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arXiv 1803.04424astro-ph.HE
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宽带ULX样品中类脉冲星发射成分的证据

Evidence for Pulsar-like Emission Components in the Broadband ULX Sample

D. J. Walton, F. Fuerst, M. Heida, F. A. Harrison, D. Barret, D. Stern, M. Bachetti, M. Brightman, A. C. Fabian, M. J. Middleton

摘要:

我们提出了一个明亮的超亮X射线源的样本的宽带X射线分析,目的是调查这个人口的光谱相似性,已知的ULX星系,M82 X-2,NGC 7793 P13和NGC 5907 ULX。对NGC 5907 ULX的宽带XMM-Newton +NuSTAR数据集进行了相位分辨分析,发现该源中吸积柱的脉冲发射具有与M82 X-2和NGC 7793 P13相似的光谱形状,这是当光谱与吸积盘模型拟合时在最高能量处观察到的过量发射的原因。然后,我们证明了类似的“硬”过剩被认为是在所有的ULX的宽带样本。最后,对于ULX的吸积体的性质目前是未知的,我们测试是否硬过剩都是由一个吸积柱类似于M82 X-2,NGC 7793 P13和NGC 5907 ULX中存在的一致。脉冲发射的平均形状的基础上,我们发现,在所有情况下,一个类似的吸积柱可以成功地再现观测数据,与假设一致,这ULX样品可能是由中子星吸积占主导地位。与已知的脉冲星ULXs相比,我们对剩余ULXs的光谱拟合表明,来自磁层之外的吸积流的非脉冲发射比与吸积柱相关的分量具有更强的相对贡献。如果这些来源也包含中子星吸积物,这可能有助于解释缺乏检测到的脉动。

英文摘要:

We present broadband X-ray analyses of a sample of bright ultraluminous X-ray sources with the goal of investigating the spectral similarity of this population to the known ULX pulsars, M82 X-2, NGC7793 P13 and NGC5907 ULX. We perform a phase-resolved analysis of the broadband XMM-Newton+NuSTAR dataset of NGC5907 ULX, finding that the pulsed emission from the accretion column in this source exhibits a similar spectral shape to that seen in both M82 X-2 and NGC7793 P13, and that this is responsible for the excess emission observed at the highest energies when the spectra are fit with accretion disk models. We then demonstrate that similar 'hard' excesses are seen in all the ULXs in the broadband sample. Finally, for the ULXs where the nature of the accretor is currently unknown, we test whether the hard excesses are all consistent with being produced by an accretion column similar to those present in M82 X-2, NGC7793 P13 and NGC5907 ULX. Based on the average shape of the pulsed emission, we find that in all cases a similar accretion column can successfully reproduce the observed data, consistent with the hypothesis that this ULX sample may be dominated by neutron star accretors. Compared to the known pulsar ULXs, our spectral fits for the remaining ULXs suggest that the non-pulsed emission from the accretion flow beyond the magnetosphere makes a stronger relative contribution than the component associated with the accretion column. If these sources do also contain neutron star accretors, this may help to explain the lack of detected pulsations.

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