Catching Up on State Transitions in Cygnus X-1

TL;DR

This study presents detailed spectral and timing analysis of Cygnus X-1, capturing a rapid state transition from hard to soft within three hours, enhancing understanding of its accretion behavior.

Contribution

It provides the first high-resolution, continuous observation of a full state transition in Cygnus X-1, revealing detailed evolution of timing properties during the process.

Findings

Detected a full state transition in less than three hours.

Observed evolution of time lags during the transition.

Confirmed similarity of behavior to long-term monitoring results.

Abstract

In 2005 February we observed Cygnus X-1 over a period of 10 days quasi-continuously with the Rossi X-ray Timing Explorer and the Ryle telescope. We present the results of the spectral and timing analysis on a timescale of 90 min and show that the behavior of Cyg X-1 is similar to that found during our years long monitoring campaign. As a highlight we present evidence for a full transition from the hard to the soft state that happened during less than three hours. The observation provided a more complete picture of a state transition than before, especially concerning the evolution of the time lags, due to unique transition coverage and analysis with high time resolution.