{"arxiv":1,"year":"2025","language":[{"iso":"eng"}],"publisher":"EDP Sciences","OA_type":"diamond","article_processing_charge":"No","date_created":"2025-11-24T14:23:22Z","_id":"20686","doi":"10.1051/0004-6361/202554574","publication":"Astronomy & Astrophysics","has_accepted_license":"1","month":"10","title":"Testing compact massive black hole binary candidates through multi-epoch spectroscopy","abstract":[{"text":"Emission from two massive black holes (MBHs) bound in a close binary is expected to be modulated by different processes, such as the Doppler boost due to the orbital motion, accretion rate variability generated by the interaction with a circumbinary disc, and binary gravitational self-lensing. When the binary is compact enough, the two black holes are thought to be surrounded by a common broad-line region that reprocesses the impinging periodically varying ionising flux, creating broad emission lines with variable line shapes. Therefore, the study of broad emission line variability through multi-epoch spectroscopic campaigns is of paramount importance for the unambiguous identification of a binary. In this work, we study the response of a disc-like broad-line region to the Doppler-boosted ionising flux emitted by sub-milliparsec MBH binaries on a circular orbit and compare it with the response of a broad-line region illuminated by a single MBH with a periodically but isotropically varying intrinsic luminosity. We show that in the binary case, the time lags of the blue and red wings of the broad emission lines, arising from diametrically opposite sides of the circumbinary disc, are out of phase by half of the binary’s orbital period, as they each respond to the periodic ‘lighthouse’ modulation from the binary’s continuum emission. This asymmetric time lag represents a new binary signature that cannot be mimicked by a single MBH.","lang":"eng"}],"author":[{"first_name":"Lorenzo","last_name":"Bertassi","full_name":"Bertassi, Lorenzo"},{"first_name":"Erika","last_name":"Sottocorno","full_name":"Sottocorno, Erika"},{"last_name":"Rigamonti","full_name":"Rigamonti, Fabio","first_name":"Fabio"},{"first_name":"Daniel","full_name":"D’Orazio, Daniel","last_name":"D’Orazio"},{"first_name":"Michael","full_name":"Eracleous, Michael","last_name":"Eracleous"},{"full_name":"Haiman, Zoltán","last_name":"Haiman","id":"7c006e8c-cc0d-11ee-8322-cb904ef76f36","first_name":"Zoltán","orcid":"0000-0003-3633-5403"},{"last_name":"Dotti","full_name":"Dotti, Massimo","first_name":"Massimo"}],"file":[{"checksum":"dbaf156cb6684bf5c3f5fb76fc890d5a","date_updated":"2025-11-25T12:56:18Z","date_created":"2025-11-25T12:56:18Z","access_level":"open_access","content_type":"application/pdf","relation":"main_file","file_id":"20693","creator":"dernst","file_name":"2025_AstronomyAstrophysics_Bertassi.pdf","file_size":2035081,"success":1}],"citation":{"ista":"Bertassi L, Sottocorno E, Rigamonti F, D’Orazio D, Eracleous M, Haiman Z, Dotti M. 2025. Testing compact massive black hole binary candidates through multi-epoch spectroscopy. Astronomy &#38; Astrophysics. 702, A165.","ieee":"L. Bertassi <i>et al.</i>, “Testing compact massive black hole binary candidates through multi-epoch spectroscopy,” <i>Astronomy &#38; Astrophysics</i>, vol. 702. EDP Sciences, 2025.","ama":"Bertassi L, Sottocorno E, Rigamonti F, et al. Testing compact massive black hole binary candidates through multi-epoch spectroscopy. <i>Astronomy &#38; Astrophysics</i>. 2025;702. doi:<a href=\"https://doi.org/10.1051/0004-6361/202554574\">10.1051/0004-6361/202554574</a>","mla":"Bertassi, Lorenzo, et al. “Testing Compact Massive Black Hole Binary Candidates through Multi-Epoch Spectroscopy.” <i>Astronomy &#38; Astrophysics</i>, vol. 702, A165, EDP Sciences, 2025, doi:<a href=\"https://doi.org/10.1051/0004-6361/202554574\">10.1051/0004-6361/202554574</a>.","short":"L. Bertassi, E. Sottocorno, F. Rigamonti, D. D’Orazio, M. Eracleous, Z. Haiman, M. Dotti, Astronomy &#38; Astrophysics 702 (2025).","chicago":"Bertassi, Lorenzo, Erika Sottocorno, Fabio Rigamonti, Daniel D’Orazio, Michael Eracleous, Zoltán Haiman, and Massimo Dotti. “Testing Compact Massive Black Hole Binary Candidates through Multi-Epoch Spectroscopy.” <i>Astronomy &#38; Astrophysics</i>. EDP Sciences, 2025. <a href=\"https://doi.org/10.1051/0004-6361/202554574\">https://doi.org/10.1051/0004-6361/202554574</a>.","apa":"Bertassi, L., Sottocorno, E., Rigamonti, F., D’Orazio, D., Eracleous, M., Haiman, Z., &#38; Dotti, M. (2025). Testing compact massive black hole binary candidates through multi-epoch spectroscopy. <i>Astronomy &#38; Astrophysics</i>. EDP Sciences. <a href=\"https://doi.org/10.1051/0004-6361/202554574\">https://doi.org/10.1051/0004-6361/202554574</a>"},"publication_identifier":{"eissn":["1432-0746"],"issn":["0004-6361"]},"acknowledgement":"MD acknowledge funding from MIUR under the grant PRIN 2017-MB8AEZ, and financial support from ICSC – Centro Nazionale di Ricerca in High Performance Computing, Big Data and Quantum Computing, funded by European Union – NextGenerationEU. This study is supported by the Italian Ministry for Research and University (MUR) under Grant ‘Progetto Dipartimenti di Eccellenza 2023-2027’ (BiCoQ). FR acknowledges the support from the Next Generation EU funds within the National Recovery and Resilience Plan (PNRR), Mission 4 – Education and Research, Component 2 – From Research to Business (M4C2), Investment Line 3.1 – Strengthening and creation of Research Infrastructures, Project IR0000012 – CTA+ – Cherenkov Telescope Array Plus. DJD acknowledges support from the Danish Independent Research Fund through Sapere Aude Starting Grant No. 121587 ZH acknowledges support from NSF grant AST-2006176 and NASA grants 80NSSC22K0822 and 80NSSC24K0440.","article_type":"original","date_updated":"2025-11-25T13:00:33Z","quality_controlled":"1","oa_version":"Published Version","day":"20","article_number":"A165","type":"journal_article","user_id":"2DF688A6-F248-11E8-B48F-1D18A9856A87","intvolume":"       702","status":"public","scopus_import":"1","ddc":["520"],"OA_place":"publisher","department":[{"_id":"ZoHa"}],"date_published":"2025-10-20T00:00:00Z","volume":702,"publication_status":"published","file_date_updated":"2025-11-25T12:56:18Z","tmp":{"short":"CC BY (4.0)","legal_code_url":"https://creativecommons.org/licenses/by/4.0/legalcode","name":"Creative Commons Attribution 4.0 International Public License (CC-BY 4.0)","image":"/images/cc_by.png"},"PlanS_conform":"1","oa":1,"external_id":{"arxiv":["2504.06349"]}}