# Ram-pressure stripping of a kicked Hill sphere: Prompt electromagnetic emission from the merger of stellar mass black holes in an AGN accretion disk

## TL;DR

This paper predicts electromagnetic signals, including UV flares and spectral changes, resulting from ram-pressure stripping of gas during stellar-mass black hole mergers in AGN disks, offering potential observational signatures.

## Contribution

It introduces a novel model for electromagnetic emissions caused by ram-pressure stripping during black hole mergers in AGN disks, linking gravitational wave events to observable electromagnetic counterparts.

## Key findings

- UV flares occur within days post-merger with luminosity around 10^42 erg/s.
- Asymmetric broad emission lines can develop weeks after the merger.
- Detectability depends on disk properties and GW error volume, guiding observational strategies.

## Abstract

Accretion disks around supermassive black holes (SMBH) 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 GW-kick at BH merger causes ram-pressure stripping of gas within the BH Hill sphere. If $R_{H}\geq H$, the disk height, an off-center UV flare at $a_{\rm BH} \sim 10^{3}r_{g}$ emerges within $t_{\rm UV} \sim \rm{O}(2 {\rm days})(a_{\rm BH}/10^{3}r_{g})(M_{\rm SMBH}/10^{8}M_{\odot})(v_{\rm kick}/10^{2}\rm{km/s})$ post-merger and lasts O$(R_{H}/v_{\rm kick}) \sim \rm{O}(5 t_{\rm UV}$). The flare emerges with luminosity O($10^{42}{\rm erg/s})(t_{\rm UV}/2{\rm days})^{-1}(M_{\rm Hill}/1M_{\odot})(v_{\rm kick}/10^{2}{\rm km/s})^{2}$. AGN optical/UV photometry alters 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 LIGO/Virgo triggers $>50M_{\odot}$.