Hard X-ray view on intermediate polars in theGaiaera
Hard X-ray view on intermediate polars in theGaiaera
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DOI：
10.1093/mnras/sty2952
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发表时间：
2018-09
影响因子：
4.8
通讯作者：
V. Suleimanov;V. Doroshenko;K. Werner
中科院分区：
文献类型：
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作者：
V. Suleimanov;V. Doroshenko;K. Werner
中间极（ip） x射线谱的硬度主要由白矮星（WD）的致密度（质量半径比，M/R）决定，因此硬x射线谱可以用来约束中间极（ip）的质量。一个精确的质量估计需要考虑到WD磁层R_m的有限大小。我们建议直接从观察到的x射线功率谱或极性光学光曲线的断裂频率推导出它，或者假设同位。本文将该方法应用于NuSTAR（10个对象）和Swift/BAT（35个对象）观测到的所有ip。对于矮新星GK Per，我们还观察到破裂频率随通量的变化，这允许约束磁层半径对质量吸积速率的依赖。在我们的分析中，我们计算了一个额外的双参数（M和R_m/R）模型光谱网格，假设吸积柱的固定高度H_sh/R=0.25，这适用于确定低质量吸积ip（如EX\，Hya）的WD质量。利用Gaia数据发布2，我们首次获得了我们样本中大部分物体的质量吸积率和WD表面磁场强度的可靠估计。我们发现大多数ip的吸积速率为~10^{-9}M_Sun/yr，磁场范围为1—10 MG。我们样本的WD质量平均值为0.79 +/- 0.16 M_Sun，这与之前的估计一致。
The hardness of the X-ray spectra of intermediate polars (IPs) is determined mainly by the white dwarf (WD) compactness (mass-radius ratio, M/R) and, thus, hard X-ray spectra can be used to constrain the WD mass. An accurate mass estimate requires the finite size of the WD magnetosphere R_m to be taken into the account. We suggested to derive it either directly from the observed break frequency in power spectrum of X-ray or optical lightcurves of a polar, or assuming the corotation. Here we apply this method to all IPs observed by NuSTAR (10 objects) and Swift/BAT (35 objects). For the dwarf nova GK Per we also observe a change of the break frequency with flux, which allows to constrain the dependence of the magnetosphere radius on the mass-accretion rate. For our analysis we calculated an additional grid of two-parameter (M and R_m/R) model spectra assuming a fixed, tall height of the accretion column H_sh/R=0.25, which is appropriate to determine WD masses in low mass-accretion IPs like EX\,Hya. Using the Gaia Data Release 2 we obtain for the first time reliable estimates of the mass-accretion rate and the magnetic field strength at the WD surface for a large fraction of objects in our sample. We find that most IPs accrete at rate of ~10^{-9} M_Sun/yr, and have magnetic fields in the range 1--10 MG. The resulting WD mass average of our sample is 0.79 +/- 0.16 M_Sun, which is consistent with earlier estimates.