Tidal Disruption Events through the Lens of the Cooling Envelope Model

TL;DR

This paper applies the cooling envelope model to interpret optical TDEs, constraining SMBH and stellar properties, and explaining observed delays between optical peaks and accretion rate maxima.

Contribution

It provides the first detailed interpretation of TDEs using the cooling envelope model, linking observed properties to SMBH and stellar parameters and delay phenomena.

Findings

Distribution of inferred SMBH and stellar masses aligns with theoretical expectations.

Detected a deficit of low-mass SMBHs and stars, possibly due to detection biases.

Model predicts a long delay between optical peak and maximum accretion rate, matching observations.

Abstract

The cooling envelope model for tidal disruption events (TDE) postulates that while the stellar debris streams rapidly dissipate their bulk kinetic energy (``circularize"), this does not necessarily imply rapid feeding of the supermassive black hole (SMBH). The bound material instead forms a large pressure-supported envelope which powers optical/UV emission as it undergoes gradual Kelvin-Helmholtz contraction. We present results interpreting a sample of 15 optical TDE within the cooling envelope model in order to constrain the SMBH mass $M_{\rm BH}$, stellar mass $M_{\star}$, and orbital penetration factor $\beta$. The distributions of inferred properties from our sample broadly follow the theoretical expectations of loss-cone analysis assuming a standard stellar initial mass function. However, we find a deficit of events with $M_{\rm BH} \lesssim 5\times 10^{5}M_{\odot}$ and $M_{\star} \lesssim 0.5M_{\odot}$, which could result in part from the reduced detectability of TDEs with these properties. Our model fits also illustrate the predicted long delay between the optical light curve peak and when the SMBH accretion rate reaches its maximum. The latter occurs only once the envelope contracts to the circularization radius on a timescale of months to years, consistent with delayed-rising X-ray and non-thermal radio flares seen in a growing number of TDE.