作为TDE冒名顶替者的碰撞EMRI的周期性吸积动力耀斑
Periodic accretion-powered flares from colliding EMRIs as TDE Imposters
摘要：
当一颗主序星在极质量比圆涡旋（EMRI）中经历洛希叶溢出到超大质量黑洞（SMBH）上时，会出现一个稳定的质量转移阶段。经过数百万年的时间，双星演化到一个最小周期，然后逆转方向向外迁移。由于连续EMRI之间的时间间隔与传质时间尺度相当，因此两个连续传质EMRI的半长轴将在<几个AU的径向尺度上交叉。我们表明，这种EMRI交叉事件不可避免地伴随着一系列温和的相对论性，放牧恒星之间的物理碰撞。每次碰撞都会剥离少量质量，主要是来自质量较大的恒星，这通常会增加它们的径向距离，以便在进一步的引力辐射导致数十年至数百年（或更长时间）的延迟后引发下一次碰撞。根据SMBH的质量，这种相互作用可以导致质量为Msun/N的N ~ 1- 1 e4气体产生事件，从而在数千年或更长的总持续时间内为SMBH吸积动力耀斑的准周期序列提供动力。虽然EMRI的速率比潮汐破裂事件（TDE）的速率低2-3个数量级，但一个相互作用的EMRI对产生大量发光耀斑的能力-以及更明智地利用可用的恒星燃料-可以使它们的观测速率与TDE速率竞争，使它们能够伪装成“TDE冒名顶替者”。“我们预测耀斑的光度衰减既有比t^（-5/3）更浅的幂律衰减，也有指数衰减。由先前质量剥离事件的累积所产生的气体盘的粘性扩散在> 10-100 AU的径向尺度上放置了大量的质量，提供了解释某些耀斑出乎意料的高光学光度所需的后处理源。
英文摘要：
When a main sequence star undergoes Roche lobe overflow onto a supermassive black hole (SMBH) in a circular extreme mass ratio inspiral (EMRI), a phase of steady mass transfer ensues. Over millions of years, the binary evolves to a period minimum before reversing course and migrating outwards. Because the time interval between consecutive EMRIs is comparable to the mass-transfer timescale, the semi-major axes of two consecutive mass-transferring EMRIs will cross on a radial scale < few AU. We show that such EMRI crossing events are inevitably accompanied by a series of mildly relativistic, grazing physical collisions between the stars. Each collision strips a small quantity of mass, primarily from the more massive star, which generally increases their radial separation to set up the next collision after a delay of decades to centuries (or longer) set by further gravitational radiation. Depending on the mass of the SMBH, this interaction can result in N ~ 1-1e4 gas production events of mass Msun/N, thus powering a quasi-periodic sequence of SMBH accretion-powered flares over a total duration of thousands of years or longer. Although the EMRI rate is 2-3 orders of magnitude lower than the rate of tidal disruption events (TDE), the ability of a single interacting EMRI pair to produce a large number of luminous flares - and to make more judicious use of the available stellar fuel - could make their observed rate competitive with the TDE rate, enabling them to masquerade as "TDE Imposters." We predict flares with luminosities that decay both as power laws shallower than t^(-5/3) or as decaying exponentials. Viscous spreading of the gas disks produced by the accumulation of previous mass-stripping events places substantial mass on radial scales > 10-100 AU, providing a reprocessing source required to explain the unexpectedly high optical luminosities of some flares.
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