GRB 120807A

F. E. Marshall (NASA/GSFC), P. A. Evans (U Leicester),
N. Gehrels (NASA/GSFC), B.P. Gompertz (U Leicester),
C. Guidorzi (U Ferrara), J. A. Kennea (PSU),
O. M. Littlejohns (U Leicester), C. B. Markwardt (NASA/GSFC),
K. L. Page (U Leicester), D. M. Palmer (LANL) and
E. Troja (NASA/GSFC/ORAU) report on behalf of the Swift Team:

At 07:09:37 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 120807A (trigger=530267).  Swift slewed immediately to the burst. 
The BAT on-board calculated location is 
RA, Dec 241.211, -47.490 which is 
   RA(J2000) = 16h 04m 51s
   Dec(J2000) = -47d 29' 23"
with an uncertainty of 3 arcmin (radius, 90% containment, including 
systematic uncertainty).  The BAT light curve showed a single peak 
structure with a duration of about 15 sec.  The peak count rate
was ~2000 counts/sec (15-350 keV), at ~2 sec after the trigger. 

The XRT began observing the field at 07:10:49.4 UT, 71.6 seconds after
the BAT trigger. Using promptly downlinked data we find a fading,
uncatalogued X-ray source with an enhanced position: RA, Dec 241.2594,
-47.4797 which is equivalent to:
   RA(J2000)  = 16h 05m 02.26s
   Dec(J2000) = -47d 28' 47.0"
with an uncertainty of 2.3 arcseconds (radius, 90% containment). This
location is 123 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 (4.94 x
10^21 cm^-2, Kalberla et al. 2005), with an excess column of 3.5
(+4.80/-2.19) x 10^21 cm^-2 (90% confidence). 

UVOT took a finding chart exposure of 150 seconds with the White filter
starting 75 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 none of
the XRT error circle. 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 mag. No correction has been made for the large, but
uncertain extinction expected. 

Burst Advocate for this burst is F. E. Marshall (marshall 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 1862 s of XRT Photon Counting mode data and 2 UVOT
images for GRB 120807A, 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 = 241.26016, -47.47972 which is equivalent
to:

RA (J2000): 16h 05m 2.44s
Dec (J2000): -47d 28' 47.0"

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.

J. R. Cummings (GSFC/UMBC), S. D. Barthelmy (GSFC), W. H. Baumgartner (GSFC/UMBC),
E. E. Fenimore (LANL), N. Gehrels (GSFC), H. A. Krimm (GSFC/USRA),
C. B. Markwardt (GSFC), F. E. Marshall (NASA/GSFC), D. M. Palmer (LANL),
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 recent telemetry downlinks,
we report further analysis of BAT GRB 120807A (trigger #530267)
(Marshall, et al., GCN Circ. 13602
Loading...
 
 ).  The BAT ground-calculated position is
RA, Dec = 241.273, -47.455 deg, which is 
   RA(J2000)  =  16h 05m 05.6s 
   Dec(J2000) = -47d 27' 16.3" 
with an uncertainty of 2.1 arcmin, (radius, sys+stat, 90% containment).
The partial coding was 89%.
 
The mask-weighted light curves shows a single pulse starting at ~T-5 sec,
peaking at ~T+2 sec, and ending at ~T+20 sec.  T90 (15-350 keV) is
20.0 +- 5.8 sec (estimated error including systematics).
 
The time-averaged spectrum from T-0.24 to T+24.07 sec is best fit by a simple
power-law model.  The power law index of the time-averaged spectrum is
1.81 +- 0.30.  The fluence in the 15-150 keV band is 2.9 +- 0.5 x 10^-7 erg/cm2.
The 1-sec peak photon flux measured from T+0.65 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/530267/BA/

Klotz A. (IRAP-CNRS-OMP), Gendre B. (ASDC/INAF-OAR),
Boer M. (UNS-CNRS-OCA), Atteia J.L. (IRAP-CNRS-OMP) report:

We imaged the field of GRB 120807 detected by SWIFT
(trigger 530267) with the TAROT robotic telescope (D=25cm)
located at the European Southern Observatory,
La Silla observatory, Chile.

The observations started 31.5s after the GRB trigger
(15.2s after the notice). The elevation of the field decreased from
8 degrees above horizon and weather conditions
were poor (due to the low elevation).

The first image is trailed with a duration of 60.0s
(see the description in Klotz et al., 2006, A&A 451, L39).
We do not detect any OT in the enhanced Swift-XRT position
(Evans et al. GCNC 13603) with a limiting magnitude of:
t0+31.5s to t0+91.5s : R > 15.5

Further images does not show OT anymore at about the
same limiting magnitude until 1500 seconds after the
trigger.

Magnitudes were estimated with the nearby USNO-B1 stars
and are not corrected for galactic dust extinction.

N.B. Galactic coordinates are lon=333.3260 lat= +3.6420
and the galactic extinction in R band is about 4 magnitudes
estimated from D. Schlegel et al. 1998ApJ...500..525S.

This message may be cited.

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 530267 (Marshall et al., GCN 13602
Loading...
 
 ) during the period
that the Swift BAT was observing gamma-ray emission.  The 10 s exposure
began at 07:09:38.7 UTC -- 1 s after the Swift trigger and 1 s before
the gamma-ray emission reached peak intensity.  We detect no new object
at the location of the refined Swift XRT location (Beardmore et al., GCN
13603
Loading...
 
 ) to a 3-sigma limiting magnitude of 10.3.  Our unfiltered images
are calibrated to the Tycho-2 V-band.

Weikang Zheng and Carl Akerlof (Umich), report on behalf of the ROTSE
collaboration:

We analyzed Fermi/LAT data of GRB 120807A (Marshall et al., GCN 13602
Loading...
 
 )
as a follow-up of routine search in Swift trigger catalogs in our LAT
data processing pipeline using both the matched filter technique
(Akerlof et al. 2010, ApJ, 725, L15; 2011 ApJ, 726, 22; 2012,
arXiv:1205.3066; Zheng et al. 2012, ApJ 745,72; 2012, arXiv:1203.5113)
and likelihood method. We do NOT detect high energy photon emission from
both methods by using a standard data selection (with Energy above 100
MeV) in 47.5s duration.

The burst location was about 50 degree from the LAT boresight, and the
zenith angle was about 96 degrees at trigger time. This location is very
close to Galactic plane (gb = 333.3 and gb= 3.6 degree).

Using the likelihood method, we estimated the upper limit in LAT energy
range (0.1 - 10 GeV) is 1.27e-05 (photons cm^-2 s^-1) by assuming a
spectral index of -2.2.

The pipeline result is given in the following link:
http://rotse.net/LAT/SwiftTriggers/366016180/

A.P. Beardmore (U. Leicester), P.A. Evans (U. Leicester), O.M.
Littlejohns (U. Leicester), G. Stratta (ASDC), P. D'Avanzo (INAF-OAB),
V. D'Elia (ASDC), J.A. Kennea (PSU), M.C. Stroh (PSU), D.N. Burrows
(PSU) and F.E. Marshall report on behalf of the Swift-XRT team:

We have analysed 2.9 ks of XRT data for GRB 120807A (Marshall  et al.
GCN Circ. 13602
Loading...
 
 ), from 56 s to 75.9 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 Beardmore et al. (GCN. Circ
13603).

The light curve can be modelled with  a power-law decay with a decay
index of alpha=1.29 (+0.15, -0.16).

A spectrum formed from the PC mode data can be fitted with an absorbed
power-law with a photon spectral index of 2.3 (+/-0.3). The
best-fitting absorption column is  1.04 (+0.25, -0.22) x 10^22 cm^-2,
in excess of the Galactic value of 4.9 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 (1.4 x 10^-10) erg
cm^-2 count^-1. 

A summary of the PC-mode spectrum is thus:
Total column:	     1.04 (+0.25, -0.22) x 10^22 cm^-2
Galactic foreground: 4.9 x 10^21 cm^-2
Excess significance: 4.1 sigma
Photon index:	     2.3 (+/-0.3)

The results of the XRT-team automatic analysis are available at
http://www.swift.ac.uk/xrt_products/00530267.

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

GRB 120807A: Swift/UVOT Upper Limits

M. H. Siegel (PSU) and F. E. Marshall (NASA/GSFC)
report on behalf of the Swift/UVOT team:

The Swift/UVOT began settled observations of the field of GRB 120807A
75 s after the BAT trigger (Marshall et al., GCN Circ. 13602
Loading...
 
 ).
No optical afterglow consistent with the XRT position (Beardmore et al., 
GCN Circ. 13603
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

white_FC            75          225          147         >20.6
u_FC               288          537          246         >20.4
white               75         1884          431         >21.8
v                  618         1935          156         >19.6
b                  543         1860          136         >20.4
u                  288         1835          363         >20.7
w1                 668         1810          136         >20.3
m2                1591         1611           19         >18.8
w2                 593         1910          117         >19.9

The magnitudes in the table are not corrected for the Galactic extinction
due to the reddening of E(B-V) = 1.41 in the direction of the burst
(Schlegel et al. 1998).

Weikang Zheng and Carl Akerlof (Umich), report on behalf of the ROTSE
collaboration (the authors are not affiliated with the Fermi Collaboration),

The recent GCN Circulars we reported about Fermi-LAT upper limits for
GRB 120807A (GCN 13608
Loading...
 
 ), 120908A (GCN 13742
Loading...
 
 ), 120909A (GCN 13742
Loading...
 
 ), and
120911A (GCN 13752
Loading...
 
 ) contain an error about the upper limits estimation
due to a wrong method. We apologize for the confusion. We thank Giacomo
Vianello from LAT group for pointing it out and making suggestion to
correct it. We've updated our pipeline result with the appropriate
method (see The Fermi LAT team, Ackermann et al., 2012, ApJ, 754, 121).
We report the corrected upper limit result (100 MeV -300 GeV; T0-T0
+47.5s) for the 4 GRBs again:

GRB 120807A : 5.42e-05 ph/cm2/s
GRB 120908A : 1.79e-04 ph/cm2/s
GRB 120909A : 8.70e-05 ph/cm2/s
GRB 120911A : 3.81e-05 ph/cm2/s