GRB 130816B

M. Stamatikos (OSU/NASA/GSFC), P. D'Avanzo (INAF-OAB),
M. H. Siegel (PSU) and T. N. Ukwatta (MSU) report on behalf of the
Swift Team:

At 04:53:38 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 130816B (trigger=566561).  Swift slewed immediately to the burst. 
The BAT on-board calculated location is 
RA, Dec 170.093, -57.558 which is 
   RA(J2000) = 11h 20m 22s
   Dec(J2000) = -57d 33' 28"
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 20 sec.  The peak count rate
was ~2440 counts/sec (15-350 keV), at ~0 sec after the trigger. 

The XRT began observing the field at 04:54:48.8 UT, 70.2 seconds after
the BAT trigger. Using promptly downlinked data we find an uncatalogued
X-ray source located at RA, Dec 170.01845, -57.55829 which is
equivalent to:
   RA(J2000)  = 11h 20m 04.43s
   Dec(J2000) = -57d 33' 29.8"
with an uncertainty of 3.9 arcseconds (radius, 90% containment). This
location is 143 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 4.04
x 10^21 cm^-2 (Kalberla et al. 2005). 

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. Because of the density of
catalogued stars, further analysis is required to report an upper limit for any
afterglow in the region. No correction has been made for the large, but
uncertain extinction expected. 

Burst Advocate for this burst is M. Stamatikos (Michael.Stamatikos-1 AT 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.)

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

Using 1915 s of XRT Photon Counting mode data and 2 UVOT
images for GRB 130816B, 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 = 170.01621, -57.55740 which is equivalent
to:

RA (J2000): 11h 20m 3.89s
Dec (J2000): -57d 33' 26.7"

with an uncertainty of 1.9 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.

B.P. Gompertz (U. Leicester), V. D'Elia (ASDC), A. Maselli 
(INAF-IASFPA), A. Melandri (INAF-OAB), M.C. Stroh (PSU), D.N. Burrows
(PSU), J.A. Kennea (PSU), J.P. Osborne (U. Leicester), K.L. Page (U.
Leicester) and M. Stamatikos report on behalf of the Swift-XRT team:

We have analysed 7.7 ks of XRT data for GRB 130816B (Stamatikos  et al.
GCN Circ. 15099
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 ),  from 77 s to 24.0 ks after the  BAT trigger. The
data are entirely in Photon Counting (PC) mode. The enhanced XRT
position for this burst was given by Osborne et al. (GCN. Circ 15102).

The light curve can be modelled with  a power-law decay with a decay
index of alpha=0.98 (+0.13, -0.11).

A spectrum formed from the PC mode data can be fitted with an absorbed
power-law with a photon spectral index of 2.1 (+0.5, -0.4). The
best-fitting absorption column is  5.3 (+2.8, -1.3) x 10^21 cm^-2,
consistent with the Galactic value of 4.0 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 4.6 x 10^-11 (8.4 x
10^-11) erg cm^-2 count^-1. 

A summary of the PC-mode spectrum is thus:
Total column:	     5.3 (+2.8, -1.3) x 10^21 cm^-2
Galactic foreground: 4.0 x 10^21 cm^-2
Excess significance: <1.6 sigma
Photon index:	     2.1 (+0.5, -0.4)

If the light curve continues to decay with a power-law decay index of
0.98, the count rate at T+24 hours will be 5.8 x 10^-4 count s^-1,
corresponding to an observed (unabsorbed) 0.3-10 keV flux of 2.7 x
10^-14 (4.9 x 10^-14) erg cm^-2 s^-1.

The results of the XRT-team automatic analysis are available at
http://www.swift.ac.uk/xrt_products/00566561.

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

K. Varela (MPE Garching), S. Klose (TLS Tautenburg)
and J. Greiner (both MPE Garching) report on behalf of the GROND team:

We observed the field of GRB 130816B (Stamatikos et al., GCN #15099
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 )
simultaneously in g'r'i'z'JHKs 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 23:12 UT on 16 August 2013, 18.3 hours after the
GRB trigger. They were performed at an average seeing of 1.6" and at and
average airmass of 2.20. We find a source inside the 1.9" Swift-XRT error
circle (Osborne et al., GCN #15102
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 ) at coordinates

RA(J2000.0) = 11:20:03.96
DEC (J200.0) = -57:33:27.1

with an uncertainty of 0.5" in each coordinate.

Based on the first 460 sec g'r'i'z and 480 sec JHK exposure,
we estimate preliminary magnitudes (all in AB) of

g' > 23.5 mag
r' = 23.1 +/- 0.2 mag,
i' = 22.5 +/- 0.2 mag,
z' = 21.6 +/- 0.1 mag,
J = 20.5 +/- 0.3 mag,
H = 20.5 +/- 0.3 mag,
K = 19.9 +/- 0.4 mag,

calibrated against GROND zero points (griz) and 2MASS (JHK) and
are not corrected for the Galactic foreground extinction corresponding to
a reddening of E_(B-V)= 0.56 mag in the direction of the burst
(Schlegel et al. 1998).

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

Using the data set from T-240 to T+963 sec from
the recent telemetry downlink, we report further
analysis of BAT GRB 130816B (trigger #566561)
(Stamatikos, et al., GCN Circ. 15099
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 ). The BAT
ground-calculated position is
RA, Dec = 170.049, -57.527 deg which is
   RA(J2000)  =  11h 20m 11.8s
   Dec(J2000) = -57d 31' 37.7"
with an uncertainty of 1.6 arcmin, (radius,
sys+stat, 90% containment).The partial
coding was 98%.

BAT mask-weighted light curve shows a single peak
starting from ~T-10 sec peaking around T+0 sec
and ending at ~T+4 sec. T90 (15-350 keV) is
10.00 +- 3.61 sec (estimated error including
systematics).

The time-averaged spectrum from T-6.50 to T+6.50 sec
is best fit by a power law with an exponential cutoff.
This fit gives a photon index 0.45 +- 0.93, and
Epeak of 47.3 +- 10.8 keV (chi squared 35.98 for
56 d.o.f.). For this model the total fluence in
the 15-150 keV band is 2.7 +- 0.4 x 10^-07 erg/cm2
and the 1-sec peak flux measured from T+0.50 sec
in the 15-150 keV band is 0.9 +- 0.1 ph/cm2/sec.
A fit to a simple power law gives a photon index
of 1.82 +- 0.17 (chi squared 44.98 for 57 d.o.f.).
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/566561/BA/

S. T. Holland (STScI) and M. Stamatikos (OSU/NASA/GSFC)
report on behalf of the Swift/UVOT team:

     The Swift/UVOT began settled observations of the field of GRB
130816B starting 75 s after the BAT trigger (Stamatikos et al. 2013,
GCNC 15099).  We do not detect any new source consistent with the
GROND afterglow position (Varela et al. 2013, GCNC 15107) 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)       75        225         147    >20.7
    u (FC)      287        537         246    >19.9
---------------------------------------------------
    v           618     12,639        1295    >20.4
    b           543       7299         530    >20.7
    u           692     19,298         923    >20.5
 uvw1           667     18,676        1238    >20.8
 uvm2           642     13,534        1227    >20.8
 uvw2           593     24,128         882    >20.7
white           567       7498         672    >21.5
---------------------------------------------------

     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) = 0.50 mag (Schlafly et al. 2011, ApJS, 737,
103).  GRB 130816B was 3 degrees above the Galactic Plane, so this
extinction value is highly uncertain.