Other
Scientific paper
Jan 2010
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2010aas...21541811s&link_type=abstract
American Astronomical Society, AAS Meeting #215, #418.11; Bulletin of the American Astronomical Society, Vol. 42, p.276
Other
Scientific paper
We present an analysis of an 68 ks, high and medium resolution XMM-Newton (EPIC/RGS-pn) spectrum of the anomalous X-ray object gamma Cas obtained in 2004. This star is the prototype of a small number of B0.5-B1e hard X-ray emitters, and the origin of their hard X-ray emissions is not yet clear. As possible outcomes, the resolution of this puzzle could result in a breakthrough in our understanding of either massive magnetic stars with disks or of active degenerate stars in highly evolved binary systems. Like a Chandra HTEG spectrum of this source obtained in 2001, our 2004 spectrum can be fit with 3-4 thermal plasma components. The temperature of the hot dominant component is unchanged at kT ≈12 keV. The secondary component temperatures are discrete from one another, have changed their values, and do not represent a continuous distribution of temperatures. The contribution of the soft X-ray flux has increased in these three years, suggesting that the intervening column density decreased dramatically and the disappearance of local X-ray absorption. We also find changes in line strengths of Fe, N, and Ne, suggesting abundance changes. The spectrum exhibits strong Hβ-like transitions of NeX and OVIII, which is a hint of mild departures from equilibrium in the warm plasma environment. We also note that an interesting property of the X-ray light curve extracted from our observation is that it exhibits `lulls' every 3.2 hours, similar to reports by other studies. These behaviors pose new challenges for models of the generation of the hard X-rays.
Lopes de Oliveira Raimundo
Motch Ch.
Smith Myron
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