  The Seyfert 1 galaxy Mrk 279 was observed by XMM-Newton in November 2005 in
three consecutive orbits, showing significant short-scale variability (average
soft band variation in flux ~20%). The source is known to host a two-component
warm absorber with distinct ionisation states from a previous Chandra
observation. We aim to study the warm absorber in Mrk 279 and investigate any
possible response to the short-term variations of the ionising flux, and to
assess whether it has varied on a long-term time scale with respect to the
Chandra observation. We find no significant changes in the warm absorber on
neither short time scales (~2 days) nor at longer time scales (two and a half
years), as the variations in the ionic column densities of the most relevant
elements are below the 90% confidence level. The variations could still be
present but are statistically undetected given the signal-to-noise ratio of the
data. Starting from reasonable standard assumptions we estimate the location of
the absorbing gas, which is likely to be associated with the putative dusty
torus rather than with the Broad Line Region if the outflowing gas is moving at
the escape velocity or larger.
