[{"title":"Can quasars, triggered by mergers, account for NANOGrav’s stochastic gravitational wave background?","intvolume":"        42","oa":1,"volume":42,"month":"04","external_id":{"isi":["001448904700001"],"arxiv":["2412.12726"]},"acknowledgement":"We thank Chengcheng Xin and Girish Kulkarni for useful discussions. ZH gratefully acknowledges the hospitality of Eötvös University during an extended sabbatical visit, where this work began. ZH acknowledges support from NSF Grant AST-2006176 and NASA Grants 80NSSC22K0822 and 80NSSC24K0440. ZF acknowledges support from the Hungarian National Research, Development and Innovation Office (NKFIH) through the Institutional Excellence Program No. TKP2021-NKTA-64.","OA_type":"green","OA_place":"repository","date_updated":"2025-09-30T11:30:11Z","_id":"19497","year":"2025","article_processing_charge":"No","arxiv":1,"oa_version":"Preprint","author":[{"last_name":"Kis-Tóth","full_name":"Kis-Tóth, Ágnes","first_name":"Ágnes"},{"last_name":"Haiman","full_name":"Haiman, Zoltán","id":"7c006e8c-cc0d-11ee-8322-cb904ef76f36","orcid":"0000-0003-3633-5403","first_name":"Zoltán"},{"full_name":"Frei, Zsolt","last_name":"Frei","first_name":"Zsolt"}],"language":[{"iso":"eng"}],"publication_identifier":{"issn":["0264-9381"],"eissn":["1361-6382"]},"publication":"Classical and Quantum Gravity","publication_status":"published","article_number":"075007","citation":{"mla":"Kis-Tóth, Ágnes, et al. “Can Quasars, Triggered by Mergers, Account for NANOGrav’s Stochastic Gravitational Wave Background?” <i>Classical and Quantum Gravity</i>, vol. 42, no. 7, 075007, IOP Publishing, 2025, doi:<a href=\"https://doi.org/10.1088/1361-6382/adbda6\">10.1088/1361-6382/adbda6</a>.","chicago":"Kis-Tóth, Ágnes, Zoltán Haiman, and Zsolt Frei. “Can Quasars, Triggered by Mergers, Account for NANOGrav’s Stochastic Gravitational Wave Background?” <i>Classical and Quantum Gravity</i>. IOP Publishing, 2025. <a href=\"https://doi.org/10.1088/1361-6382/adbda6\">https://doi.org/10.1088/1361-6382/adbda6</a>.","ama":"Kis-Tóth Á, Haiman Z, Frei Z. Can quasars, triggered by mergers, account for NANOGrav’s stochastic gravitational wave background? <i>Classical and Quantum Gravity</i>. 2025;42(7). doi:<a href=\"https://doi.org/10.1088/1361-6382/adbda6\">10.1088/1361-6382/adbda6</a>","ista":"Kis-Tóth Á, Haiman Z, Frei Z. 2025. Can quasars, triggered by mergers, account for NANOGrav’s stochastic gravitational wave background? Classical and Quantum Gravity. 42(7), 075007.","apa":"Kis-Tóth, Á., Haiman, Z., &#38; Frei, Z. (2025). Can quasars, triggered by mergers, account for NANOGrav’s stochastic gravitational wave background? <i>Classical and Quantum Gravity</i>. IOP Publishing. <a href=\"https://doi.org/10.1088/1361-6382/adbda6\">https://doi.org/10.1088/1361-6382/adbda6</a>","short":"Á. Kis-Tóth, Z. Haiman, Z. Frei, Classical and Quantum Gravity 42 (2025).","ieee":"Á. Kis-Tóth, Z. Haiman, and Z. Frei, “Can quasars, triggered by mergers, account for NANOGrav’s stochastic gravitational wave background?,” <i>Classical and Quantum Gravity</i>, vol. 42, no. 7. IOP Publishing, 2025."},"doi":"10.1088/1361-6382/adbda6","user_id":"317138e5-6ab7-11ef-aa6d-ffef3953e345","department":[{"_id":"ZoHa"}],"article_type":"original","publisher":"IOP Publishing","date_created":"2025-04-06T22:01:32Z","scopus_import":"1","date_published":"2025-04-04T00:00:00Z","quality_controlled":"1","type":"journal_article","issue":"7","status":"public","abstract":[{"text":"The stochastic gravitational wave (GW) background recently discovered by several pulsar timing array experiments is consistent with arising from a population of coalescing super-massive black hole binaries. The amplitude of the background is somewhat higher than expected in most previous population models or from the local mass density observations. Such binaries are expected to be produced in galaxy mergers, which are also thought to trigger bright quasar activity. Under the assumptions that (i) a fraction fbin∼1 of all quasars are associated with mergers, (ii) the typical quasar lifetime is tQ∼108 yr, and (iii) adopting Eddington ratios fEdd∼0.25 for the luminosity of quasars, we compute the GW background associated directly with the empirically measured quasar luminosity function. This approach bypasses the need to model the cosmological evolution of black holes or galaxy mergers from simulations or semi-analytical models. We find the amplitude matching the value measured by NANOGrav. Our results are consistent with most quasars being associated with black hole binaries and being the sources of the GW background, and imply a joint constraint on tQ, fEdd and the typical mass ratio q≡M2/M1. The signal in this case would be dominated by relatively distant ∼109M⊙ sources at z≈2−3, at the peak of quasar activity. Similarly to other models, our results remain in tension with the local super-massive black hole mass density.","lang":"eng"}],"main_file_link":[{"open_access":"1","url":"https://doi.org/10.48550/arXiv.2412.12726"}],"isi":1,"day":"04"},{"date_updated":"2024-09-24T11:39:17Z","_id":"17638","oa":1,"month":"11","volume":30,"external_id":{"arxiv":["1309.2302"]},"title":"Electromagnetic signatures of supermassive black hole binaries resolved by PTAs","intvolume":"        30","publication":"Classical and Quantum Gravity","publication_status":"published","article_number":"224012","citation":{"apa":"Tanaka, T. L., &#38; Haiman, Z. (2013). Electromagnetic signatures of supermassive black hole binaries resolved by PTAs. <i>Classical and Quantum Gravity</i>. IOP Publishing. <a href=\"https://doi.org/10.1088/0264-9381/30/22/224012\">https://doi.org/10.1088/0264-9381/30/22/224012</a>","ista":"Tanaka TL, Haiman Z. 2013. Electromagnetic signatures of supermassive black hole binaries resolved by PTAs. Classical and Quantum Gravity. 30(22), 224012.","short":"T.L. Tanaka, Z. Haiman, Classical and Quantum Gravity 30 (2013).","ieee":"T. L. Tanaka and Z. Haiman, “Electromagnetic signatures of supermassive black hole binaries resolved by PTAs,” <i>Classical and Quantum Gravity</i>, vol. 30, no. 22. IOP Publishing, 2013.","mla":"Tanaka, Takamitsu L., and Zoltán Haiman. “Electromagnetic Signatures of Supermassive Black Hole Binaries Resolved by PTAs.” <i>Classical and Quantum Gravity</i>, vol. 30, no. 22, 224012, IOP Publishing, 2013, doi:<a href=\"https://doi.org/10.1088/0264-9381/30/22/224012\">10.1088/0264-9381/30/22/224012</a>.","ama":"Tanaka TL, Haiman Z. Electromagnetic signatures of supermassive black hole binaries resolved by PTAs. <i>Classical and Quantum Gravity</i>. 2013;30(22). doi:<a href=\"https://doi.org/10.1088/0264-9381/30/22/224012\">10.1088/0264-9381/30/22/224012</a>","chicago":"Tanaka, Takamitsu L, and Zoltán Haiman. “Electromagnetic Signatures of Supermassive Black Hole Binaries Resolved by PTAs.” <i>Classical and Quantum Gravity</i>. IOP Publishing, 2013. <a href=\"https://doi.org/10.1088/0264-9381/30/22/224012\">https://doi.org/10.1088/0264-9381/30/22/224012</a>."},"author":[{"first_name":"Takamitsu L","last_name":"Tanaka","full_name":"Tanaka, Takamitsu L"},{"last_name":"Haiman","full_name":"Haiman, Zoltán","id":"7c006e8c-cc0d-11ee-8322-cb904ef76f36","first_name":"Zoltán"}],"language":[{"iso":"eng"}],"publication_identifier":{"issn":["0264-9381","1361-6382"]},"arxiv":1,"oa_version":"Preprint","year":"2013","article_processing_charge":"No","type":"journal_article","issue":"22","publisher":"IOP Publishing","date_created":"2024-09-06T07:16:12Z","scopus_import":"1","date_published":"2013-11-04T00:00:00Z","quality_controlled":"1","doi":"10.1088/0264-9381/30/22/224012","user_id":"317138e5-6ab7-11ef-aa6d-ffef3953e345","extern":"1","article_type":"original","day":"04","status":"public","main_file_link":[{"url":" https://doi.org/10.48550/arXiv.1309.2302","open_access":"1"}],"abstract":[{"lang":"eng","text":"Pulsar timing arrays (PTAs) may eventually be able to detect not only the stochastic gravitational-wave (GW) background of SMBH binaries, but also individual, particularly massive binaries whose signals stick out above the background. In this contribution, we discuss the possibility of identifying and studying such 'resolved' binaries through their electromagnetic emission. The host galaxies of such binaries are themselves expected to be also very massive and rare, so that out to redshifts z ≈ 0.2 a unique massive galaxy may be identified as the host. At higher redshifts, the PTA error boxes are larger and may contain as many as several hundred massive-galaxy interlopers. In this case, the true counterpart may be identified, if it is accreting gas efficiently, as an active galactic nucleus (AGN) with a peculiar spectrum and variable emission features. Specifically, the binary's tidal torques expel the gas from the inner part of the accretion disc, making it unusually dim in x-ray and UV bands and in broad optical emission lines. The tails of the broad wings of any FeKα emission line may also be 'clipped' and missing. The binary's orbital motion, as well as the gas motions it induces, may trigger quasiperiodic variations. These include coherent flux variability, such as luminous, multi-wavelength flares, as well as Doppler shifts of broad emission lines and 'see-saw' oscillations in the FeKα line. Additional features, such as evidence for a recent major merger or dual collimated jets, could also corroborate the counterpart. These properties would make resolved PTA sources stand out among AGN with similar overall luminosities and allow their identification."}]},{"day":"07","status":"public","abstract":[{"text":"Supermassive black hole binaries (SMBHBs) with masses in the mass range ∼(10^4–10^7) M⊙/(1 + z), produced in galaxy mergers, are thought to complete their coalescence due to the emission of gravitational waves (GWs). The anticipated detection of the GWs by the future Laser Interferometric Space Antenna (LISA) will constitute a milestone for fundamental physics and astrophysics. While the GW signatures themselves will provide a treasure trove of information, if the source can be securely identified in electromagnetic (EM) bands, this would open up entirely new scientific opportunities, to probe fundamental physics, astrophysics and cosmology. We discuss several ideas, involving wide-field telescopes, that may be useful in locating electromagnetic counterparts to SMBHBs detected by LISA. In particular, the binary may produce a variable electromagnetic flux, such as a roughly periodic signal due to the orbital motion prior to coalescence, or a prompt transient signal caused by shocks in the circumbinary disc when the SMBHB recoils and 'shakes' the disc. We discuss whether these time-variable EM signatures may be detectable, and how they can help in identifying a unique counterpart within the localization errors provided by LISA. We also discuss a possibility of identifying a population of coalescing SMBHBs statistically, in a deep optical survey for periodically variable sources, before LISA detects the GWs directly. The discovery of such sources would confirm that gas is present in the vicinity and is being perturbed by the SMBHB—serving as a proof of concept for eventually finding actual LISA counterparts.","lang":"eng"}],"main_file_link":[{"open_access":"1","url":"https://doi.org/10.1088/0264-9381/26/9/094032"}],"scopus_import":"1","publisher":"IOP Publishing","date_created":"2024-09-06T09:51:19Z","quality_controlled":"1","date_published":"2009-05-07T00:00:00Z","issue":"9","type":"journal_article","extern":"1","user_id":"317138e5-6ab7-11ef-aa6d-ffef3953e345","doi":"10.1088/0264-9381/26/9/094032","article_type":"original","author":[{"first_name":"Zoltán","id":"7c006e8c-cc0d-11ee-8322-cb904ef76f36","full_name":"Haiman, Zoltán","last_name":"Haiman"},{"last_name":"Kocsis","full_name":"Kocsis, Bence","first_name":"Bence"},{"first_name":"Kristen","last_name":"Menou","full_name":"Menou, Kristen"},{"first_name":"Zoltán","last_name":"Lippai","full_name":"Lippai, Zoltán"},{"last_name":"Frei","full_name":"Frei, Zsolt","first_name":"Zsolt"}],"publication_identifier":{"issn":["0264-9381","1361-6382"]},"language":[{"iso":"eng"}],"publication":"Classical and Quantum Gravity","citation":{"chicago":"Haiman, Zoltán, Bence Kocsis, Kristen Menou, Zoltán Lippai, and Zsolt Frei. “Identifying Decaying Supermassive Black Hole Binaries from Their Variable Electromagnetic Emission.” <i>Classical and Quantum Gravity</i>. IOP Publishing, 2009. <a href=\"https://doi.org/10.1088/0264-9381/26/9/094032\">https://doi.org/10.1088/0264-9381/26/9/094032</a>.","ama":"Haiman Z, Kocsis B, Menou K, Lippai Z, Frei Z. Identifying decaying supermassive black hole binaries from their variable electromagnetic emission. <i>Classical and Quantum Gravity</i>. 2009;26(9). doi:<a href=\"https://doi.org/10.1088/0264-9381/26/9/094032\">10.1088/0264-9381/26/9/094032</a>","mla":"Haiman, Zoltán, et al. “Identifying Decaying Supermassive Black Hole Binaries from Their Variable Electromagnetic Emission.” <i>Classical and Quantum Gravity</i>, vol. 26, no. 9, 094032, IOP Publishing, 2009, doi:<a href=\"https://doi.org/10.1088/0264-9381/26/9/094032\">10.1088/0264-9381/26/9/094032</a>.","short":"Z. Haiman, B. Kocsis, K. Menou, Z. Lippai, Z. Frei, Classical and Quantum Gravity 26 (2009).","ieee":"Z. Haiman, B. Kocsis, K. Menou, Z. Lippai, and Z. Frei, “Identifying decaying supermassive black hole binaries from their variable electromagnetic emission,” <i>Classical and Quantum Gravity</i>, vol. 26, no. 9. IOP Publishing, 2009.","ista":"Haiman Z, Kocsis B, Menou K, Lippai Z, Frei Z. 2009. Identifying decaying supermassive black hole binaries from their variable electromagnetic emission. Classical and Quantum Gravity. 26(9), 094032.","apa":"Haiman, Z., Kocsis, B., Menou, K., Lippai, Z., &#38; Frei, Z. (2009). Identifying decaying supermassive black hole binaries from their variable electromagnetic emission. <i>Classical and Quantum Gravity</i>. IOP Publishing. <a href=\"https://doi.org/10.1088/0264-9381/26/9/094032\">https://doi.org/10.1088/0264-9381/26/9/094032</a>"},"publication_status":"published","article_number":"094032","year":"2009","article_processing_charge":"No","oa_version":"Published Version","date_updated":"2024-09-30T09:19:04Z","_id":"17764","intvolume":"        26","title":"Identifying decaying supermassive black hole binaries from their variable electromagnetic emission","volume":26,"month":"05","oa":1}]