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GCN Circular 10083

Subject
Konus-Wind and Konus-RF observations of GRB 091024
Date
2009-10-26T17:18:48Z (15 years ago)
From
Valentin Pal'shin at Ioffe Inst <val@mail.ioffe.ru>
S. Golenetskii, R.Aptekar, E. Mazets, V. Pal'shin, D. Frederiks,
P. Oleynik, M. Ulanov, and D. Svinkin on behalf of
the Konus-Wind and Konus-RF teams, and
T. Cline on behalf of the Konus-Wind team, report:

The long GRB 091024 (Swift-BAT trigger #373674: Marshall et al. GCN 
10062, Sakamoto et al. GCN 10072) was observed by Konus-Wind in the 
waiting mode. The emission was detected in all three Konus-Wind energy 
bands: G1 (18-70  keV), G2 (70-360 keV) and G3 (360-1360 keV) with high 
S/N.

The burst light curve shows three pulses: the first pulse starts at 
~T0-10 s and has a duration of ~90 s, the second starts at ~T0+600 s and 
has a duration of ~100 s, and the most intense third pulse starts at 
T0+840 s and has a duration of ~400 s; there is a low-level emission 
between the first and second pulses.

The most intense part of the third pulse was also detected by Konus-RF, 
while Coronas-F was exiting the SAA.

The GBM localizations suggest a common origin of these events (Bissaldi 
& Connaughton, GCN 10070). Both the K-W light curve and the K-W ecliptic 
latitude response confirms this suggestion. So, we believe all these 
pulses belong to the extremely long burst, GRB 091024, which has a total 
duration of ~1200 s. Hence, some optical observations of this burst were 
performed during the most intense part of the prompt emission, but no 
bright optical flares have been reported.

Modeling of the K-W 3-channel spectra by
a power law with exponential cutoff model:
dN/dE ~ E^(-alpha)*exp(-E*(2-alpha)/Ep)
yields the following parameters:
--------------------------------------------------
       Tstart    Tstop       alpha      Ep (keV)
--------------------------------------------------
P1     -7          80   -1.1+/-0.2    500+/-160
P2    606         703   -1.6+/-0.2    200+/-120
P3    835        1194   -1.4+/-0.2    230+/-50
Total  -7        1194   -1.5+/-0.4    280+/-120
--------------------------------------------------
Tstart, Tstop - seconds since the BAT trigger time


As observed by Konus-Wind, the burst had a fluence of (1.13 +/- 
0.12)x10^-4 erg/cm2 (in the 20 - 1300 keV energy range).

Assuming z = 1.092 (Cucchiara, Fox & Tanvir, GCN 10065) and a standard 
cosmology model with H_0 = 70 km/s/Mpc, Omega_M=0.27, Omega_\Lambda = 
0.7, the isotropic energy release E_iso ~3.2x10^53 erg.

All the quoted errors are estimated at the 1 sigma confidence level.

The K-W light curve of this burst is available at
http://www.ioffe.rssi.ru/LEA/GRBs/GRB091024/
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