Peak energy of the prompt emission of long Gamma Ray Bursts vs their fluence and peak flux
Abstract
The spectral-energy and (luminosity) correlations in long GRBs are being hotly debated to establish, first of all, their reality against possible selection effects. These are best studied in the observer planes, namely the peak energy Epeakobs vs the fluence F or the peak flux P. In a recent paper we started to attack this problem considering all GRBs with known z and spectral properties. Here we consider instead all bursts with known Epeakobs, irrespective of z, adding to those a sample of 100 faint BATSE bursts representative of a larger population. This allows us to construct a complete, fluence limited, sample, to study the selection/instrumental effects. We found that fainter bursts have smaller Epeakobs than those of bright events. As a consequence, the Epeakobs of these bursts is correlated with the fluence, though with a slope flatter than that defined by bursts with z. Selection effects, which are present, are shown not to be responsible for the existence of such a correlation. About 6% of these bursts are surely outliers of the Epeak-Eiso correlation (updated to include 83 bursts), since they are inconsistent with it for any z. Epeakobs correlates also with P, with a slope similar to the Epeak-Liso correlation.In this case there is only one sure outlier.The scatter of the Epeakobs-P correlation defined by the BATSE bursts of our sample is smaller than the Epeakobs-F correlation of the same bursts, while for the bursts with known z the Epeak-Eiso correlation is tighter than the Epeak-Liso one. Once a very large number of bursts with Epeakobs and z will be available, we thus expect that the Epeak-Liso correlation will be similar to that currently found, whereas it is likely that the Epeak-Eiso correlation will become flatter and with a larger scatter.