The NuSTAR view of reflection and absorption in NGC 7582

TL;DR

This study uses NuSTAR observations to analyze the complex reflection and absorption features in NGC 7582, concluding that increased obscuration by a patchy torus explains the spectral changes rather than a decrease in intrinsic luminosity.

Contribution

It provides new high-quality X-ray data and demonstrates that increased obscuration, not a source shut-off, accounts for spectral variability in NGC 7582.

Findings

NGC 7582 is heavily obscured by a patchy torus with 80-90% covering fraction.

An additional variable full-covering absorber with N_H=4-6×10^23 cm^-2 is present.

Spectral changes are due to increased absorption, not decreased intrinsic luminosity.

Abstract

NGC 7582 is a well-studied X-ray bright Seyfert 2 with moderately heavy ($N_{\text{H}}\sim10^{23}-10^{24}$~cm$^{-2}$), highly variable absorption and strong reflection spectral features. The spectral shape changed around the year 2000, dropping in observed flux and becoming much more highly absorbed. Two scenarios have been put forth to explain this spectral change: 1) the central X-ray source partially ``shut off'' around this time, decreasing in intrinsic luminosity, with a delayed decrease in reflection features due to the light-crossing time of the Compton-thick material or 2) the source became more heavily obscured, with only a portion of the power law continuum leaking through. NuSTAR observed NGC~7582 twice in 2012, two weeks apart, in order to quantify the reflection using high-quality data above 10 keV. We find that the most plausible scenario is that NGC 7582 has recently become more heavily absorbed by a patchy torus with a covering fraction of $\sim\,80-90\%$ and an equatorial column density of $\sim 3 \times10^{24}$ cm$^{-2}$. We find the need for an additional highly variable full-covering absorber with $N_{\text{H}}= 4-6 \times10^{23}$ cm$^{-2}$ in the line of sight, possibly associated with a hidden broad line region.