GRB 130816A

S. T. Holland (STScI), P. D'Avanzo (INAF-OAB), N. Gehrels (NASA/GSFC),
J. A. Kennea (PSU), D. Malesani (DARK/NBI), V. Mangano (PSU),
C. B. Markwardt (NASA/GSFC), D. M. Palmer (LANL),
M. Stamatikos (OSU/NASA/GSFC) and T. N. Ukwatta (MSU) report on behalf
of the Swift Team:

At 01:46:55 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 130816A (trigger=566545).  Swift slewed immediately to the burst. 
The BAT on-board calculated location is 
RA, Dec 197.167, -58.948 which is 
   RA(J2000) = 13h 08m 40s
   Dec(J2000) = -58d 56' 51"
with an uncertainty of 3 arcmin (radius, 90% containment, including 
systematic uncertainty).  The BAT light curve showed a single-peaked
structure with a duration of about 10 sec.  The peak count rate
was ~1500 counts/sec (15-350 keV), at ~0 sec after the trigger. 

The XRT began observing the field at 01:48:23.2 UT, 87.5 seconds after
the BAT trigger. Using promptly downlinked data we find an uncatalogued
X-ray source with an enhanced position: RA, Dec 197.1399, -58.9452
which is equivalent to:
   RA(J2000)  = 13h 08m 33.59s
   Dec(J2000) = -58d 56' 42.6"
with an uncertainty of 2.2 arcseconds (radius, 90% containment). This
location is 51 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 (3.87 x
10^21 cm^-2, Kalberla et al. 2005), with an excess column of 4
(+4.03/-3.22) x 10^21 cm^-2 (90% confidence). 

UVOT took a finding chart exposure of 150 seconds with the White filter
starting 91 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 large, but uncertain extinction expected. The
crowded field also makes the identification of a new source more difficult. 

Burst Advocate for this burst is S. T. Holland (sholland AT stsci.edu). 
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.)

S. Covino, D. FUgazza, V. D'Elia report on behalf of the REM team:

We observed the field of GRB 130816A (Holland et al., GCN 15097
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 ) simultaneously in the optical and near-infrared with the the 60-cm robotic telescope REM at La Silla Observatory (Chile). The observations started at 01:47:56 UT, about 1 min after the GRB.

We detect a faint source compatible with the XRT position and not present in the 2MASS catalogue with coordinates:

RA (J2000) = 13:08:33.80
DEC (J2000) = -58:56:41.2

with an estimated uncertainty of +- 0.5 arcsec.
Preliminary photometry indicates that the sources was at H = 15.0 +- 0.20 (Vega) about 100 s after the burst. 

Further observations are in progress to assess its variability.

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

Using 1820 s of XRT Photon Counting mode data and 1 UVOT
images for GRB 130816A, 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 = 197.14081, -58.94476 which is equivalent
to:

RA (J2000): 13h 08m 33.79s
Dec (J2000): -58d 56' 41.1"

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.

K. Varela (MPE Garching), D.A. Kann, S. Klose (both TLS Tautenburg), 
J. Elliott and J. Greiner (both MPE Garching) report on behalf of 
the GROND team:
  
We observed the field of GRB 130816A (Holland et al., GCN #15097
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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 01:49 UT on 16 August 2013, 3 min after the GRB
trigger. We confirm the presence of the NIR source inside the 2.2 arcsec
Swift-XRT error circle (Holland et al.) found by Covino et al. 
(GCN 15098
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 ).
  
Based on the first 140 sec g'r'i'z and 240 sec JHK exposure,
we estimate preliminary magnitudes (all in AB) of      
  
g' = 21.8 +/- 0.2 mag,
r' = 20.3 +/- 0.1 mag,
i' = 19.5 +/- 0.1 mag,         
z' = 18.9 +/- 0.1 mag,         
J = 18.0 +/- 0.1 mag,
H = 17.4 +/- 0.1 mag, and      
K = 17.1 +/- 0.1 mag,
  
calibrated against GROND zero points (g'r'i'z') and 2MASS (JHK).
Correcting for the Galactic foreground extinction corresponding to 
a reddening of E_(B-V)= 0.80 in the direction of the burst 
(Schlegel et al. 1998), the SED is well fit with a powerlaw of
slope 0.8, typical of GRB afterglows.

The object rapidly faded (by about 1.5 mag) during the following 
40 min., leaving no doubt that this is the afterglow of GRB 130816A.

G. Fitzpatrick (UCD) and G. Younes (NASA/USRA)
report on behalf of the Fermi GBM Team:

At 01:46:28.52 UT on 16 August 2013, the Fermi Gamma-Ray Burst Monitor
triggered and located the precursor to GRB130816A (trigger
398310391/130816074)
which was detected by the Swift/BAT (Holland et al. 15097, GCN 14527
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 ).
The GBM on-ground location is consistent with the Swift position.

The GBM light curve consists of the precursor and the main pulse
with a duration (T90) of about 32  s (50-300 keV).
The time-averaged spectrum from T0+23 s to T0+32 s is
adequately fit by a simple power law function with index -1.83 +/- 0.05.

The event fluence (10-1000 keV) in this time interval is
(1.3 +/- 0.1)E-06 erg/cm^2. The 1-sec peak photon flux measured
starting from T0+27 s in the 10-1000 keV band is 1.9 +/- 0.2 ph/s/cm^2.

The spectral analysis results presented above are preliminary;
final results will be published in the GBM GRB Catalog.

T. Sakamoto (AGU), S. D. Barthelmy (GSFC),
W. H. Baumgartner (GSFC/UMBC),
J. R. Cummings (GSFC/UMBC), E. E. Fenimore (LANL),
N. Gehrels (GSFC), S. T. Holland (STScI),
H. A. Krimm (GSFC/USRA), A. Y. Lien (NASA/GSFC/ORAU),
C. B. Markwardt (GSFC), D. M. Palmer (LANL),
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-240 to T+962 sec from
the recent telemetry downlink, we report further
analysis of BAT GRB 130816A (trigger #566545)
(Holland , et al., GCN Circ. 15097
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 ). The BAT
ground-calculated position is
RA, Dec = 197.093, -58.996 deg which is
   RA(J2000)  =  13h 08m 22.3s
   Dec(J2000) = -58d 59' 46.8"
with an uncertainty of 2.6 arcmin, (radius, sys+stat,
90% containment). The partial coding was 35%.

BAT mask-weighted light curve shows a two-peak structure.
The first peak starts around T-28 sec and lasts for about
5 sec. The second peak starts around T-3 sec and ends
around T+3 sec. BAT triggered on the second peak
and the first peak may be considered as a precursor
to the burst. T90 (15-350 keV) is 29.97 +- 1.36 sec
(estimated error including systematics).

The time-averaged spectrum from T-28.06 to T+2.56 sec
is best fit by a simple power-law model.  The power
law index of the time-averaged spectrum is
1.86 +- 0.34.  The fluence in the 15-150 keV band
is 4.3 +- 1.0 x 10^-07 erg/cm2. The 1-sec peak photon
flux measured from T-0.04 sec in the 15-150 keV band
is 1.5 +- 0.2 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/566545/BA/

A. Maselli  (INAF-IASFPA), A. Melandri (INAF-OAB), B. Sbarufatti
(INAF-OAB/PSU), D.N. Burrows (PSU), J.A. Kennea (PSU), V. Mangano
(PSU), J.P. Osborne (U. Leicester), K.L. Page (U. Leicester), C. Pagani
(U. Leicester) and S.T. Holland report on behalf of the Swift-XRT team:

We have analysed 2.8 ks of XRT data for GRB 130816A (Holland  et al.
GCN Circ. 15097
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 ),  from 99 s to 11.2 ks after the  BAT trigger. The
data are entirely in Photon Counting (PC) mode. The enhanced XRT
position for this burst was given by Goad et al. (GCN. Circ 15100).

The light curve can be modelled with  a power-law decay with a decay
index of alpha=0.62 (+/-0.08).

A spectrum formed from the PC mode data can be fitted with an absorbed
power-law with a photon spectral index of 2.1 (+/-0.3). The
best-fitting absorption column is  6.2 (+2.0, -1.7) x 10^21 cm^-2, in
excess of 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 4.7 x 10^-11 (9.1 x 10^-11) erg
cm^-2 count^-1. 

A summary of the PC-mode spectrum is thus:
Total column:	     6.2 (+2.0, -1.7) x 10^21 cm^-2
Galactic foreground: 3.9 x 10^21 cm^-2
Excess significance: 2.3 sigma
Photon index:	     2.1 (+/-0.3)

If the light curve continues to decay with a power-law decay index of
0.62, the count rate at T+24 hours will be 7.8 x 10^-3 count s^-1,
corresponding to an observed (unabsorbed) 0.3-10 keV flux of 3.7 x
10^-13 (7.1 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/00566545.

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

S. T. Holland (STScI) reports on behalf of the Swift/UVOT team:

     The Swift/UVOT began settled observations of the field of GRB
130816A starting 91 s after the BAT trigger (Holland et al. 2013, GCNC
15097).  We do not detect any new source consistent with the REM
afterglow position (Covino et al. 2013, GCNC 15098) 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)       91        241         147    >20.8
    u (FC)      303        554         246    >19.9
---------------------------------------------------
    v           633       1924         156    >19.2
    b           559       1850         136    >20.0
    u           707       1825         117    >19.5
 uvw1           682       1801         117    >19.3
 uvm2           658       1944         151    >19.4
 uvw2           609       1900         156    >19.7
white           584       1875         284    >21.1
---------------------------------------------------

     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) = 0.70 mag (Schlafly et al. 2011, ApJS, 737,
103).  GRB 130816A was 4 degrees above the Galactic Plane, so this
extinction value is highly uncertain.