GRB 130806A

B.P. Gompertz (U Leicester), D. N. Burrows (PSU),
N. Gehrels (NASA/GSFC), J. A. Kennea (PSU),
H. A. Krimm (CRESST/GSFC/USRA), F. E. Marshall (NASA/GSFC),
C. J. Mountford (U Leicester), K. L. Page (U Leicester),
D. M. Palmer (LANL), M. H. Siegel (PSU), M. Stamatikos (OSU/NASA/GSFC)
and C. A. Swenson (PSU) report on behalf of the Swift Team:

At 02:51:33 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 130806A (trigger=565562).  Swift slewed immediately to the burst. 
The BAT on-board calculated location is 
RA, Dec 35.872, +67.530 which is 
   RA(J2000) = 02h 23m 29s
   Dec(J2000) = +67d 31' 48"
with an uncertainty of 3 arcmin (radius, 90% containment, including 
systematic uncertainty).  The BAT light curve showed a double-peaked
structure with a duration of about 10 sec.  The peak count rate
was ~3000 counts/sec (15-350 keV), at ~0 sec after the trigger. 

The XRT began observing the field at 02:52:40.2 UT, 66.2 seconds after
the BAT trigger. Using promptly downlinked data we find a possible
X-ray source located at RA, Dec 35.92827, 67.53242 which is equivalent
to:
   RA(J2000)  = 02h 23m 42.8s
   Dec(J2000) = 67d 31' 56.7"
with an uncertainty of 9.0 arcseconds (radius, 90% containment). This
location is 78 arcseconds from the BAT onboard position, within the
BAT error circle. We cannot determine whether the source is
fading at the present time. 

UVOT took a finding chart exposure of 150 seconds with the White filter
starting 68 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 19.6 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 mag. No
correction has been made for the expected extinction corresponding to E(B-V) of
1.19. 

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.)

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

Using 1580 s of XRT Photon Counting mode data and 4 UVOT
images for GRB 130806A, 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 = 35.92894, +67.53196 which is equivalent
to:

RA (J2000): 02h 23m 42.95s
Dec (J2000): +67d 31' 55.1"

with an uncertainty of 2.2 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.

A. Y. Lien (NASA/GSFC/ORAU), S. D. Barthelmy (GSFC), J. R. Cummings (GSFC/UMBC),
N. Gehrels (GSFC), B.P. Gompertz (U Leicester), H. A. Krimm (GSFC/USRA),
C. B. Markwardt (GSFC), D. M. Palmer (LANL), T. Sakamoto (AGU),
M. Stamatikos (OSU), T. N. Ukwatta (MSU) (i.e. the Swift-BAT team):

Using the data set from T-61 to T+242 sec from the recent telemetry downlink,
we report further analysis of BAT GRB 130806A (trigger #565562)
(Gompertz, et al., GCN Circ. 15071
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 ).  The BAT ground-calculated position is
RA, Dec = 35.907, 67.525 deg which is
     RA(J2000)  =  02h 23m 37.7s
     Dec(J2000) = +67d 31' 30.5"
with an uncertainty of 1.6 arcmin, (radius, sys+stat, 90% containment).
The partial coding was 95%.

The mask-weighted light curves shows a faint initial 2-sec long peak
starting at T-5 sec, followed by the main peak from T-1 to T+2 sec.
T90 (15-350 keV) is 6.1 +- 0.5 sec (estimated error including systematics).

The time-averaged spectrum from T-4.5 to T+2.2 sec is best fit by a simple
power-law model.  The power law index of the time-averaged spectrum is
2.50 +- 0.22.  The fluence in the 15-150 keV band is 1.7 +- 0.2 x 10^-07
erg/cm2. The 1-sec peak photon flux measured from T+0.32 sec in the 15-150 keV
band is 1.3 +- 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/565562/BA/

We note that the fluence ratio in a simple power-law fit between the
25-50 keV band and the 50-100 keV band is 1.41.  This fluence ratio is larger
than 1.32 which can be achieved in the Band function of alpha=-1.0, beta=-2.5,
and Epeak=30 keV.  Thus, preliminary analysis shows that Epeak of the burst
is very likely around or below 30 keV.  Therefore the burst can be classified
as an X-ray flash (e.g. Sakamoto et al. 2008, ApJ, 679, 570).  A fit to a Band
model gives nearly the same reduced chi-squared as a simple power=law fit.  The
Band fit gives Epeak = 18.9 (+3.2, -5.8) and beta = -2.6 � 0.3.  The alpha
parameter is not constrained by the fit.

D. Kuroda, K. Yanagisawa, Y. Shimizu, H. Toda (OAO, NAOJ),
S. Nagayama (NAOJ), M. Yoshida (Hiroshima), K. Ohta (Kyoto)
and N. Kawai(Tokyo Tech)
report on behalf of MITSuME collaboration:

We observed the field of GRB 130806A (Gompertz et al., GCNC 15071)
with the optical three color (g', Rc and Ic) CCD camera attached
to the MITSuME 50cm telescope of Okayama Astrophysical Observatory.

The observation started on 2013-08-06 12:29:43 UT (~9.6 h after the burst).
We did not find any new point source within the enhanced XRT error circle
(Beardmore et al., GCNC 15072) in all the three bands.

Three sigma upper limits of the OT are listed below.
We used GSC 2.3 catalog for flux calibration.

#T0+[day]  MID-UT    T-EXP[sec]   g'     Rc     Ic
-----------------------------------------------------
0.54100    15:50:36    4020.0   >19.4  >19.5  >18.7
-----------------------------------------------------
T0+ : Elapsed time after the burst [day]
T-EXP: Total Exposure time [sec]

K.L. Page (U. Leicester) and B.P. Gompertz (U Leicester) report on
behalf of the Swift-XRT team:

We have analysed 12 ks of XRT data for GRB 130806A (Gompertz  et al.
GCN Circ. 15071
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 ),  from 77 s to 57.9 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
15072).

The light curve can be modelled with  a power-law decay with a decay
index of alpha=0.57 (+0.08, -0.09).

A spectrum formed from the PC mode data can be fitted with an absorbed
power-law with a photon spectral index of 1.6 (+0.6, -0.5). The
best-fitting absorption column is  6.8 (+4.7, -2.9) x 10^21 cm^-2,
consistent with the Galactic value of 3.9 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 6.1 x 10^-11 (9.0 x
10^-11) erg cm^-2 count^-1. 

A summary of the PC-mode spectrum is thus:
Total column:	     6.8 (+4.7, -2.9) x 10^21 cm^-2
Galactic foreground: 3.9 x 10^21 cm^-2
Excess significance: <1.6 sigma
Photon index:	     1.6 (+0.6, -0.5)

If the light curve continues to decay with a power-law decay index of
0.57, the count rate at T+24 hours will be 2.8 x 10^-3 count s^-1,
corresponding to an observed (unabsorbed) 0.3-10 keV flux of 1.7 x
10^-13 (2.5 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/00565562.

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

T. Yoshii, K. Ito, Y. Saito, Y. Yano, R. Usui, Y. Tachibana, 
S. Kurita, Y. Yatsu, and N. Kawai (Tokyo Tech)
report on behalf of the MITSuME collaboration:

We observed the field of GRB 130806A (B.P. Gompertz et al., GCNC 15071) with the 
optical three color (g', Rc, and Ic) CCD cameras attached to the MITSuME 50 cm
telescope of Akeno Observatory, Yamanashi, Japan.

The observation started on 2013-08-06 14:11:23 UT ( ~11.3 h afterthe burst).
And we could not find any new point source within the XRT
error circle (A.P. Beardmore et al., GCNC 15072) in all the three bands.

The results of photometry (3 sigma upper limits) are listed below.
We used GSC2.3 catalog for flux calibration.


T0+[hour]      MID-UT        T-EXP[sec]           g'                Rc                Ic
----------------------------------------------------------------------------------------------------
   ~15.0         17:50:01          5580               >21.3         >20.4           >19.7
----------------------------------------------------------------------------------------------------
T0+ : Elapsed time after the burst [hour]
T-EXP: Total Exposure time [sec]

S. T. Holland (STScI) 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
130806A starting 69 s after the BAT trigger (Gompertz et al. 2013,
GCNC 15071).  We do not detect any new source consistent with the
UVOT-enhanced XRT position (Beardmore et al. 2013, GCNC 15072) in any
of the UVOT exposures.  Preliminary 3-sigma upper limits using the
UVOT photometric system (Breeveld et al. 2011, AIP Conf. Proc. 1358,
373) for the finding chart (FC) exposures and initial summed exposures
are presented below.

-------------------------------------------------
Filter      TSTART      TSTOP   Exposure      Mag
-------------------------------------------------
white (FC)      69        218        147    >20.6
   u (FC)     282        305         23    >18.2
-------------------------------------------------
   b         3571     11,831       1028    >21.3           
   u         4801     11,172       1082    >21.4
   v         4187       5823        393    >19.9
uvw1         4597     10,259       1116    >21.2
uvm2         4391     15,843       1066    >20.9
uvw2         3982       5618        393    >20.7
white         3776       5411        393    >21.8
-------------------------------------------------

    The quoted upper limits have not been corrected for the expected
extinction due to the Galactic reddening along the line of sight to
this burst of E(B-V) = 1.02 mag (Schlafly et al. 2011, ApJS, 737,
103).  GRB 130806A was 6 degrees above the Galactic Plane, so this
extinction value is highly uncertain.