用JED-SAD模型跟踪MAXI J1820 +070硬态吸积流的演化
Tracking the evolution of the accretion flow in MAXI J1820+070 during its hard state with the JED-SAD model
摘要：
爆发中的X射线双星通常表现出两种典型的X射线谱态，即硬态和软态，其中吸积流和喷流的物理性质已知会发生变化。最近，针对黑洞X射线双星提出了JED-SAD范式，旨在解决这些系统中的吸积-喷射相互作用。根据该模型，吸积流由外部的标准沙库拉-孙亚耶夫盘（SAD）和内部的热喷流发射盘（JED）组成。JED产生硬X射线发射，有效地扮演热日冕的角色，以及无线电喷流。本文用JED-SAD模型描述了瞬态黑洞MAXI J1820+070在硬态和硬中间态吸积流的演化。与以往模型的应用不同，本文考虑了康普顿反射分量。我们使用八个宽带X射线光谱，包括NuSTAR，NICER和Swift数据，提供0.8-190 keV的总光谱覆盖范围。数据直接用JED-SAD模型拟合。我们的研究结果表明，光学厚盘（即SAD）不延伸到ISCO在任何考虑的时代。特别是，随着系统向硬/中间态的演化，我们发现内半径从第一次观察的$\sim$ 60 R $_{\rm G}$减小到最后一次观察的$\sim$ 30 R $_{\rm G}$。这一趋势伴随着质量增长率的增加。在所有硬中间态观测中，需要两个反射分量，其特征在于不同的电离值，以充分解释数据。这些组成部分可能来自SAD的不同地区。我们表明，一个喇叭形的外盘，在原则上，可以解释双反射分量。
英文摘要：
X-ray binaries in outburst typically show two canonical X-ray spectral states, i.e. hard and soft states, in which the physical properties of the accretion flow and of the jet are known to change. Recently, the JED-SAD paradigm has been proposed for black hole X-ray binaries, aimed to address the accretion-ejection interplay in these systems. According to this model, the accretion flow is composed by an outer standard Shakura-Sunyaev disk (SAD) and an inner hot Jet Emitting Disk (JED). The JED produces both the hard X-ray emission, effectively playing the role of the hot corona, and the radio jets. In this paper, we use the JED-SAD model to describe the evolution of the accretion flow in the black hole transient MAXI J1820+070 during its hard and hard-intermediate states. Contrarily to the previous applications of this model, the Compton reflection component has been taken into account. We use eight broadband X-rays spectra, including NuSTAR, NICER and Swift data, providing a total spectral coverage of 0.8-190 keV. The data were directly fitted with the JED-SAD model. Our results suggest that the optically thick disk (i.e. the SAD) does not extend down to the ISCO in any of the considered epochs. In particular, as the system evolves towards the hard/intermediate state, we find that the inner radius decreases from $\sim$60 R$_{\rm G}$ in the first observation down to $\sim$30 R$_{\rm G}$ in the last one. This trend is accompanied by an increase of the mass-accretion rate. In all hard-intermediate state observations, two reflection components, characterized by different values of ionization, are required to adequately explain the data. These components likely originate from different regions of the SAD. We show that a flared outer disk could, in principle, explain the double reflection component.
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