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arXiv 1101.5380astro-ph.HEastro-ph.COastro-ph.GA
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射电超新星中的电子冷却和膨胀与通量密度演化之间的联系

Electron cooling and the connection between expansion and flux-density evolution in radio supernovae

I. Marti-Vidal, M. A. Perez-Torres, A. Brunthaler

摘要:

射电超新星(Radio Supernovae,RSNe)是一种微弱而罕见的事件。它们典型的最大射电光度只有$10^{27}$ \,erg\,s $^{-1}$ \,Hz $^{-1}$的量级。然而,有非常少的情况下,相对明亮(和/或关闭)RSNe,其中的冲击波的扩展和无线电光变曲线在几个频率已被监测覆盖数年。应用超新星射电辐射的标准模型,通过假设同步辐射电子的磁场和能量密度的演化规律,可以用简单的代数方法将模拟膨胀曲线的定义参数与模拟光变曲线的定义参数联系起来。然而,电子的冷却机制可能会极大地影响光变曲线和膨胀曲线之间的这种联系,并导致对电子加速细节和/或CSM径向密度分布的错误结论。在本文中,我们研究如何电子冷却修改的磁通密度衰减率的RSNe的一组似是而非/现实的值的磁场和不同的膨胀制度。我们使用这些结果来估计迄今为止观察到的不同RSNe的磁场,并将它们与通过假设粒子和磁场之间的能量均分而获得的结果进行比较。对于一些监测最好的RSNe,已经观察到减速测量,光学薄光谱指数和幂律时间衰减(SN\,1979 C,SN\,1986 J,SN\,1993 J,和SN\,2008 iz),我们找到了幂律拱星密度分布指数的自洽解(所有情况下的$s=2$)、幂律相对论电子布居指数(相当陡的值,$ p = 2.3 - 3.0$)和初始磁场(范围从$\sim 20$到$> 100$ \,G)。

英文摘要:

Radio supernovae (RSNe) are weak and rare events. Their typical maximum radio luminosities are of the order of only $10^{27}$\,erg\,s$^{-1}$\,Hz$^{-1}$. There are, however, very few cases of relatively bright (and/or close) RSNe, from which the expansion of the shock and the radio light curves at several frequencies have been monitored covering several years. Applying the standard model of radio emission from supernovae, it is possible to relate the defining parameters of the modelled expansion curve to those of the modelled light curves in a simple algebraic way, by assuming an evolution law for the magnetic field and for the energy density of the population of synchrotron-emitting electrons. However, cooling mechanisms of the electrons may affect considerably this connection between light curves and expansion curve, and lead to wrong conclusions on the details of the electron acceleration and/or on the CSM radial density profile. In this paper, we study how electron cooling modifies the flux-density decay rate of RSNe for a set of plausible/realistic values of the magnetic field and for different expansion regimes. We use these results to estimate the magnetic fields of different RSNe observed to date and compare them to those obtained by assuming energy equipartition between particles and magnetic fields. For some of the best monitored RSNe, for which deceleration measurements, optically thin spectral index, and power-law time decay have been observed (SN\,1979C, SN\,1986J, SN\,1993J, and SN\,2008iz), we find self-consistent solutions for the index of the power-law circumstellar density profile ($s=2$ for all cases), the index of the power-law relativistic electron population (rather steep values, $ p = 2.3 - 3.0$) and the initial magnetic field (ranging from $\sim 20$ to $> 100$\,G).

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