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arXiv 2104.09389astro-ph.HEastro-ph.GAastro-ph.SR
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活动星系核吸积盘中白矮星的热核爆炸和吸积坍缩

Thermonuclear Explosions and Accretion-induced Collapses of White Dwarfs in Active Galactic Nucleus Accretion Disks

Jin-Ping Zhu, Yuan-Pei Yang, Bing Zhang, Liang-Duan Liu, Yun-Wei Yu, He Gao

摘要:

嵌入活动星系核(AGN)气体盘中的白矮星(WD)可以快速吸积盘中的物质,并使质量增长到甚至超过克拉塞卡极限。活动星系核吸积盘中也发生了WD(BWD)双星合并。我们研究这些事件的观测特征。我们认为,在活动星系核盘的质量吸积WD和BWD合并可以导致热核爆炸,驱动从磁盘表面的喷出物冲击爆发和动力缓慢上升,相对暗淡的Ia型超新星(SN)。这样的Ia超新星可能总是被质量为$M_{\rm SMBH}\gtrsim 10^8\,M_\odot$的超大质量黑洞(BH)周围活动星系核盘的辐射所掩盖。此外,有时活动星系盘中的白矮星也会发生吸积诱导坍缩,从而形成高磁化毫秒中子星。这个新生磁星随后的自旋下降过程可以将其旋转能量沉积到磁盘材料中,导致磁星驱动的冲击爆发和发光的磁星动力瞬变。我们表明,这样的AIC事件可以为$B\sim10^{15}\,{\rm G}$的磁场提供快速发展和发光的瞬态。由一颗含$B\sim10^{14}\,{\rm G}$的磁星提供动力的瞬变上升时间和峰值亮度,被预测具有与超亮超新星相似的性质。发生在相对较小质量的超大质量黑洞($M_{\rm SMBH}\lesssim10^8\,M_\odot$)周围的盘内部的AIC事件更有可能为比活动星系核盘发射亮得多的瞬变提供能量,因此更容易被识别。

英文摘要:

White dwarfs (WDs) embedded in gaseous disks of active galactic nucleus (AGNs) can rapidly accrete materials from the disks and grow in mass to reach or even exceed the Chandrasekhar limit. Binary WD (BWD) mergers are also believed to occur in AGN accretion disks. We study observational signatures from these events. We suggest that mass-accreting WDs and BWD mergers in AGN disks can lead to thermonuclear explosions that drive an ejecta shock breakout from the disk surface and power a slow-rising, relatively dim Type Ia supernova (SN). Such SNe Ia may be always outshone by the emission of the AGN disk around the supermassive black hole (BH) with a mass of $M_{\rm SMBH}\gtrsim 10^8\,M_\odot$. Besides, accretion-induced collapses (AICs) of WDs in AGN disks may occur sometimes, which may form highly-magnetized millisecond neutron stars (NSs). The subsequent spin-down process of this nascent magnetar can deposit its rotational energy into the disk materials, resulting in a magnetar-driven shock breakout and a luminous magnetar-powered transient. We show that such an AIC event could power a rapidly evolving and luminous transient for a magnetic field of $B\sim10^{15}\,{\rm G}$. The rising time and peak luminosity of the transient, powered by a magnetar with $B\sim10^{14}\,{\rm G}$, are predicted to have similar properties with those of superluminous supernovae. AIC events taking place in the inner parts of the disk around a relatively less massive supermassive BHs ($M_{\rm SMBH}\lesssim10^8\,M_\odot$) are more likely to power the transients that are much brighter than the AGN disk emission and hence easily to be identified.

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