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Published October 20, 2019 | Published + Accepted Version
Journal Article Open

Ram-pressure Stripping of a Kicked Hill Sphere: Prompt Electromagnetic Emission from the Merger of Stellar Mass Black Holes in an AGN Accretion Disk


Accretion disks around supermassive black holes (SMBHs) are promising sites for stellar mass black hole (BH) mergers due to mass segregation and merger acceleration by disk gas torques. Here we show that a gravitational-wave (GW) kick at BH merger causes ram-pressure stripping of gas within the BH Hill sphere. If R_H ≥ H, the disk height, an off-center UV flare at a_(BH) ~ 10³ r_g, emerges within t_(UV) ~ O(2 days)(a_(BH)/10³ r_g)(M_(SMBH)/10⁸ M_⊙)(v_(kick)/10² km s⁻¹) postmerger and lasts O(R_H/v_(kick)) ~ O(5t_(UV)). The flare emerges with luminosity O(10⁴² erg s⁻¹(t_(UV)/2 days)⁻¹(M_(Hill)/1M_⊙)(v_(kick)/10² km s⁻¹)². Active galactic nucleus optical/UV photometry is altered and asymmetric broad emission line profiles can develop after weeks. If R_H < H, detectability depends on disk optical depth. Follow-up by large optical sky surveys is optimized for small GW error volumes and for Laser Interferometer Gravitational-Wave Observatory/Virgo triggers >50M_⊙.

Additional Information

© 2019 The American Astronomical Society. Received 2019 July 5; revised 2019 September 8; accepted 2019 September 27; published 2019 October 17. B.M. dedicates this paper to the memory of his mother, Treasa McKernan. B.M. and K.E.S.F. are supported by NSF 1831412. The work of D.S. was carried out at the Jet Propulsion Laboratory, California Institute of Technology, under a contract with NASA. Thanks to the referee for highlighting the GW kick and participants in the 1st workshop on stellar mass BH mergers in AGN disks, held 2019 March 11–13, and sponsored by the CCA at the Flatiron Institute in New York City.

Attached Files

Published - McKernan_2019_ApJL_884_L50.pdf

Accepted Version - 1907.03746.pdf


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August 22, 2023
October 18, 2023