Calculating Time Lags from Unevenly Sampled Light Curves
Abstract
Timing techniques are powerful tools to study dynamical astrophysical phenomena. In the X-ray band, they offer the potential of probing accretion physics down to the event horizon. Recent work has used frequency- and energy-dependent time lags as tools for studying relativistic reverberation around the black holes in several Seyfert galaxies. This was achieved due to the evenly sampled light curves obtained using XMM-Newton. Continuously sampled data are, however, not always available and standard Fourier techniques are not applicable. Here, building on the work of Miller et al., we discuss and use a maximum likelihood method to obtain frequency-dependent lags that takes into account light curve gaps. Instead of calculating the lag directly, the method estimates the most likely lag values at a particular frequency given two observed light curves. We use Monte Carlo simulations to assess the method's applicability and use it to obtain lag-energy spectra from Suzaku data for two objects, NGC 4151 and MCG-5-23-16, that had previously shown signatures of iron K reverberation. The lags obtained are consistent with those calculated using standard methods using XMM-Newton data.
- Publication:
-
The Astrophysical Journal
- Pub Date:
- November 2013
- DOI:
- 10.1088/0004-637X/777/1/24
- arXiv:
- arXiv:1308.5852
- Bibcode:
- 2013ApJ...777...24Z
- Keywords:
-
- black hole physics;
- galaxies: active;
- galaxies: nuclei;
- methods: data analysis;
- Astrophysics - High Energy Astrophysical Phenomena
- E-Print:
- Accepted for publication in ApJ