共查询到11条相似文献,搜索用时 46 毫秒
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Gavin Ramsay Mark Cropper France Córdova Keith Mason Rudi Much Dirk Pandel Robert Shirey 《Monthly notices of the Royal Astronomical Society》2001,326(2):L27-L32
We present an analysis of the X-ray spectra of two strongly magnetic cataclysmic variables, DP Leo and WW Hor, made using XMM-Newton . Both systems were in intermediate levels of accretion. Hard optically thin X-ray emission from the shocked accreting gas was detected from both systems, while a soft blackbody X-ray component from the heated surface was detected only in DP Leo. We suggest that the lack of a soft X-ray component in WW Hor is owing to the fact that the accretion area is larger than in previous observations with a resulting lower temperature for the re-processed hard X-rays. Using a multi-temperature model of the post-shock flow, we estimate that the white dwarf in both systems has a mass greater than 1 M⊙ . The implications of this result are discussed. We demonstrate that the 'soft X-ray excess' observed in many magnetic cataclysmic variables can be partially attributed to using an inappropriate model for the hard X-ray emission. 相似文献
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Dirk Pandel France A. Cordova Robert E. Shirey Gavin Ramsay Mark Cropper Keith O. Mason Rudi Much Dave Kilkenny 《Monthly notices of the Royal Astronomical Society》2002,332(1):116-126
XMM-Newton was used to observe two eclipsing, magnetic cataclysmic variables, DP Leo and WW Hor, continuously for three orbital cycles each. Both systems were in an intermediate state of accretion. For WW Hor we also obtained optical light curves with the XMM-Newton Optical Monitor and from ground-based observations. Our analysis of the X-ray and optical light curves allows us to constrain physical and geometrical parameters of the accretion regions and derive orbital parameters and eclipse ephemerides of the systems. For WW Hor we directly measure horizontal and vertical temperature variations in the accretion column. From comparisons with previous observations we find that changes in the accretion spot longitude are correlated with the accretion rate. For DP Leo the shape of the hard X-ray light curve is not as expected for optically thin emission, showing the importance of optical depth effects in the post-shock region. We find that the spin period of the white dwarf is slightly shorter than the orbital period and that the orbital period is decreasing faster than expected for energy loss by gravitational radiation alone. 相似文献
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Chen-Hui Niu Qun-Xiong Wang David MacMahon Feng-Quan Wu Xue-Lei Chen Ji-Xia Li Hai-Jun Tian Guillaume Shippee Dan Werthimer Xiao-Ping Zheng 《天文和天体物理学研究(英文版)》2019,(7)
A digital correlator is a crucial element in a modern radio telescope. In this paper, we describe a scalable design for the correlator system of the Tianlai pathfinder array, which is an experiment dedicated to testing key technologies for conducting a 21 cm intensity mapping survey. The correlator implements the FX design, which firstly performs a fast Fourier transform(FFT) including polyphase filter bank(PFB) computation using a Collaboration for Astronomy Signal Processing and Electronics Research(CASPER) Reconfigurable Open Architecture Computing Hardware-2(ROACH2) board, then computes cross-correlations by employing Graphics Processing Units(GPUs). The design has been tested both in laboratory and in actual observation. 相似文献