发表机构
Inter University Centre for Astronomy and Astrophysics; Government Girls’ General Degree College（天文大学联合中心; 女子政府普通学位学院）
机构由 AI 辅助整理，请以论文原文为准。AI 中文总结
利用 AstroSat 对比研究 UCXB 候选体 1A 1246$-$588 与 4U 0614$+$091 的光谱-时间特性，发现前者存在未确认的 kHz QPO，后者经历硬到软态演化，揭示日冕冷却与热发射增强的关键作用。
AI 中文摘要
我们利用 AstroSat 观测，对超致密X射线双星（UCXB）候选体 1A 1246$-$588 和 4U 0614$+$091 进行了对比宽带光谱-时间研究。光谱建模显示，1A 1246$-$588 的光谱可由热康普顿化以及一个软的 thermally 热盘成分很好地描述。我们在 $993\pm4$ Hz 处识别出一个候选窄准周期振荡（QPO），其单探测器显著性约为 $3.7\sigma$，与先前报道的该源的上 kHz QPO 初步一致。独立的跨仪器检查未能确认该特征，因此我们将其视为暂定的、未经确认的信号，而非确凿的探测。相比之下，在 4 次观测中，4U 0614$+$091 从康普顿化主导的硬态演化为热主导的软态，电子温度从约 19 keV 降至约 2.3 keV，而盘和黑体温度则升高。这种演化伴随着盘对总通量贡献从约 18% 增加到约 50%，以及在软态中出现了接近 6.97 keV 的 Fe 发射线。内盘半径大致保持在约 13-15 $R_g$ 不变，表明观测到的演化主要由吸积流热性质的变化驱动，而非盘截断的显著变化。当源处于最硬状态时，它展现出最丰富的时间行为，变异性成分跨越约 12 Hz 至近 1 kHz，而较软的观测则以低频变异性为主，同时在 O4 中还存在约 140 Hz 附近的持续成分和一个显著的约 100 Hz 特征。这些结果表明，康普顿化日冕的逐渐冷却，以及盘和边界层热发射的增强，在塑造 4U 0614$+$091 的光谱和时间演化中起着关键作用。
英文摘要
We present a comparative broadband spectro-temporal study of the ultra-compact X-ray binary (UCXB) candidates 1A 1246$-$588 and 4U 0614$+$091 using AstroSat observations. Spectral modelling shows that the spectrum of 1A 1246$-$588 is well described by thermal Comptonization and a soft thermal disk component. We identify a candidate narrow quasi-periodic oscillation (QPO) at $993\pm4$ Hz with a single-detector significance of $ ~ 3.7σ$, tentatively consistent with the upper kHz QPO previously reported from this source. An independent cross-instrument check does not confirm this feature, and we therefore treat it as a tentative, unconfirmed signature rather than a secure detection. In contrast, across the 4 observations, 4U 0614$+$091 evolves from a Comptonization-dominated hard state to a thermally dominated soft state, with the electron temperature decreasing from ~ 19 keV to ~2.3 keV, while the disk and blackbody temperatures increase. This evolution is accompanied by an increase in the disk contribution to the total flux from ~ 18% to ~ 50% and the appearance of an Fe emission line near 6.97 keV in the soft state. The inner disk radius remains approximately constant at ~13- 15 $R_g$, suggesting that the observed evolution is driven primarily by changes in the thermal properties of the accretion flow rather than substantial variations in disk truncation. When the source is in its hardest state, it displays the richest timing behaviour, with variability components spanning from ~ 12 Hz to nearly 1 kHz, whereas the softer observations are dominated by low frequency variability, along with a persistent component near ~140 Hz and a prominent ~ 100 Hz feature in O4. These results suggest that progressive cooling of the Comptonizing corona, along with enhanced thermal emission from the disk and boundary layer, play a key role in shaping the spectral and timing evolution of 4U 0614$+$091.
Comments11 pages, 6 figures, 4 tables
Journal refJournal of High Energy Astrophysics, 56 (2027), 100757
DOI：10.1016/j.jheap.2026.100757
