XRISM Spectroscopy of the Fe Kα Emission Line in the Seyfert Active Galactic Nucleus NGC 4151 Reveals the Disk, Broad-line Region, and Torus

Abstract We present an analysis of the first two XRISM/Resolve spectra of the well-known Seyfert-1.5 active galactic nucleus (AGN) in NGC 4151, obtained in 2023 December. Our work focuses on the nature of the narrow Fe K α 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 Fe K α ,1 (6.404 keV) and K α ,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 ≃ 100 GM / c 2 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 Fe K α 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 <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mspace width="0.25em"/> <mml:mo>=</mml:mo> <mml:mspace width="0.25em"/> <mml:msubsup> <mml:mrow> <mml:mn>1600</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>200</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>+</mml:mo> <mml:mn>400</mml:mn> </mml:mrow> </mml:msubsup> <mml:mspace width="0.25em"/> <mml:mi>km</mml:mi> <mml:mspace width="0.25em"/> <mml:msup> <mml:mrow> <mml:mi mathvariant="normal">s</mml:mi> </mml:mrow> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>1</mml:mn> </mml:mrow> </mml:msup> </mml:math> . Overall, the resolution and sensitivity of XRISM show that the narrow Fe K line in AGN is an effective probe of all key parts of the accretion flow, as it is currently understood. We discuss the implications of these findings for our understanding of AGN accretion, future studies with XRISM, and X-ray-based black hole mass measurements.

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Publication Details

Journal
The Astrophysical Journal Letters
Published
2024-09-01
DOI
https://doi.org/10.3847/2041-8213/ad7397
Citations
33
Primary Topic
Astrophysical Phenomena and Observations
Type
article
Field-Weighted Citation Impact
10.94

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article

XRISM Spectroscopy of the Fe Kα Emission Line in the Seyfert Active Galactic Nucleus NGC 4151 Reveals the Disk, Broad-line Region, and Torus

Kotaro Fukushima, Lía Corrales, Chris Done, Katsuhiro Hayashi et al.
33 citations
The Astrophysical Journal Letters
Astrophysical Phenomena and Observations
10.94
article

XRISM Spectroscopy of the Fe Kα Emission Line in the Seyfert Active Galactic Nucleus NGC 4151 Reveals the Disk, Broad-line Region, and Torus

Kotaro Fukushima, Lía Corrales, Chris Done, Katsuhiro Hayashi, Ehud Behar, Aya Kubota, Kyoko Matsushita, Kouichi Hagino, M. Shidatsu, M. Audard, J. S. Kaastra, Paul P. Plucinsky, Kazuhiro Nakazawa, Erin Kara, S. Eguchi, Hirokazu Odaka, Luigi Gallo, Hideki Uchiyama, Hirofumi Noda, Kosuke Sato, Y. Terada, María Díaz Trigo, Aya Bamba, Eric D. Miller, Yoshiaki Kanemaru, J. M. Mïller, Ryuichi Fujimoto, Satoshi Yamada, Yutaka Fujita, Javier A. García, Andrew E. Szymkowiak, Kenji Hamaguchi, Takayuki Hayashi, T. R. Kallman, Anna Ogorzałek, A. Simionescu, Megan E. Eckart, S. Paltani, Edmund Hodges‐Kluck, Renata Cumbee, Hiroyuki Uchida, Hironori Matsumoto, A. E. Hornschemeier, Irina Zhuravleva, Mai Takeo, Gregory V. Brown, Hiroya Yamaguchi, Adam Foster, Laura Brenneman, Masahiro Tsujimoto, Yoshitomo Maeda, Liyi Gu, Noriko Y. Yamasaki, D. McCammon, Shōgo Kobayashi, K. Yamaoka, Jan‐Uwe Ness, Takeo Minezaki, Michael Loewenstein, Hiromasa Suzuki, Naomi Ota, M. Guainazzi, Takaaki Tanaka, Satoru Katsuda, Tsunefumi Mizuno, Randall K. Smith, Yoshihiro Ueda, M. Tashiro, M. Yamauchi, Ikuyuki Mitsuishi, Teruaki Enoto, Takeshi Go Tsuru, Isamu Hatsukade, Ken Ebisawa, Maurice A. Leutenegger, Takashi Okajima, F. S. Porter, D. Eckert, Maxim Markevitch, R. F. Mushotzky, Natalie Hell, Kumiko Nobukawa, Y. Fukazawa, Makoto Sawada, Scott Hagen, Ralf Ballhausen, Mihoko Yukita, B. R. McNamara, Brian J. Williams, Masayoshi Nobukawa, Misaki Mizumoto, Rozenn Boissay-Malaquin, Margaret Z. Buhariwalla, François Mernier, K. Pottschmidt, Shunji Kitamoto, T. Yoneyama, Xin Xiang, Toshiki Sato, E. Costantini, H. Takahashi, S. Yamada, Yuusuke Uchida, Yuichi Terashima, Yuto Ichinohe, A. Tanimoto, Caroline A. Kilbourne, Shoji Ogawa, Dimitra Gerolymatou, Nagomi Uchida, Shin Watanabe, Yoshitaka Ishisaki, Shinichiro Uno, Manabu Ishida, Kumi Ishikawa, Robert Petre, Hiromi Seta, Hiroshi Murakami, Koji Mori, Hiroshi Nakajima, Hisamitsu Awaki, Richard L. Kelley, Hiroshi Tsunemi, Tadayasu Dotani, Jacco Vink, Akihiro Furuzawa, Yohko Tsuboi, Yuichiro Ezoe, Toru Tamagawa, Keisuke Tamura, Tessei Yoshida, Koji Mukai, Takayoshi Kohmura, Shigeo Yamauchi, Tahir Yaqoob
article en
33 citations

Abstract

Abstract We present an analysis of the first two XRISM/Resolve spectra of the well-known Seyfert-1.5 active galactic nucleus (AGN) in NGC 4151, obtained in 2023 December. Our work focuses on the nature of the narrow Fe K α 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 Fe K α ,1 (6.404 keV) and K α ,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 ≃ 100 GM / c 2 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 Fe K α 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 <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mspace width="0.25em"/> <mml:mo>=</mml:mo> <mml:mspace width="0.25em"/> <mml:msubsup> <mml:mrow> <mml:mn>1600</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>200</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>+</mml:mo> <mml:mn>400</mml:mn> </mml:mrow> </mml:msubsup> <mml:mspace width="0.25em"/> <mml:mi>km</mml:mi> <mml:mspace width="0.25em"/> <mml:msup> <mml:mrow> <mml:mi mathvariant="normal">s</mml:mi> </mml:mrow> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>1</mml:mn> </mml:mrow> </mml:msup> </mml:math> . Overall, the resolution and sensitivity of XRISM show that the narrow Fe K line in AGN is an effective probe of all key parts of the accretion flow, as it is currently understood. We discuss the implications of these findings for our understanding of AGN accretion, future studies with XRISM, and X-ray-based black hole mass measurements.

The Astrophysical Journal LettersVol. 973(1)
National Science Foundation, U.S. Department of Energy, National Aeronautics and Space Administration, Alfred P. Sloan Foundation, Kagoshima University, Nuclear Safety and Security Commission, Rikkyo University, Goddard Space Flight Center, Canadian Space Agency, Science and Technology Facilities Council, Japan Society for the Promotion of Science, RIKEN, Lawrence Livermore National Laboratory
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