A Note on “ Probing the existence of the E peak - E iso correlation in long Gamma Ray Bursts ” by Ghirlanda et al . - astro - ph / 0502186 .

In Nakar & Piran (2004) we have shown that a large fraction of BATSE bursts cannot satisfy the Amati relation between the isotropic energy peak energy of GRBs. Our results have been corroborated by a further analysis carried out by Band and Preece (2005). Recently Ghirlanda et al. (2005) claimed that when the exact distribution of the scatter around the Amati relation is taken into account, the BATSE sample is consistent with the Amati relation. We show that the probability that the BATSE sample is consistent with the Amati relation (including the scattering), as found by Ghirlanda et al. (2005) for a sample of 23 bursts with known redshift, is vanishingly small. Amati et al., (2002) suggested a tight relation between the isotropic equivalent energy and the peak energy within GRBs (see also Lamb et al., 2004; Atteia et al., 2004). This possible relation between the intrinsic quantities of GRBs has generated a lot of interest in view of its implication on the way GRBs operate and on its potential applications. However this relation have been tested so far only for a small sub-sample of GRBs with a known redshift. Recently we (Nakar & Piran, 2004) have questioned this relationship and have shown that it cannot be satisfied by a large fraction of the bursts in the much larger BATSE sample. Our results have been supported by Band and Preece (2005) who performed a similar test on a larger BATSE sample. In a recent paper Ghirlanda et al. 2005 (GGF05) repeated a similar test to the one preformed in Nakar & Piran (2004) and Band & Preece (2005) with respect the Amati relation found from a sample of 23 bursts (their Eq. 1). This test checks the possibility that a sample of bursts for which the redshifts are unknown is potentially consistent with the Amati relation. GGF05 claim that they find that a large sample of 546 BATSE bursts is consistent with the Amati relation. GGF05 argue that the difference between their result Theoretical Astrophysics, Caltech, Pasadena, CA 91125 USA Racah Institute for Physics, The Hebrew University, Jerusalem 91904, Israel Note that while a burst that does not satisfy the test cannot satisfy the Amati relation a burst that satisfied this test does not necessarily satisfy the relation (see Nakar & Piran, 2004).