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内容記述 |
We present an analysis of the first two XRISM/Resolve spectra of the well-known Seyfert-1.5 active galactic nucleus (AGN) in NGC4151, obtained in 2023 December. Our work focuses on the nature of the narrow FeKα emission line at 6.4 keV, the strongest and most common X-ray line observed in AGN. The total line is found to consist of three components. Even the narrowest component of the line is resolved with evident FeKα,1 (6.404 keV) and Kα,2 (6.391 keV) contributions in a 2:1 flux ratio, fully consistent with neutral gas with negligible
bulk velocity. Subject to the limitations of our models, the narrowest and intermediate-width components are consistent with emission from optically thin gas, suggesting that they arise in a disk atmosphere and/or wind.
Modeling the three line components in terms of Keplerian broadening, they are readily associated with (1) the inner wall of the “torus,” (2) the innermost optical “broad-line region” (or “X-ray BLR”), and (3) a region with a radius of r;100GM/c2 that may signal a warp in the accretion disk. Viable alternative explanations of the broadest
component include a fast-wind component and/or scattering; however, we find evidence of variability in the narrow FeKα line complex on timescales consistent with small radii. The best-fit models are statistically superior
to simple Voigt functions, but when fit with Voigt profiles the time-averaged lines are consistent with a projected velocity broadening of FWHM = 1600+ 400 200 kms1
. Overall, the resolution and sensitivity of XRISM show that the narrow FeK line in AGN is an effective probe of all key parts of the accretion flow, as it is currently understood.
Wediscuss the implications of these findings for our understanding of AGN accretion, future studies with XRISM, and X-ray-based black hole mass measurements. |
https://iopscience.iop.org/article/10.3847/2041-8213/ad7397
