Effects of ultrafast outflows on X-ray time lags in active galactic nuclei

Context. The time lag between soft (e.g., 0.3-1 keV) and hard (e.g., 1-4 keV) X-ray photons has been observed in many active galactic nuclei (AGNs) and can reveal the accretion process and geometry around supermassive black holes. 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. Ultrafast outflows (UFOs) with a velocity range of similar to 0.03 to 0.3c have also been discovered in numerous AGNs and are believed to be launched from the inner accretion disk. However, it remains unclear whether UFOs can affect the X-ray time lags. Aims. As a pilot work, we aim to investigate the potential influence of UFOs on X-ray time lags of AGNs in a small sample. Methods. By performing the UFO-resolved Fourier spectral timing analysis of archival XMM-Newton observations of three AGNs with transient UFOs - PG 1448+273, IRAS 13224-3809, and PG 1211+143 - we compare the X-ray timing products, such as lag-frequency and lag-energy spectra, of observations with and without UFO obscuration. Results. Our results find that in each AGN, low-frequency hard lags become weak or even disappear when they are accompanied by UFOs. This change is confirmed by Monte Carlo simulations at a confidence level of at least 2.7 sigma. 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 AGNs 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. Conclusions. The presence of UFOs can affect X-ray time lags of AGNs by suppressing the low-frequency hard lags, which can be explained by an additional time delay introduced by UFOs or disk accretion energy, which should transferred to heat the corona, carried away by UFOs.