Complex absorption and reflection of a multitemperature cyclotron–bremsstrahlung X-ray cooling shock in BY Cam |
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| Authors: | C Done & P Magdziarz |
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| Institution: | Department of Physics, University of Durham, South Road, Durham DH1 3LE,;Astronomical Observatory, Jagiellonian University, Orla 171, 30-244 Cracow, Poland,;N. Copernicus Astronomical Center, Bartycka 18, 00-716 Warsaw, Poland |
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| Abstract: | We re-analyse the ASCA 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 kT max = 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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| Keywords: | accretion accretion discs binaries: close stars: individual: BY Cam novae cataclysmic variables X-rays: stars |
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