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We measure the local rates of ``low-luminosity'' (LL-GRBs, i. e. L<10^48--49erg/sec) and ``high-luminosity'' Gamma-ray Bursts (HL-GRBs). The values are in the range n0=100--1800 Gpc^ (-3) yr^ (-1) and n0=100--550 Gpc^ (-3) yr^ (-1), respectively, and the ratios to SNe-Ibc \ 1%-9% and 0. 4% -3%. These data may suggest the existence of two physically distinct classes of GRBs in which LL-GRBs are (intrinsically) more frequent events than HL-GRBs. However, with the present data we cannot exclude the possibility of a single population of GRBs which give rise to both an isotropic low-luminous emission (LL-GRBs: detectable only in nearby GRBs) and to a highly collimated high-luminous emission (HL-GRBs: detectable preferentially at high-z). We compute also the rate of SNe-Ibc characterized by broad-lined spectra (Hypernovae) and found it to be about 1. 5\ 10^ (-4) HNe yr^ (-1) 10^ (10) L_ (B\) (i. e less than 10% of SNe-Ibc occurring in Spirals). This result implies that the ratio HL-GRBs/HNe is smaller than 1, possibly in the range 0. 04--0. 3. We have used the ratio between Hypernovae and LL-GRBs to constrain their beaming factor to fb^ (-1) \ 10 or less.
Guetta et al. (Wed,) studied this question.