TITLE:   GCN CIRCULAR
NUMBER:  32828
SUBJECT: GRB 221009A: Determination of the black holes mass and spin
DATE:    22/10/24 15:43:08 GMT
FROM:    Remo Rufinni at ICRA  <ruffini@icra.it>

Y. Aimuratov, L. Becerra, C.L. Bianco, C. Cherubini, S. Filippi, M.
Karlica, Liang Li, R. Moradi, F. Rastegar Nia, J.A. Rueda, R. Ruffini, N.
Sahakyan, Y. Wang, S.S. Xue, on behalf of the ICRANet team, report:

In GRB 221009A, as in GRB 130427A (Ackermann et al. 2014, Science, 343, 42;
and Ruffini et al. 2019, ApJ, 886, 82), the Fermi-GBM data in the prompt
phase are piled up (Lesage et al. 2022, GCN 32642). In both cases there are
missing the ultra-relativistic prompt emission (UPE) phases originating
from quantum electrodynamical process around a Kerr BH (Ruffini et al.
2019, ApJ, 886, 82; and Rueda et al. 2022, ApJ, 929, 56), which were well
observed in GRB 190114C (Moradi et al. 2021, Phys Rev D 104, 063043) and
GRB 180720B (Rastegarnia et al. 2022, EPJC 82, 77). Under these conditions,
for GRB 130427A the 0.1-100 GeV data of Fermi-LAT had allowed to determine
only the lower limit on the BH mass, M>2.31 solar masses, and the upper
limit of its spin parameter, α<0.4 (Ruffini et al. 2019, ApJ, 886, 82). For
the BDHNI GRB 190114C (Ruffini et al. 2019, GCN 23715), the values of the
BH mass and spin had been determined by taking into account the UPE
contribution: M=4.53 solar masses, α=0.54 (Moradi et al. 2021, Phys Rev D
104, 063043). The analysis of GRB 130427A applied to GRB 221009A gives for
the BH mass and spin parameters: M>2.36 solar masses and α<0.5.

We identify the spike at 500s as the X-ray flare (see e.g. Ruffini et al.
2021 MNRAS 504, 5301–5326 for similar GRBs). We also identify the trigger
in the 10 keV-10 MeV data of Fermi-GBM as the dawn of the supernova
(SN-rise), associated with the gravitational collapse of the progenitor
CO-core. The SN ejecta, accreting on the binary NS companion, give origin
to the BH (BH rise, Rueda & Ruffini 2012, ApJL, 758, L7) and accreting on
the vNS they originate the afterglow (vNS rise, Ruffini et al. 2018, ApJ,
869.101; Becerra, et al. 2022, Phys Rev D 106, 083002).

Additional data analysis from AGILE (GCN 32650), Fermi (GCN 32636, 32637,
32642, 32819), Swift (GCN 32635), LHAASO (GCN 32677), HXMT (Atel 15660) are
needed to relate the SN-rise to the first appearance of the vNS (the
vNS-rise) by the TeV radiation (GCN 32780, 32820, 32808), and also to
relate the appearance of the BH (BH-rise) to the identification of the
first GeV emission.