  We present the results of a three-week daily monitoring campaign on the
quasar 3C 279 by the X-ray satellites RXTE and ROSAT. A cross correlation
provides no evidence for any time lag between the very similar soft and hard
X-ray light curves, and the source shows no significant spectral variability
over the observing period. There is no evidence to support the presence of a
soft excess, with a 99 per cent upper limit on any such component of 25 per
cent of the total observed luminosity in the 0.1-2 keV band (< 3 x 10^38 W).
This fraction (but not the luminosity) is significantly less than that of the
soft excess observed in 3C 273.

Astrophysics