GRB 170826A

S. Poolakkil (UAH), E. Bissaldi (Politecnico & INFN Bari) and C. Meegan
(UAH)
report on behalf of the Fermi GBM Team:

"At 08:51:07.51 UT on 26 August 2017, the Fermi Gamma-Ray Burst Monitor
triggered and located GRB 170826A (trigger 525430272/ 170826369).

The on-ground calculated location, using the GBM trigger
data, is RA = 82.4, DEC = 32.8, with an uncertainty
of 7.2 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 angle from the Fermi LAT boresight at the GBM trigger time is 101
degrees.

The GBM triggered on a single pulse over a
total duration (T90) of about 0.2 s (50-300 keV).
The time-averaged spectrum from T0-0.2 to T0+0.1 s is
best fit by a power law function with an exponential
high-energy cutoff. The power law index is -1.05 +/- 0.11 and
the cutoff energy, parameterized as Epeak, is 685 +/- 236 keV.

The event fluence (10-1000 keV) in this time interval is
 (8.2 +/- 0.6)E-07 erg/cm^2. The 64 ms peak photon flux measured
starting from T0+0.1 s in the 10-1000 keV band
is 18.6 +/- 2.1 ph/s/cm^2.

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

-- 
Suraj Poolakkil
Fermi GBM Graduate Research Assistant
Dept. of Space Science
University of Alabama in Huntsville

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, and

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

The short GRB 170826A (Poolakkil et al., GCN Circ. 21715
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 ) was detected
by Fermi (GBM trigger 525430272), Konus-Wind, and INTEGRAL (SPI-ACS)
at about 31868 s UT (08:51:08).

We have triangulated it to a preliminary, 3 sigma error box whose 
coordinates are:
  ---------------------------------------------
   RA(2000), deg                 Dec(2000), deg
  ---------------------------------------------
  Center:
    64.338 (04h 17m 21s) +21.074 (+21d 04' 26")
  Corners:
    65.488 (04h 21m 57s) +16.011 (+16d 00' 39")
    63.331 (04h 13m 19s) +25.959 (+25d 57' 32")
    63.050 (04h 12m 12s) +26.051 (+26d 03' 05")
    65.226 (04h 20m 54s) +16.124 (+16d 07' 27")
  ---------------------------------------------
The error box area is 2.3 sq. deg, and its maximum
dimension is 10.29 deg (the minimum one is 13.56 arcmin).
The Sun distance was 87 deg.

This box may be improved.

A triangulation map is posted at
http://www.ioffe.ru/LEA/GRBs/GRB170826_T31868/IPN/

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

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 GRB 170826A
(Fermi GBM observation: Poolakkil et al., GCN Circ. 21715
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 ;
IPN Triangulation: Svinkin et al., GCN Circ. 21734
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 )
triggered Konus-Wind at T0=31868.408 s UT (08:51:08.408).

The burst light curve shows a single pulse which starts
at ~T0-0.250 s and has a total duration of ~0.3 s.

As observed by Konus-Wind, the burst
had a fluence of 1.1(-0.2,+1.1)x10^-6 erg/cm2,
and a 16-ms peak flux, measured from T0-0.032 s,
of 1.1(-0.4,+1.2)x10^-5 erg/cm2/s
(both in the 20 keV - 10 MeV energy range).

Modeling the KW 3-channel time-integrated spectrum
(from T0-0.248 s to T0+0.040 s)
by a power law with exponential cutoff model:
dN/dE ~ (E^alpha)*exp(-E*(2+alpha)/Ep)
yields alpha = -1.15(-0.26,+0.46) and Ep = 682(-261,+3960) keV.

The Konus-Wind light curve of this GRB is available at
http://www.ioffe.ru/LEA/GRBs/GRB170826_T31868/

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