GRB 150824A

E. Bissaldi (INFN Bari) and E. Burns (UAH)
report on behalf of the Fermi GBM Team:


"At 01:53:31.76 UT on 24 August 2015, the Fermi Gamma-Ray Burst Monitor
triggered and located GRB 150824A (trigger 462074015 / 150824079).

The on-ground calculated location, using the GBM trigger
data, is

RA = 161.3
DEC = -55.9

(J2000 degrees, equivalent to 10h 45m, -55d 55'),
with an uncertainty of 1.0 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 74 degrees.

The GBM light curve consists of several peaks
with a duration (T90) of about 13 s (50-300 keV).
The time-averaged spectrum from T0 to T0+15 s is
best fit by a Band function with Epeak = 187 +/- 9 keV,
alpha = -0.77 +/- 0.03, and beta = -2.40 +/- 0.10.

The event fluence (10-1000 keV) in this time interval is
(2.03 +/- 0.03)E-05 erg/cm^2. The 1-sec peak photon flux measured
starting from T0+1 s in the 10-1000 keV band
is 22.2 +/- 0.5 ph/s/cm^2.

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

K. Hurley, on behalf of the IPN,

I. G. Mitrofanov, D. Golovin, M. L. Litvak, and A. B. Sanin,
on behalf of the HEND-Odyssey GRB team,

S. Golenetskii, R. Aptekar, V. Pal'shin, D. Frederiks,
D. Svinkin, and T. Cline on behalf of the Konus-Wind team,

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

W. Boynton, C. Fellows, K. Harshman, H. Enos, and R. Starr,
on behalf of the GRS-Odyssey GRB team, report:

The long-duration, bright GRB 150824A has been detected by Fermi (GBM: 
Bissaldi and Burns, GCN Circ. 18201
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 ), Konus-Wind, INTEGRAL (SPI-ACS), 
and Mars-Odyssey (HEND), so far, at about 6812 s UT (01:53:32).

We have triangulated it to a preliminary, 3 sigma error box whose 
coordinates are:
  ---------------------------------------------
   RA(2000), deg                 Dec(2000), deg
  ---------------------------------------------
  Center:
   167.550 (11h 10m 12s) -56.964 (-56d 57' 49")
  Corners:
   166.891 (11h 07m 34s) -57.136 (-57d 08' 10")
   167.182 (11h 08m 44s) -57.159 (-57d 09' 31")
   168.205 (11h 12m 49s) -56.787 (-56d 47' 12")
   167.915 (11h 11m 40s) -56.767 (-56d 46' 03")
  ---------------------------------------------
The error box area is 253 sq. arcmin, and its maximum
dimension is 48 arcmin (the minimum one is 6.2 arcmin).
The Sun distance was 69 deg.

This box may be improved.

A triangulation map is posted at
http://www.ioffe.ru/LEA/GRBs/GRB150824_T06810/IPN/

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

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 long-duration, bright GRB 150824A
(Fermi-GBM detection: Bissaldi & Burns, GCN 18201
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 ;
IPN triangulation: Hurley et al., GCN 18202
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 )
triggered Konus-Wind at T0=6810.119 s UT (01:53:30.119).

The light curve shows several pulses in the interval
from ~T0-0.5 s to ~T0+15 s.
The emission is seen up to ~5 MeV.

As observed by Konus-Wind, the burst had a fluence
of 1.8(-0.2,+0.2)x10^-5 erg/cm2, and a 64-ms peak flux,
measured from T0+0.896 s, of 7.6(-0.8,+0.9)x10^-6 erg/cm2/s
(both in the 20 keV - 10 MeV energy range).

The time-averaged spectrum (measured from T0 to T0+16.384 s)
is best fit in the 20 keV - 15 MeV range
by the GRB (Band) function with the following model parameters:
the low-energy photon index alpha = -0.96 (-0.16,+0.11),
the high energy photon index beta = -3.11 (-6.89,+0.44),
the peak energy Ep = 197 (-16,+22) keV,
chi2 = 106/97 dof.

The spectrum near the peak count rate (measured from T0 to T0+8.192 s)
is best fit in the 20 keV - 15 MeV range
by the GRB (Band) function with the following model parameters:
the low-energy photon index alpha = -0.83 (-0.11,+0.12),
the high energy photon index beta = -2.79 (-0.56,+0.29),
the peak energy Ep = 200 (-19,+20) keV,
chi2 = 90/92 dof.

The Konus-Wind light curve of this GRB is available at
http://www.ioffe.ru/LEA/GRBs/GRB150824_T06810/

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