类新星激变变星MV Lyr、BZ Cam和V592 Cas的SWIFT XRT观测
SWIFT XRT Observations of the Nova-like Cataclysmic Variables MV Lyr, BZ Cam and V592 Cas
摘要：
为了研究类新星激变变星（MV Lyr，BZ Cam，V592 Cas）的边界层特征，我们对3颗类新星激变变星进行了45 ksec（3 $\times$ 15 ksec）的SWIFT XRT观测。发现的非线性大部分处于高质量吸积率状态（$\ge$ 1 $\times$ 10 $^{-9}$ Msun yr $^{-1}$），偶尔也有低质量吸积率状态。使用XRT数据，我们发现光学薄的多温冷却流型发射光谱的X射线温度（kT $_{max}$）为21-50 keV。这些硬X射线发射边界层发散从简单的等压冷却流表示的X射线温度是维里值的磁盘。此外，我们检测到MV Lyr和BZ Cam的幂律发射分量，并且可能是V592 Cas的幂律发射分量，这可能是这些系统中快风流出的光学薄发射的康普顿散射和/或软盘光子的康普顿上散射的结果。在0.1-50.0 keV范围内（多温度）热等离子体发射的X射线光度为（0.9-5.0）$\times$ 10 $^{32}$ erg/sec。X射线和圆盘光度之比（根据紫外光波长计算）产生的效率（L $_{x}$ /L $_{disk}$）约为0.01-0.001。考虑到这种非辐射比的X射线发射边界层没有显着的光学厚黑体发射的软X射线（与ROSAT观测一致），以及高/维里X射线温度，我们认为，高状态NL系统可能有光学薄BL合并ADAF类流和/或X射线日冕。此外，我们注意到，轴对称的双极和/或旋转为主的快速风外流检测在这三个NL（特别是BZ凸轮和V592 Cas）或其他一些NL也可以解释的ADAF的BL区域的上下文中。
英文摘要：
We present a total of ~ 45 ksec (3$\times$15 ksec) of SWIFT XRT observations for three non-magnetic nova-like (NL) Cataclysmic Variables (CVs) (MV Lyr, BZ Cam, V592 Cas) in order to study characteristics of Boundary Layers (BL) in CVs. The nonmagnetic NLs are found mostly in a state of high mass accretion rate ($\ge$1$\times$10$^{-9}$ Msun yr$^{-1}$) and some show occasional low states. Using the XRT data, we find optically thin multiple-temperature cooling flow type emission spectra with X-ray temperatures (kT$_{max}$) of 21-50 keV. These hard X-ray emitting boundary layers diverge from simple isobaric cooling flows indicating X-ray temperatures that are of virial values in the disk. In addition, we detect power law emission components from MV Lyr and BZ Cam and plausibly from V592 Cas which may be a result of the Compton scattering of the optically thin emission from the fast wind outflows in these systems and/or Compton up-scattering of the soft disk photons. The X-ray luminosities of the (multi-temperature) thermal plasma emission in the 0.1-50.0 keV range are (0.9-5.0)$\times$10$^{32}$ erg/sec. The ratio of the X-ray and disk luminosities (calculated from the UV-optical wavelengths) yield an efficiency (L$_{x}$/L$_{disk}$) ~ 0.01-0.001. Given this non-radiative ratio for the X-ray emitting boundary layers with no significant optically thick blackbody emission in the soft X-rays (consistent with ROSAT observations) together with the high/virial X-ray temperatures, we suggest that high state NL systems may have optically thin BLs merged with ADAF-like flows and/or X-ray coronae. In addition, we note that the axisymmetric bipolar and/or rotation dominated fast wind outflows detected in these three NLs (particularly BZ Cam and V592 Cas) or some other NL may also be explained in the context of ADAF-like BL regions.
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