Black hole discharge: Very-high-energy gamma rays from black hole-neutron star mergers

Zhen Pan and Huan Yang
Phys. Rev. D 100, 043025 – Published 23 August 2019

Abstract

With mass ratio larger than 5 (which depends on the black hole spin and the star radius), star disruption is not expected for a black hole merging with a neutron star during the final plunge phase. In the late inspiral stage, the black hole is likely charged as it cuts through the magnetic field carried by the neutron star, leaving a temporarily charged black hole after merger. The unstable charged state of the remnant black hole rapidly neutralizes by interacting with the surrounding plasma and photons, which we investigate in first principle by numerically solving a coupled set of Boltzmann equations of 1+1 form for nonspinning BH background. The resulting basic picture is as follows. Electrons and positrons are accelerated in the BH electric field, which then lose energy to surrounding soft photons via Compton scattering; more electrons and positrons will be created from pair production as the hard photons colliding with soft photons, or through the Schwinger process in strong electromagnetic fields. The cascade stops when the charged black hole accretes enough opposite charges and becomes neutralized. We find that 10% (which depends on the soft photon energy and number density) of the total electric energy is carried away to infinity in a time interval 1ms by very-high-energy (>50GeV, the low energy detection threshold of the MAGIC telescope) gamma rays whose spectrum is approximately a power law with spectral index 2.3. We expect the discharge picture to be true for spinning charged BHs as well.

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  • Received 14 May 2019

DOI:https://doi.org/10.1103/PhysRevD.100.043025

© 2019 American Physical Society

Physics Subject Headings (PhySH)

Gravitation, Cosmology & Astrophysics

Authors & Affiliations

Zhen Pan1,* and Huan Yang1,2,†

  • 1Perimeter Institute for Theoretical Physics, Ontario N2L2Y5, Canada
  • 2University of Guelph, Guelph, Ontario N2L 3G1, Canada

  • *zpan@perimeterinstitute.ca
  • hyang@perimeterinstitute.ca

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Vol. 100, Iss. 4 — 15 August 2019

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