Probing the circumnuclear absorbing medium of the buried AGN in NGC 1068 through NuSTAR observations

We present the results of the latest NuSTAR monitoring campaign of the Compton-thick Seyfert 2 galaxy NGC 1068, composed of four ∼50 ks observations performed between 2017 July and 2018 February to search for flux and spectral variability on time-scales from 1 to 6 months. We detect one unveiling and one eclipsing event with time-scales less than 27 and 91 d, respectively, ascribed to Compton-thick material with NH = (1.8 ± 0.8) × 1024 and ≥ (2.4 ± 0.5) × 1024 cm−2 moving across our line of sight. This gas is likely located in the innermost part of the torus or even further inward, thus providing further evidence of the clumpy structure of the circumnuclear matter in this source. Taking advantage of simultaneous Swift–XRT observations, we also detected a new flaring ULX, at a distance d ∼ 30 arcsec (i.e. ∼2 kpc) from the nuclear region of NGC 1068, with a peak X-ray intrinsic luminosity of (3.0 ± 0.4) × 1040 erg s−1 in the 2–10 keV band.
AZ, SB, and GM acknowledge financial support from the Italian Space Agency under grant no. 2017-14-H.O. SB acknowledges financial support from the Italian Space Agency under grant ASI-INAF I/037/12/0. AM and GM acknowledge financial support from the Italian Space Agency under grant ASI-INAF I/037/12/0-011/13. FEB acknowledges support from CONICYT-Chile (Basal AFB-170002) and the Ministry of Economy, Development, and Tourism’s Millennium Science Initiative through grant IC120009, awarded to the Millennium Institute of Astrophysics, MAS. CR acknowledges support from the CONICYT + PAI Convocatoria Nacional subvencion a instalacion en la academia convocatoria año 2017 PAI77170080.