Constraints on Off-Axis Gamma-Ray Burst Jets in Type Ibc Supernovae from Late-Time Radio Observations
Abstract
It has been suggested that the peculiar properties of the luminous Type Ic supernova SN 1998bw and its low-energy gamma-ray burst GRB 980425 may be understood if they originated in a standard gamma-ray burst explosion viewed far from the axis of the relativistic jet. In this scenario, strong radio emission is predicted from the jet on a timescale 1-10 yr after the explosion as it decelerates and spreads into our line of sight. To test this hypothesis, we have carried out late-time radio observations of SN 1998bw at t=5.6 yr, yielding upper limits that are consistent with the continued fading of the supernova. We find these limits to be consistent with an off-axis jet only if the progenitor mass-loss rate is M<~4×10-7 Msolar yr-1 (for a wind velocity vw=1000 km s-1) or the fraction of the shock energy in magnetic fields is ɛB<~10-3. These values are low relative to those inferred for cosmological gamma-ray bursts. We combine the SN 1998bw measurements with existing observations for a sample of 15 local Type Ibc supernovae to estimate that at most 6% produce collimated, relativistic outflows.
- Publication:
-
The Astrophysical Journal
- Pub Date:
- May 2004
- DOI:
- 10.1086/421722
- arXiv:
- arXiv:astro-ph/0402163
- Bibcode:
- 2004ApJ...607L..13S
- Keywords:
-
- Gamma Rays: Bursts;
- Stars: Supernovae: Individual: Alphanumeric: SN 1998bw;
- Astrophysics
- E-Print:
- Revised version, as it appears in ApJL