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تسجيل مستخدم جديدJets from Tidal Disruption Events
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The discovery of jets from tidal disruption events (TDEs) rejuvenated the old field of relativistic jets powered by accretion onto supermassive black holes. In this Chapter, we first review the extensive multi-wavelength observations of jetted TDEs. Then, we show that these events provide valuable information on many aspects of jet physics from a new prospective, including the on-and-off switch of jet launching, jet propagation through the ambient medium, $gamma/$X-ray radiation mechanism, jet composition, and the multi-messenger picture. Finally, open questions and future prospects in this field are summarized.
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Tidal disruption events are an excellent probe for supermassive black holes in distant inactive galaxies because they show bright multi-wavelength flares lasting several months to years. AT2019dsg presents the first potential association with neutrino emission from such an explosive event.
The concept of stars being tidally ripped apart and consumed by a massive black hole (MBH) lurking in the center of a galaxy first captivated theorists in the late 1970s. The observational evidence for these rare but illuminating phenomena for probin
g otherwise dormant MBHs, first emerged in archival searches of the soft X-ray ROSAT All-Sky Survey in the 1990s; but has recently accelerated with the increasing survey power in the optical time domain, with tidal disruption events (TDEs) now regarded as a class of optical nuclear transients with distinct spectroscopic features. Multiwavelength observations of TDEs have revealed panchromatic emission, probing a wide range of scales, from the innermost regions of the accretion flow, to the surrounding circumnuclear medium. I review the current census of 56 TDEs reported in the literature, and their observed properties can be summarized as follows: $bullet$ The optical light curves follow a power-law decline from peak that scales with the inferred central black hole mass as expected for the fallback rate of the stellar debris, but the rise time does not. $bullet$ The UV/optical and soft X-ray thermal emission come from different spatial scales, and their intensity ratio has a large dynamic range, and is highly variable, providing important clues as to what is powering the two components. $bullet$ They can be grouped into three spectral classes, and those with Bowen fluorescence line emission show a preference for a hotter and more compact line-emitting region, while those with only He II emission lines are the rarest class.
Recent claimed detections of tidal disruption events (TDEs) in multi-wavelength data have opened potential new windows into the evolution and properties of otherwise dormant supermassive black holes (SMBHs) in the centres of galaxies. At present, the
re are several dozen TDE candidates, which share some properties and differ in others. The range in properties is broad enough to overlap other transient types, such as active galactic nuclei (AGN) and supernovae (SNe), which can make TDE classification ambiguous. A further complication is that TDE signatures have not been uniformly observed to similar sensitivities or even targeted across all candidates. This chapter reviews those events that are unusual relative to other TDEs, including the possibility of TDEs in pre-existing AGN, and summarises those characteristics thought to best distinguish TDEs from continuously accreting AGN, strongly flaring AGN, SNe, and Gamma-Ray Bursts (GRBs), as well as other potential impostors like stellar collisions, micro-TDEs, and circumbinary accretion flows. We conclude that multiple observables should be used to classify any one event as a TDE. We also consider the TDE candidate population as a whole, which, for certain host galaxy or SMBH characteristics, is distinguishable statistically from non-TDEs, suggesting that at least some TDE candidates do in fact arise from SMBH-disrupted stars.
A tidal disruption event (TDE) occurs when a star plunges through a supermassive black holes tidal radius, at which point the stars self-gravity is overwhelmed by the tidal gravity of the black hole. In a partial TDE, where the star does not reach th
e full disruption radius, only a fraction of the stars mass is tidally stripped while the rest remains intact in the form of a surviving core. Analytical arguments have recently suggested that the temporal scaling of the fallback rate of debris to the black hole asymptotes to $t^{-9/4}$ for partial disruptions, effectively independently of the mass of the intact core. We present hydrodynamical simulations that verify the existence of this predicted, $t^{-9/4}$ scaling. We also define a break timescale -- the time at which the fallback rate transitions from a $t^{-5/3}$ scaling to the characteristic $t^{-9/4}$ scaling -- and measure this break timescale as a function of the impact parameter and the surviving core mass. These results deepen our understanding of the properties and breadth of possible fallback curves expected from TDEs and will therefore facilitate more accurate interpretation of data from wide-field surveys.
Numerical simulations have historically played a major role in understanding the hydrodynamics of the tidal disruption process. Given the complexity of the geometry of the system, the challenges posed by the problem have indeed stimulated much work o
n the numerical side. Smoothed Particles Hydrodynamics methods, for example, have seen their very first applications in the context of tidal disruption and still play a major role to this day. Likewise, initial attempts at simulating the evolution of the disrupted star with the so-called affine method have been historically very useful. In this Chapter, we provide an overview of the numerical techniques used in the field and of their limitations, and summarize the work that has been done to simulate numerically the tidal disruption process.
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