  The RXTE observed four outbursts of the accreting X-ray binary transient
source, GX 304-1 in 2010 and 2011. We present results of detailed 3-100 keV
spectral analysis of 69 separate observations, and report a positive
correlation between cyclotron line parameters, as well as other spectral
parameters, with power law flux. The cyclotron line energy, width and depth
versus flux, and thus luminosity, correlations show a flattening of the
relationships with increasing luminosity, which are well described by
quasi-spherical or disk accretion that yield the surface magnetic field to be
~60 keV. Since HEXTE cluster A was fixed aligned with the PCA field of view and
cluster B was fixed viewing a background region 1.5 degrees off of the source
direction during these observations near the end of the RXTE mission, the
cluster A background was estimated from cluster B events using HEXTEBACKEST.
This made possible the detection of the ~55 keV cyclotron line and an accurate
measurement of the continuum. Correlations of all spectral parameters with the
primary 2-10 keV power law flux reveal it to be the primary driver of the
spectral shape. The accretion is found to be in the collisionless shock braking
regime.
