GRB 171108A

R. Hamburg (UAH) and C. Meegan (UAH)
report on behalf of the Fermi GBM Team:

"At 15:44:46.50 UT on 8 November 2017, the Fermi Gamma-Ray Burst Monitor
triggered and located GRB 171108A (trigger 531848691 / 171108656).
The on-ground calculated location, using the GBM trigger
data, is RA = 115.0, DEC = +39.8 (J2000 degrees,
equivalent to 07 h 40 m, 39 d 48'), with an uncertainty
of 4.7 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]).

Although this GRB is soft in nature, the trigger resulted in an
Autonomous Repoint Request (ARR) by the GBM Flight Software
owing to high peak flux in the background before trigger time.
This ARR was accepted and the spacecraft slewed to the GBM in-flight
location. The initial angle from the Fermi LAT boresight to
the best GBM ground location is 84 degrees.

The GBM light curve shows a bright peak
with a duration (T90) of about 0.03 s (50-300 keV).
The time-averaged spectrum from T0-0.064 s to T0+0.064 s is
adequately fit by a power law function with an exponential
high-energy cutoff and a blackbody. The power law index is -1.6 +/- 0.4,
the cutoff energy, parameterized as Epeak, is 47 +/- 28 keV,
and the temperature is 18.0 +/- 3.0 kT.

The event fluence (10-1000 keV) in this time interval is
(1.0 +/- 0.1)E-05 erg/cm^2. The 0.064-sec peak photon flux measured
starting from T0-0.064 s in the 10-1000 keV band
is 687 +/- 166 ph/s/cm^2.

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

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

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

The short-duration GRB 171108A (Hamburg and Meegan, GCN Circ. 22112
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 ) was 
detected by Fermi (GBM trigger 531848691), Konus-Wind, and Swift (BAT) 
at about 56686 s UT (15:44:46).
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:
   109.952 (07h 19m 48s) +29.091 (+29d 05' 28")
  Corners:
   112.518 (07h 30m 04s) +45.785 (+45d 47' 05")
   107.816 (07h 11m 16s) +12.385 (+12d 23' 05")
   107.666 (07h 10m 40s) +12.387 (+12d 23' 12")
   112.309 (07h 29m 14s) +45.789 (+45d 47' 21")
  ---------------------------------------------
The error box area is 4.9 sq. deg, and its maximum
dimension is 33.6 deg (the minimum one is 8.8 arcmin).
The Sun distance was 116 deg.

A triangulation map is posted at
http://www.ioffe.ru/LEA/GRBs/GRB171108_T56686/IPN

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

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 short-duration, soft-spectrum GRB 171108A
(Fermi GBM detection: Hamburg et al., GCN 22112
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 ;
IPN triangulation: Svinkin et al., GCN 22117
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 )
triggered Konus-Wind at T0=56686.93 s UT (15:44:46.930).

The burst light curve shows a single pulse
which starts at T0-22 ms and has a total duration of ~30 ms.

As observed by Konus-Wind, the burst
had a fluence of 2.73(-0.38,+0.48)x10^-7 erg/cm2,
and a 16-ms peak flux, measured from T0-0.016 s,
of 1.25(-0.23,+0.27)x10^-5 erg/cm2/s
(both in the 20 keV - 10 MeV energy range).

Since the most intense part of the burst was detected before
the trigger, the spectral analysis was performed using
the KW 3-channel light curve data.

Modeling the KW 3-channel time-integrated spectrum
(from T0-0.022 s to T0+0.008 s)
by a power law with exponential cutoff model:
dN/dE ~ (E^alpha)*exp(-E*(2+alpha)/Ep)
yields alpha = 0.86 (-1.20,+4.43), and Ep = 115 (-20,+30) keV.

Fitting this spectrum by a blackbody function
yields kT = 26.6 (-3.3, +4.3) keV.

The Konus-Wind light curve of this GRB is available at
http://www.ioffe.ru/LEA/GRBs/GRB171108_T56686/

The burst is not seen in the waiting mode data.

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