Revisiting Black Hole Mass Estimates and Variability in Narrow-Line Seyfert 1 Galaxies

Narrow-Line Seyfert 1 (NLSy1) galaxies are a subclass of active galactic nuclei (AGN) characterized by their narrow Hβ emission lines, strong Fe ii emission, and relatively weak [O iii] lines. Black hole mass in AGNs can be measured using techniques like reverber- ation mapping, which analyzes the time delay between continuum emission variations and the broad emission lines response, establishing scaling relations based on luminos- ity and FWHM. These relations allow for black hole mass estimates from single-epoch spectroscopic data. When applying these scaling relations, NLSy1s show smaller black hole masses (106-108 solar masses) compared to their counterpart, the broad-line Seyfert 1 (BLSy1) galaxies. However, multiple studies show that these analyses overlook the orientation dependence of NLSy1s. For example, Fermi-LAT has identified gamma-ray emitting radio-loud NLSy1s (RL-NLSy1s), some of which show blazar-like properties, sug- gesting that RL-NLSy1s may predominantly be pole-on type 1 AGN. However, are the traditionally estimated black hole masses in NLSy1s accurate, or are they observationally biased, for instance, due to orientation effects? To address this question, we opt for another strategy based on UV/optical variability for the AGN light curves. An AGN light curve’s power spectral density (PSD) is typically modeled as a broken power law, with the break frequency indicating a turnover between white and red noise flux variability. The transition frequency between the high-frequency end and the low-frequency end is f = 1/2πτ where τ represents the intrinsic damping timescale, characterizes the light curve. Burke et al. [2021] demonstrated a corre- lation between this damping time scale and single epoch masses. Using archival g-band light curve data from the ZTF facility, we analyzed the PSDs of 5666 NLSy1s along with a controlled sample of 5556 BLSy1s and found that the average mass of NLSy1s is comparable to that of BLSy1s which is higher than previously observed (Paliya et al. [2024]). Some studies also indicate that, in addition to the damping timescale, black hole mass estimation is influenced by the Eddington ratio. NLSy1s are known to accrete at high Eddington ratios, are often close to or exceeding the Eddington limit. By recalibrating the correlation between black hole mass and damping timescale to account for the effect of the Eddington ratio, we found that NLSy1s and BLSy1s exhibit distinct black hole masses. This supports the conclusion that NLSy1s typically harbor lower-mass black holes.