Possible Electromagnetic Manifestations of Merging Black Holes

Abstract

The scenario of a merger of two black holes surrounded by an accretion disk is considered. As a result of the emission of gravitational waves, the mass of the central object decreases, and the accretion disk is perturbed. Computational results show that the main consequence of this perturbation is the formation of a shock propagating from the center to the periphery of the disk. The light curve is calculated and the duration of the flare estimated, assuming that the flare ends when the luminosity decreases to its initial value. If themass of the merging binary is 55M_⊙ (as in the case ofGW170814), the flare from the shock will lead to an increase in the disk’s bolometric luminosity by four to six orders of magnitude, up to 10⁴⁵ erg/s (an absolute magnitude of −23.8^m). With a source distance of 540Mpc and reasonable assumptions about the parameters of the accretion disk, the apparent brightness of the flare at the maximum of the spectral flux density should be 12.8^m−14.2^m, and the duration of the flare should be several minutes. The main radiation flux from the shock lies in the X-ray and gamma-ray ranges. In the spectral band of the XMM-Newton EPIC instrument or the eROSITA telescope of the Spectr-RG Observatory (0.3−10 keV), the luminosity will increase by three to four orders of magnitude (7.5^m−10^m), up to 10⁴⁴ erg/s, corresponding to an apparent magnitude of approximately 17^m. The luminosity is maximum in the observing band of the INTEGRAL IBIS instrument (20 keV−10 MeV), where it is 10⁴⁴−10⁴⁵ erg/s, corresponding to an apparent flux of 10⁻⁴ photons cm⁻² s⁻¹ keV⁻¹ at 100 keV. There is almost no brightening starting from the far ultraviolet and continuing towards longer wavelengths: the lumnosity at 10 eV grows by about a factor of two, corresponding to an absolute magnitude of −6^m and a visual magnitude of 32^m.