Abstract
When a black hole tidally disrupts a star, accretion of the debris will produce a luminous flare and reveal the presence of a dormant black hole. The accretion flare can also photoionize a portion of the post-disruption debris. We present models of the emission line spectrum produced in the debris released when a white dwarf or a horizontal branch star is tidally disrupted by an intermediate-mass black hole, and discuss the possibility of using the emission lines to identify such events and constrain the properties of the black hole. We also compare the white dwarf disruption models with observations of white dwarf tidal disruption candidates in globular clusters associated with NGC 4472 and NGC 1399. The bright [O III] lines observed in each system are consistent with these models, but there are some drawbacks to interpreting these sources as tidally disrupted white dwarfs. On the other hand, models of the emission line spectrum produced when a horizontal branch star is disrupted by a ∼ 100 M ʘ black hole are in good agreement with the source in the NGC 1399 globular cluster. Finally, we describe light curves for the emission lines produced in the debris of a tidally disrupted helium core. The modeled light curves are consistent with the recent observations of Gezari et al. (2012).
Highlights
Several luminous UV/X-ray flares observed in the cores of normal galaxies have been identified as candidate tidal disruption events (TDEs) [e.g., 1, 2]
If the disrupted star was initially on a parabolic orbit, at least half of the debris will remain unbound from the black hole (BH) after tidal disruption [5]. This debris tail will be photoionized by the accretion flare, resulting in an emission line spectrum that differentiates TDE flares from other transient events such, as supernovae or AGN outbursts
To aid in the identification of white dwarf (WD) TDEs, we modeled the distinctive emission line spectra radiated by the stream of unbound debris created when a WD is disrupted by an intermediate mass black hole (IMBH)
Summary
Several luminous UV/X-ray flares observed in the cores of normal galaxies have been identified as candidate tidal disruption events (TDEs) [e.g., 1, 2]. If the disrupted star was initially on a parabolic orbit, at least half of the debris will remain unbound from the BH after tidal disruption [5]. This debris tail will be photoionized by the accretion flare, resulting in an emission line spectrum that differentiates TDE flares from other transient events such, as supernovae or AGN outbursts. The emission lines produced in the debris of a solar type star that has been disrupted by a supermassive BH have been studied using both numerical [6] and analytic [7] models. These investigations found that the emission line spectra, which are dominated by hydrogen lines, could be used to characterize the disruption scenario
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