On the consistency of peculiar GRBs 060218 and 060614 with the e p,i - Eiso correlation

Abstract

We analyze and discuss the position of GRB 060218 and GRB 060614 in the Ep,i - Eiso plane. GRB 060218 is important because of its similarity with GRB 980425, the prototypical event of the GRB-SN connection. While GRB 980425 is an outlier of the Ep,i - Eiso correlation, we find that GRB 060218 is fully consistent with it. This evidence, combined with the "chromatic" behavior of the afterglow light curves, is at odds with the hypothesis that GRB 060218 was a "standard" GRB seen off-axis and supports the existence of a class of truly sub-energetic GRBs. GRB 060614 is a peculiar event not accompanied by a bright supernova. Based on published spectral information, we find that also this event is consistent with the Ep,i - Eiso correlation. We discuss the implications of our results for the rate of sub-energetic GRBs, the GRB/SN connection and the properties of the newly discovered sub-class of long GRBs not associated with bright supernovae. We have included in our analysis other recent GRBs with clear evidence (or clear evidence of lack) of associated SNe. © ESO 2007.