GRB 150819B

S. Golenetskii, R. Aptekar, V. Pal'shin, 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, 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-duration, very intense GRB 150819B has been detected by Fermi 
(GBM trigger 461673203 / 150819440), Konus-Wind, and INTEGRAL (SPI-ACS), 
so far, at about 37999 s UT (10:33:19).

We have triangulated it to a preliminary, 3 sigma error box whose 
coordinates are:
  ---------------------------------------------
   RA(2000), deg                 Dec(2000), deg
  ---------------------------------------------
  Center:
    59.386 (03h 57m 33s) +39.701 (+39d 42' 05")
  Corners:
    59.157 (03h 56m 38s) +40.372 (+40d 22' 21")
    59.671 (03h 58m 41s) +39.060 (+39d 03' 35")
    59.608 (03h 58m 26s) +39.029 (+39d 01' 45")
    59.093 (03h 56m 22s) +40.341 (+40d 20' 29")
  ---------------------------------------------
The error box area is 272 sq. arcmin, and its maximum
dimension is 1.4 deg (the minimum one is 3.4 arcmin).
The Sun distance was 81 deg.

This box may be improved.

A triangulation map is posted at
http://www.ioffe.ru/LEA/GRBs/GRB150819_T38000/IPN/

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

H.-F. Yu (MPE) and E. Burns (UAH)
report on behalf of the Fermi GBM Team:

"At 10:33:19.50 UT on 19 August 2015, the Fermi Gamma-Ray Burst Monitor
triggered and located GRB 150819B (trigger 461673203 / 150819440).

The on-ground calculated location, using the GBM trigger
data, is RA = 62.72, Dec = 40.60 (J2000 degrees,
equivalent to 04h 10m 53s, 40d 36'), 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 trigger resulted in an Autonomous Repoint Request (ARR)
by the GBM Flight Software owing to the high peak flux 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 best location is 104 degrees .

The GBM light curve consists of two pulses
with a duration (T90) of about 0.96 s (50-300 keV).
The time-averaged spectrum from T0-0.064 s to T0+0.896 s is
best fit by a power law function with an exponential
high-energy cutoff. The power law index is -1.04 +/- 0.02 and
the cutoff energy, parameterized as Epeak, is 532 +/- 27 keV

The event fluence (10-1000 keV) in this time interval is
(7.6 +/- 0.1)E-06 erg/cm^2. The 64-ms peak photon flux measured
starting from T0+0.000 s in the 10-1000 keV band
is 148.4 +/- 3.8 ph/s/cm^2.

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

S. Golenetskii, R. Aptekar, D. Frederiks, V. Pal'shin, 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-duration, very intense GRB 150819B
(IPN triangulation: Golenetskii et al., GCN 18176
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 ;
Fermi GBM detection: Yu and Burns, GCN 18178
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 )
triggered Konus-Wind at T0=38000.750 s UT (10:33:20.750).

The burst light curve shows at least three separate peaks.
A total duration of the burst is  ~1.2 s.
The emission is seen up to ~3 MeV.

As observed by Konus-Wind, the burst
had a fluence of 6.61(-0.88,+1.10)x10^-6 erg/cm2,
and a 16-ms peak flux, measured from T0+0.008 s,
of 1.20(-0.17,+0.19)x10^-4 erg/cm2/s
(both in the 20 keV - 10 MeV energy range).

The time-averaged spectrum of the burst
(measured from T0 to T0+8.448 s)
is best fit in the 20 keV - 5 MeV range
by a power law with exponential cutoff model:
dN/dE ~ (E^alpha)*exp(-E*(2+alpha)/Ep)
with  alpha = -1.03(-0.21,+0.24)
and Ep = 348(-70,+116) keV (chi2 = 74/89 dof).
Fitting by the GRB (Band) model yields the same alpha and Ep,
and an upper limit on the high energy photon index:
beta < -2.3 (chi2 = 74/88 dof).

The spectrum near the maximum count rate
(measured from T0 to T0+0.064 s)
is best fit in the 20 keV - 5 MeV range
by a power law with exponential cutoff model
with  alpha = -0.41(-0.15,+0.17)
and Ep = 618(-86,+95) keV (chi2 = 57/43 dof).
Fitting by the GRB (Band) model yields the same alpha and Ep,
and an upper limit on the high energy photon index:
beta < -2.8 (chi2 = 57/42 dof).

The Konus-Wind light curve of this GRB is available at
http://www.ioffe.ru/LEA/GRBs/GRB150819_T38000/

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