We re–analyse the ASCA and GINGA X–ray data from BY Cam , a slightly asynchronous magnetic accreting white dwarf .
The spectra are strongly affected by complex absorption , which we model as a continuous ( power law ) distribution of covering fraction and column of neutral material .
This absorption causes a smooth hardening of the spectrum below \sim 3 keV , and is probably produced by material in the preshock column which overlies the X–ray emission region .
The ASCA data show that the intrinsic emission from the shock is not consistent with a single temperature plasma .
Significant iron L emission co–existing with iron K shell lines from H and He–like iron clearly shows that there is a wide range of temperatures present , as expected from a cooling shock structure .
The GINGA data give the best constraints on the maximum temperature emission in the shocked plasma , with kT _ { max } = 21 ^ { +18 } _ { -4 } keV .
Cyclotron cooling should also be important , which supresses the highest temperature bremsstrahlung components , so the X–ray data only give a lower limit on the mass of the white dwarf of M \geq 0.5 M _ { \odot } .
Reflection of the multi–temperature bremsstrahlung emission from the white dwarf surface is also significantly detected .

We stress the importance of modelling all these effects in order to gain a physically self–consistent picture of the X–ray spectra from polars in general and BY Cam in particular .