Searching for EM signatures from stellar black hole mergers in AGN with ZTF

Despite LIGO reporting nearly thirty stellar black hole (BH) merger events in its current O3 run, almost no EM followup activity has been spent looking for EM counterparts. However, accretion disks around supermassive BHs are promising sites for such events due to mass segregation and merger acceleration by disk gas torques. McKernan et al. (2019) have recently proposed that a GW-kick at BH merger would cause ram-pressure stripping of gas with the BH Hill sphere and a UV flare. The AGN optical/UV photometry of the associated AGN would alter and asymmetric broad emission line profiles develop on week to month timescales. With its 47 sq. deg. field of view, ZTF is well placed to search for such signals over large regions of sky and we report here the results of a systematic search for candidate counterparts to the LIGO O3 triggers within the ZTF alert stream.