Electromagnetic Emission post Spinning Black Hole-Magnetized Neutron Star Mergers

Understand

For a binary composed of a spinning black hole (BH) (with mass $\gtrsim 7M_\odot$) and a strongly magnetized neutron star (NS) (with surface magnetic field strength $B_{\rm S,NS}\gtrsim10^{12}$\,G and mass $\sim 1.4M_\odot$), the NS as a whole will possibly eventually plunge into the BH.

• During the inspiral phase, the spinning BH could be charged to the Wald charge quantity $Q_{\rm W}$ until merger in an electro-vacuum approximation.
• During the merger, if the spinning charged BH creates its own magnetosphere due to an electric field strong enough for pair cascades to spark, the charged BH would transit from electro-vacuum to force-free cases and could discharge in a time $\gtrsim1~{\rm ms}$.
• As the force-free magnetosphere is full of a highly conducting plasma, the magnetic flux over the NS's caps would be retained outside the BH's event horizon under the frozen-in condition.