Spectral variability of IRAS 18325-5926 and constraints on the geometry of the scattering medium

TL;DR

This study analyzes X-ray data of IRAS 18325-5926 to determine the size, density, and location of its scattering medium, revealing a highly ionized region extending over 10^16 cm and varying on specific timescales.

Contribution

It provides new constraints on the geometry and physical properties of the scattering medium in a Seyfert 2 galaxy using spectral variability analysis.

Findings

Scattered emission varies only on timescales >10^5 s.

Scattering medium has a column density of ~10^23 cm^-2.

Location of the scattering medium is less than 10^17 cm from the source.

Abstract

We analyze Suzaku and XMM-Newton data of the highly variable Seyfert 2, IRAS 18325-5926. The spectra of the source are well modeled as a primary component described as an absorbed power law and a secondary power law component which is consistent with being scattered emission from an on-axis extended highly ionized medium. We show that while the primary component varies on a wide range of timescales from $10^{4} - 10^{8}$ s, the scattered emission is variable only on timescales longer than $10^{5}$ s. This implies that the extent of the scattering medium is greater than $10^{16}$ cm. The ratio of the scattered to primary flux ($\sim 0.03$) implies a column density for the scattering medium to be $\sim 10^{23}$ cm$^{-2}$. We argue that for such a medium to be highly ionized it must be located less than $10^{17}$ cm from the X-ray source. Thus we localize the position and extent of scattering region to be $\sim$ a few $\times 10^{16}$ cm, with an average particle density of $\sim 10^{6}$ cm$^{-3}$. We consider the physical interpretation of these results and as an aside, we confirm the presence of a broad Iron line emission in both the {\it XMM-Newton} and {\it Suzaku} observations.