Spectral Properties of NGC 4151 and the Estimation of Black Hole Mass Using TCAF Solution

We present X-ray spectral analysis of Seyfert 1.5 Active Galactic Nuclei (AGNs) NGC 4151 using NuSTAR observations during 2012. This is the first attempt to fit AGN data using the physical Two Component Advective flow (TCAF) solution. We disentangle the continuum emission properties of the source in the energy range 3.0-70.0 keV using the spectrum obtained from the TCAF model. This model was used as an additive local model directly in XSPEC. Additionally, we used a power-law component, to take care of possible X-ray contribution from the jet, which is not incorporated in the present version of TCAF. Our primary aim is to obtain the flow properties and the mass of the central supermassive black hole from the available archival data. Our best estimate of the average mass obtained from spectral fits of three observations is M _BH = 3.03^+0.26 _-0.26 × 10⁷ M _⊙. This is consistent with earlier estimations in the literature such as reverberation mapping, gas kinematics, and stellar dynamics around black holes. We also discuss the accretion dynamics and the flow geometry on the basis of model-fitted physical parameters. Model-fitted disk accretion rate is found to be lower than the low angular momentum halo accretion rate, indicating that the source was in a hard state during the observation.