L. Amati (INAF/IASF Bologna, Italy), F. Frontera (Univ. Ferrara and INAF/IASF
Bologna, Italy), C. Guidorzi (Univ. Ferrara, Italy), E. Palazzi (INAF/IASF
Bologna, Italy) report:
On the basis of the spectral parameters and fluence measured by Swift/BAT
(Palmer et al., GCN 9204) and the redshift of ~7.5 - 8.5 suggested by
photometry and spectroscopy of the optical counterpart (Cucchiara et al.,
GCN 9213; Olivares et al., GCN 9215; Thoene et al., GCN 9216; Perley et
al., GCN 9217; Tanvir et al., GCN 9219; Fernandez-Soto et al., GRB 9222)
we find that GRB 090423 is fully consistent with the Ep,i - Eiso
correlation (Ep,i ~ 440 keV and Eiso ~10^53 erg for z = 8, assuming
a flat LambdaCDM cosmology with H0=70 km/s/Mpc and Omega_M = 0.27).
In addition, the track of this GRB in the Ep,i - Eiso plane
(http://www.iasfbo.inaf.it/~amati/grb090423.ps) implies a lower limit to
the redshift of 1.4 (68% c.l.) and 0.9 (90% c.l.) in order to be
consistent with the correlation. This further suggests that the event is
not a local very reddened GRB.
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