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