NuSTAR catches the unveiling nucleus of NGC 1068

TL;DR

This study used NuSTAR and XMM-Newton observations to detect a temporary decrease in obscuring material in NGC 1068, revealing the AGN's direct nuclear radiation and estimating its intrinsic luminosity.

Contribution

First detection of a transient decrease in obscuring column density unveiling the AGN's direct emission in NGC 1068.

Findings

Transient decrease in column density from ~10^25 to 6.7×10^24 cm^-2

Unveiled the direct nuclear radiation of NGC 1068's AGN

Estimated intrinsic 2-10 keV luminosity of the AGN

Abstract

We present a NuSTAR and XMM-Newton monitoring campaign in 2014/2015 of the Compton-thick Seyfert 2 galaxy, NGC 1068. During the August 2014 observation, we detect with NuSTAR a flux excess above 20 keV ($32\pm6 \%$) with respect to the December 2012 observation and to a later observation performed in February 2015. We do not detect any spectral variation below 10 keV in the XMM-Newton data. The transient excess can be explained by a temporary decrease of the column density of the obscuring material along the line of sight (from N$_{\rm H}\simeq10^{25}$ cm$^{-2}$ to N$_{\rm H}=6.7\pm1.0\times10^{24}$ cm$^{-2}$), which allows us for the first time to unveil the direct nuclear radiation of the buried AGN in NGC 1068 and to infer an intrinsic 2-10 keV luminosity L$_{\rm X}=7^{+7}_{-4} \times 10^{43}$ erg s$^{-1}$.