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arXiv 0912.2330gr-qcastro-ph.HE
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双黑洞并合的真空电磁对应体

Vacuum Electromagnetic Counterparts of Binary Black-Hole Mergers

Philipp Mösta, Carlos Palenzuela, Luciano Rezzolla, Luis Lehner, Shin'ichirou Yoshida, Denis Pollney

摘要:

作为一个系统的建模电磁(EM)发射从一个螺旋黑洞的二进制,我们考虑一个简单的情况下,二进制移动在一个统一的磁场锚定到一个遥远的circumbinary盘。我们通过求解Einstein-麦克斯韦方程组来研究这个系统,其中电磁场的强度与天体物理学一致。我们考虑自旋与轨道角动量对齐或反对齐的双星,并研究这些自旋配置的引力和电磁信号的依赖性。总的来说,我们发现,在最低的l=2,m=2多极的EM辐射准确地反映了引力的,具有相同的相位演化和振幅,不同的只有一个比例因子。我们还计算了电磁波的能量发射效率,发现它由E^rad_EM/M ~ 10^-15(M/10^8 M_Sun)^2(B/10^4 G)^2给出,因此比实际磁场的引力能小13个数量级。如果系统以接近爱丁顿速率吸积,则相应的光度远小于吸积光度。最重要的是,这种电磁辐射的频率为10^-4(10^8 M_Sun/M)Hz,远远超出了天文射电观测的范围。因此,这里讨论的电磁辐射不太可能与引力波辐射同时被直接探测到。然而,由EM场行为的变化驱动的间接过程可以产生可观察到的事件。特别是,如果环双星盘的吸积率很小,并且在最终的螺旋时间尺度上足够稳定,那么EM发射可以间接观察到,因为它将通过扭曲的磁场线施加的磁矩改变吸积率。

英文摘要:

As one step towards a systematic modeling of the electromagnetic (EM) emission from an inspiralling black hole binary we consider a simple scenario in which the binary moves in a uniform magnetic field anchored to a distant circumbinary disc. We study this system by solving the Einstein-Maxwell equations in which the EM fields are chosen with astrophysically consistent strengths. We consider binaries with spins aligned or anti-aligned with the orbital angular momentum and study the dependence of gravitational and EM signals with these spin configurations. Overall we find that the EM radiation in the lowest l=2, m=2 multipole accurately reflects the gravitational one, with identical phase evolutions and amplitudes that differ only by a scaling factor. We also compute the efficiency of the energy emission in EM waves and find that it is given by E^rad_EM/M ~ 10^-15 (M/10^8 M_Sun)^2 (B/10^4 G)^2, hence 13 orders of magnitude smaller than the gravitational energy for realistic magnetic fields. The corresponding luminosity is much smaller than the accretion luminosity if the system is accreting at near the Eddington rate. Most importantly, this EM emission is at frequencies of 10^-4 (10^8 M_Sun/M) Hz, well outside those accessible to astronomical radio observations. As a result, it is unlikely that the EM emission discussed here can be detected directly and simultaneously with the gravitational-wave one. However, indirect processes, driven by changes in the EM fields behavior could yield observable events. In particular if the accretion rate of the circumbinary disc is small and sufficiently stable over the timescale of the final inspiral, then the EM emission may be observable indirectly as it will alter the accretion rate through the magnetic torques exerted by the distorted magnetic field lines.

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