标题： 低光度X射线脉动的探测来自吸积毫秒脉冲星IGR J17511-3057：明亮吸积与低光度状态之间的越来越细的联系 显示英文标题

标题： Detection of low-luminosity X-ray pulsations from the accreting millisecond pulsar IGR J17511-3057: an ever-thinning thread between bright accretion and sub-luminous states

摘要： 在几乎十年的休眠后，吸积毫秒脉冲星 IGR J17511$-$3057 在 2025 年 2 月 11 日出现了新的爆发，这是自发现以来的第三次，此前曾在 2009 年和 2015 年有过活动。 我们报告了一次 XMM-Newton 机会目标观测，该观测于 2025 年 3 月 4 日进行，即爆发开始后二十多天。 从 X 射线谱来看——很好地由一个吸收康普顿化模型描述——我们估计了未被吸收的 0.5$-$10 keV 光度为$L_X \sim 7 \times 10^{33} \, \mathrm{erg \, s^{-1}}$（假设源距离等于$6.9$kpc 的上限）。 为了将其置于背景中，我们分析了一次 2019 年进行的档案钱德拉观测，该观测在同一能量带中得到了静止光度$L_\mathrm{X,q} \sim 2 \times 10^{32} \, \mathrm{erg \, s^{-1}}$。 尽管这种比较表明在 XMM-Newton 观测期间该源仍然远高于其静止水平，但 2025 年爆发后期估计的低光度通常会将该源置于螺旋桨模式。 然而，我们意外地检测到了相干 X 射线脉动，在 0.3$-$3 keV 波段幅度峰值达到$\sim$42% 。 我们还观察到与爆发早期阶段相比光谱变软。 最后，我们报告了在2025年4月12日通过ATCA观测获得的源通量密度在5.5 GHz处的3$\sigma$上限为60$\mu$Jy beam$^{-1}$，在吸积活动下降后，如我们对2025年3月15日NICER数据的分析所表明的，在光度水平为$L_X \sim 1 \times 10^{34} \, \mathrm{erg \, s^{-1}}$时没有明显的X射线脉动。 我们在其他吸积毫秒脉冲星的背景下讨论了我们的发现，并与亚低光度盘状态中的过渡系统进行了比较。 显示英文摘要

摘要： After nearly a decade in quiescence, the accreting millisecond pulsar IGR J17511$-$3057 displayed a new outburst on 2025 February 11, its third since discovery, following previous activity in 2009 and 2015. We report on an XMM-Newton Target of Opportunity observation performed on 2025 March 4, more than twenty days after the outburst onset. From the X-ray spectrum - well described by an absorbed Comptonization model - we estimated an unabsorbed 0.5$-$10 keV luminosity of $L_X \sim 7 \times 10^{33} \, \mathrm{erg \, s^{-1}}$ (assuming a source distance equal to the upper limit of $6.9$ kpc). To place this in context, we analyzed an archival Chandra observation performed in 2019, which yielded a quiescent luminosity of $L_\mathrm{X,q} \sim 2 \times 10^{32} \, \mathrm{erg \, s^{-1}}$ in the same energy band. Although this comparison indicates that the source was still well above its quiescent level during the XMM-Newton observation, the estimated low luminosity during the late stage of the 2025 outburst would typically place the source in the propeller regime. Nevertheless, we unexpectedly detected coherent X-ray pulsations with an amplitude peaking at $\sim$42% in the 0.3$-$3 keV band. We also observed a spectral softening compared to the early stages of the outburst. Finally, we report a 3$\sigma$ upper limit of 60 $\mu$Jy beam$^{-1}$ on the source flux density at 5.5 GHz from ATCA observations acquired on 2025 April 12, following a decline of the accretion activity, as indicated by our analysis of NICER data from 2025 March 15, which revealed no significant X-ray pulsations at a luminosity level of $L_X \sim 1 \times 10^{34} \, \mathrm{erg \, s^{-1}}$. We discuss our findings in the context of other accreting millisecond pulsars and draw comparisons with transitional systems in the sub-luminous disk state.