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Table 1.

Best-fitting parameters obtained in the spectral analysis of NICER and NuSTAR data during the three periods of observation.

Component Parameter (unit) Description Values
Period 1 Period 2 Period 3
tbabs NH(1022 cm−2) Hydrogen column density 0.17 ± 0.01 0.18 ± 0.01 0.19 ± 0.01

kerrbb η Inner-torque modification 0 ( † )
a BH spin 0.992 ± 0.003
i (deg) Inclination 75 ( † )
MBH (M) BH mass 4.6 ( † )
(1016 g s−1) Mass accretion rate 3.47 ± 0.04 3.59 ± 0.04 3.72 ± 0.05
D (kpc) Distance 7.8 ( † )
hd hardening factor 1.7 ( † )
rflag Self-irradiation 1 ( † )
sflag Limb-darkening 0 ( † )
Norm Normalisation 1 ( † )

expabs EC (keV) e-folding energy 1.39 ± 0.02 1.41 ± 0.02 1.44 ± 0.02

powerlaw Γ Photon index 1.93 ± 0.21
Norm (10−3) Normalisation 10.05 ± 4.67 4.74 ± 2.11 2.79 ± 1.29

χ2/d.o.f. 975.4/951

Notes. The expabs e-folding energy was obtained from an initial modelling using diskbb. Parameters marked with ( † )are kept frozen in the spectral analysis.

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