根据VLT和XMM-牛顿观测的食极VV船尾座的快速准周期振荡
Fast quasi-periodic oscillations in the eclipsing polar VV Puppis from VLT and XMM-Newton observations
摘要：
我们目前的高时间分辨率光学光度数据的极地VV船尾座同时获得三个过滤器（u '，HeII $λ$ 4686，r'）与ULTRACAM相机安装在ESO-VLT望远镜。还提供了从数据库中检索的源的长50 KS XMM-牛顿观测的分析。准周期振荡（QPOs）被清楚地检测到在源明亮的相位间隔时，吸积极是可见的，确认关联的QPOs与吸积柱的基础上的光学。在平均频率为$\sim$ 0.7 Hz且振幅相似为$\sim$ 1\%的三个滤波器中检测到QPO。在亮相期间的平均轨道平均功率谱显示出相当宽的过量，品质因数Q= $ν$ / $Δν$ = 5-7，但较小的数据段通常显示出高得多的相干性，Q高达30。XMM（0.5- 10 keV）观测首次提供了高kT $\sim$ 40 keV温度下硬X射线成分的精确估计，并证实VV Pup的高EUV-软硬比在（4- 15）范围内。详细的X射线轨道光变曲线显示了一个短的$Δϕ\simeq 0.05$进入活动极的日食，表明吸积激波高度为$\sim$ 75公里。在（0.1--5）Hz范围内，振幅上限为$\sim$ 30\%时，未检测到显著的X射线QPO。对激波后吸积区的详细流体动力学数值模拟表明，对于X射线和光学区域，辐射不稳定性的预期频率是相同的，其值为$ν$ $\sim$（40- 70）Hz，比观测值高一个数量级以上。这证实了先前的陈述，即目前的不稳定性模型无法解释完整的QPO特性内的参数通常已知的极地。
英文摘要：
We present high time resolution optical photometric data of the polar VV Puppis obtained simultaneously in three filters (u', HeII $λ$4686, r') with the ULTRACAM camera mounted at the ESO-VLT telescope. An analysis of a long 50 ks XMM-Newton observation of the source, retrieved from the database, is also provided. Quasi-periodic oscillations (QPOs) are clearly detected in the optical during the source bright phase intervals when the accreting pole is visible, confirming the association of the QPOs with the basis of the accretion column. QPOs are detected in the three filters at a mean frequency of $\sim$ 0.7 Hz with a similar amplitude $\sim$ 1\%. Mean orbitally-averaged power spectra during the bright phase show a rather broad excess with a quality factor Q= $ν$/$Δν$ = 5-7 but smaller data segments commonly show a much higher coherency with Q up to 30. The XMM (0.5--10 keV) observation provides the first accurate estimation of the hard X-ray component with a high kT $\sim$ 40 keV temperature and confirms the high EUV-soft/hard ratio in the range of (4--15) for VV Pup. The detailed X-ray orbital light curve displays a short $Δϕ\simeq 0.05$ ingress into self-eclipse of the active pole, indicative of a accretion shock height of $\sim$ 75 km. No significant X-ray QPOs are detected with an amplitude upper limit of $\sim$30\% in the range (0.1--5) Hz. Detailed hydrodynamical numerical simulations of the post-shock accretion region with parameters consistent with VV Pup demonstrate that the expected frequencies from radiative instability are identical for X-rays and optical regime at values $ν$ $\sim$ (40--70) Hz, more than one order magnitude higher than observed. This confirms previous statements suggesting that present instability models are unable to explain the full QPO characteristics within the parameters commonly known for polars.
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