Kavli Affiliate: Erin Kara
| First 5 Authors: Yerong Xu, Ciro Pinto, Erin Kara, Stefano Bianchi, William Alston
| Summary:
The time lag between soft and hard X-ray photons has been observed in many
active galactic nuclei (AGN) and can reveal the accretion process and geometry
around supermassive black holes (SMBHs). High-frequency Fe K and soft lags are
considered to originate from the light-travel distances between the corona and
the accretion disk, while the propagation of the inward mass accretion
fluctuation usually explains the low-frequency hard lags. Ultra-fast outflows
(UFOs), with a velocity range of 0.03-0.3c, have also been discovered in
numerous AGN and are believed to be launched from the inner accretion disk.
However, it remains unclear whether UFOs can affect the X-ray time lags. As a
pilot work, we aim to investigate the potential influence of UFOs on X-ray time
lags of AGN in a small sample. By performing the UFO-resolved Fourier spectral
timing analysis of archival XMM-Newton observations of three AGN with transient
UFOs: PG 1448+273, IRAS 13224-3809, and PG 1211+143, we compare their X-ray
timing products, such as lag-frequency and lag-energy spectra, of observations
with and without UFO obscuration. Our results find that in each AGN,
low-frequency hard lags become weak or even disappear when they are accompanied
by UFOs. In the high-frequency domain, soft lags remain unchanged while the Fe
K reverberation lags tentatively disappear. The comparison between timing
products of low- and high-flux observations on another three AGN without UFOs
(Ark 564, NGC 7469, and Mrk 335) suggests that the disappearance of
low-frequency hard lags is likely related to the emergence of UFOs, not
necessarily related to the source flux. We conclude that the presence of UFOs
can affect X-ray time lags of AGN by suppressing the low-frequency hard lags,
which can be explained by an additional time delay introduced by UFOs or disk
accretion energy carried away by UFOs.
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