Waxman 2004 GRB 980425的射电辐射的偏轴解释

主要内容:
GRB 980425的暴本身的流量很低，一种解释是偏轴观测。如果这样的话，在一年以后的射电辐射应该会很亮（就像GRB 970508, (970508的晚期射电很亮吗？它被确认是一个偏轴观测的暴吗？)）。不过实际射电观测SN 1998bw比预计的流量低三个量级，作者归结为环境的影响。

同样建议对近处的超新星的射电进行普查。

精彩摘抄:


文章信息:

Title:		The Nature of GRB 980425 and the Search for Off-Axis Gamma-Ray Burst Signatures in Nearby Type Ib/c Supernova Emission
Authors:		Waxman, Eli
Publication:		The Astrophysical Journal, Volume 602, Issue 2, pp. 886-891. (ApJ Homepage)
Publication Date:		02/2004
Bibliographic Code:		2004ApJ...602..886W

Abstract

The identification of Type Ib/c supernovae (SNe Ib/c) as gamma-ray burst (GRB) progenitors is motivated by the association of GRB 980425 with SN 1998bw and of GRB 030329 with SN 2003dh. While the gamma-ray luminosity of GRB 030329 was typical to cosmological GRBs, the luminosity of the nearby (40 Mpc) GRB 980425 was ~5 orders of magnitude lower. The large luminosity difference is commonly explained by hypothesizing either that SNe Ib/c produce two different classes of GRBs or that GRB 980425 was a typical cosmological GRB jet viewed off-axis. In the latter scenario, strong radio emission, L_ν~10³⁰ν^-1/2_10GHz ergs s^-1 Hz^-1, is expected at ~1 yr delay as a result of jet deceleration to subrelativistic speed, as observed from GRB 970508. The radio luminosity of SN 1998bw was 3 orders of magnitude lower than this value. We show that the low radio flux may be consistent with the off-axis jet interpretation, if the density of the wind surrounding the progenitor is lower than typically expected, m≡(M/10^-5M_solaryr^-1)/(v_w/10³kms^-1)~=0.1 instead of m>~1. The lower value of m is consistent with the observed radio emission from the SN shock driven into the wind. This interpretation predicts transition to subrelativistic expansion at ~10 yr delay, with current ~1 mJy 10 GHz flux and m_V~23 optical flux, and with ~10 mas angular source size. It also implies that in order to search for the signature of off-axis GRBs associated with nearby SNe Ib/c, follow-up observations should be carried out on a multiyear timescale.