Evidence for Nonlinear X-Ray Variability from the Broad-Line Radio Galaxy 3C 390.3

摘要

We present an analysis of the light curve from ROSAT HRI monitoring observations of the broad- line radio galaxy 3C 390.3. Observed every 3 days for about 9 months, this is the first well-sampled X-ray light curve on these timescales. The flares and quiescent periods in the light curve suggest that the variability is nonlinear, and a statistical test yields a detection with ≥6 σconfidence. The structure function has a steep slope, ～0.7, while the periodogram is much steeper, with a slope ～2.6, with the difference partially due to a linear trend in the data. The nonstationary character of the light curve could be evidence that the variability power spectrum has not turned over to low frequencies, or it could be an essential part of the nonlinear process.