Seeing Double: The Theory Defying Twin Flares of TDE 2022dbl

Partial tidal disruption events, in which a star survives a close passage by a supermassive black hole and may be disrupted again on a subsequent encounter, provide a unique probe of supermassive black hole properties and accretion physics. We examine TDE 2022dbl, a partial tidal disruption event candidate that exhibits two separate UV/optical flares, using 11 new optical spectra, updated UV/optical photometry, and a Keck-II/ESI host-galaxy spectrum. We trace the evolution of the prominent blended N III + He II feature across both flares and find that the blend evolves from N III-dominated to He II-dominated emission, which may reflect changing ionization conditions and a declining efficiency of Bowen fluorescence. The two flares show similar thermal evolution and spectral features, supporting a partial-disruption scenario. The second flare exhibits a broader, plateau-like peak, a longer decline timescale, and less extreme line velocities than the first flare. We suggest that these differences arise from the interaction between debris from the second disruption and an accretion disk formed during the first flare. From the host-galaxy velocity dispersion, we infer a black hole mass of 10(M BH/M)=6.01 plus or minus0.45. No third flare has been detected at the expected recurrence epoch, leading us to propose a new interpretation in which a positive-energy kick during ballistic core reformation delays the return of the surviving remnant.