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arXiv 2107.06289astro-ph.HEastro-ph.GA
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潮汐扰动事件对外流的无线电约束

Radio constraint on outflows from tidal disruption events

Tatsuya Matsumoto, Tsvi Piran

摘要:

潮汐破裂事件(TDEs)产生的射电耀斑通常被解释为外流与周围环核介质(CNM)相互作用产生的同步辐射。我们推广了常见的均分分析适用于缺乏明确的谱峰或甚至只有上限的情况。我们发现,对于检测到的事件,有一个下限的组合流出的速度$v$和立体角$Ω$,$\simeq vΩ^{a}$(与$a \simeq 0.5$),约束流出的属性。考虑到伴随TDEs的几种可能的外流分量,我们发现:各向同性的外流,如带有$v\sim10^4\,\rm km\,s^{-1}$和$Ω= 4 π$的盘状风,很容易产生观测到的耀斑;未结合碎片的弓形激波具有楔形几何形状,它必须具有几何厚度,带有$Ω\gtrsim1$和它的一小部分质量($\gtrsim 0.01 \,M_{\odot}$),必须在$v \gtrsim 2 \times 10^4\,\rm km\,s^{-1}$移动;锥形牛顿外流,如射流,也可以是一个无线电源,但它们的速度和CNM密度都应该比各向同性风大$\sim(Ω/4π)^{-0.5}$的一个因素。我们对CNM密度的限制通常是以前分析发现的30-100倍,忽略了不发射同步辐射的非相对论电子。我们表明,除非$v$和$Ω$是已知的无线电观测单独不能确定的CNM密度。我们还发现,晚(几年后的TDE)无线电上限排除了精力充沛,$\sim 10^{51-52}\,\rm erg$,相对论喷流像在TDE SW J1644+57观察到的,这意味着这样的喷流是罕见的。

英文摘要:

Radio flares from tidal disruption events (TDEs) are generally interpreted as synchrotron emission arising from the interaction of an outflow with the surrounding circumnuclear medium (CNM). We generalize the common equipartition analysis to be applicable in cases lacking a clear spectral peak or even with just an upper limit. We show that, for detected events, there is a lower limit on the combination of the outflow's velocity $v$ and solid angle $Ω$, $\simeq vΩ^{a}$ (with $a \simeq 0.5$) that constrains the outflow's properties. Considering several possible outflow components accompanying TDEs, we find that: Isotropic outflows such as disk winds with $v\sim10^4\,\rm km\,s^{-1}$ and $Ω= 4 π$ can easily produces the observed flares; The bow shock of the unbound debris has a wedge-like geometry and it must be geometrically thick with $Ω\gtrsim1$ and a fraction of its mass ($\gtrsim 0.01 \,M_{\odot}$), has to move at $v \gtrsim 2 \times 10^4\,\rm km\,s^{-1}$; Conical Newtonian outflows such as jets can also be a radio source but both their velocity and the CNM density should be larger than those of isotropic winds by a factor of $\sim(Ω/4π)^{-0.5}$. Our limits on the CNM densities are typically 30-100 times larger than those found by previous analysis that ignored non-relativistic electrons that do not emit synchrotron radiation. We show that unless $v$ and $Ω$ are known radio observation alone cannot determine the CNM density. We also find that late (a few years after the TDE) radio upper-limits rule out energetic, $\sim 10^{51-52}\,\rm erg$, relativistic jets like the one observed in TDE Sw J1644+57, implying that such jets are rare.

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