Logo
ScienceStack
Table of Contents
Fetching ...
Sign In

State-dependent broadband X-ray timing reconfiguration in the changing-look AGN NGC 1566

Yu Tao, Jie Tang, Xuan Wei, Xiaohan Zhang

Abstract

NGC 1566 has exhibited dramatic state changes in its X-ray spectrum, but the evolution of its broadband timing properties remains poorly constrained. We combine long-term Swift monitoring with high-time-resolution XMM-Newton observations to model the broadband X-ray power spectral density (PSD) in the dim and bright states. In the hard band, the PSD bend frequency shifts by about 1 dex between the two states, implying a substantially longer characteristic variability timescale in the bright state. The relative timing behaviour of the soft and hard bands also changes with state. In the dim state, the soft-band bend frequency is higher than the hard-band value by about 0.49 dex, whereas in the bright state the two become broadly consistent. The broadband variability evolution of NGC 1566 therefore involves not only an overall shift in characteristic timescale, but also a state-dependent change in the soft-hard timing relation, from a more stratified to a more tightly coupled configuration. Combined with previous spectral results, this supports a genuine reconfiguration of the inner radiative structure during the changing-look transition.

State-dependent broadband X-ray timing reconfiguration in the changing-look AGN NGC 1566

Abstract

NGC 1566 has exhibited dramatic state changes in its X-ray spectrum, but the evolution of its broadband timing properties remains poorly constrained. We combine long-term Swift monitoring with high-time-resolution XMM-Newton observations to model the broadband X-ray power spectral density (PSD) in the dim and bright states. In the hard band, the PSD bend frequency shifts by about 1 dex between the two states, implying a substantially longer characteristic variability timescale in the bright state. The relative timing behaviour of the soft and hard bands also changes with state. In the dim state, the soft-band bend frequency is higher than the hard-band value by about 0.49 dex, whereas in the bright state the two become broadly consistent. The broadband variability evolution of NGC 1566 therefore involves not only an overall shift in characteristic timescale, but also a state-dependent change in the soft-hard timing relation, from a more stratified to a more tightly coupled configuration. Combined with previous spectral results, this supports a genuine reconfiguration of the inner radiative structure during the changing-look transition.
Paper Structure (10 sections, 5 equations, 5 figures, 4 tables)

This paper contains 10 sections, 5 equations, 5 figures, 4 tables.

Table of Contents

  1. Introduction
  2. Data and methods
  3. Data reduction and state selection
  4. PSD modelling and joint constraints
  5. Results
  6. State dependence of the broadband hard-band PSD
  7. State separation in parameter space
  8. State evolution of the energy dependence
  9. Discussion and conclusions
  10. Supplementary joint-constraint distributions

Figures (5)

  • Figure 1: Swift/XRT 2--10 keV light curve of NGC 1566.
  • Figure 2: XMM-Newton 2--10 keV light curve of NGC 1566.
  • Figure 3: Joint broadband PSD constraints for NGC 1566 in the 2--10 keV band. Left: dim state. Right: bright state. Shaded regions show the 16th--84th weighted percentile range derived from the normalized joint weights; dashed lines mark the best-supported bend frequencies.
  • Figure 4: Joint-constraint contours in the $\alpha_{\rm high}$--$\log f_{\rm b}$ plane for the dim (blue) and bright (pink) states. Left: 2--10 keV band. Right: 0.3--2 keV band. Contours enclose 68, 90, and 99 per cent of the normalized joint weight, with shading for the innermost 68 per cent region.
  • Figure 5: Joint broadband PSD constraints for NGC 1566 in the 0.3--2 keV band. Left: dim state. Right: bright state. Shaded regions show the 16th--84th weighted percentile range derived from the normalized joint weights; dashed lines mark the best-supported bend frequencies.