Deciphering radiation pressure instability signatures in GRS 1915 + 105 and its implications on perceiving other black hole X-ray transients
破译 GRS 1915+105 的辐射压不稳定性信号及其对认识其他黑洞 X 射线暂现源的启示
We analysed Nuclear Spectroscopic Telescope Array data of GRS 1915 + 105 (2012─2024) to trace its outburst evolution and clues to the physical processes involved through different phases of intensity, especially those related to the radiation pressure instability. We examined its 1-s binned light curves and observation-long spectra to investigate the short- and long-term variability of GRS 1915 + 105, as an extension of the previous studies, which did not cover the fainter period that started in mid-2018. We assigned a new spectral group of variability, 'states group 2' (SG2), which consists of known classes, <inline-formula><tex-math>$\gamma$</tex-math></inline-formula> and <inline-formula><tex-math>$\omega$</tex-math></inline-formula>, variation of <inline-formula><tex-math>$\phi$</tex-math></inline-formula> (<inline-formula><tex-math>$\phi _1$</tex-math></inline-formula>), and an unclassified feature 'uc'. SG2 is evident when GRS 1915 + 105 entered its most luminous state, when its innermost part of the accretion disc transformed to a slim disc state. Other previously known peculiar classes, <inline-formula><tex-math>$\kappa$</tex-math></inline-formula> and <inline-formula><tex-math>$\rho$</tex-math></inline-formula>, can be considered as the transition class between standard and slim disc, which act as signatures of the starting phase of radiation pressure instability. Only the basic variability classes (<inline-formula><tex-math>$\chi$</tex-math></inline-formula> and <inline-formula><tex-math>$\phi _2$</tex-math></inline-formula>), which represent the standard disc, were commonly found in other black hole X-ray transients (e.g. GX 339─4, MAXI J1820 + 070, and 4U 1543─475). However, a class that represents the slim disc was found in 4U 1543─475, possibly due to both GRS 1915 + 105 and 4U 1543─475 having successfully reached a luminosity of <inline-formula><tex-math>$\ge 0.49\ L_{\rm Edd}$</tex-math></inline-formula>. Our analysis of the fainter period (mid-2018─2024) provides more evidence that GRS 1915 + 105 has not slipped into a quiescent phase.
展开 ▾首次覆盖 2018 年中以来该源明显变暗的时期，定义新光谱变异性组 SG2；提出 κ 和 ρ 类可作为辐射压不稳定性起始的观测标志，并发现类似特征在 4U 1543−475 中出现。
本文作为此前研究的延伸，填补了 GRS 1915+105 在 2018 年中期后变暗阶段的观测空白。过去对该源 X 射线光谱变异性的分类工作多集中于亮态，对其极高光度下辐射压不稳定性的具体表现缺乏系统梳理。本研究通过分析不间断的 NuSTAR 档案数据，识别出与标准盘向细盘转换密切相关的特殊变异性类别（如 SG2、κ 和 ρ），并将其确立为辐射压不稳定性的潜在探针。对比其他暂现源发现，只有达到高爱丁顿光度（≥0.49 L_Edd）的系统才呈现细盘相关特征，这预示着未来借助更高灵敏度的设备（如 Athena）可系统探索辐射压不稳定性在各类吸积系统中的触发条件和表现。
刊出 2026-07-01 · 收录 2026-07-22