X-ray lags in PDS 456 revealed by Suzaku observations
Monthly Notices of the Royal Astronomical Society
Oxford University Press
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Chiang, C., Cackett, E., Zoghbi, A., Fabian, A., Kara, E., Parker, M., Reynolds, C., & et al. (2017). X-ray lags in PDS 456 revealed by Suzaku observations. Monthly Notices of the Royal Astronomical Society, 472 (2), 1473-1481. https://doi.org/10.1093/mnras/stx2069
X-ray reverberation lags from the vicinity of supermassive black holes have been detected in almost 30 active galactic nuclei (AGNs). The soft lag, which is the time delay between the hard and soft X-ray light curves, is usually interpreted as the time difference between the direct and reflected emission, but is alternatively suggested to arise from the direct and scattering emission from distant clouds. By analysing the archival Suzaku observations totalling an exposure time of ∼770 ks, we discover a soft lag of 10 ± 3.4 ks at 9.58 × 10−6 Hz in the luminous quasar PDS 456, which is the longest soft lag and lowest Fourier frequency reported to date. In this study, we use the maximum likelihood method to deal with non-continuous nature of the Suzaku light curves. The result follows the mass–scaling relation for soft lags, which further supports that soft lags originate from the innermost areas of AGNs and hence are best interpreted by the reflection scenario. Spectral analysis has been performed in this work and we find no evidence of clumpy partial-covering absorbers. The spectrum can be explained by a self-consistent relativistic reflection model with warm absorbers, and spectral variations over epochs can be accounted for by the change of the continuum, and of column density and ionization states of the warm absorbers.
galaxies: Seyfert, X-rays: galaxies
EMC gratefully acknowledges support from the NSF through CAREER award number AST-1351222. CSR thanks NASA for support under grant NNX15AU54G. ACF acknowledges ERC Advanced Grant 340442.
SCIENCE & TECHNOLOGY FACILITIES COUNCIL (ST/N000927/1)
European Research Council (340442)
External DOI: https://doi.org/10.1093/mnras/stx2069
This record's URL: https://www.repository.cam.ac.uk/handle/1810/274627