\gamma Cas is the prototypical classical Be star and is recently best known for its variable hard X-ray emission .
To elucidate the reasons for this emission , we mounted a multiwavelength campaign in 2010 centered around four XMM-Newton observations .
The observational techniques included long baseline optical interferometry ( LBOI ) from two instruments at CHARA , photometry carried out by an Automated Photometric Telescope and H \alpha observations .
Because \gamma Cas is also known to be in a binary , we measured radial velocities from the H \alpha line and redetermined its period as 203.55 { \pm 0.20 } days and its eccentricity as near zero .
The LBOI observations suggest that the star ’ s decretion disk was axisymmetric in 2010 , has an system inclination angle near 45 ^ { \circ } , and a larger radius than previously reported .
In addition , the Be star began an “ outburst ” at the beginning of our campaign , made visible by a brightening and reddening of the disk during our campaign and beyond .
Our analyses of the new high resolution spectra disclosed many attributes also found from spectra obtained in 2001 ( Chandra ) and 2004 ( XMM-Newton ) .
As well as a dominant hot ( \approx 14 keV ) thermal component , the familiar ones included : ( i ) a fluorescent feature of Fe K even stronger than observed at previous times , ( ii ) strong lines of N VII and Ne XI lines indicative of overabundances , and ( iii ) a subsolar Fe abundance from K-shell lines but a solar abundance from L-shell ions .
We also found that two absorption columns are required to fit the continuum .
While the first one maintained its historical average of 1 \times 10 ^ { 21 } cm ^ { -2 } , the second was very large and doubled to 7.4 \times 10 ^ { 23 } cm ^ { -2 } during our X-ray observations .
Although we found no clear relation between this column density and orbital phase , it correlates well with the disk brightening and reddening both in the 2010 and earlier observations .
Thus , the inference from this study is that much ( perhaps all ? )
of the X-ray emission from this source originates behind matter ejected by \gamma Cas into our line of sight .