Precursor Events Involving Plasma Structures Around Collapsing Black Hole Binaries

The plasma structures that can exist around black hole binaries can sustain intrinsic plasma collective modes [1] that have characteristic low frequencies related to the particle rotation frequencies around the binary system. As the collapse approaches, with the loss of angular momentum by emission of gravitational waves [2] from the binary system we have suggested [3] that the frequency of the fluctuating component of the gravitational potential can go through that of the intrinsic modes of the surrounding plasma structure and lead to a sharp amplification of them. Then the precursor to the event reported in Ref. [2], tentatively identified by the Agile X-$\gamma$-ray observatory [4] may be associated with the high energy radiation emission due to the fields produced by excitation of the proposed plasma modes. M. Tavani is thanked for bringing Ref. [4] to our attention while Ref. [3] was being completed.\\ [1] B. Coppi, Plasma Physics Report, 43, 3, 289–297 (2017).\\ [2] B. Abbot, R. Abbot, T. Abbot et al. Phys. Rev. Lett. 118, 221101 (2017).\\ [3] B. Coppi and M. Medvedev, MIT-LNS HEP 17/02 June 2016. To be submitted to Physics Letters.\\ [4] F. Verrecchia, M. Tavani, A. Ursi, et al., to be published in Ap.J. Letters.