Principal Component Analysis of X-ray Variations in the Hard X-ray Emitting Symbiotic Binary RT Cru

Hard X-ray-emitting Symbiotic binaries consist of an accreting degenerate core and a cool giant star, which produce hard X-ray emission above 3 keV. The Suzaku telescope has observed a spectrum transition in the hard X-ray-emitting symbiotic binary RT Cru from 2007 to a fainter/harder state in 2012, as well as sporadic hourly fluctuations in X-rays seen by both the Suzaku and XMM-Newton missions. To investigate the characteristics of these X-ray variations, we employ principal component analysis (PCA) to evaluate the multi-mission X-ray data. This also allows us to identify the spectral components that contribute to the occurrence of hourly X-ray brightening. The Suzaku PCA study reveals three main components: an absorbing column (50%), a continuum (20%), and a likely soft thermal emission (9%). Moreover, the XMM-Newton data analysis yields the PCA component, which may include some emission features, particularly in the soft excess. Our findings suggest that the change in X-ray state seen by the Suzaku telescope between 2007 and 2012 was mostly caused by changes in the absorbing materials and some in the X-ray continuum. In the soft excess, there may also be a faint collisionally-ionized thermal emission with a temperature of 1 keV, which is likely from a colliding wind.