Supernova explosions in active galactic nuclear discs

Abstract

Active galactic nuclei (AGN) are prominent environments for stellar capture, growth and formation. These environments may catalyze stellar mergers and explosive transients, such as thermonuclear and core-collapse supernovae (SNe). SN explosions in AGN discs generate strong shocks, leading to unique observable signatures. We develop an analytical model which follows the evolution of the shock propagating in the disc until it eventually breaks out. We derive the peak luminosity, bolometric lightcurve, and breakout time. The peak luminosities may exceed 10 45 erg s −1 and last from hours to days. The brightest explosions occur in regions of reduced density; either off-plane, or in discs around low-mass central black holes (∼ 10 6 M ), or in starved subluminous AGNs. Explosions in the latter two sites are easier to observe due to a reduced AGN background luminosity. We perform suites of 1D Lagrangian radiative hydrodynamics SNEC code simulations to validate our results and obtain the luminosity in different bands, and 2D axisymmetric Eulerian hydrodynamics code HORMONE simulations to study the morphology of the ejecta and its deviation from spherical symmetry. The observed signature is expected to be a bright blue, UV or X-ray flare on top of the AGN luminosity from the initial shock breakout, while the subsequent red part of the lightcurve will largely be unobservable. We estimate the upper limit for the total event rate to be R 100 yr −1 Gpc −3 for optimal conditions and discuss the large uncertainties in this estimate. Future high-cadence transient searches may reveal these events. Some existing tidal disruption event candidates may originate from AGN supernovae.

High-energy Neutrinos from Stellar Explosions in Active Galactic Nuclei Accretion Disks

“…It is expected that AGN stellar explosions could be ideal targets for future joint neutrino and EM multimessenger observations. We show the EM emission of the ejecta due to its interaction with the AGN disk materials and the SN Ia emission powered by radioactive decay, respectively, in Figure 1, as predicted by Grishin et al (2021) and Zhu et al (2021b). The neutrino burst may occur shortly after the shock breakout, while the associated EM signals last in much longer timescale, even up to several hundred days.…”

“…For the calculations of the diffuse neutrino background emission, we show that SNe Ia, kilonovae, CCSNe, GRB-SNe, and choked GRBs in AGN disks may contribute to 10% of the observed diffuse neutrino background. SNe (Grishin et al 2021), Bondi explosions of stellar BHs (Wang et al 2021a) and mTDEs (Yang et al 2021) are predicted to have very high event rate densities in AGN disks. Such energetic events can contribute more considerably to the diffuse neutrino background.…”

“…Very recently, the field of stellar explosions in AGN accretion disks is exploding. The event rates and possible observable signatures for several kinds of stellar explosions occurring in AGN disks, such as SNe (Zhu et al 2021b;Grishin et al 2021;Moranchel-Basurto et al 2021), gamma-ray bursts (GRBs; Cheng & Wang 1999;Perna et al 2021a;Zhu et al 2021c,a), NS mergers (McKernan et al 2020;Zhu et al 2021c), binary BH (BBH) mergers (e.g., McKernan et al 2012;Bartos et al 2017;Yang et al 2019Yang et al , 2020McKernan et al 2019;Graham et al 2020;Tagawa et al 2020Tagawa et al , 2021Wang et al 2021b), Bondi explosions (Wang et al 2021a), microtidal disruption events (mTDEs; Yang et al 2021) and accretion-induced collapses of WDs (Zhu et al 2021b) and NSs (Perna et al 2021b), have been investigated in detail. Different from the classical low-density environments in which these stellar explosions occur, the AGN environment allows the ejecta launched from AGN stellar explosions to interact with the AGN gaseous disk to drive an energetic shock.…”

“…Different from the classical low-density environments in which these stellar explosions occur, the AGN environment allows the ejecta launched from AGN stellar explosions to interact with the AGN gaseous disk to drive an energetic shock. Such a shock can finally break out from the disk surface and power observable lumi-nous electromagnetic (EM) signals (Zhu et al 2021c,b;Grishin et al 2021). Neutrino emissions from the interaction between SN ejecta and the dense circumstellar medium have been studied intensively within the context of type II SNe (SNe II, e.g., Waxman & Loeb 2001;Katz et al 2011;Murase et al 2011;Murase 2018;Murase et al 2019;Li 2019;Wang et al 2019).…”

“…The gray dotted lines represent the timescale of the shock breakout. The blue and green solid lines show the EM emission of the ejecta due to its interaction with the AGN disk materials(Grishin et al 2021) and SN Ia emission powered by radioactive decay(Zhu et al 2021b), respectively. For comparsion, we also show the neutrino lightcurve for a classical SN IIn (Murase 2018) (orange dash-dotted line).…”