Challenges in the modeling of tidal disruption events lightcurves

Lodato, Giuseppe

doi:10.1051/epjconf/20123901001

Cited by 22 publications

(14 citation statements)

References 29 publications

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“…This reprocessing layer might be a quasi-static configuration of gas [85,71,86,87] or an outflowing wind generated by the disk or the circularization process [88,89]. The second category of solutions argues that the observed optical emission is actually unrelated to accretion power, and is generated in the circularization process itself, as debris streams first dissipate, and then radiate, a fraction of their orbital-energy excess [90,91,72]. The true origin of optical emission in TDEs remains an open question at the time of writing.…”

Section: Accretion-disk Evolutionmentioning

confidence: 99%

Stellar tidal disruption events in general relativity

et al. 2019

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A tidal disruption event (TDE) ensues when a star passes too close to the supermassive black hole (SMBH) in a galactic center and is ripped apart by the tidal field of the SMBH. The gaseous debris produced in a TDE can power a bright electromagnetic flare as it is accreted by the SMBH; so far, several dozen TDE candidates have been observed. For SMBHs with masses above ∼ 10 7 M , the tidal disruption of solar-type stars occurs within ten gravitational radii of the SMBH, implying that general relativity (GR) is needed to describe gravity. Three promising signatures of GR in TDEs are: (1) a super-exponential cutoff in the volumetric TDE rate for SMBH masses above ∼ 10 8 M due to direct capture of tidal debris by the event horizon, (2) delays in accretion disk formation (and a consequent alteration of the early-time light curve) caused by the effects of relativistic precession on stream circularization, and (3) quasi-periodic modulation of X-ray emission due to global precession of misaligned accretion disks and the jets they launch. We review theoretical models and simulations of TDEs in Newtonian gravity, then describe how relativistic modifications give rise to these proposed observational signatures, as well as more speculative effects of GR. We conclude with a brief summary of TDE observations and the extent to which they show indications of these predicted relativistic signatures.

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Section: Accretion-disk Evolutionmentioning

confidence: 99%

Stellar tidal disruption events in general relativity

et al. 2019

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“…A tidal disruption event (TDE) occurs when an unfortunate star passes so close to a supermassive black hole (SMBH) that the tidal force of the SMBH exceeds the self-gravity of the star (Hills 1975). If this takes place outside of the Schwarzschild radius, the result is a luminous flare with L bol ∼ 10 41−45 erg s −1 , powered either by accretion onto the SMBH (Kochanek 1994;Jiang et al 2016b;Lodato 2012;Piran et al 2015). Observationally, these are differentiated from more common transients like supernovae by their higher blackbody temperatures (T ∼ 20, 000 − 50, 000 K) and coincidence with the centres of galaxies.…”

Section: Introductionmentioning

confidence: 99%

The tidal disruption event AT2017eqx: spectroscopic evolution from hydrogen rich to poor suggests an atmosphere and outflow

Nicholl

Blanchard

Berger

et al. 2019

Monthly Notices of the Royal Astronomical Society

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ABSTRACT We present and analyse a new tidal disruption event (TDE), AT2017eqx at redshift z = 0.1089, discovered by Pan-STARRS and ATLAS. The position of the transient is consistent with the nucleus of its host galaxy; the spectrum shows a persistent blackbody temperature T ≳ 20 000 K with broad H i and He ii emission; and it peaks at a blackbody luminosity of L ≈ 1044 erg s−1. The lines are initially centred at zero velocity, but by 100 d, the H i lines disappear while the He ii develops a blueshift of ≳ 5000 km s−1. Both the early- and late-time morphologies have been seen in other TDEs, but the complete transition between them is unprecedented. The evolution can be explained by combining an extended atmosphere, undergoing slow contraction, with a wind in the polar direction becoming visible at late times. Our observations confirm that a lack of hydrogen a TDE spectrum does not indicate a stripped star, while the proposed model implies that much of the diversity in TDEs may be due to the observer viewing angle. Modelling the light curve suggests AT2017eqx resulted from the complete disruption of a solar-mass star by a black hole of ∼106.3 M⊙. The host is another Balmer-strong absorption galaxy, though fainter and less centrally concentrated than most TDE hosts. Radio limits rule out a relativistic jet, while X-ray limits at 500 d are among the deepest for a TDE at this phase.

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“…In the simplest scenario it is possible to estimate the lightcurve of the event through the mass return rate at pericenter: the two quantities will be proportional under the assumption that the circularization and accretion time are considerably shorter than the orbital period of the debris. While the validity of the previous assumptions is currently under debate (the disc might not form efficiently, Svirski et al 2017, and even if the disc forms the single wavelength lightcurve might deviate significantly from the bolometric behaviour, Lodato & Rossi 2011), there is some empirical evidence that the optical luminosity does follow approximately the behaviour predicted analytically, hence giving credit that it might be related directly to the fallback process (Lodato 2012). In this picture, the luminosity of the event will scale as the rate at which the stellar debris fall back onto the black hole, which is easily computed from Kepler's third law, assuming the debris to follow Keplerian orbits after disruption.…”

Section: The Standard Picturementioning

confidence: 99%

‘Failed’ tidal disruption events and X-ray flares from the Galactic Centre

Sacchi

Lodato

2019

Monthly Notices of the Royal Astronomical Society

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The process of tidal disruption of stars by a supermassive black hole (SMBH) provides luminous UV and soft X-ray flares with peak luminosities of ≈ 10 46 ergs/sec and duration of a few months. As part of a wider exploration of the effects of stellar rotation on the outcome of a TDE, we have performed hydrodynamical simulations of the disruption of a rotating star whose spin axis is opposite to the orbital axis. Such a retrograde rotation makes the star more resilient to tidal disruption, so that, even if its orbit reaches the formal tidal radius, it actually stays intact after the tidal encounter. However, the outer layers of the star are initially stripped away from the core, but then fall back onto the star itself, producing a newly formed accretion disc around the star. We estimate that the accretion rate onto the star would be strongly super-Eddington (for the star) and would result in an X-ray flare with luminosity of the order of ≈ 10 40 ergs/sec and duration of a few months. We speculate that such events might be responsible for the known X-ray flares from Sgr A* in the recent past.

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Challenges in the modeling of tidal disruption events lightcurves

Cited by 22 publications

References 29 publications

Stellar tidal disruption events in general relativity

Stellar tidal disruption events in general relativity

The tidal disruption event AT2017eqx: spectroscopic evolution from hydrogen rich to poor suggests an atmosphere and outflow

‘Failed’ tidal disruption events and X-ray flares from the Galactic Centre

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