The Galactic black hole transient GRS 1915+105 is famous for its markedly variable X-ray and radio behaviour, and for being the archetypal galactic source of relativistic jets. It entered an X-ray outburst in 1992 and has been active ever since. Since 2018 GRS 1915+105 has declined into an extended low-flux X-ray plateau, occasionally interrupted by multiwavelength flares. Here, we report the radio and X-ray properties of GRS 1915+105 collected in this new phase, and compare the recent data to historic observations. We find that while the X-ray emission remained unprecedentedly low for most of the time following the decline in 2018, the radio emission shows a clear mode change half way through the extended X-ray plateau in 2019 June: from low flux (∼3 mJy) and limited variability, to marked flaring with fluxes two orders of magnitude larger. GRS 1915+105 appears to have entered a low-luminosity canonical hard state, and then transitioned to an unusual accretion phase, characterized by heavy X-ray absorption/obscuration. Hence, we argue that a local absorber hides from the observer the accretion processes feeding the variable jet responsible for the radio flaring. The radio–X-ray correlation suggests that the current low X-ray flux state may be a signature of a super-Eddington state akin to the X-ray binaries SS433 or V404 Cyg.

中文翻译：

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对射电明亮、X 射线遮挡的 GRS 1915+105 的观测

银河黑洞瞬变 GRS 1915+105 以其显着变化的 X 射线和无线电行为以及作为相对论喷流的原型银河源而闻名。它于 1992 年进入 X 射线爆发，并一直活跃至今。自 2018 年以来，GRS 1915+105 已经下降到一个扩展的低通量 X 射线平台，偶尔会被多波长耀斑打断。在这里，我们报告了在这个新阶段收集到的 GRS 1915+105 的无线电和 X 射线特性，并将最近的数据与历史观测数据进行了比较。我们发现，虽然 X 射线发射在 2018 年下降后的大部分时间里保持前所未有的低水平，但无线电发射在 2019 年 6 月扩展 X 射线平台的中途显示出明显的模式变化：从低通量（~3 mJy) 和有限的可变性，以两个数量级的通量显着燃烧。GRS 1915+105 似乎已经进入了低光度的典型硬态，然后过渡到不寻常的吸积阶段，其特征是大量的 X 射线吸收/遮蔽。因此，我们认为局部吸收体向观察者隐藏了吸积过程，为负责无线电燃烧的可变喷流提供了食物。射电-X 射线相关性表明，当前的低 X 射线通量状态可能是类似于 X 射线双星 SS433 或 V404 Cyg 的超级爱丁顿状态的特征。