A large number of tidal disruption event (TDE) candidates have been observed recently, often differing in their observational features. Two classes appear to stand out: X-ray and optical TDEs, the latter featuring lower effective temperatures and luminosities. These differences can be explained if the radiation detected from the two categories of events originates from different locations. In practice, this location is set by the evolution of the debris stream around the black hole and by the energy dissipation associated with it. In this paper, we build an analytical model for the stream evolution, whose dynamics is determined by both magnetic stresses and shocks. Without magnetic stresses, the stream always circularizes. The ratio of the circularization time-scale to the initial stream period is t(ev)/t(min) = 8.3(M-h/10(6) M-circle dot)(-5/3)ss(-3), where M-h is the black hole mass and ss is the penetration factor. If magnetic stresses are strong, they can lead to the stream ballistic accretion. The boundary between circularization and ballistic accretion corresponds to a critical magnetic stresses efficiency v(A)/v(c) approximate to 10(-1), largely independent of M-h and ss. However, the main effect of magnetic stresses is to accelerate the stream evolution by strengthening self-crossing shocks. Ballistic accretion therefore necessarily occurs on the stream dynamical time-scale. The shock luminosity associated with energy dissipation is sub-Eddington but decays as t(-5/3) only for a slow stream evolution. Finally, we find that the stream thickness rapidly increases if the stream is unable to cool completely efficiently. A likely outcome is its fast evolution into a thick torus, or even an envelope completely surrounding the black hole.
Long-term stream evolution in tidal disruption events / C. Bonnerot, E.M. Rossi, G. Lodato. - In: MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY. - ISSN 0035-8711. - 464:3(2017 Jan), pp. 2816-2830. [10.1093/mnras/stw2547]
Long-term stream evolution in tidal disruption events
G. LodatoUltimo
2017
Abstract
A large number of tidal disruption event (TDE) candidates have been observed recently, often differing in their observational features. Two classes appear to stand out: X-ray and optical TDEs, the latter featuring lower effective temperatures and luminosities. These differences can be explained if the radiation detected from the two categories of events originates from different locations. In practice, this location is set by the evolution of the debris stream around the black hole and by the energy dissipation associated with it. In this paper, we build an analytical model for the stream evolution, whose dynamics is determined by both magnetic stresses and shocks. Without magnetic stresses, the stream always circularizes. The ratio of the circularization time-scale to the initial stream period is t(ev)/t(min) = 8.3(M-h/10(6) M-circle dot)(-5/3)ss(-3), where M-h is the black hole mass and ss is the penetration factor. If magnetic stresses are strong, they can lead to the stream ballistic accretion. The boundary between circularization and ballistic accretion corresponds to a critical magnetic stresses efficiency v(A)/v(c) approximate to 10(-1), largely independent of M-h and ss. However, the main effect of magnetic stresses is to accelerate the stream evolution by strengthening self-crossing shocks. Ballistic accretion therefore necessarily occurs on the stream dynamical time-scale. The shock luminosity associated with energy dissipation is sub-Eddington but decays as t(-5/3) only for a slow stream evolution. Finally, we find that the stream thickness rapidly increases if the stream is unable to cool completely efficiently. A likely outcome is its fast evolution into a thick torus, or even an envelope completely surrounding the black hole.File | Dimensione | Formato | |
---|---|---|---|
Bonnerot2016c.pdf
accesso aperto
Tipologia:
Pre-print (manoscritto inviato all'editore)
Dimensione
2.1 MB
Formato
Adobe PDF
|
2.1 MB | Adobe PDF | Visualizza/Apri |
Bonnerot2017_MN.pdf
accesso riservato
Tipologia:
Publisher's version/PDF
Dimensione
1.82 MB
Formato
Adobe PDF
|
1.82 MB | Adobe PDF | Visualizza/Apri Richiedi una copia |
Pubblicazioni consigliate
I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.