GRB 170808B

P Veres and C Meegan (both UAH)
report on behalf of the Fermi GBM Team:

"At 22:27:43.10 UT on 8 August 2017, the Fermi Gamma-Ray Burst Monitor
triggered and located GRB 170808B (trigger 523924068 / 170808936).

The on-ground calculated location, using the GBM trigger
data, is RA = 146.49, DEC = -2.96 (J2000 degrees,
equivalent to 09 h 46 m, -02 d 58 '), with an uncertainty
of 1 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] ).

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

The trigger resulted in an Autonomous Repoint Request (ARR)
by the GBM Flight Software owing to the high fluence
of the GRB. This ARR was accepted and the spacecraft slewed to the GBM in-flight
location. The initial angle from the Fermi LAT boresight to
the GBM ground best location is 69 degrees.

The GBM light curve shows multiple overlapping pulses
with a duration (T90) of about 17.7 s (50-300 keV).
The time-averaged spectrum from T0 to T0+27.1 s is
best fit by a Band function with Epeak = 262 +/- 5 keV,
alpha = -1.01+/- 0.01, and beta = -2.30 +/- 0.03.

The event fluence (10-1000 keV) in this time interval is
(1.176 +/- 0.005)E-4 erg/cm^2. The 1-sec peak photon flux measured
starting from T0+15.9 s in the 10-1000 keV band
is 169.4 +/- 0.7 ph/s/cm^2.


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

F. Longo (University and INFN, Trieste) and D. Kocevski (NASA MSFC) report on behalf of the Fermi-LAT team:

At 22:27:43.10 UT on August 08, 2017, Fermi-LAT detected high-energy emission from GRB 170808B, which was also detected by Fermi-GBM (Veres and Meegan GCN 21429
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 ). 
The best LAT on-ground location is found to be
RA, Dec  145.66, 2.18 deg, J2000
with an error radius of 0.34 deg (90% containment, statistical error only). This was 69 deg from the LAT boresight at the time of the trigger and triggered an autonomous repoint of the spacecraft.
The data from the Fermi-LAT show a significant increase in the event rate that is spatially and temporally correlated with the GBM detection with high significance.
The highest-energy photon is a 1.62 GeV event which is observed 162 seconds after the GBM trigger.
A Swift ToO has been requested for this burst.
The Fermi-LAT point of contact for this burst is Francesco Longo (francesco.longo@ts.infn.it).
The Fermi-LAT is a pair conversion telescope designed to cover the energy band from 20 MeV to greater than 300 GeV. It is the product of an international collaboration between NASA and DOE in the U.S. and many scientific institutions across France, Italy, Japan and Sweden.

[GCN OPS NOTE(09aug17):  Per author's request, the extraneous url listed in the original distribution has been removed.]

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

The long-duration, very bright GRB 170808B
(Fermi GBM observation: Veres et al., GCN 21429
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 ;
Fermi LAT Detection: Longo et al., GCN 21430
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 )
triggered Konus-Wind at T0=80859.187 s UT (22:27:39.187).

The burst light curve shows a double-peaked structure
which starts at ~T0-2.3 s and has a total duration of ~18.5 s.
The emission is seen up to ~10 MeV.

As observed by Konus-Wind, the burst
had a fluence of 2.20(-0.08,+0.08)x10^-4 erg/cm2,
and a 64-ms peak flux, measured from T0+15.008 s,
of 7.54(-1.02,+1.03)x10^-5 erg/cm2/s
(both in the 20 keV - 10 MeV energy range).

The time-averaged spectrum of the burst
(measured from T0 to T0+23.808 s)
is best fit in the 20 keV - 10 MeV range
by the GRB (Band) model with the following parameters:
the low-energy photon index alpha = -0.92(-0.06,+0.07),
the high energy photon index beta = -2.33(-0.09,+0.07),
the peak energy Ep = 238(-16,+17) keV
(chi2 = 96/98 dof)

The spectrum near the maximum count rate
(measured from T0+14.848 to T0+15.616 s)
is best fit in the 20 keV - 10 MeV range
by the GRB (Band) model with the following parameters:
the low-energy photon index alpha = -0.52(-0.12,+0.13),
the high energy photon index beta = -2.45(-0.13,+0.10),
the peak energy Ep = 282(-26,+29) keV
(chi2 = 80/67 dof)

The Konus-Wind light curve of this GRB is available at
http://www.ioffe.ru/LEA/GRBs/GRB170808_T80859/

All the quoted errors are at the 90% confidence level.
All the quoted values are preliminary.