GRB 170816A

O.J. Roberts (USRA), C. Meegan (UAH) and A. von Kienlin (MPE) report on behalf of the Fermi GBM Team:

"At 14:23:03.96 UT on 16 August 2017, the Fermi Gamma-Ray Burst Monitor
triggered and located GRB 170816A (trigger 524586188 / 170816599).
The on-ground calculated location, using the GBM trigger
data, is RA = 351.4, DEC = +19.1, with an uncertainty
of 2.2 degrees (radius, 1-sigma containment,
statistical only; there is additionally a systematic
error which we have characterized as a core-plus-tail model, with 90% of
GRBs having a 3.7 deg error and a small tail suffering a larger than 10 deg
systematic error. [Connaughton et al. 2015, ApJS, 216, 32] ).

The initial angle from the Fermi LAT boresight to
the GBM best location is 97 degrees.

This burst was also independently detected by INTEGRAL SPI-ACS.

The GBM triggered on an initial bright peak that
was followed ~1 s later by a slightly dimmer peak. The
total duration (T90) was about 2 s (50-300 keV).
The time-averaged spectrum from T0-0.064 to T0+1.600 s is
best fit by a power law function with an exponential
high-energy cutoff.  The power law index is -0.5 +/- 0.1  and
the cutoff energy, parameterized as Epeak, is 1250.00 +/- 150.00 keV

The event fluence (10-1000 keV) in this time interval is
(4.0+/- 0.2)E-06 erg/cm^2. The 1-sec peak photon flux measured
starting from T0-0.45 s in the 10-1000 keV band
is 7.3 +/- 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. Kozlova, S. Golenetskii, R. Aptekar, D. Frederiks, D. Svinkin,
and T. Cline on behalf of the Konus-Wind team,

K. Hurley, on behalf of the IPN,

V. Connaughton, M. S. Briggs, C. Meegan, V. Pelassa,
and A. Goldstein, on behalf of the Fermi GBM team,

A. von Kienlin, X. Zhang, A. Rau, V. Savchenko, E. Bozzo,
and C. Ferrigno, on behalf of the INTEGRAL SPI-ACS GRB team, and

S. Barthelmy, J. Cummings, H. Krimm, and D. Palmer,
on behalf of the Swift-BAT team, report:

A short-duration, hard-spectrum GRB 170816A was detected by
by Fermi (GBM; Roberts et al., GCN 21504
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 ), Konus-Wind, INTEGRAL
(SPI-ACS), and Swift (BAT), so far, at about 51784 s UT (14:23:04).
The burst was outside the coded field of view of the BAT.

We have triangulated it to a preliminary, 3 sigma error box whose 
coordinates are:
---------------------------------------------
   RA(2000), deg                 Dec(2000), deg
  ---------------------------------------------
  Center:
   350.841 (23h 23m 22s) +12.853 (+12d 51' 11")
  Corners:
   349.856 (23h 19m 25s) +13.372 (+13d 22' 19")
   352.036 (23h 28m 09s) +12.535 (+12d 32' 07")
   351.782 (23h 27m 08s) +12.294 (+12d 17' 38")
   349.591 (23h 18m 22s) +13.118 (+13d 07' 06")
  ---------------------------------------------
The error box area is 2650 sq. arcmin, and its maximum
dimension is 2.45 deg (the minimum one is 19 arcmin).
The Sun distance was 144 deg.

This box may be improved.

A triangulation map is posted at
http://www.ioffe.ru/LEA/GRBs/GRB170816_T51789/IPN

The Konus-Wind time history and spectrum will be given in a forthcoming
GCN Circular.

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

The long-duration GRB 170816A (Roberts et al., GCN Circ. 21504
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 ; Kozlova et al.,
GCN Circ. 21517
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 ) triggered the CALET Gamma-ray Burst Monitor (CGBM)
at 14:23:03.81 on 16 August 2017.  The burst signal was clearly seen by the SGM
instrument.

The light curve of the SGM shows a bright single peak.  The emission starts at
T+0.1 sec, peaks at T+0.3 sec and ends at T+0.5 sec.  The T90 duration measured
by the SGM data is 0.25 +- 0.13 sec (40-1000 keV).

The light curve is available at

http://cgbm.calet.jp/cgbm_trigger/flight/1186927993/

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

D. Frederiks, S. Golenetskii, R.Aptekar, P. Oleynik, M. Ulanov,
D. Svinkin, A. Tsvetkova, A.Lysenko, A. Kozlova, and T. Cline,
on behalf of the Konus-Wind team, report:

The short/hard GRB 170816A
(Fermi GBM detection: Roberts et al., GCN 21504
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 ;
IPN triangulation: Kozlova et al., GCN 21517
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 ;
CALET Gamma-Ray Burst Monitor detection: Ishizaki et al., GCN 21615
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 )
triggered Konus-Wind at T0=51789.108 s UT (14:23:09.108).

The burst light curve shows a bright, multi-peaked pulse
which started at ~T0-0.064 s and had a total duration of ~0.3 s.
A weaker count rate increase is also visible around ~T0+1.5 s
The emission is seen up to ~10 MeV.

As observed by Konus-Wind, the burst had a fluence of
6.6(-2.4, +4.2)x10^-6 erg/cm2 and a 16-ms peak energy flux,
measured from T0+0.175s of (5.9 �� 0.7)x10^-5 erg/cm2
(both in the 20 keV - 10 MeV energy range).

The time-integrated spectrum (measured from T0 to T0+8.448 s)
is best fit in the 20 keV - 15 MeV range by a cutoff power-law
(CPL) function with the following model parameters:
the photon index alpha = -0.87(-0.36,+0.60),
and the peak energy Ep = 1156(-556,+1626) keV,
chi2 = 86/98 dof.
Fitting this spectrum with the GRB (Band) function yields
the same alpha and Ep, and an upper limit on beta of -1.9,
chi2 = 86/97 dof.

The spectrum near the peak count rate (measured from T0+0.128
to T0+0.192 s) is best fit in the 20 keV - 15 MeV range
by the CPL function with the following model parameters:
the photon index alpha = +0.49(-0.50,+0.66),
and the peak energy Ep = 1339(-285,+462) keV,
chi2 = 17/19 dof.
Fitting this spectrum with the GRB (Band) function yields
the same alpha and Ep, and an upper limit on beta of -1.6,
chi2 = 17/18 dof.

The Konus-Wind light curve of this GRB is available at
http://www.ioffe.ru/LEA/GRBs/GRB170816_T51789/

All the quoted errors are estimated at the 90% confidence level.
All the presented results are preliminary.

[GCN OPS NOTE(21aug17): Per R.Hamberg's request, in the 2ndline
the Hamburg citation was changed to Roberts.]