Pre-peak Emission in Tidal Disruption Events

Abstract

The rising part of a tidal disruption event light curve provides unique insight into early emission and the onset of accretion. Various mechanisms are proposed to explain the pre-peak emission, including shocks from debris interaction and reprocessing of disk emission. We study the pre-peak emission and its influence on the gas circularization by a series of gray radiation hydrodynamic simulations with varying black hole mass. We find that, given a super-Eddington fallback rate of $10{\dot{M}}_{\mathrm{Edd}}$ , the stream–stream collision can occur multiple times and drive strong outflows of up to $9{\dot{M}}_{\mathrm{Edd}}$ . By dispersing gas to ≳100 r _s , the outflow can delay gas circularization and leads to sub-Eddington accretion rates during the first few stream–stream collisions. The stream–stream collision shock and circularization shock can sustain a luminosity of ∼10 ^44 erg s ^−1 for days. The luminosity is generally sub-Eddington and shows a weak correlation with accretion rate at early times. The outflow is optically thick, yielding a reprocessing layer with a size of ∼10 ^14 cm and photospheric temperature of ∼4 × 10 ^4 K.

Keywords

• Tidal disruption
• Accretion
• Compact radiation sources
• Hydrodynamical simulations