GCN Circular 9235

L. Nava (INAF-OAB/Univ.Insubria); D. Burlon (MPE-Garching);
G. Ghirlanda (INAF-OAB); G. Ghisellini (INAF-OAB); M. Nardini (SISSA)

With the spectral parameters and fluence of GRB090423 as measured by  
Fermi (von Kienlin et al., GCN 9229
Not found
 
 
)
and given its redshift z=8.1 (Fernandez-Soto et al., GCN 9222
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), we  
estimate the isotropic equivalent energy
Eiso = 1.03E53 and the isotropic equivalent peak luminosity Liso =  
1.88E53 (the value of Eiso is consistent
with that obtained with the Swift spectral results given in Palmer et  
al. GCN 9204
Not found
 
 
).

Given the rest frame peak energy Ep= 746 keV, we show ( http://www.brera.inaf.it/utenti/ghirla/GRB/090423.html 
  )
that GRB090423 is consistent both with the Ep-Liso correlation  
(Yonetoku et al. 2004) and with the Ep-Eiso
correlation (Amati et al. 2002, Ghirlanda et al. 2008, Nava et al.  
2008; see also GCN 9227
Not found
 
 
).

Noteworthly, GRB090423 is remarkably similar to GRB 080913 and GRB  
071020 with respect to the Amati and
Yonetoku correlations. It is worth mentioning that these three GRBs  
are long bursts according to their observed
T90 (12 s, 8 s and 4 s respectively) although, given their  redshifts,  
T90 ~ 1 sec in the rest frame.

Finally, considering the collimation corrected Ep-Egamma correlation  
(e.g. Ghirlanda et al. 2007), we estimate that a
jet break should occur in the afterglow light curve between ~22 and 54  
days (1 sigma consistency) or between ~10 and  130 days
(3 sigma consistency) assuming a homogeneous circum-burst environment  
with standard parameters
(see Nava et al. 2006, Ghirlanda et al. 2007). However, this break may  
not be observed in the
X-ray which, given the typical steep-flat-steep decay already observed  
for this burst
( http://www.swift.ac.uk/xrt_curves/00350184/ ), could likely be due  
to another emission component (e.g. Ghisellini et al. 2009).

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