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Cooling Envelope Model for Tidal Disruption Events
Abstract

We present a toy model for the thermal optical/UV/X-ray emission from tidal disruption events (TDEs). Motivated by recent hydrodynamical simulations, we assume that the debris streams promptly and rapidly circularize (on the orbital period of the most tightly bound debris), generating a hot quasi-spherical pressure-supported envelope of radiusRv∼ 1014cm (photosphere radius ∼1015cm) surrounding the supermassive black hole (SMBH). As the envelope cools radiatively, it undergoes Kelvin–Helmholtz contractionRvt−1, its temperature risingTefft1/2while its total luminosity remains roughly constant; the optical luminosity decays as$νLν∝Rv2Teff∝t−3/2$. Despite this similarity to the mass fallback rate$Ṁfb∝t−5/3$, envelope heating from fallback accretion is subdominant compared to the envelope cooling luminosity except near optical peak (where they are comparable). Envelope contraction can be delayed by energy injection from accretion from the inner envelope onto the SMBH in a regulated manner, leading to a late-time flattening of the optical/X-ray light curves, similar to those observed in some TDEs. Eventually, as the envelope contracts to near the circularization radius, the SMBH accretion rate rises to its maximum, in tandem with the decreasing optical luminosity. This cooling-induced (rather than circularization-induced) delay of up to several hundred days may account for the more »

Authors:
Publication Date:
NSF-PAR ID:
10371935
Journal Name:
The Astrophysical Journal Letters
Volume:
937
Issue:
1
Page Range or eLocation-ID:
Article No. L12
ISSN:
2041-8205
Publisher:
DOI PREFIX: 10.3847
Sponsoring Org:
National Science Foundation
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