Granot 2004 SN 2001em可能是偏轴的jet

主要内容:
由于晚期（2yr）的射电和X射线依然很强，认为可能是偏轴的喷流，进而推出Ibc型超新星都是有喷流的。

不过07年有一篇针锋相对的文章：
SN 2001em: No Jet-Driven Gamma Ray Burst Event

Authors: M. F. Bietenholz, N. Bartel
arXiv:0706.3344v2 [astro-ph]

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Title:		The Case for a Misaligned Relativistic Jet from SN 2001em
Authors:		Granot, Jonathan; Ramirez-Ruiz, Enrico
Affiliation:		AA(Institute for Advanced Study, Einstein Drive, Princeton, NJ 08540), AB(Institute for Advanced Study, Einstein Drive, Princeton, NJ 08540)
Publication:		The Astrophysical Journal, Volume 609, Issue 1, pp. L9-L12. (ApJ Homepage)
Publication Date:		07/2004
Origin:		UCP
ApJ Keywords:		Gamma Rays: Bursts, ISM: Jets and Outflows, Stars: Supernovae: General, Stars: Supernovae: Individual: Alphanumeric: SN 2001em
Abstract Copyright:		(c) 2004: The American Astronomical Society
DOI:		10.1086/422516
Bibliographic Code:		2004ApJ...609L...9G

Abstract

SN 2001em, identified as a Type Ic supernova (SN Ic), has recently been detected in the radio and X-rays, >~2 yr after the explosion. The high luminosities at such late times might arise from a relativistic jet viewed substantially off-axis that becomes visible only when it turns mildly relativistic and its emission is no longer strongly beamed away from us. Alternatively, the emission might originate from the interaction of the SN shell with the circumstellar medium. We find that the latter scenario is hard to reconcile with the observed rapid rise in the radio flux and optically thin spectrum, F_ν~ν^-0.36+/-0.16t^1.9+/-0.4, while these features arise naturally from a misaligned relativistic jet. The high X-ray luminosity provides an independent and more robust constraint; it requires ~10⁵¹ ergs in mildly relativistic ejecta. The source should therefore currently have a large angular size (~2 mas), which could be resolved in the radio with the Very Long Baseline Array. It is also expected to be bipolar and is thus likely to exhibit a large degree of linear polarization (~10%-20%). The presence of a relativistic outflow in SN 2001em would have interesting implications. It would suggest that several percent of SNe Ib/c produce mildly relativistic jets, with an initial Lorentz factor Γ₀>~2, while the fraction that produces gamma-ray burst (GRB) jets (with Γ₀>~100) is ~100 times smaller. This could considerably increase the expected number of transients similar to orphan GRB afterglows in the radio and to a lesser extent in the optical and X-rays, if there is a continuous distribution in Γ₀. Furthermore, this may give further credence to the idea that core-collapse SNe, and in particular SNe Ib/c, are triggered by bipolar jets.

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