High-Frequency Power Spectrum of AGN NGC 4051 Revealed by NICER

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Rani_2025_ApJL_981_L18.pdf (1.29 MB)

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https://iopscience.iop.org/article/10.3847/2041-8213/adace8

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http://doi.org/10.3847/2041-8213/adace8
 http://hdl.handle.net/11603/37675

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UMBC Faculty Collection
UMBC Center for Space Sciences and Technology (CSST) / Center for Research and Exploration in Space Sciences & Technology II (CRSST II)

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Author/Creator ORCID

https://orcid.org/0000-0001-5711-084X

Date

2025-02-27

Type of Work

journal articles
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Citation of Original Publication

Rani, B., Jungeun Kim, I. Papadakis, K. C. Gendreau, M. Masterson, K. Hamaguchi, E. Kara, S.-S. Lee, and R. Mushotzky. “High-Frequency Power Spectrum of Active Galactic Nucleus NGC 4051 Revealed by NICER.” The Astrophysical Journal Letters 981, no. 1 (February 2025): L18. https://doi.org/10.3847/2041-8213/adace8.

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This work was written as part of one of the author's official duties as an Employee of the United States Government and is therefore a work of the United States Government. In accordance with 17 U.S.C. 105, no copyright protection is available for such works under U.S. Law.
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Astrophysics - High Energy Astrophysical Phenomena

Abstract

Variability studies offer a compelling glimpse into black hole dynamics, and Neutron Star Interior Composition Explorer's (NICER's) remarkable temporal resolution propels us even further. NICER observations of an active galactic nucleus (AGN), NGC 4051, have charted the geometry of the emission region of the central supermassive black hole. Our investigation of X-ray variability in NGC 4051 has detected extreme variations spanning a factor of 40–50 over a mere 10–12 hr. For the first time, we have constrained the X-ray power spectral density (PSD) of the source to 0.1 Hz, corresponding to a temporal frequency of 10⁴ Hz in a galactic X-ray binary with a mass of 10 M⊙. No extra high-frequency break/bend or any quasiperiodic oscillations are found. Through detailed analysis of energy-dependent PSDs, we found that the PSD normalization, the high-frequency PSD slope, as well as the bending frequency remain consistent across all energies within the 0.3–3 keV band, revealing the presence of a constant temperature corona. These significant findings impose critical constraints on current models of X-ray emission and variability in AGN.