  We present results from X-ray observations of the quadruply lensed quasar RX
J0911.4+0551 using data obtained with the Advanced CCD Imaging Spectrometer
(ACIS) on board the Chandra X-ray Observatory. The 29 ks observation detects a
total of ~404 X-ray photons (0.3 to 7.0 keV) from the four images of the lensed
quasar. Deconvolution of the aspect corrected data resolves all four lensed
images, with relative positions in good agreement with optical measurements.
When compared to contemporaneous optical data, one of the lensed images
(component A3) is dimmer by a factor of ~6 in X-rays with respect to the 2
brighter images (components A1 and A2). Spectral fitting for the combined
images shows significant intrinsic absorption in the soft (0.2 to 2.4 keV)
energy band, consistent with the mini-BAL nature of this quasar, while a
comparison with ROSAT PSPC observations from 1990 shows a drop of ~6.5 in the
total soft bandpass flux. The observations also detect ~157 X-ray photons
arising from extended emission of the nearby cluster (peaked ~42" SW of
RXJ0911.4+0551) responsible for the large external shear present in the system.
The Chandra observation reveals the cluster emission to be complex and
non-spherical, and yields a cluster temperature of kT = 2.3^{+1.8}_{-0.8} keV
and a 2.0 to 10 keV cluster luminosity within a 1 Mpc radius of L_X =
7.6_{-0.2}^{+0.6} x 10^{43} ergs/s (error bars denote 90% confidence limits).
Our mass estimate of the cluster within its virial radius is 2.3^{+1.8}_{-0.7}
x 10^{14} solar, and is a factor of 2 smaller than, although consistent with,
previous mass estimates based on the observed cluster velocity dispersion.
