# Superluminous transients at AGN centers from interaction between black-hole disk winds and broad-line region clouds

## TL;DR

This paper proposes that superluminous transients at AGN centers are caused by interactions between accretion disk winds and broad-line region clouds, producing observable phenomena similar to Type IIn supernovae.

## Contribution

It introduces a new interaction model explaining superluminous transients in AGNs as shock-driven events from disk wind and cloud interactions, linking AGN activity cycles to transient luminosities.

## Key findings

- Transients have luminosities around 10^44 erg/s and durations of about 100 days.
- The kinetic energy of the ejecta is approximately 10^52 erg for about 1 solar mass ejected.
- The model explains observed properties of CSS100217 and PS16dtm as related to AGN activity cycles.

## Abstract

We propose that superluminous transients that appear at central regions of active galactic nuclei (AGNs) such as CSS100217:102913+404220 (CSS100217) and PS16dtm, which reach near or super-Eddington luminosities of the central black holes, are powered by the interaction between accretion disk winds and clouds in broad-line regions (BLRs) surrounding them. If the disk luminosity temporary increases by, e.g., limit-cycle oscillations, leading to a powerful radiatively driven wind, strong shock waves propagate in the BLR. Because the dense clouds in the AGN BLRs typically have similar densities to those found in Type IIn supernovae, strong radiative shocks emerge and efficiently convert the ejecta kinetic energy to radiation. As a result, transients similar to Type IIn supernovae can be observed at AGN central regions. Since a typical black-hole disk wind velocity is ~ 0.1c where c is the speed of light, the ejecta kinetic energy is expected to be ~ 1e52 erg when ~ 1 Msun is ejected. This kinetic energy is transformed to radiation energy in a timescale for the wind to sweep up a similar mass to itself in the BLR, which is a few hundred days. Therefore, both luminosities (~ 1e44 erg/s) and timescales (~ 100 days) of the superluminous transients from AGN central regions match to those expected in our interaction model. If CSS100217 and PS16dtm are related to the AGN activities triggered by limit-cycle oscillations, they become bright again in coming years or decades.