# Comparison of the X-ray emission from Tidal Disruption Events with those of Active Galactic Nuclei

## TL;DR

This study compares X-ray properties of Tidal Disruption Events (TDEs) and Active Galactic Nuclei (AGN) to identify distinguishing features, analyze their luminosity functions, and estimate TDE rates, revealing key differences in brightness, variability, and spectral hardness.

## Contribution

The paper provides a detailed comparison of X-ray characteristics of TDEs and AGN, derives the X-ray luminosity function for TDEs, and estimates their occurrence rate, enhancing understanding of their roles in galaxy evolution.

## Key findings

- TDEs are brighter than AGN at similar redshifts at peak.
- TDEs decay more monotonically and have stable spectral hardness.
- X-ray TDEs are less absorbed and exhibit softer emission than AGN.

## Abstract

One of the main challenges of current tidal disruption events (TDEs) studies is that emission arising from AGN activity may potentially mimic the expected X-ray emission of a TDE. Here we compare the X-ray properties of TDEs and AGN to determine a set of characteristics which would allow us to discriminate between flares arising from these two objects. We find that at peak, TDEs are brighter than AGN found at similar redshifts. However, compared to preflare upperlimits, highly variable AGN can produce flares of a similar order of magnitude as those seen from X-ray TDEs. Nevertheless, TDEs decay significantly more monotonically, and their emission exhibits little variation in spectral hardness as a function of time. We also find that X-ray TDEs are less absorbed, and their emission is much softer than the emission detected from AGN found at similar redshifts. We derive the X-ray luminosity function (LF) for X-ray TDEs using the events from Auchettl et al. (2017). Interestingly, our X-ray LF matches closely the theoretically derived LF by Milosavljevi\'c et al. (2006). which assumes a higher TDE rate currently estimated from observations. Using our results and the results of Stone & Metzger (2016), we estimate a TDE rate of $(0.7-4.7)\times10^{-4}$ yr$^{-1}$ per galaxy, higher than current observational estimates. We find that TDEs can contribute significantly to the LF of AGN for $z\lesssim0.4$, while there is no evidence that TDEs influence the growth of $10^{6-7}M_{\odot}$ BHs. However, BHs $<10^{6}M_{\odot}$ can grow from TDEs arising from super-Eddington accretion without contributing significantly to the observed AGN LF at $z=0$.