The hard state of black hole candidates: XTE J1752-223

TL;DR

This study presents detailed spectral and timing analysis of the black hole candidate XTE J1752-223 during its hard state, revealing stable properties, a broken power-law spectrum, and characteristic variability features similar to Cyg X-1.

Contribution

First detailed spectral and timing characterization of XTE J1752-223 in its hard state, demonstrating similarities to Cyg X-1 and providing insights into black hole accretion states.

Findings

Spectral fit by broken power-law with high energy cut-off.

Detection of a cold disc (~0.3 keV).

Presence of broad-band Lorentzians and QPO-like features.

Abstract

We present a two-day long RXTE observation and simultaneous Swift data of the bright X-ray transient XTE J1752-223. Spectral and timing properties were stable during the observation. The energy spectrum is well described by a broken power-law with a high energy cut-off. A cold disc (~ 0.3 keV) is observed when Swift/XRT data are considered. The fractional rms amplitude of the aperiodic variability (0.002-128 Hz) is 48.2 +- 0.1% and it is not energy dependent. The continuum of the power density spectrum can be fitted by using four broad-band Lorentzians. A high frequency (~ 21 Hz) component and two weak QPO-like features are also present. Time-lags between soft and hard X-rays roughly follow the relation time-lag~vnu^ {-0.7}, with delays dropping from ~ 0.5 (0.003 Hz) to ~ 0.0015 (>10 Hz) seconds. Our results are consistent with XTE J1752-223 being a black-hole candidate, with all timing and spectral components very similar to those of Cyg X-1 during its canonical hard state.