  The spectral and temporal evolution during X-ray outbursts give important
clues on the accretion process and radiation mechanism in black-hole X-ray
binaries (BH XRBs). A set of Swift and RXTE observations were executed to
monitor the 2008 outburst of the black-hole candidate Swift J1842.5-1124. We
investigate these data to explore the accretion physics in BH XRBs. We carry
out a comprehensive spectral and timing analysis on all the available pointing
observations, including fitting both X-ray spectra and power density spectra,
measuring the optical and near-ultraviolet flux density. We also search for
correlations among the spectral and timing parameters. The observed properties
of Swift J1842.5-1124 are similar to other BH XRBs in many respects, for
example the hardness-intensity diagram and hardness-rms diagram. The type-C
quasi-periodic oscillations (QPOs) were observed as the source started to
transit from the low-hard state to the high-soft state. The frequency of QPOs
correlate with intensity and the hard component index, and anti-correlate with
the hardness and the total fractional rms. These relations are consistent with
the Lense-Thirring precession model. The estimated U-band flux changed with the
X-ray flux, while the flux density at the V band remained 0.26 mJy. These
results imply that the X-ray reprocessing or the tail of thermal emission from
the outer disk contributes a significant fraction of the U-band radiation;
alternatively, the companion star or the jet dominates the flux at longer
wavelengths.
