  Focal plane X-ray polarimetry is intended for relatively bright sources with
a negligible impact of background. However this might not be always possible
for IXPE (Imaging X-ray Polarimetry Explorer) when observing faint extended
sources like supernova remnants. We present for the first time the expected
background of IXPE by Monte Carlo simulation and its impact on real
observations of point and extended X-ray sources. The simulation of background
has been performed by Monte Carlo based on GEANT4 framework. The spacecraft and
the detector units have been modeled, and the expected background components in
IXPE orbital environment have been evaluated. We studied different background
rejection techniques based on the analysis of the tracks collected by the Gas
Pixel Detectors on board IXPE. The estimated background is about 2.9 times
larger than the requirement, yet it is still negligible when observing point
like sources. Albeit small, the impact on supernova remnants indicates the need
for a background subtraction for the observation of the extended sources.
