The effects of X-ray absorption variability in NGC 4395

Abstract

We present a new X-ray analysis of the dwarf Seyfert galaxy NGC 4395, based on two archival XMM-Newton and Suzaku observations. This source is well known for a series of remarkable properties: one of the smallest estimated black hole masses among active galactic nuclei (AGN) (of the order of ∼10⁵ M_⊙), intense flux variability on very short time-scales (a few tens of seconds) and an unusually flat X-ray continuum (Γ∼ 1.4 over the 2-10 keV energy range). NGC 4395 is also characterized by significant variations of the X-ray spectral shape, and here we show that such behaviour can be explained through the partial occultation by circumnuclear cold absorbers with column densities of ∼10²²-10²³ cm^-2. In this scenario, the primary X-ray emission is best reproduced by means of a power law with a standard Γ∼ 1.8 photon index, consistent with both the spectral slope observed at higher energies and the values typical of local AGN.