Evidence of Heavy Obscuration in the Low-Luminosity AGN NGC 4941

TL;DR

This study reveals heavy obscuration and spectral features of the low-luminosity AGN NGC 4941, including high column density, strong reflection, and a high-energy cutoff, using broad-band X-ray observations.

Contribution

First detailed spectral and timing analysis of NGC 4941 showing heavy obscuration and physical properties of the Compton cloud in a low-luminosity AGN.

Findings

Heavy obscuration with N_H ~ 3 x 10^24 cm^-2

Detection of a strong iron line (~1 keV EW)

High-energy cutoff at ~177 keV

Abstract

We present the results obtained from timing and spectral studies of the highly obscured low luminosity active galactic nucleus NGC~4941 using data obtained from the {\it Nuclear Spectroscopic Telescope Array} and the {\it Neil Gehrels Swift} Observatories. We find similar variability in $3-10$~keV and $10-60$~keV energy ranges with fractional rms variability of $\sim$14\%. We investigate broad-band spectral properties of the source in 3-150 keV range, using data from {\it NuSTAR} and {\it Swift}/BAT, with phenomenological slab model and physically motivated {\tt mytorus} model. From the spectral analysis, we find heavy obscuration with the global average column density of the obscured material as $3.09^{+1.68}_{-1.01} \times 10^{24}$ cm$^{-2}$. Evidence of a strong reflection component is observed in the spectrum. We detect a strong iron line with an equivalent width of $\sim$1~keV. From the slab model, we obtain the exponential cutoff energy as $177^{+92}_{-16}$~keV. From this, we estimate the Compton cloud properties with the hot electron temperature $kT_{\rm e} = 59^{+31}_{-5}$~keV and the optical depth $\tau = 2.7^{+0.2}_{-1.6}$.