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Through their radio loudness, lack of thermal UV emission from the accretiondisk and power-law dominated spectra, Low Luminosity AGN (LLAGN) displaysimilarity with the hard state of stellar-mass black hole X-Ray Binaries(BHBs). In this work we perform a systematic hard X-ray spectral study of acarefully selected sample of unobscured LLAGN using archival $NuSTAR$ data, tounderstand the central engine properties in the lower accretion regime. Weanalyze the $NuSTAR$ spectra of a sample of 16 LLAGN. We model the continuumemission with detailed Comptonization models. We find a strong anti-correlationbetween the optical depth and the electron temperature of the corona,previously also observed in the brighter Seyferts. This anti-correlation ispresent irrespective of the shape of the corona, and the slope of thisanti-correlation in the log space for LLAGN (0.68-1.06) closely matches that ofthe higher accretion rate Seyferts (0.55-1.11) and hard state of BHBs($\sim$0.87). This anti-correlation may indicate a departure from a fixeddisk-corona configuration in radiative balance. Our result, therefore,demonstrates a possible universality in Comptonization processes of black holeX-ray sources across multiple orders of magnitude in mass and accretion rate.

Universality of coronal properties in accreting black holes across mass and accretion rate