\gamma Cas is a classical B0.5e star known to be a unique X-ray source by virtue of its moderate L _ { x } ( 10 ^ { 33 } erg s ^ { -1 } ) , hard X-ray spectrum , and light curve punctuated by ubiquitous flares and slow undulations .
The peculiarities of this star have led to a controversy concerning the origin of these emissions ; whether they are from wind infall onto a putative degenerate companion , as in the case of normal Be/X-ray binaries , or from the Be star itself .
Recently , much progress has been made to resolve this question : ( 1 ) the discovery that \gamma Cas is a moderately eccentric binary system ( P = 203.59 d ) with unknown secondary type , ( 2 ) the addition of RXTE observations at 6 epochs in 2000 , adding to 3 others in 1996-8 , ( 3 ) the collation of robotic telescope ( APT ) B and V -band photometric observations over 4 seasons which show a 3 % , cyclical flux variation with cycle lengths of 55 - 93 days .

We find that X-ray fluxes at all 9 epochs show random variations with orbital phase , thereby contradicting the binary accretion model , which predicts a substantial modulation .
However , these fluxes correlate well with the cyclical optical variations .
In particular , the 6 flux measurements in 2000 , which vary by a factor of 3 , closely track the interpolated optical variations between the 2000 and 2001 observing seasons .

The energy associated with the optical variations greatly exceeds the energy in the X-rays , so that the optical variability can not simply be due to reprocessing of X-ray flux .
However , the strong correlation between the two suggests that they are driven by a common mechanism .
We propose that this mechanism is a cyclical magnetic dynamo excited by a Balbus-Hawley instability located within the inner part of the circumstellar disk .
According to our model , variations in the field strength directly produce the changes in the magnetically related X-ray activity .
Turbulence associated with the dynamo results in changes to the density ( and therefore the emission measure ) distribution within the disk and creates the observed optical variations .