## [astro-ph/0507147] Late-time Radio Observations of 74 Type Ibc Supernovae: Strong Constraints on Off-Axis Gamma-ray Bursts

 Authors: A. M. Soderberg, E. Nakar, S. R. Kulkarni Abstract: We present late-time radio observations of 74 local Type Ibc supernovae, including six events with broad optical absorption lines (hypernovae''). None of these objects show evidence for radio emission attributable to off-axis gamma-ray burst jets spreading into our line-of-sight. Comparison with our afterglow models reveals the following conclusions: (1) Less than ~ 1.4% of Type Ibc supernovae are associated with typical gamma-ray bursts initially directed away from our line-of-sight; this places an empirical constraint on the GRB beaming factor of f_b^{-1} < 1300 corresponding to an average jet opening angle, \theta_j > 2 degrees. (2) This holds in particular for the broad-lined supernovae (including SNe 1997dq, 1997ef, 1998ey, 2002ap, 2002bl and 2003jd) which have been argued to host GRB jets. Our observations reveal no evidence for typical (or even sub-energetic) GRBs, constraining the fraction of broad-lined events harboring relativistic jets to < 17%. Their large photospheric velocities and mildly asymmetric ejecta (inferred from spectropolarimetry and nebular spectroscopy) appear to be characteristic of the non-relativistic supernova explosion and do not necessarily imply the existence of associated GRB jets. [PDF]  [PS]  [BibTex]  [Bookmark]

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Sergei Popov
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### [astro-ph/0507147] Late-time Radio Observations of 74 Type I

A. M. Soderberg, E. Nakar, S. R. Kulkarni present observations (in radio) of 74 Ibc supernova. No traces of off-axis GRBs are found.
It gives an upper limit 1.4% of SN Ibc which produce GRBs.

As it was mentioned earlier (see, for example, astro-ph/0412024 by Fryer and Heger) rotation is extremely important for the collapsar model. So, coalescence of two helium stars were proposed as reasonable candidates for GRB progenitors.
The rate of such coalescence (see astro-ph/0505406 subsec.3.3) was estimated to be about 1 in 106 – 1 in 2*105 years, which is too low to explain the rate of GRBs. So, other channels of binary evolution are necessary.