The structure of the ultrarelativistic prompt emission phase and the properties of the black hole in GRB 180720B

In analogy with GRB 190114C, we here analyze the ultrarelativistic prompt emission (UPE) of 180720B observed in rest-frame time interval $t_{\rm rf}=4.84$--$10.89$~s by Fermi-GBM. We reveal UPE hierarchical structure from time-resolved spectral analysis performed sub-intervals: spectrum each shorter is always fitted a composite blackbody plus cutoff power-law model. explain this \textit{inner engine} binary-driven hypernova (BdHN) model operating quantum electrodynamics (QED) regime. regime, electric field induced gravitomagnetic interaction newborn Kerr BH surrounding magnetic overcritical, i.e., $|{\bf E}|\geq E_c$, where $E_c=m_e^2 c^3/(e\hbar)$. The overcritical polarizes vacuum leading to an $e^+~e^-$ pair plasma that loads baryons surroundings during its expansion. calculate dynamics self-acceleration pair-electromagnetic-baryon (PEMB) pulses their point transparency. characterize polarization process sequences decreasing bins determining radiation timescale, Lorentz factors, and transparency radius PEMB pulses. also estimate strength $\sim 10^{14}$ G, obtain lower limit mass, $M=2.4~M_\odot$, correspondingly upper spin, $\alpha = 0.6$, conditions powered extractable energy mass bound below NS critical mass.