发表机构
Durham University; McGill University; University of Warwick; New York University Abu Dhabi; INAF, Osservatorio Astronomico di Brera; Anton Pannekoek Institute for Astronomy, Universiteit van Amsterdam; Yale University（杜伦大学; 麦吉尔大学; 华威大学; 阿布扎比纽约大学; 意大利国家天体物理研究所布里拉天文台; 阿姆斯特丹大学安东·潘内克天文研究所; 耶鲁大学）
机构由 AI 辅助整理，请以论文原文为准。AI 中文总结
本研究首次对 EXO 0748-676 在 2024/25 年短暂爆发进行多波段观测，发现其光变曲线稳定、处于硬态且未发生软态转变，呈现失败转变爆发的特征。
AI 中文摘要
在沉寂十六年之后，EXO 0748-676 于 2024 年 3 月意外地再次进入爆发期。然而，与其之前的爆发期（1985 年至 2008 年）形成鲜明对比的是，EXO 0748-676 在爆发约 10 个月后，于 2025 年 1 月回到了沉寂状态。在此，我们汇集了来自九个观测设施的数据，覆盖从射电到 X 射线的波段，以提供对 2024/25 爆发期的首次多波段研究。与 1985 年爆发不同，此次爆发的上升期和衰减期在 X 射线和光学波段均被完整捕捉。光变曲线并未展现出典型的瞬态低质量 X 射线双星爆发的特征。相反，在 2024/25 爆发期间，X 射线和光学通量保持相对稳定。丰富的 EXO 0748-676 光学数据显示出一个倾斜的光学相位曲线和一个以辐照为主导的光学光变曲线，该曲线一直持续到外盘氢复合开始（约 11000 K），在爆发末期触发了快速变暗。XMM-Newton 和 NICER 的 X 射线观测揭示，EXO 0748-676 在早期受到严重遮蔽，光谱显示出被抑制的软 X 射线成分。我们发现，包含团块状、电离吸收体的光谱模型可以描述这种遮蔽，尽管早期遮蔽的确切原因仍不确定。X 射线颜色分析表明，EXO 0748-676 在约 10 个月的爆发期大部分时间处于暗淡的硬态。EXO 0748-676 在爆发末期亮度略有增加，但从未进入软光谱态。这种行为是失败转变爆发的特征。
英文摘要
After sixteen years in quiescence, EXO 0748-676 unexpectedly returned to outburst in March 2024. However, in stark contrast to its previous outburst (1985 - 2008), EXO 0748-676 returned to quiescence in January 2025, after ~ 10 months in outburst. Here, we collate data from nine observing facilities, covering wavelengths from radio to X-ray, to provide the first multi-wavelength study of the 2024/25 outburst. Unlike the 1985 outburst, both the rise and decay are fully captured at X-ray and optical wavelengths. The light curves do not exhibit the hallmarks of a canonical transient low-mass X-ray binary outburst. Instead, the X-ray and optical fluxes remain reasonably stable during the 2024/25 outburst. The wealth of optical data of EXO 0748-676 reveals a skewed optical phase curve and an irradiation-dominated optical light curve which lasts until the onset of hydrogen recombination in the outer disc at ~11000K, triggering a rapid fade at the end of the outburst. X-ray observations by XMM-Newton and NICER revealed that EXO 0748-676 was heavily obscured early on, with spectra exhibiting a dampened soft X-ray contribution. We find that a spectral model including a clumpy, ionised absorber describes the obscuration, although the exact cause of the early-time obscuration remains uncertain. X-ray colour analysis indicates that EXO 0748-676 spent most of the ~10 month outburst in a faint, hard state. EXO 0748-676 increased marginally in brightness towards the end of the outburst, but never entered a soft spectral state. This behaviour is characteristic of a failed transition outburst.
Comments26 Pages, 9 Figures, Accepted for Publication in MNRAS
