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GCN Circular 12663

Konus-Wind observation of GRB 111209A
2011-12-11T14:10:38Z (13 years ago)
Valentin Pal'shin at Ioffe Inst <>
S. Golenetskii, R.Aptekar, E. Mazets, V. Pal'shin, D. Frederiks, P.
Oleynik, M. Ulanov, D. Svinkin, and T. Cline on behalf of the Konus-Wind
team report:

The exceptionally long GRB 111209A (Swift-BAT trigger #509336: Hoversten 
  et al., GCN 12632; Palmer et al., GCN 12640) was detected by 
Konus-Wind in the waiting mode.

The burst light curve shows the main multipeaked episode of emission 
started at ~T0(BAT)-1900 s and lasted until ~T0(BAT)+4400 s (the 
duration is ~6300 s; T0(BAT)=25928 s UT (07:12:08)). There is also a 
weaker broad pulse of emission seen before the main pulse from 
~T0(BAT)-5400 s to ~T0(BAT)-2600 s and a hint of an additional episode 
of emission after the main pulse from ~T0(BAT)+5000 s to ~T0(BAT)+10000 
s. Both these episodes might be related to GRB 111209A (they were 
detected by the same KW detector, and the KW ecliptic latitude responses 
for them are consistent with the common origin with the main episode). 
The most intense peak in the Konus-Wind light curve, (which started at 
~T0+1740 s, peaked at ~T0+2040 s, and ended at ~T0+2300 s), corresponds 
to a significant raise in the XRT lc 
( - Grupe & Hoversten GCN 
12643) and a bright optical flash (Klotz et al., GCN 12637).

As observed by Konus-Wind, the burst (the main episode) had a fluence of 
(4.86 � 0.61)x10^-4 erg/cm2 (in the 20 - 1400 keV energy range).

Modeling the KW 3-channel time-integrated spectrum (from T0-1890 s to
T0+4400 s) by a power law with exponential cutoff model:
dN/dE ~ (E^alpha)*exp(-E*(2+alpha)/Ep)
yields alpha = -1.31 � 0.09, and Ep = 310 � 53 keV.

Assuming z = 0.677 (Vreeswijk, Fynbo, & Melandri GCN 12648) and a 
standard cosmology model with H_0 = 71 km/s/Mpc, Omega_M = 0.27,
Omega_Lambda = 0.73, the isotropic energy release, E_iso, is (5.82 � 
0.73)x10^53 erg, and Ep_rest is 520 �  89 keV.

Thus, the prompt gamma-ray emission properties of this GRB: fluence, Ep, 
and E_iso are similar to those observed in other long energetic GRBs. 
The only exceptional feature of the prompt gamma-ray emission is the 
huge duration.

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

The K-W light curve of this burst is available at
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