4U 1538-52 in a Heartbeat: Broadband X-ray Spectral Properties from XMM-Newton and NuSTAR

[2608.14938] 4U 1538-52 in a Heartbeat: Broadband X-ray Spectral Properties from XMM-Newton and NuSTAR Skip to main content Search Submit Donate Log in Search arXiv Press Enter to search · Advanced search Astrophysics > High Energy Astrophysical Phenomena arXiv:2608.14938 (astro-ph) [Submitted on 14 Aug 2026] Title: 4U 1538-52 in a Heartbeat: Broadband X-ray Spectral Properties from XMM-Newton and NuSTAR Authors: C. M. Diez , S. Dupourqué , A.-L. Doherty , D. Dickson , A. Zainab , S. Martínez-Núñez , J. M. Torrejón , S. Guillot , A. Rouco Escorial , F. Fürst , P. Kretschmar View a PDF of the paper titled 4U 1538-52 in a Heartbeat: Broadband X-ray Spectral Properties from XMM-Newton and NuSTAR, by C. M. Diez and 10 other authors View PDF HTML (experimental) Abstract: Galactic high-mass X-ray binaries (HMXBs) are important systems for studying accretion mechanisms onto compact objects and for investigating the complex stellar winds of massive stars. In particular, HMXBs hosting a neutron star allow us to reveal the structure of the accreted material in X-ray pulsars and consequently to investigate how matter behaves under extreme conditions of pressure and density. These are major scientific goals for XRISM and NewAthena. Here we report on the first out-of-eclipse XMM-Newton observation of the HMXB 4U 1538-52, complemented by NuSTAR coverage. Our campaign aimed to investigate stellar-wind variability and continuum changes with high-resolution spectroscopy at a critical orbital phase: when the neutron star is in inferior conjunction. Thanks to simultaneous observations covering both soft and hard X-rays, we obtain the most detailed X-ray view of the accreted material in 4U 1538-52 to date. In particular, we perform time-resolved spectroscopy down to the pulse period of the neutron star to highlight wind clumping properties and accretion structures. In this dataset, we observe a bright flare reaching $\sim$10$^{37}\,\rm{erg\,s^{-1}}$ probably induced by the accretion of a $10^{20}\,\rm{g}$ clump, followed by a luminosity dip forming a heartbeat-like episode. This event is followed by three local absorption peaks with local variability of the order of the pulse period, and a gradual hardening of the underlying spectrum throughout the observation. This could indicate the presence of both small-scale and large-scale overdense structures in the vicinity of the neutron star, which can be attributed to clumps and filamentary structures embedded in the accretion wake. These observational evidences are further supported and reproduced by 3D hydrodynamic simulations. Comments: 13 pages, 9 figures, accepted for publication in A&A on 12 Aug. 2026 Subjects: High Energy Astrophysical Phenomena (astro-ph.HE) Cite as: arXiv:2608.14938 [astro-ph.HE] (or arXiv:2608.14938v1 [astro-ph.HE] for this version) https://doi.org/10.48550/arXiv.2608.14938 Focus to learn more arXiv-issued DOI via DataCite Submission history From: Camille Diez [ view email ] [v1] Fri, 14 Aug 2026 23:27:51 UTC (2,150 KB) Full-text links: Access Paper: View a PDF of the paper titled 4U 1538-52 in a Heartbeat: Broadband X-ray Spectral Properties from XMM-Newton and NuSTAR, by C. M. Diez and 10 other authors View PDF HTML (experimental) TeX Source view license Additional Features Audio Summary Current browse context: astro-ph.HE < prev | next > new | recent | 2026-08 Change to browse by: astro-ph References & Citations INSPIRE HEP NASA ADS Google Scholar Semantic Scholar export BibTeX citation Loading... BibTeX formatted citation × loading... 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