The XMM-Newton long look of NGC 1365: uncovering of the obscured X-ray source

TL;DR

This study analyzes rapid X-ray obscuration variability in NGC 1365, revealing that the X-ray source is uncovered over hours, with implications for the size and location of the obscuring clouds, likely in the broad line region.

Contribution

First detailed monitoring of rapid X-ray obscuration changes in NGC 1365, estimating the size and location of the X-ray source and obscuring clouds.

Findings

X-ray source size < 10^13 cm

Obscuring clouds at ~10^16 cm from the source

Absorbing clouds likely in the broad line region

Abstract

We present an analysis of the extreme obscuration variability observed during an XMM-Newton 5-days continuous monitoring of the AGN in NGC 1365. The source was in a reflection-dominated state in the first ~1.5 days, then a strong increase of the 7-10 keV emission was observed in ~10 hours, followed by a symmetric decrease. The spectral analysis of the different states clearly shows that this variation is due to an uncovering of the X-ray source. From this observation we estimate a size of the X-ray source D_S<10^13 cm, a distance of the obscuring clouds R~10^16 cm and a density n~10^11 cm^{-3}. These values suggest that the X-ray absorption/reflection originate from the broad line region clouds. This is also supported by the resolved width of the iron narrow Kalpha emission line, consistent with the width of the broad Hbeta line.