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NuStar Hard X-Ray View of Low-Luminosity Active Galactic Nuclei: High-Energy Cutoff and Truncated Thin DiskWe report the analysis of simultaneous XMM-Newton+Nuclear Spectroscopic Telescope Array (NuSTAR) observations of two low-luminosity active galactic nuclei (LLAGNs), NGC3998 and NGC4579. We do not detect any significant variability in either source over the ∼3 day length of the NuSTAR observations. The broadband 0.5–60 keV spectrum of NGC3998 is best fit with a cutoff power law, while the one for NGC4579 is best fit with a combination of a hot thermal plasma model, a power law, and a blend of Gaussians to fit an Fe complex observed between 6 and 7 keV. Our main spectral results are the following: (1) neither source shows any reflection hump with 3σ reflection fraction upper limits of R < 0.3 and R < 0.18 for NGC3998 and NGC4579, respectively; (2) the 6–7 keV line complex in NGC4579 could be fit with either a narrow Fe K line at 6.4 keV and a moderately broad Fe XXV line or with three relatively narrow lines, which include contribution from Fe XXVI; (3) the NGC4579 flux is 60% brighter than previously detected with XMM-Newton, accompanied by a hardening in the spectrum; (4) we measure a cutoff energy = - E 107+ cut 18 27 keV in NGC3998, which represents the lowest and best constrained high-energy cutoff ever measured for an LLAGN; (5) the NGC3998 spectrum is consistent with a Comptonization model with either a sphere (τ ≈ 3 ± 1) or slab (τ ≈ 1.2 ± 0.6) geometry, corresponding to plasma temperatures between 20 and 150 keV. We discuss these results in the context of hard X-ray emission from bright AGNs, other LLAGNs, and hot accretion flow models.
Document ID
20190002393
Acquisition Source
Goddard Space Flight Center
Document Type
Reprint (Version printed in journal)
External Source(s)
doi:10.3847/1538-4357/aaf38b
Authors
Younes, George (George Washington Univ. Washington, DC, United States)
Ptak, Andrew (NASA Goddard Space Flight Center Greenbelt, MD, United States)
Ho, Luis C. (Peking University Beijing, China)
Xie, Fu-Guo (Shanghai Astronomical Observatory China)
Terasima, Yuichi (Ehime University Matsuyama, Japan)
Yuan, Feng (Shanghai Astronomical Observatory China)
Huppenkothen, Daniela (Washington Univ. Seattle, WA, United States)
Yukita, Mihoko (Johns Hopkins Univ. Baltimore, MD, United States)
Date Acquired
April 11, 2019
Publication Date
January 10, 2019
Publication Information
Publication: The Astrophysical Journal
Publisher: American Astronomical Society
Volume: 870
Issue: 2
ISSN: 0004-637X
e-ISSN: 1538-4357
Subject Category
Astrophysics
Report/Patent Number
GSFC-E-DAA-TN66139
Funding Number(s)
CONTRACT_GRANT: QYZDJSSW-SYS008
CONTRACT_GRANT: NSFS 17ZR1435800
CONTRACT_GRANT: NSFC 11573051
CONTRACT_GRANT: NSFC 11661161012
CONTRACT_GRANT: NSFC 11473002
CONTRACT_GRANT: NSFC 11633006
CONTRACT_GRANT: NSFC 11650110427
CONTRACT_GRANT: NSFC 11873074
CONTRACT_GRANT: QYZDB-SSW-SYS033
CONTRACT_GRANT: JSPS 15H02070
CONTRACT_GRANT: 2016YFA0400804
CONTRACT_GRANT: 2016YFA0400704
CONTRACT_GRANT: JSPS 16K05296
CONTRACT_GRANT: NSFC 11303008
Distribution Limits
Public
Copyright
Use by or on behalf of the US Gov. Permitted.

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