92.402, -13.295 which is 
   RA(J2000)  =  06h 09m 37s
   Dec(J2000) = -13d 17' 42"
with an uncertainty of 3 arcmin (radius, 90% containment, including 
systematic uncertainty).  The BAT light curve shows multiple peaks
with a total duration of about 10 sec.  The peak count rate
was ~4500 counts/sec (15-350 keV), at ~0 sec after the trigger. 

The XRT began observing the field at 22:24:09.6 UT, 77.0 seconds after
the BAT trigger. Using promptly downlinked data we find a fading,
uncatalogued X-ray source with an enhanced position: RA, Dec 92.3955,
-13.2875 which is equivalent to:
   RA(J2000)  = 06h 09m 34.92s
   Dec(J2000) = -13d 17' 15.1"
with an uncertainty of 2.1 arcseconds (radius, 90% containment). This
location is 35 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. 

A power-law fit to a spectrum formed from promptly downlinked event
data gives a column density in excess of the Galactic value (1.51 x
10^21 cm^-2, Kalberla et al. 2005), with an excess column of 1.5
(+1.52/-1.37) x 10^21 cm^-2 (90% confidence). 

UVOT took a finding chart exposure of 250 seconds with the U filter starting
138 seconds after the BAT trigger. No credible afterglow candidate has been
found in the initial data products. The 2.7'x2.7' sub-image covers 100% of the
XRT error circle. The typical 3-sigma upper limit has been about 19.2 mag. The
8'x8' region for the list of sources generated on-board covers 100% of the XRT
error circle. The list of sources is typically complete to about 18.0 mag. No
correction has been made for the expected extinction corresponding to E(B-V) of
0.23. 

Burst Advocate for this burst is V. D'Elia (delia AT asdc.asi.it). 
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.)

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

Using 2469 s of XRT Photon Counting mode data and 5 UVOT
images for GRB 130812A, 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 = 92.39590, -13.28816 which is equivalent
to:

RA (J2000): 06h 09m 35.02s
Dec (J2000): -13d 17' 17.4"

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.

P.A. Evans (U. Leicester), B.P. Gompertz (U. Leicester), P. D'Avanzo
(INAF-OAB), A. Maselli	(INAF-IASFPA), V. Mangano (PSU), M.C. Stroh
(PSU), D.N. Burrows (PSU), J.P. Osborne (U. Leicester) and V. D'Elia
report on behalf of the Swift-XRT team:

We have analysed 8.9 ks of XRT data for GRB 130812A (D'Elia  et al. GCN
Circ. 15088
Loading...
 
 ),  from 62 s to 22.3 ks after the  BAT trigger. The data
comprise 8 s in Windowed Timing (WT) mode (taken while Swift was
slewing), with the remainder in Photon Counting (PC) mode. The enhanced
XRT position for this burst was given by Evans et al. (GCN. Circ
15089).

The light curve can be modelled with  a power-law decay with a decay
index of alpha=0.86 (+/-0.03).

A spectrum formed from the PC mode data can be fitted with an absorbed
power-law with a photon spectral index of 2.04 (+0.17, -0.16). The
best-fitting absorption column is  3.0 (+/-0.6) x 10^21 cm^-2, in
excess of the Galactic value of 1.5 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 4.1 x 10^-11 (6.6 x 10^-11) erg
cm^-2 count^-1. 

A summary of the PC-mode spectrum is thus:
Total column:	     3.0 (+/-0.6) x 10^21 cm^-2
Galactic foreground: 1.5 x 10^21 cm^-2
Excess significance: 4.3 sigma
Photon index:	     2.04 (+0.17, -0.16)

If the light curve continues to decay with a power-law decay index of
0.86, the count rate at T+24 hours will be 7.1 x 10^-3 count s^-1,
corresponding to an observed (unabsorbed) 0.3-10 keV flux of 2.9 x
10^-13 (4.6 x 10^-13) erg cm^-2 s^-1.

The results of the XRT-team automatic analysis are available at
http://www.swift.ac.uk/xrt_products/00566228.

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

K. Varela (MPE Garching), D.A. Kann (TLS Tautenburg), J. Greiner 
(MPE Garching) report on behalf of the GROND team:

We observed the field of GRB 130812A (Swift trigger 566228; 
D'Elia et al. 2013, GCN #15088
Loading...
 
 ) simultaneously in g'r'i'z'JHK with 
GROND (Greiner et al. 2008, PASP 120, 405) mounted at the 
2.2 m MPG/ESO telescope at La Silla Observatory (Chile).

Observations started at 10:13 UT on 13 Aug. 2013, 11.8 hrs after the 
GRB trigger. They were performed at an average seeing of 2.5" and at 
an average airmass of 1.4.

In 212 sec exposure in g'r'i'z' and 360 sec exposure in JHK 
we do not detect a source within the 1.8 arcsec Swift-XRT error 
circle reported by Evans et al. (2013; GCN #15089
Loading...
 
 ) down to
(all in the AB system)

g' > 22.4,

r' > 22.6,

i' > 21.9,

z' > 21.7,

J > 20.3,

H > 19.4 and

K > 18.8

The given limits are derived based on calibrating the images against 
GROND zeropoints and 2MASS field stars and are not corrected for the 
Galactic foreground extinction corresponding to a reddening of 
E_(B-V)= 0.23 in the direction of the burst (Schlegel et al. 1998).

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

Using the data set from T-144 to T+431 sec from the recent telemetry downlink,
we report further analysis of BAT GRB 130812A (trigger #566228)
(D'Elia, et al., GCN Circ. 15088
Loading...
 
 ).  The BAT ground-calculated position is
RA, Dec = 92.387, -13.285 deg which is 
  RA(J2000)  =  06h 09m 32.8s 
  Dec(J2000) = -13d 17' 06.6" 
with an uncertainty of 1.0 arcmin, (radius, sys+stat, 90% containment).
The partial coding was 75%.

The mask-weighted light curve shows multiple spikes peaking at T0, T0+4 sec and T0+7 sec.  
T90 (15-350 keV) is 7.6 +- 0.5 sec (estimated error including systematics).

The time-averaged spectrum from T-0.3 to T+8.5 sec is best fit by a simple
power-law model.  The power law index of the time-averaged spectrum is
2.52 +- 0.11.  The fluence in the 15-150 keV band is 5.9 +- 0.3 x 10^-7 erg/cm2.
The 1-sec peak photon flux measured from T-0.14 sec in the 15-150 keV band
is 2.8 +- 0.2 ph/cm2/sec.  All the quoted errors are at the 90% confidence
level. 

The results of the batgrbproduct analysis will be available at
http://gcn.gsfc.nasa.gov/notices_s/566228/BA/

A. A. Breeveld (UCL-MSSL) and V. D'Elia (ASDC) report on behalf of the 
Swift/UVOT team:

The Swift/UVOT began settled observations of the field of GRB 130812A 
139 s after the BAT trigger (D'Elia et al., GCN Circ. 15088
Loading...
 
 ).
No optical afterglow consistent with the XRT position (Evans et al. GCN 
Circ. 15089
Loading...
 
 ) 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

u_FC               139          389          246         >20.3
v                  445        12868         1191         >20.5
b                  394        11236         1459         >21.7
u                  139         7030          884         >20.8
w1                 494         6825          491         >20.5
m2                 469         6619          452         >20.3
w2                 421        12142         1376         >21.3

The magnitudes in the table are not corrected for the Galactic 
extinction due to the reddening of E(B-V) = 0.23 in the direction of the 
burst (Schlegel et al. 1998).