The X-Ray Through Optical Fluxes and Line Strengths of Tidal Disruption Events

Roth, Nathaniel; Kasen, Daniel; Guillochon, James; Ramírez-Ruiz, E.

doi:10.3847/0004-637x/827/1/3

Cited by 212 publications

(277 citation statements)

References 64 publications

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“…In some parameter regimes, they reproduced the observed very large He IIλ4686/Hβ without invoking a supersolar metallicity of He, which was proposed originally by Peterson & Ferland(1986). Roth et al (2016) considered a model in which both continuum and emission lines are formed in a spherical, optically-thick envelope, whose optical depth to electron scattering is very large. By considering the effect of radiation transfer, they were able to explain the large He II λ4686/Hα with gas at the solar abundance.…”

Section: General Considerationsmentioning

confidence: 89%

The Carbon and Nitrogen Abundance Ratio in the Broad Line Region of Tidal Disruption Events

Yang

Wang

Ferland

et al. 2017

ApJ

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The rest-frame UV spectra of three recent tidal disruption events (TDEs), ASASSN-14li, PTF15af and iPTF16fnl display strong nitrogen emission lines but weak or undetectable carbon lines. In these three objects, the upper limits of the C iii] λ1908/N iii] λ1750 ratio are about two orders of magnitude lower than those of quasars, suggesting a high abundance ratio of [N/C]. With detailed photoionization simulations, we demonstrate that C 2+ and N 2+ are formed in the same zone, so the Ciii]/N iii] ratio depends only moderately on the physical conditions in the gas and weakly on the shape of the ionizing continuum. There are smaller than 0.5 dex variations in the line ratio over wide ranges of gas densities and ionization parameters at a given metallicity. This allows a robust estimate of the relative abundance ratio nitrogen to carbon. We derive a relative abundance ratio of [N/C]> 1.5 for ASASSN-14li, and even higher for PTF15af and iPTF16fnl. This suggests that the broad line region in those TDE sources is made of nitrogen-enhanced core material that falls back at later times. Based on stellar evolution models, the lower limit of the disrupted star should be larger than 0.6M ⊙ . The chemical abundance of the line emitting gas gives a convincing evidence that the flares origin from stellar tidal disruptions. The coincidence of the weakness of the X-ray emission with the strong broad absorption lines in PTF15af, iPTF16fnl and the strong X-ray emission without such lines in ASASSN-li14 are in analogy to quasars with and without broad absorption lines.

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Section: General Considerationsmentioning

confidence: 89%

The Carbon and Nitrogen Abundance Ratio in the Broad Line Region of Tidal Disruption Events

Yang

Wang

Ferland

et al. 2017

ApJ

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“…Kochanek (2016b) found that stellar evolution can play a role in producing this spectral diversity. Roth et al (2016) modeled the emission from TDEs through an extended, optically thick envelope formed from stellar debris. They find that due to optical depth effects, hydrogen Balmer line emission is often strongly suppressed relative to helium line emission.…”

Section: Composition Of Debrismentioning

confidence: 99%

Low-mass White Dwarfs with Hydrogen Envelopes as a Missing Link in the Tidal Disruption Menu

Law-Smith

MacLeod

Guillochon

et al. 2017

ApJ

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We construct a menu of objects that can give rise to bright flares when disrupted by massive black holes (BHs), ranging from planets to evolved stars. Through their tidal disruption, main sequence and evolved stars can effectively probe the existence of otherwise quiescent supermassive BHs and white dwarfs can probe intermediate mass BHs. Many low-mass white dwarfs possess extended hydrogen envelopes, which allow for the production of prompt flares in disruptive encounters with moderately massive BHs of 10 5 -10 7 M -masses that may constitute the majority of massive BHs by number. These objects are a missing link in two ways: (1) for probing moderately massive BHs and (2) for understanding the hydrodynamics of the disruption of objects with tenuous envelopes. A flare arising from the tidal disruption of a 0.17 M white dwarf by a 10 5 M BH reaches a maximum between 0.6 and 11 days, with a peak fallback rate that is usually super-Eddington and results in a flare that is likely brighter than a typical tidal disruption event. Encounters stripping only the envelope can provide hydrogen-only fallback, while encounters disrupting the core evolve from H-to He-rich fallback. While most tidal disruption candidates observed thus far are consistent with the disruptions of main sequence stars, the rapid timescales of nuclear transients such as Dougie and PTF10iya are naturally explained by the disruption of low-mass white dwarfs. As the number of observed flares continues to increase, the menu presented here will be essential for characterizing nuclear BHs and their environments through tidal disruptions.

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“…Hence, for the same physical parameters, the lines are far less optically thick than assumed by the CLOUDY models. Roth et al (2015), however, find that extreme hydrogen to helium line ratios are achievable at Solar metallicity using broad line widths and radiation transfer models better suited to high optical depths than CLOUDY.…”

Section: Introductionmentioning

confidence: 99%

Abundance anomalies in tidal disruption events

Kochanek

2016

Mon. Not. R. Astron. Soc.

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The ∼ 10% of tidal disruption events (TDEs) due to stars more massive than M * > ∼ M ⊙ should show abundance anomalies due to stellar evolution in helium, carbon and nitrogen, but not oxygen. Helium is always enhanced, but only by up to ∼ 25% on average because it becomes inaccessible once it is sequestered in the high density core as the star leaves the main sequence. However, portions of the debris associated with the disrupted core of a main sequence star can be enhanced in helium by factors of 2-3 for debris at a common orbital period. These helium abundance variations may be a contributor to the observed diversity of hydrogen and helium line strengths in TDEs. A still more striking anomaly is the rapid enhancement of nitrogen and the depletion of carbon due to the CNO cycle -stars with M * > ∼ M ⊙ quickly show an increase in their average N/C ratio by factors of 3-10. Because low mass stars evolve slowly and high mass stars are rare, TDEs showing high N/C will almost all be due to 1-2M ⊙ stars disrupted on the main sequence. Like helium, portions of the debris will show still larger changes in C and N, and the anomalies decline as the star leaves the main sequence. The enhanced [N/C] abundance ratio of these TDEs provides the first natural explanation for the rare, nitrogen rich quasars and also explains the strong nitrogen emission seen in ultraviolet spectra of ASASSN-14li.

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The X-Ray Through Optical Fluxes and Line Strengths of Tidal Disruption Events

Cited by 212 publications

References 64 publications

The Carbon and Nitrogen Abundance Ratio in the Broad Line Region of Tidal Disruption Events

The Carbon and Nitrogen Abundance Ratio in the Broad Line Region of Tidal Disruption Events

Low-mass White Dwarfs with Hydrogen Envelopes as a Missing Link in the Tidal Disruption Menu

Abundance anomalies in tidal disruption events

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