# Long term variability of Swift J1753.5-0127]{Long term variability of Swift J1753.5-0127: X-ray spectral-temporal correlations during state transitions

## TL;DR

This study analyzes the long-term spectral and temporal variability of Swift J1753.5-0127 during its outburst, revealing correlations during state transitions and proposing X-ray time lags as indicators of these transitions.

## Contribution

It provides new insights into the spectral-temporal evolution of Swift J1753.5-0127 and identifies X-ray time lags as potential markers for state transitions in black hole candidates.

## Key findings

- Frequency-dependent time lag increases during state transition.
- Type-C QPO frequency correlates with fractional rms and photon index.
- Source exhibits typical hard state behavior with transitions to intermediate state.

## Abstract

We studied the long-term evolution of the spectral-temporal correlated properties of the black hole candidate Swift J1753.5-0127 from the onset of its outburst until 2011 with the Rossi X-ray Timing Explorer (RXTE). The source stayed most of its lifetime during hard state, with occasionally transitioned to the hard intermediate state. Similar to typical black hole transients, Swift J1753.5-0127 traces a clear hard line in absolute rms - intensity diagram during the low hard state, with expected highest absolute rms, while shows a clear turn during the hard intermediate state, accompanied by lower absolute rms. Different from Cyg X-1, we found that frequency-dependent time lag increased significantly in the 0.02 -- 3.2 Hz band during state transition in this source. The X-ray time lags in 0.02 -- 3.2 Hz can therefore be used as indicators of state transition in this source. Type-C QPO frequency is positively related with its fractional rms and X-ray photon index, suggesting a moving inwards disk/corona scenario. We discussed the physical interpretation of our results in our paper.