Detecting and Identifying Supernovae in AGN Accretion Disks

Stars may become embedded in active galactic nucleus (AGN) accretion disks and eventually explode as supernovae (SNe), whose detection would provide direct evidence for the existence and evolution of stars in AGN disks. We investigate the electromagnetic emission of such disk SNe using an analytic shock dynamics model coupled with a one-zone radiation model. Applying this framework to four progenitor types over a range of AGN black hole masses and Eddington ratios, we find that disk SNe around lower-mass black holes (BHs) or at lower Eddington ratios are more readily detectable against the underlying AGN emission and can remain detectable over a broader range of electromagnetic bands, from the infrared to soft X-rays. However, detectability against the AGN background does not guarantee that disk SNe can be distinguished from isolated SNe with CSM interaction. We therefore further compare disk SNe with isolated SNe with and without CSM interaction and find substantial degeneracies in their macroscopic observables. Nevertheless, we identify distinctive signatures that are robust across progenitor types. The characteristic emission shifts from the EUV for $M_{\mathrm{B}\mathrm{H}}\lesssim {10}^7{M}_{\odot }$ toward the UV/optical for $M_{\mathrm{B}\mathrm{H}}={10}^8{M}_{\odot }$, with the visibility timescale increasing from less than a day to $\sim 3\text{–}70$ days and $T_{\mathrm{p}\mathrm{e}\mathrm{a}\mathrm{k}}\sim 3\text{–}8$ eV in the latter case. The UV/optical regime around ${10}^8{M}_{\odot }$ BHs therefore offers particularly promising prospects for detecting disk SNe.