We report on the discovery of variable circular polarization in the SW Sex star LS Pegasi .
The observed modulation has an amplitude of \approx 0.3 ~ { } \% and a period of 29.6 minutes , which we assume as the spin period of the magnetic white dwarf .
We also detected periodic flaring in the blue wing of H _ { \beta } , with a period of 33.5 minutes .
The difference between both frequencies is just the orbital frequency , so we relate the 33.5-min modulation to the beat between the orbital and spin period .
We propose a new accretion scenario in SW Sex stars , based on the shock of the disk-overflown gas stream against the white dwarf ’ s magnetosphere , which extends to the corotation radius .
From this geometry , we estimate a magnetic field strength of B _ { \mathrm { 1 } } \sim 5 –15 MG. Our results indicate that magnetic accretion plays an important role in SW Sex stars and we suggest that these systems are probably Intermediate Polars with the highest mass accretion rates .