Super-Eddington accretion in tidal disruption events: the impactof realistic fallback rates on accretion rates

Wu, Samantha; Coughlin, Eric R.; Nixon, Chris

doi:10.1093/mnras/sty971

Cited by 49 publications

(48 citation statements)

References 51 publications

(72 reference statements)

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“…Actually, the strongly blueshifted hot Fe Kα fluorescent lines from super-Eddington disks, as modeled here, have been observed from the jetted TDE, Swift J1644 (Kara et al 2016). TDEs are believed to be super-Eddington accretors if the BH mass is smaller than a few×10 7 M (Rees 1988;Evans & Kochanek 1989;Ramirez-Ruiz & Rosswog 2009;Guillochon & Ramirez-Ruiz 2013;Dai et al 2015;Wu et al 2018), and the existence of a relativistic jet in Swift J1644 (Burrows et al 2011;Bloom et al 2011;Berger et al 2012;De Colle et al 2012) further supports that a transient magnetized thick disk has been formed by the stellar debris . In Kara et al (2016), the observed Fe line has an energy peaked at ≈ 8 keV, which for an Fe Kα line with a rest-frame energy of 6.97 keV corresponds to an energy-shift of g = 1.15 or an outflow velocity of 0.2 − 0.5c (depending on the half-opening angle of the funnel and thus the lamppost height, see Fig.…”

supporting

confidence: 77%

X-Ray Fluorescence from Super-Eddington Accreting Black Holes

Thomsen

Dai

Ramírez-Ruiz

et al. 2019

ApJL

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X-ray reverberation has proven to be a powerful tool capable of probing the innermost region of accretion disks around compact objects. Current theoretical effort generally assumes that the disk is geometrically thin, optically thick and orbiting with Keplerian speed. Thus, these models cannot be applied to systems where super-Eddington accretion happens because the thin disk approximation fails in this accretion regime. Furthermore, state-of-the-art numerical simulations show that optically thick winds are launched from the super-Eddington accretion disks, and thereby changing the reflection geometry significantly from the thin disk picture. We carry out theoretical investigations on this topic by focusing on the Fe Kα fluorescent lines produced from super-Eddington disks, and show that their line profiles are shaped by the funnel geometry and wind acceleration. We also systematically compare the Fe line profiles from super-Eddington thick disks to those from thin disks, and find that the former are substantially more blueshifted and symmetric in shape. These results are consistent with the observed Fe Kα line from the jetted tidal disruption event, Swift J1644, in which a transient super-Eddington accretion disk was formed out of stellar debris. Therefore, careful analysis of the Fe Kα line profile can be used to identify systems undergoing super-Eddington accretion.

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supporting

confidence: 77%

X-Ray Fluorescence from Super-Eddington Accreting Black Holes

Thomsen

Dai

Ramírez-Ruiz

et al. 2019

ApJL

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“…file at the time the energy is frozen-in is independent of the black hole mass, which the simulations of Wu et al (2018) verify 7 (see their Figure 1), then it follows that any physical timescale in a TDE can be written…”

mentioning

confidence: 75%

“…We use the Smoothed Particle Hydrodynamics (SPH) code phantom (Price et al 2018) to model the hydrodynamics of the disruption process. Following previous work (e.g., Coughlin & Nixon 2015;Coughlin et al 2016;Wu et al 2018;Golightly et al 2019) we model the central SMBH as a Newtonian point mass at the origin with an accretion radius, inside which particles are removed from the simulation. We include the selfgravity of the star, and we model the stellar pressure using an adiabatic equation of state P = Kρ γ where K is a conserved quantity for each fluid element, but can be spatially dependent within the original star.…”

Section: Hydrodynamic Simulations 41 Setupmentioning

confidence: 99%

“…Since then, a number of other authors have analyzed the tidal disruption of polytropes, with the aim of assessing one or another aspect of the tidal disruption process (e.g. Hayasaki et al 2013;Coughlin & Nixon 2015;Shiokawa et al 2015;Bonnerot et al 2016;Hayasaki et al 2016;Coughlin et al 2016;Mainetti et al 2017;Guillochon & McCourt 2017;Bonnerot et al 2017;Coughlin et al 2017;Wu et al 2018;Golightly et al 2019). However, only relatively few authors have analyzed the disruption of a star with a density profile other than a polytrope.…”

Section: Introductionmentioning

confidence: 99%

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On the Diversity of Fallback Rates from Tidal Disruption Events with Accurate Stellar Structure

Golightly

Nixon

Coughlin

2019

ApJL

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The tidal disruption of stars by supermassive black holes (SMBHs) can be used to probe the SMBH mass function, the properties of individual stars, and stellar dynamics in galactic nuclei. Upcoming missions will detect thousands of TDEs, and accurate theoretical modeling is required to interpret the data with precision. Here we analyze the influence of more realistic stellar structure on the outcome of TDEs; in particular, we compare the fallback rates -being the rate at which tidally-disrupted debris returns to the black hole -from progenitors generated with the stellar evolution code mesa to γ ≃ 4/3 and γ = 5/3 polytropes. We find that mesa-generated density profiles yield qualitatively-different fallback rates as compared to polytropic approximations, and that only the fallback curves from lowmass (1M ⊙ or less), zero-age main-sequence stars are well fit by either a γ ≃ 4/3 or 5/3 polytrope. Stellar age has a strong affect on the shape of the fallback curve, and can produce characteristic timescales (e.g., the time to the peak of the fallback rate) that greatly differ from the polytropic values. We use these differences to assess the degree to which the inferred black hole mass from the observed lightcurve can deviate from the true value, and find that the discrepancy can be at the order of magnitude level. Accurate stellar structure also leads to a substantial variation in the critical impact parameter at which the star is fully disrupted, and can increase the susceptibility of the debris stream to fragmentation under its own self-gravity. These results suggest that detailed modeling is required to accurately interpret observed lightcurves of TDEs.

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“…This deflection causes the outgoing and incoming material to intersect, dissipate kinetic energy through shocks, and form an accretion disk after several orbits (Cannizzo et al 1990;Kochanek 1994;Lee et al 1996;Kim et al 1999;Hayasaki et al 2013Hayasaki et al , 2016Guillochon et al 2014;Bonnerot et al 2016;Shiokawa et al 2015). When the black hole mass satisfies M 10 7 M , the fallback rate is super-Eddington (for full disruptions of Solar-like stars; Evans & Kochanek 1989;Wu et al 2018), which can lead to the production of radiation driven winds (Strubbe & Quataert 2009) and jets (Coughlin & Begelman 2014). The accretion (and associated outflows) produces a highly luminous, short-lived emission event, in which the lightcurve rapidly rises, reaches a peak, and decays as a power-law.…”

Section: Introductionmentioning

confidence: 99%

Ultra-deep tidal disruption events: prompt self-intersections and observables

Darbha

Coughlin

Kasen

et al. 2019

Monthly Notices of the Royal Astronomical Society

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A star approaching a supermassive black hole (SMBH) can be torn apart in a tidal disruption event (TDE). We examine ultra-deep TDEs, a new regime in which the disrupted debris approaches close to the black hole's Schwarzschild radius, and the leading part intersects the trailing part at the first pericenter passage. We calculate the range of penetration factors β vs SMBH masses M that produce these prompt self-intersections using a Newtonian analytic estimate and a general relativistic (GR) geodesic model. We find that significant self-intersection of Solar-type stars requires β ∼ 50 − 127 for M/M = 10 4 , down to β ∼ 5.6 − 5.9 for M/M = 10 6 . We run smoothedparticle hydrodynamic (SPH) simulations to corroborate our calculations and find close agreement, with a slightly shallower dependence on M. We predict that the shock from the collision emits an X-ray flare lasting t ∼ 2 s with L ∼ 10 47 ergs/s at E ∼ 2 keV, and the debris has a prompt accretion episode lasting t ∼ several min. The events are rare and occur with a rateṄ 10 −7 Mpc −3 yr −1 . Ultra-deep TDEs can probe the strong gravity and demographics of low-mass SMBHs.

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Super-Eddington accretion in tidal disruption events: the impactof realistic fallback rates on accretion rates

Cited by 49 publications

References 51 publications

X-Ray Fluorescence from Super-Eddington Accreting Black Holes

X-Ray Fluorescence from Super-Eddington Accreting Black Holes

On the Diversity of Fallback Rates from Tidal Disruption Events with Accurate Stellar Structure

Ultra-deep tidal disruption events: prompt self-intersections and observables

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