Journal
ASTRONOMY & ASTROPHYSICS
Volume 664, Issue -, Pages -Publisher
EDP SCIENCES S A
DOI: 10.1051/0004-6361/202142473
Keywords
galaxies: active; X-rays: galaxies; methods: data analysis
Categories
Funding
- European Union [860744]
- ANID - Millennium Science Initiative Program [ICN12_009]
- CATA-Basal [AFB-170002]
- CATA-Puente [ACE210002]
- CATA2 [FB210003]
- FONDECYT [1190818, 1200495, PIA ACT172033, NCN19_058]
- Max-Planck Society
- Fondecyt Iniciacion [11190831]
- ANID BASAL [FB210003]
- Science and Technology Facilities Council [ST/T000244/1]
- FONDECYT Postdoctorado [3190213]
- Marie Curie Actions (MSCA) [860744] Funding Source: Marie Curie Actions (MSCA)
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This study clarifies the nature and origin of the narrow Fe K alpha emission in active galactic nuclei (AGN) through X-ray spectral, timing, and imaging analysis. The majority of the narrow Fe K alpha emission is found to originate from the outer broad line region or outer accretion disk.
Context. The 6.4 keV Fe K alpha emission line is a ubiquitous feature in X-ray spectra of active galactic nuclei (AGN), and its properties track the interaction between the variable primary X-ray continuum and the surrounding structure from which it arises. Aims. We clarify the nature and origin of the narrow Fe K alpha emission using X-ray spectral, timing, and imaging constraints, plus possible correlations to AGN and host galaxy properties, for 38 bright nearby AGN (z < 0.5) from the Burst Alert Telescope AGN Spectroscopic Survey. Methods. Modeling Chandra and XMM-Newton spectra, we computed line full-width half-maxima (FWHMs) and constructed Fe K alpha line and 2-10 keV continuum light curves. The FWHM provides one estimate of the Fe K alpha emitting region size, R-FeK alpha, assuming virial motion. A second estimate comes from comparing the degree of correlation between the variability of the continuum and line-only light curves, compared to simulated light curves. Finally, we extracted Chandra radial profiles to place upper limits on R-FeK alpha. Results. For 90% (21/24) of AGN with FWHM measurements, R-FeK alpha is smaller than the fiducial dust sublimation radius, R-sub. From timing analysis, 37 and 18 AGN show significant continuum and Fe K alpha variability, respectively. Despite a wide range of variability properties, the constraints on the Fe K alpha photon reprocessor size independently confirm that R-FeK alpha is smaller than R-sub in 83% of AGN. Finally, the imaging analysis yields loose upper limits for all but two sources; notably, the Circinus Galaxy and NGC 1068 show significant but subdominant extended Fe K alpha emission out to similar to 100 and similar to 800 pc, respectively. Conclusions. Based on independent constraints, we conclude that the majority of the narrow Fe K alpha emission in typical AGN predominantly arises from regions smaller than and presumably inside R-sub, and thus it is associated either with the outer broad line region or outer accretion disk. However, the large diversity of continuum and narrow Fe K alpha variability properties are not easily accommodated by a universal scenario.
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