  This study confirms MLS110213:022733+130617 as a new eclipsing polar. We
performed optical spectroscopic, polarimetric and photometric follow-up of this
variable source identified by the Catalina Real Time Transient Survey. Using
the mid-eclipse times, we estimated an orbital period of 3.787 h, which is
above the orbital period gap of the cataclysmic variables. There are nine other
known polars with longer orbital periods, and only four of them are eclipsing.
We identified high and low-brightness states and high polarization modulated
with the orbital period. The spectra are typical of polars, with strong high
ionization emission lines and inverted Balmer decrement. The HeII4686 A line is
as strong as Hbeta. We modelled the photometric and polarimetric bright-state
light curves using the CYCLOPS code. Our modelling suggests an extended
emitting region on the WD surface, with a mean temperature of 9 keV and B in
the range 18 -- 33 MG, although the possibility that it could be a two-pole
accretor cannot yet be ruled out. The WD mass estimated from the shock
temperature is 0.67 Msol. The derived parameters are consistent with the
eclipse profile. The distance was estimated as 406+- 54 pc using the
Period-Luminosity-Colours method. MLS110213 populates a rare sub-group of
polars, near the upper limit of the period distribution, important to
understand the evolution of mCVs.
