Millihertz quasi-periodic oscillations (mHz QPOs) observed in neutron-star low-mass X-ray binaries (NS LMXBs) are generally explained as marginally stable thermonuclear burning on the neutron star surface. We report the discovery of mHz QPOs in an XMM-Newton observation of the transient 1RXS J180408.9$-$342058, during a regular bursting phase of its 2015 outburst. We found significant periodic signals in the March observation, with frequencies in the range $5-8\,\mathrm{mHz}$, superimposed on a strong $\sim1/f$ power-law noise continuum. Neither the QPO signals nor the power-law noise were present during the April observation, which exhibited a $2.5\times$ higher luminosity and had correspondingly more frequent bursts. When present, the QPO signal power decreases during bursts and disappears afterwards, similar to the behaviour in other sources. 1RXS J180408.9$-$342058 is the eighth source known to date that exhibits such QPOs driven by thermonuclear burning. We examine the range of properties of the QPO signals in different sources. Whereas the observed oscillation profile is similar to that predicted by numerical models, the amplitudes are significantly higher, challenging their explanation as originating from marginally stable burning.
XMM-Newton and NICER measurement of the rms spectrum of the millihertz quasi-periodic oscillations in the neutron-star low-mass X-ray binary 4U 1636-53
A Phase-resolved View of Millihertz Quasi-periodic Oscillations in the Ultraluminous X-ray Source M51 ULX-7: Evidence for a Magnetically Truncated Disk and Geometrical Beaming
Persistence of the Millihertz X-ray Quasi-Periodic Oscillation in the Active Galactic Nucleus 1ES 1927+654
MIT Kavli Institute for Astrophysics and Space Research, Massachusetts Institute of Technology（麻省理工学院）；Black Hole Initiative at Harvard University（哈佛大学黑洞倡议）；JILA, University of Colorado and National Institute of Standards and Technology（科罗拉多大学与美国国家标准与技术研究院）；Department of Astrophysical and Planetary Sciences, University of Colorado（科罗拉多大学）；Institute of Astronomy, University of Cambridge（剑桥大学天文学研究所）；Centro de Astrobiología (CAB), CSIC-INTA（西班牙国家航空航天技术研究所与西班牙国家科学研究委员会天体生物学中心）；School of Mathematics, Statistics, and Physics, Newcastle（纽卡斯尔大学）
Discovery of a correlation between the frequency of the mHz quasi-periodic oscillations and the neutron-star temperature in the low-mass X-ray binary 4U 1636-53
Timing and spectral analysis of the 2025 outburst of 4U 1630$-$47 with \textit{NICER}
Kapteyn Astronomical Institute, University of Groningen（格罗宁根大学卡普坦天文研究所）；Department of Physics, College of Science, Southern University of Science and Technology（南方科技大学理学院物理系）；Department of Astronomy, School of Physics and Technology, Wuhan University（武汉大学物理科学与技术学院天文学系）
