GRB 160820A

D. Svinkin, S. Golenetskii, R. Aptekar, D. Frederiks, A. Kozlova,
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, N. Gehrels, H. Krimm, and D. Palmer,
on behalf of the Swift-BAT team, report:

A short-duration, hard-spectrum GRB 160820A was detected by Fermi
(GBM; trigger 493386854), Konus-Wind, INTEGRAL (SPI-ACS),
and Swift (BAT) at about 42851 s UT (11:54:11).
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:
    11.338 (00h 45m 21s) +24.933 (+24d 55' 59")
  Corners:
     8.000 (00h 32m 00s) +28.159 (+28d 09' 33")
    15.644 (01h 02m 35s) +22.544 (+22d 32' 38")
    14.155 (00h 56m 37s) +21.358 (+21d 21' 28")
     6.447 (00h 25m 47s) +26.868 (+26d 52' 04")
  ---------------------------------------------
The error box area is 16.23 sq. deg, and its maximum
dimension is 9.4 deg (the minimum one is 1.82 deg).
The Sun distance was 123 deg.

This box may be improved.

A triangulation map is posted at
http://www.ioffe.ru/LEA/GRBs/GRB160820_T42855/IPN/

The time history and spectrum will be given in forthcoming GCN Circulars.

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

The short-duration, hard-spectrum GRB 160820A
(IPN triangulation: Svinkin et al., GCN 19850
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triggered Konus-Wind at T0=42855.115 s UT (11:54:15.115).

The burst light curve shows a single pulse with a total duration
of ~0.2 s.

As observed by Konus-Wind, the burst
had a fluence of 7.54(-0.86,+0.94)x10^-7 erg/cm2
and a 16-ms peak flux, measured from T0-0.058 s,
of 5.63(-1.50,+1.52)x10^-6 erg/cm2/s
(both in the 20 - 1000 keV energy range).

Since a major fraction of the burst counts was accumulated
before the trigger, the spectral analysis was performed using
the KW 3-channel light curve data.
Modeling the 3-channel time-integrated spectrum
(measured from T0-0.158 s to T0+0.074 s)
by the cutoff power law yields the following model parameters:
the photon index alpha=0.87(-0.78,+2.13),
and the peak energy Ep=383(-67,+73) keV.

The Konus-Wind light curve of this GRB is available at
http://www.ioffe.ru/LEA/GRBs/GRB160820_T42855/

All the quoted errors are at the 68% confidence level.
All the quoted values are preliminary.

H.-F. Yu (MPE) and C.A. Meegan (UAH)
report on behalf of the Fermi GBM Team:

"At 11:54:10.65 UT on 20 August 2016, the Fermi Gamma-Ray Burst Monitor
triggered and located GRB 160820A (trigger 493386854 / 160820496),
which was also detected by the Konus-Wind (Svinkin et al., GCN 19851
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and located by the Interplanetary Network (Svinkin et al., GCN 19850
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 ).
The GBM on-ground location is consistent with the IPN position.

The angle from the Fermi LAT boresight at the GBM trigger time is 63 degrees.

The GBM light curve shows a single pulse
with a duration (T90) of about 0.4 s (50-300 keV).
The time-averaged spectrum from T0-0.064 s to T0+0.192 s is
best fit by a Band function with Epeak = 810 +/- 200 keV,
alpha = -0.7 +/- 0.1, and beta = -2.6 +/- 0.8.

The event fluence (10-1000 keV) in this time interval is
(7.7 +/- 0.4)E-07 erg/cm^2. The 64-ms peak photon flux measured
starting from T0+0.000 s in the 10-1000 keV band
is 13 +/- 1 ph/s/cm^2.

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