Examining the nature of the ultraluminous X-ray source Holmberg II X-1
Examining the nature of the ultraluminous X-ray source Holmberg II X-1
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检查超发光 X 射线源 Holmberg II X-1 的性质
DOI：
10.1051/0004-6361/202348471
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发表时间：
2023
影响因子：
6.5
通讯作者：
Barra F
中科院分区：
文献类型：
--
作者：
Barra F
我们利用最近一次活动的数据，使用 XMM-Newton 卫星在 19 年期间拍摄的宽带和高分辨率 X 射线光谱，对超发光 X 射线源 Holmberg II X-1 进行了全面的光谱分析。我们测试了几种宽带光谱模型，其中包括双热组件，它为 0.3 至 10 keV 之间的连续谱提供了合理的描述，并使我们能够限制吸积盘的属性。尽管斜率的精确值对所采用的模型稍微敏感，但内部和外部圆盘组件的光度-温度趋势与薄圆盘的预期大致一致。然而，所有测试的模型都显示 L−T 趋势偏离幂律，辐射光度高于约 5 × 1039erg s−1，特别是对于与内部吸积流相关的热成分。假设这种偏差是由于吸积率超过了爱丁顿极限，或者很可能是超临界率，则推断出一个质量为 16-36M 的致密天体，特别是恒星质量的黑洞。时间平均（2021）高分辨率光谱呈现出主要来自 Ne IX-X 的 1 keV 窄发射线和来自 NVII 的 0.5 keV 非常强的发射线，这表明富含 Ne-N 的气体具有非太阳丰度。这有利于富含氮的供体星，例如蓝色或红色超巨星，它们已经逃离了其以低金属环境为特征的原生星团。
We present a comprehensive spectral analysis of the ultraluminous X-ray source Holmberg II X-1 using broadband and high-resolution X-ray spectra taken with theXMM-Newtonsatellite over a period of 19 yr, taking advantage of data from a recent campaign. We tested several models for the broadband spectra, including a double thermal component provided a reasonable description for the continuum between 0.3 and 10 keV and enabled us to constrain the properties of the accretion disc. The luminosity–temperature trends of the inner and outer disc components broadly agree with the expectations for a thin disc, although the exact values of the slopes are slightly sensitive to the adopted model. However, all tested models showL−Ttrends that deviate from a power law above a bolometric luminosity of about 5 × 1039erg s−1, particularly for the hot thermal component associated with the inner accretion flow. Assuming that such deviations are due to the accretion rate exceeding its Eddington limit or, most likely, the super-critical rate, a compact object with a mass of 16–36M⊙was inferred, specifically, a stellar-mass black hole. The time-averaged (2021) high-resolution spectra present narrow emission lines at 1 keV primarily from Ne IX-X and a very strong at 0.5 keV from N VII, which indicate Ne–N-rich gas with non-solar abundances. This favours a nitrogen-rich donor star, such as a blue or red supergiant, which has escaped from its native stellar cluster characterised by a low-metallicity environment.