English

NuSTAR Uncovers an Extremely Local Compton-thick AGN in NGC 4968

High Energy Astrophysical Phenomena 2020-01-08 v1 Astrophysics of Galaxies

Abstract

We present the analysis of Chandra and NuSTAR spectra of NGC 4968, a local (D\sim44 Mpc) 12μ\mum-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 years), and 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 AGN X-ray emission, is well within the Compton-thick regime, with a minimum column density of 2×10242\times10^{24} cm2^{-2}. The average global column density is high (>3×1023> 3\times10^{23} cm2^{-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 (L210keV,intrinsicL_{\rm 2-10keV,intrinsic}), where the higher end of L210keV,intrinsicL_{\rm 2-10keV,intrinsic} is consistent with expectations from the 12μ\mum luminosity (L210keV,intrinisc7×1042L_{\rm 2-10keV,intrinisc} \sim 7\times10^{42} erg s1^{-1}). Compared with Compton-thick AGN previously observed by {\it 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-BAT survey, underscoring the importance of multi-wavelength selection for obtaining the most complete census of the most hidden black holes.

Keywords

Cite

@article{arxiv.1911.05813,
  title  = {NuSTAR Uncovers an Extremely Local Compton-thick AGN in NGC 4968},
  author = {Stephanie M. LaMassa and Tahir Yaqoob and Peter G. Boorman and Panayiotis Tzanavaris and N. A. Levenson and Poshak Gandhi and Andrew F. Ptak and Timothy M. Heckman},
  journal= {arXiv preprint arXiv:1911.05813},
  year   = {2020}
}

Comments

accepted for publication in ApJ; 20 pages, 8 figures