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NuSTAR Observations of Four Nearby X-ray Faint AGN: Low Luminosity or Heavy Obscuration?

Zappacosta, L.; Stern, D.; Ricci, C.; Nardini, E.; Masini, A.; Marchesi, S.; Lanz, L.; Koss, M.J.; Harrison, F.A.; Farrah, D.; Moro, A. Del; Chen, C-TJ.; Brightman, M.; Brandt, W.N.; Boorman, P.G.; Bauer, F.E.; Ballantyne, D.R.; Baloković, M.; Asmus, D.; Lansbury, G.B.; Gandhi, P.; Alexander, D.M.; Annuar, A.

NuSTAR Observations of Four Nearby X-ray Faint AGN: Low Luminosity or Heavy Obscuration? Thumbnail


L. Zappacosta

D. Stern

C. Ricci

E. Nardini

A. Masini

S. Marchesi

L. Lanz

M.J. Koss

F.A. Harrison

D. Farrah

A. Del Moro

C-TJ. Chen

M. Brightman

W.N. Brandt

P.G. Boorman

F.E. Bauer

D.R. Ballantyne

M. Baloković

D. Asmus

G.B. Lansbury

P. Gandhi

A. Annuar


We present NuSTAR observations of four active galactic nuclei (AGN) located within 15 Mpc. These AGN, namely ESO 121-G6, NGC 660, NGC 3486 and NGC 5195, have observed X-ray luminosities of L2-10 keV, obs ≲ 1039 erg s−1, classifying them as low luminosity AGN (LLAGN). We perform broadband X-ray spectral analysis for the AGN by combining our NuSTAR data with Chandra or XMM-Newton observations to directly measure their column densities (NH) and infer their intrinsic power. We complement our X-ray data with archival and new high angular resolution mid-infrared (mid-IR) data for all objects, except NGC 5195. Based on our X-ray spectral analysis, we found that both ESO 121-G6 and NGC 660 are heavily obscured (NH > 1023 cm−2; L2-10 keV, int ∼ 1041 erg s−1), and NGC 660 may be Compton-thick. We also note that the X-ray flux and spectral slope for ESO 121-G6 have significantly changed over the last decade, indicating significant changes in the obscuration and potentially accretion rate. On the other hand, NGC 3486 and NGC 5195 appear to be unobscured and just mildly obscured, respectively, with L2-10 keV, int < 1039 erg s−1; i.e., genuine LLAGN. Both of the heavily obscured AGN have Lbol > 1041 erg s−1 and λEdd ≳ 10−3, and are detected in high angular resolution mid-IR imaging, indicating the presence of obscuring dust on nuclear scale. NGC 3486 however, is undetected in high-resolution mid-IR imaging, and the current data do not provide stringent constraints on the presence or absence of obscuring nuclear dust in the AGN.

Journal Article Type Article
Acceptance Date Jun 15, 2020
Online Publication Date Jun 27, 2020
Publication Date 2020-09
Deposit Date Jun 29, 2020
Publicly Available Date Aug 23, 2020
Journal Monthly Notices of the Royal Astronomical Society
Print ISSN 0035-8711
Electronic ISSN 1365-2966
Publisher Royal Astronomical Society
Peer Reviewed Peer Reviewed
Volume 497
Issue 1
Pages 229-245
Public URL


Published Journal Article (3.8 Mb)

Copyright Statement
This article has been accepted for publication in Monthly Notices of the Royal Astronomical Society ©: 2020 The Author(s). Published by Oxford University Press on behalf of the Royal Astronomical Society. All rights reserved.

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