NuSTAR Uncovers an Extremely Local Compton-thick AGN in NGC 4968
Abstract
We present the analysis of Chandra and NuSTAR spectra of NGC 4968, a local (D ∼ 44 Mpc) 12 μm selected Seyfert 2 galaxy, enshrouded within Compton-thick layers of obscuring gas. We find no evidence of variability between the Chandra and NuSTAR observations (separated by 2 yr), nor between the two NuSTAR observations (separated by 10 months). Using self-consistent X-ray models, we rule out the scenario where the obscuring medium is nearly spherical and uniform, contradicting the results implied by the <10 keV Chandra spectrum. The line-of-sight column density, from intervening matter between the source and observer that intercepts the intrinsic active galactic nucleus (AGN) X-ray emission, is well within the Compton-thick regime, with a minimum column density of 2 × 1024 cm-2. The average global column density is high (>3 × 1023 cm-2), with both Compton-thick and Compton-thin solutions permitted, depending on the X-ray spectral model. The spectral models provide a range of intrinsic AGN continuum parameters and implied 2-10 keV luminosities (L 2-10 keV,intrinsic), where the higher end of L 2-10 keV,intrinsic is consistent with expectations from the 12 μm luminosity (L 2-10 keV,intrinisc ∼ 7 × 1042 erg s-1). Compared with Compton-thick AGN previously observed by NuSTAR, NGC 4968 is among the most intrinsically X-ray luminous. However, despite its close proximity and relatively high intrinsic X-ray luminosity, it is undetected by the 105 month Swift-Burst Alert Telescope survey, underscoring the importance of multiwavelength selection for obtaining the most complete census of the most hidden black holes.
- Publication:
-
The Astrophysical Journal
- Pub Date:
- December 2019
- DOI:
- 10.3847/1538-4357/ab552c
- arXiv:
- arXiv:1911.05813
- Bibcode:
- 2019ApJ...887..173L
- Keywords:
-
- Active galactic nuclei;
- X-ray active galactic nuclei;
- Seyfert galaxies;
- 16;
- 2035;
- 1447;
- Astrophysics - High Energy Astrophysical Phenomena;
- Astrophysics - Astrophysics of Galaxies
- E-Print:
- accepted for publication in ApJ