NuSTAR catches the unveiling nucleus of NGC 1068

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 ($32\pm 6\%$) 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${}_{\mathrm{H}}\simeq 10^{25}$ cm${}^{-2}$ to N${}_{\mathrm{H}}=6.7\pm 1.0\times 10^{24}$ 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${}_{\mathrm{X}}=7_{-4}^{+7}\times 10^{43}$ erg s${}^{-1}$.

5 pages, 3 figures, accepted for publication on MNRAS letters