Variable mass accretion and failed wind explain changing-look phenomena in NGC 1365

Abstract

Changing-look active galactic nuclei (CLAGNs) show a complex nature in their X-ray spectral shape and line-of-sight column-density variation. The physical mechanisms responsible for these variations are unclear. Here, we study the spectral properties of a CLAGN, NGC 1365 using combined XMM-Newton and NuSTAR observations to understand the CL behavior. The model-fitted mass-accretion rate varied between 0.003 ± 0.001 and 0.009 ± 0.002 ṀEdd and the dynamic corona changed from 28 ± 3 to 10 ± 1 rg. We found that the variable absorption column density correlates with the mass accretion rate and the geometry of the corona. The derived wind velocity was sufficiently low compared to the escape velocity to drive the wind away from the disc for the epochs during which column densities were high. This suggests that the high and variable absorption can be due to failed winds from the disc. Our estimated ratio of mass outflow to inflow rate from the inner region of the disc lies between 0.019 ± 0.006 and 0.12 ± 0.04. From spectral fitting of the combined data, we found the mass of the central black hole to be constant 4.38 ± 0.34−4.51 ± 0.29 × 106 M⊙, consistent with earlier findings. The confidence contours of NH with other model parameters show that the model-fitted parameters are robust and non-degenerate. Our study construed that the changing accretion rate, which is a fundamental physical quantity and the geometry of the corona are driving the CL phenomena in NGC 1365. The physical picture considered in this work connects both variable continuum and variable absorbing medium scenarios.