Timing and spectral study of XB 1254-690 using new RXTE PCA data
  We have analyzed the new Rossi X-ray Timing Explorer Proportional Counter
Array data of the atoll neutron star (NS) low-mass X-ray binary (LMXB) system
XB 1254-690. The colour-colour diagram shows that the source was in the
high-intensity banana state. We have found two low-frequency candidate peaks
with single trial significances of ~ 2.65 X 10^{-8} and ~ 7.39 X 10^{-8} in the
power spectra. After taking into account the number of trials, the joint
probability of appearance of these two peaks in the data set only by chance is
~ 4.5 X 10^{-4}, and hence a low-frequency QPO can be considered to be detected
with a significance of ~ 4.5 X 10^{-4}, or, ~ 3.5\sigma for the first time from
this source. We have also done the first systematic X-ray spectral study of XB
1254-690, and found that, while one-component models are inadequate,
three-component models are not required by the data. We have concluded that a
combined broken-powerlaw and Comptonization model best describes the source
continuum spectrum among 19 two-component models. The plasma temperature (~ 3
keV) and the optical depth (~ 7) of the Comptonization component are consistent
with the previously reported values for other sources. However, the use of a
broken-powerlaw component to describe NS LMXB spectra has recently been
started, and we have used this component for XB 1254-690 for the first time. We
have attempted to determine the relative energy budgets of the accretion disc
and the boundary layer using the best-fit spectral model, and concluded that a
reliable estimation of these budgets requires correlations among time
variations of spectral properties in different wavelengths.
