{"oa":1,"department":[{"_id":"ZoHa"}],"type":"journal_article","intvolume":"       543","day":"01","OA_place":"publisher","arxiv":1,"has_accepted_license":"1","date_updated":"2026-02-10T07:10:21Z","volume":543,"status":"public","publisher":"Oxford University Press","issue":"3","PlanS_conform":"1","publication":"Monthly Notices of the Royal Astronomical Society","file":[{"creator":"dernst","access_level":"open_access","file_size":3689696,"file_id":"21203","relation":"main_file","date_updated":"2026-02-10T07:07:17Z","content_type":"application/pdf","file_name":"2025_MonthlyNoticesRAS_Krauth.pdf","date_created":"2026-02-10T07:07:17Z","checksum":"f9b4c6a606df9493f6eb6af5ebcca6db","success":1}],"_id":"21122","date_created":"2026-01-31T09:28:28Z","publication_status":"published","OA_type":"gold","language":[{"iso":"eng"}],"doi":"10.1093/mnras/staf1583","acknowledgement":"We acknowledge support from the Nationale Wetenschapsagenda Roadmap grant ‘Gravitational Waves Laser Interferometer Space Antenna/Einstein Telescope: Shivers from the Deep Universe: A National Infrastructure for Gravitational Wave Research’ (LMK), National Science Foundation grant AST-2006176 (ZH), and National Aeronautics and Space Administration Astrophysics Theory Program grant 80NSSC22K0822 (AM and ZH). JD was supported by National Aeronautics and Space Administration through the National Aeronautics and Space Administration Hubble Fellowship grant HST-HF2-51552.001A, awarded by the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Incorporated, under National Aeronautics and Space Administration contract NAS5-26555. This research was supported in part by the National Science Foundation under grant no. NSF PHY-1748958. This research has made use of National Aeronautics and Space Administration’s Astrophysics Data System. Resources supporting this work were provided by the National Aeronautics and Space Administration High-End Computing (HEC) Program through the National Aeronautics and Space Administration Advanced Supercomputing (NAS) Division at Ames Research Center. Software:  python (Oliphant 2007; Millman & Aivazis 2011), scipy (Jones et al. 2001), numpy (van der Walt, Colbert & Varoquaux 2011), and matplotlib (Hunter 2007).","user_id":"2DF688A6-F248-11E8-B48F-1D18A9856A87","tmp":{"name":"Creative Commons Attribution 4.0 International Public License (CC-BY 4.0)","short":"CC BY (4.0)","legal_code_url":"https://creativecommons.org/licenses/by/4.0/legalcode","image":"/images/cc_by.png"},"page":"2670-2685","year":"2025","publication_identifier":{"eissn":["1365-2966"],"issn":["0035-8711"]},"abstract":[{"text":"The multimessenger combination of gravitational waves (GWs) from merging massive black hole binaries (MBHBs) and the electromagnetic (EM) counterpart from the surrounding circumbinary disc (CBD) will open avenues to new scientific pursuits. In order to realize this science, we need to correctly localize the host galaxy of the merging MBHB. Multiwavelength, time-dependent EM signatures can greatly facilitate the identification of the unique EM counterpart among many sources in LISA’s localization volume. To this end, we studied merging unequal-mass MBHBs embedded in a CBD using high-resolution 2D simulations, with a $\\Gamma$-law equation of state, incorporating viscous heating, shock heating, and radiative cooling. We simulate each binary starting from before it decouples from the CBD until just after the merger. We compute EM signatures and identify distinct features before, during, and after the merger. We corroborate previous findings of a several orders of magnitude drop in the thermal X-ray luminosity near the time of merger, but with delayed timing compared to an equal-mass system. The source remains X-ray dark for hours post-merger. Our main results are a potential new signature of a sharp spike in the thermal X-ray emission just before the tell-tale steep drop occurs. This feature may further help to identify EM counterparts of LISA’s unequal MBHBs before merger without the need for extensive pre-merger monitoring. Additionally, we find a role-reversal in which the primary out-accretes the secondary during late inspiral, which may diminish signatures originating from Doppler modulation.","lang":"eng"}],"DOAJ_listed":"1","ddc":["520"],"citation":{"chicago":"Krauth, Luke Major, Jordy Davelaar, Zoltán Haiman, John Ryan Westernacher-Schneider, Jonathan Zrake, and Andrew MacFadyen. “Thermal X-Ray Signatures in Late-Stage Unequal-Mass Massive Black Hole Binary Mergers.” <i>Monthly Notices of the Royal Astronomical Society</i>. Oxford University Press, 2025. <a href=\"https://doi.org/10.1093/mnras/staf1583\">https://doi.org/10.1093/mnras/staf1583</a>.","ista":"Krauth LM, Davelaar J, Haiman Z, Westernacher-Schneider JR, Zrake J, MacFadyen A. 2025. Thermal X-ray signatures in late-stage unequal-mass massive black hole binary mergers. Monthly Notices of the Royal Astronomical Society. 543(3), 2670–2685.","ama":"Krauth LM, Davelaar J, Haiman Z, Westernacher-Schneider JR, Zrake J, MacFadyen A. Thermal X-ray signatures in late-stage unequal-mass massive black hole binary mergers. <i>Monthly Notices of the Royal Astronomical Society</i>. 2025;543(3):2670-2685. doi:<a href=\"https://doi.org/10.1093/mnras/staf1583\">10.1093/mnras/staf1583</a>","mla":"Krauth, Luke Major, et al. “Thermal X-Ray Signatures in Late-Stage Unequal-Mass Massive Black Hole Binary Mergers.” <i>Monthly Notices of the Royal Astronomical Society</i>, vol. 543, no. 3, Oxford University Press, 2025, pp. 2670–85, doi:<a href=\"https://doi.org/10.1093/mnras/staf1583\">10.1093/mnras/staf1583</a>.","ieee":"L. M. Krauth, J. Davelaar, Z. Haiman, J. R. Westernacher-Schneider, J. Zrake, and A. MacFadyen, “Thermal X-ray signatures in late-stage unequal-mass massive black hole binary mergers,” <i>Monthly Notices of the Royal Astronomical Society</i>, vol. 543, no. 3. Oxford University Press, pp. 2670–2685, 2025.","short":"L.M. Krauth, J. Davelaar, Z. Haiman, J.R. Westernacher-Schneider, J. Zrake, A. MacFadyen, Monthly Notices of the Royal Astronomical Society 543 (2025) 2670–2685.","apa":"Krauth, L. M., Davelaar, J., Haiman, Z., Westernacher-Schneider, J. R., Zrake, J., &#38; MacFadyen, A. (2025). Thermal X-ray signatures in late-stage unequal-mass massive black hole binary mergers. <i>Monthly Notices of the Royal Astronomical Society</i>. Oxford University Press. <a href=\"https://doi.org/10.1093/mnras/staf1583\">https://doi.org/10.1093/mnras/staf1583</a>"},"file_date_updated":"2026-02-10T07:07:17Z","month":"11","oa_version":"Published Version","author":[{"last_name":"Krauth","full_name":"Krauth, Luke Major","first_name":"Luke Major"},{"last_name":"Davelaar","first_name":"Jordy","full_name":"Davelaar, Jordy"},{"first_name":"Zoltán","orcid":"0000-0003-3633-5403","full_name":"Haiman, Zoltán","id":"7c006e8c-cc0d-11ee-8322-cb904ef76f36","last_name":"Haiman"},{"last_name":"Westernacher-Schneider","first_name":"John Ryan","full_name":"Westernacher-Schneider, John Ryan"},{"last_name":"Zrake","first_name":"Jonathan","full_name":"Zrake, Jonathan"},{"first_name":"Andrew","full_name":"MacFadyen, Andrew","last_name":"MacFadyen"}],"quality_controlled":"1","article_type":"original","article_processing_charge":"Yes","date_published":"2025-11-01T00:00:00Z","external_id":{"arxiv":["2503.01494"]},"title":"Thermal X-ray signatures in late-stage unequal-mass massive black hole binary mergers"}