Long gamma-ray bursts without visible supernovae: a case study of redshift estimators and alleged novel objects

There is an ongoing debate on whether or not the observational limits on a supernova (SN) associated with GRB060614 convincingly exclude a SN akin to SN1998bw as its originator, and provide evidence for a new class of long-duration GRBs. We discuss this issue in the contexts of indirect `redshift estimators' and of the fireball and cannonball models of GRBs. The latter explains the unusual properties of GRB060614: at its debated low redshift (0.125) they are predicted, as opposed to exceptional, if the associated SN is of `Pastorello's class'. Long-baseline radio data and deep optical data may test the proposed alternatives.