Complex absorption and reflection of a multitemperature cyclotron-bremsstrahlung X-ray cooling shock in BY Cam

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Abstract

We re-analyse the ASCA and Ginga X-ray data from BY Cam, a slightly asynchronous magnetic accreting white dwarf. The spectra are strongly affected by complex absorption, which we model as a continuous (power-law) distribution of covering fraction and column of neutral material. This absorption causes a smooth hardening of the spectrum below ∼3 keV, and is probably produced by material in the pre-shock column which overlies the X-ray emission region. The ASCA data show that the intrinsic emission from the shock is not consistent with a single-temperature plasma. Significant iron L emission coexisting with iron K shell lines from H- and He-like iron clearly shows that there is a wide range of temperatures present, as expected from a cooling shock structure. The Ginga data provide the best constraints on the maximum temperature emission in the shocked plasma, with kTmax = 21+18-4 keV. Cyclotron cooling should also be important; it suppresses the highest temperature bremsstrahlung components, so the X-ray data provide only a lower limit on the mass of the white dwarf of M ≥ 0.5 M⊙. Reflection of the multitemperature bremsstrahlung emission from the white dwarf surface is also significantly detected. We stress the importance of modelling all these effects in order to gain a physically self-consistent picture of the X-ray spectra from polars in general and BY Cam in particular.

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Done, C., & Magdziarz, P. (1998). Complex absorption and reflection of a multitemperature cyclotron-bremsstrahlung X-ray cooling shock in BY Cam. Monthly Notices of the Royal Astronomical Society, 298(3), 737–746. https://doi.org/10.1046/j.1365-8711.1998.01636.x

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