GRB 160815A

S. Ricciarini (U of Florence), A. Yoshida, T. Sakamoto, Y. Kawakubo, M. Moriyama,
Y. Yamada (AGU), K. Yamaoka (Nagoya U), S. Nakahira (JAXA), I. Takahashi (IPMU),
Y. Asaoka, S. Ozawa, S. Torii (Waseda U), Y. Shimizu, T. Tamura (Kanagawa U),
W. Ishizaki (ICRR), M. L. Cherry (LSU), P. S. Marrocchesi (U of Siena)
and the CALET collaboration:

The long-duration GRB 160815A (Markwardt et al., GCN Circ. 19794
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 ;
Hamburg et al., GCN Circ. 19797
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 ) triggered the CALET Gamma-ray Burst Monitor
(CGBM) at 11:45:10.86 on 15 August 2016.  The burst signal was seen by
the SGM instrument.  Because of a problem in one of the ground alert processing
computer, the GCN notice was not distributed automatically for this event.

The light curve of the SGM shows several two peaks.  The whole emission starts
at T0 and ends at T+4 sec.  The two spikes peak at T+0.5 sec and T+3 sec.
The T90 duration measured by the SGM data is 3.6 +- 0.6 sec (40-100 keV).

The light curve is available at

http://cgbm.calet.jp/cgbm_trigger/flight/1155296575/

The CALET data used in this analysis are provided by the Waseda
CALET Operation Center located at the Waseda University.

L. P. Xin,   Y. J. Xiao,   X. M. Meng,   J. Y. Wei,   E. W. Liang,  X. G. Wang,
Y. G. Yang,  X. M. Lu,  L. Huang,   X. H. Han ,  H. B. Cai,   Y. L. Qiu,
J. Wang,   C. Wu,   J. S. Deng and H. L. Li  report:
 
We  observed  GRB 160815A (Markwardt et al. GCN 19794
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 )  with
GWAC-F60A 60cm optical telescope at 17:10:08 UT,  Aug. 15th 2016, 
about 5.41 hours after the burst. 

The optical afterglow (Marshall et al., GCN 19795
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 ; LaPorte et al., GCN 19081
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 ) 
was  not detected in our 20*300 sec stacked R-band  images  down to the 3 sigma 
limit  of  about 19.7 mag at the mid time  of 6.42 hours after the burst.
The brightness was calibrated by  USNO B1.0 stars.
 
GWAC-F60A is operated by Guangxi university and NAOC, CAS, 
at Xinglong observatory, China.

The message may be cited.

S.J. LaPorte (PSU) and C. B. Markwardt (NASA/GSFC)
report on behalf of the Swift/UVOT team:

The Swift/UVOT began settled observations of the field of GRB 160815A
90 s after the BAT trigger (Markwardt et al., GCN Circ. 19794
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 ). We detect a
fading source consistent with the XRT position (Beardmore et al. GCN Circ.
19796
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 ).

Preliminary detections using the UVOT photometric system (Breeveld et al.
2011, AIP Conf. Proc. 1358, 373) for the early exposures are:

Filter         T_start(s)   T_stop(s)  Exp(s)   Mag

white           90             239       146     18.17+-0.14   
white          582            5549       402    >19.72   
v              632            5960       274    >17.99   
b              557            5344       254    >18.64   
u              301            6449       554    >18.85   
uvw1           681            6370       432    >18.67   
uvm2           656            6165       274    >18.64   
uvw2           607            5755       274    >18.70   


The magnitude is not corrected for the Galactic extinction
due to the reddening of E(B-V) = 0.12 in the direction of the burst
(Schlegel et al. 1998).

A. Y. Lien (GSFC/UMBC), S. D. Barthelmy (GSFC), J. R. Cummings (GSFC/UMBC),
N. Gehrels (GSFC), H. A. Krimm (GSFC/USRA), C. B. Markwardt (GSFC),
D. M. Palmer (LANL), T. Sakamoto (AGU), M. Stamatikos (OSU), T. N. Ukwatta (LANL)
(i.e. the Swift-BAT team):
  
Using the data set from T-239 to T+963 sec from the recent telemetry downlink,
we report further analysis of BAT GRB 160815A (trigger #708598)
(Markwardt, et al., GCN Circ. 19794
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 ).  The BAT ground-calculated position is
RA, Dec = 288.616, 84.298 deg which is
    RA(J2000)  =  19h 14m 27.8s
    Dec(J2000) = +84d 17' 53.9"
with an uncertainty of 1.0 arcmin, (radius, sys+stat, 90% containment).
The partial coding was 41%.
  
The mask-weighted light curve shows several overlapping peaks starting
at T-7 sec and ending at T+11 sec.  Two main pulses peaks at T+0.3 sec
and T+2.5 sec.  T90 (15-350 keV) is 8.6 +- 1.8 sec (estimated error
including systematics).

The time-averaged spectrum from T-6.41 to T+5.20 sec is best fit by a power law
with an exponential cutoff.  This fit gives a photon index 0.96 +- 0.41,
and Epeak of 68 +- 16 keV (chi squared 48.11 for 56 d.o.f.).  For this
model the total fluence in the 15-150 keV band is 1.4 +- 0.1 x 10^-6 erg/cm2
and the 1-sec peak flux measured from T+2.14 sec in the 15-150 keV band is
4.7 +- 0.4 ph/cm2/sec.  A fit to a simple power law gives a photon index
of 1.72 +- 0.09 (chi squared 59.91 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/708598/BA/

V. D'Elia (ASDC), L.M. McCauley (PSU), J.A. Kennea (PSU), B. Sbarufatti
(INAF-OAB/PSU), P.A. Evans (U. Leicester), S.L. Gibson (U. Leicester),
J.P. Osborne (U. Leicester), A. D'Ai (INAF-IASFPA), A. Maselli 
(INAF-IASFPA) and C.B. Markwardt report on behalf of the Swift-XRT
team:

We have analysed 11 ks of XRT data for GRB 160815A (Markwardt et al.
GCN Circ. 19794
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 ), from 78 s to 34.8 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.
19796
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 ).

The light curve can be modelled with an initial power-law decay with an
index of alpha=6.1 (+1.9, -1.8), followed by a break at T+115 s to an
alpha of 0.88 (+/-0.03).

A spectrum formed from the WT mode data can be fitted with an absorbed
power-law with a photon spectral index	of 3.25 (+0.31, -0.26). The
best-fitting absorption column is  3.2 (+0.7, -0.6) x 10^21 cm^-2, in
excess of the Galactic value of 7.5 x 10^20 cm^-2 (Willingale et al.
2013). The PC mode spectrum has a photon index of 1.90 (+/-0.15) and a
best-fitting absorption column of 2.6 (+0.7, -0.6) x 10^21 cm^-2. The
counts to observed (unabsorbed) 0.3-10 keV flux conversion factor
deduced from this spectrum  is 3.8 x 10^-11 (5.3 x 10^-11) erg cm^-2
count^-1. 

A summary of the PC-mode spectrum is thus:
Total column:	     2.6 (+0.7, -0.6) x 10^21 cm^-2
Galactic foreground: 7.5 x 10^20 cm^-2
Excess significance: 5.1 sigma
Photon index:	     1.90 (+/-0.15)

If the light curve continues to decay with a power-law decay index of
0.88, the count rate at T+24 hours will be 0.013 count s^-1,
corresponding to an observed (unabsorbed) 0.3-10 keV flux of 4.9 x
10^-13 (6.7 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/00708598.

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

R. Hamburg (UAH)
reports on behalf of the Fermi GBM Team:

"At 11:45:11.64 UT on 15 August 2016, the Fermi Gamma-Ray Burst Monitor
triggered and located GRB 160815A (trigger 492954315 / 160815490)
which was also detected by the Swift/BAT
(Markwardt et al., GCN Circ. 19794
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 )
The GBM on-ground location is consistent with the Swift position.

The angle from the Fermi LAT boresight at the GBM trigger time is 37
degrees.

The GBM light curve consists of two peaks
with a duration (T90) of about 6.8 s (50-300 keV).
The time-averaged spectrum from T0-2.7 s to T0+5.5 s
is best fit by a power law function with an exponential
high-energy cutoff.  The power law index is -0.68 +/- 0.12 and
the cutoff energy, parameterized as Epeak, is 71 +/- 4 keV.

The event fluence (10-1000 keV) in this time interval is
(1.64 +/- 0.06)E-06 erg/cm^2. The 1-sec peak photon flux measured
starting from T0+1.9 s in the 10-1000 keV band
is 6.7 +/- 0.3 ph/s/cm^2.

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

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

Using 1093 s of XRT Photon Counting mode data and 2 UVOT
images for GRB 160815A, 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 = 288.54101, +84.31383 which is equivalent
to:

RA (J2000): 19h 14m 9.84s
Dec (J2000): +84d 18' 49.8"

with an uncertainty of 1.7 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.

F. E. Marshall (NASA/GSFC) and C. B. Markwardt (NASA/GSFC) 
report on behalf of the Swift/UVOT team:

The Swift/UVOT has discovered an optical afterglow for 
GRB 160815A (Markwardt et al., GCN Circ. 19794
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 ) in
an exposure with the white filter.

The preliminary UVOT position is:
   RA  (J2000) =  19:14:09.63 = 288.5401 (deg.)
   Dec (J2000) =  +84:18:50.4  =  84.3140 (deg.)
with an estimated uncertainty of 1.0 arcsec. (radius, 90% confidence).

The preliminary magnitude using the UVOT photometric system
(Breeveld et al. 2011, AIP Conf. Proc. 1358, 373) is:

Filter         T_start(s)   T_stop(s)    Exp(s)       Mag

white           863        1013          150          19.1

The magnitude is not corrected for the Galactic extinction
due to the reddening of E(B-V) = 0.12 in the direction of the burst
(Schlegel et al. 1998).

C. B. Markwardt (NASA/GSFC), P.A. Evans (U Leicester),
N. Gehrels (NASA/GSFC), J. A. Kennea (PSU),
F. E. Marshall (NASA/GSFC), B. Mingo (U Leicester),
K. L. Page (U Leicester), T. Sakamoto (AGU) and
B. Sbarufatti (INAF-OAB/PSU) report on behalf of the Swift Team:

At 11:45:11 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 160815A (trigger=708598).  Swift slewed immediately to the burst. 
The BAT location calculated from the downlinked detector histogram is 
RA, Dec 288.733, 84.282 which is 
   RA(J2000) = 19h 14m 56s
   Dec(J2000) = +84d 16m 55.2s
with an uncertainty of 3 arcmin (radius, 90% containment, including 
systematic uncertainty).  No BAT lightcurve is immediately available
due to a gap in TDRSS coverage. 

Using promptly downlinked data we find a fading, uncatalogued X-ray
source with an enhanced position: RA, Dec 288.5364, 84.3138 which is
equivalent to:
   RA(J2000)  = 19h 14m 08.73s
   Dec(J2000) = +84d 18' 49.8"
with an uncertainty of 2.0 arcseconds (radius, 90% containment). This
location is 134 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 (7.52 x
10^20 cm^-2, Willingale et al. 2013), with an excess column of 4.6
(+1.72/-1.57) x 10^21 cm^-2 (90% confidence). 

UVOT took a finding chart exposure of 250 seconds with the U filter starting
309 seconds after the BAT trigger. No credible afterglow candidate has been
found in the initial data products. Data from the 2.7'x2.7' sub-image are not
available at this time. The 8'x8' region for the list of sources generated
on-board covers none of the BAT error circle. No correction has been made for
extinction. 

Burst Advocate for this burst is C. B. Markwardt (Craig.Markwardt 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.)