黑洞X射线双星GRS 1739-278 2025年迷你爆发的NuSTAR观测：软态下的谱与时变演化
NuSTAR View of the 2025 Mini-Outburst of the Black Hole X-ray Binary GRS 1739-278: Spectral and Timing Evolution in the Soft State
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中文总结 AI 辅助
本文通过NuSTAR观测研究黑洞X射线双星GRS 1739-278 2025年迷你爆发衰减阶段的软态演化，确认其为高自旋黑洞低速率吸积的经典软态，内盘锚定最内稳定圆轨道。
中文摘要 AI 辅助
我们对2025年9月18日至30日期间，NuSTAR望远镜对银道面黑洞候选体GRS 1739-278的三次观测开展了专门的时变与谱分析，该观测是在该源2025年迷你爆发的衰减阶段完成的。研究发现该源全程处于以吸积盘为主的软态，3-79 keV能段的计数率从112.4 cts s⁻¹降至99.4 cts s⁻¹，硬度比低且仅轻微变化，约为0.14-0.16，分数变率从3.2%降至1.1%；在所有观测的功率谱或Lomb-Scargle周期图中均未探测到周期或准周期信号。联合FPMA与FPMB的谱拟合采用吸收盘黑体加热康普顿化的连续谱模型，同时叠加了10-12 keV处的宽而高显著性（11.7-15.0σ）曲率特征（作为强吸积盘反射/返回辐射成分的经验代理），该模型能很好地描述4-30 keV的谱，卡方自由度比χ²/dof为1.04-1.15。内盘温度从1.021±0.001 keV平稳冷却至1.002⁺⁰.⁰⁰³₋₀.₀₀₂ keV，而盘归一化因子及由此推导的内半径R_in≈27.7 km≈0.95 R_ISCO的变化在0.3%以内，与吸积盘全程锚定在最内稳定圆轨道的结论一致。未吸收的4-30 keV光度从1.35×10³⁷ erg s⁻¹降至1.15×10³⁷ erg s⁻¹，对应爱丁顿光度占比为0.67%至0.57%。这些2025年迷你爆发的谱时变表征结果，与高自旋黑洞在经典软态下以低且平稳下降的速率吸积的情况大致相符。
英文摘要
We present a dedicated timing and spectral analysis of three NuSTAR observations of the Galactic black hole candidate GRS 1739-278 obtained during the decay of its 2025 mini-outburst (September 18-30, 2025). The source is found in a soft, disk-dominated state throughout, with a declining $3$-$79$ keV count rate (from $112.4$ to $99.4$ cts s$^{-1}$), a low and only mildly evolving hardness ratio ($\approx0.14$-$0.16$) and a fractional variability that drops from $3.2\%$ to $1.1\%$; no periodic or quasi-periodic signal is detected in the power spectrum or the Lomb-Scargle periodogram of any observation. Joint FPMA+FPMB spectral fits with an absorbed disk-blackbody plus thermal-Comptonization continuum, together with a broad, high-significance ($11.7$-$15.0σ$) curvature feature near $10$-$12$ keV (an empirical proxy for a strong disk-reflection/returning-radiation component) describe the $4$-$30$ keV spectra well ($χ^2/{\rm dof}=1.04$-$1.15$). The inner-disk temperature cools steadily from $1.021\pm0.001$ to $1.002^{+0.003}_{-0.002}$ keV while the disk normalization and hence the derived inner radius, $R_{\rm in}\simeq27.7$ km $\simeq0.95\,R_{ISCO}$ remains constant to within $0.3\%$, consistent with a disk anchored at the innermost stable circular orbit throughout. The unabsorbed $4$-$30$ keV luminosity declines from $1.35\times10^{37}$ to $1.15\times10^{37}$ erg s$^{-1}$ ($0.67\%$ to $0.57 L_{Edd}$). These results of the spectral-timing characterization of the 2025 mini-outburst are broadly consistent with a high-spin black hole accreting at a low, steadily declining rate in the canonical soft state.
发表机构
- Dibrugarh University（迪布鲁加尔大学）
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