Tidal Disruption Event Candidate Research Articles

The late flare in tidal disruption events due to the interaction of disk wind with dusty torus

A late (t ∼ 1,500 days) multi-wavelength (UV, optical, IR, and X-ray) flare was found in PS1-10adi, a tidal disruption event (TDE) candidate that took place in an active galactic nucleus (AGN). TDEs usually involve super-Eddington accretion, which drives fast mass outflow (disk wind). So here we explore a possible scenario that such a flare might be produced by the interaction of the disk wind with a dusty torus for TDEs in AGN. Due to the high velocity of the disk wind, strong shocks will emerge and convert the bulk of the kinetic energy of the disk wind to radiation. We calculate the dynamics and then predict the associated radiation signatures, taking into account the widths of the wind and torus. We compare our model with the bolometric light curve of the late flare in PS1-10adi constructed from observations. We find from our modeling that the disk wind has a total kinetic energy of about 1051 erg and a velocity of 0.1 c (i.e., a mass of 0.3 M⊙); the gas number density of the clouds in the torus is 3×107cm−3. Observation of such a late flare can be an evidence of the disk wind in TDEs and can be used as a tool to explore the nuclear environment of the host.

Supernova explosions in active galactic nuclear discs

ABSTRACT Active galactic nuclei (AGNs) are prominent environments for stellar capture, growth, and formation. These environments may catalyse stellar mergers and explosive transients, such as thermonuclear and core-collapse supernovae (SNe). SN explosions in AGN discs generate strong shocks, leading to unique observable signatures. We develop an analytical model that follows the evolution of the shock propagating in the disc until it eventually breaks out. We derive the peak luminosity, bolometric light curve, and breakout time. The peak luminosities may exceed 1045 erg s−1 and last from hours to days. The brightest explosions occur in regions of reduced density: either off-plane, or in discs around low-mass central black holes (${\sim} 10^6\ \rm {M}_\odot$), or in starved subluminous AGNs. Explosions in the latter two sites are easier to observe due to a reduced AGN background luminosity. We perform suites of 1D Lagrangian radiative hydrodynamics snec code simulations to validate our results and obtain the luminosity in different bands, and 2D axisymmetric Eulerian hydrodynamics code hormone simulations to study the morphology of the ejecta and its deviation from spherical symmetry. The observed signature is expected to be a bright blue, UV or X-ray flare on top of the AGN luminosity from the initial shock breakout, while the subsequent red part of the light curve will largely be unobservable. We estimate the upper limit for the total event rate to be $\mathcal {R}\lesssim 100\ \rm yr^{-1}\ Gpc^{-3}$ for optimal conditions and discuss the large uncertainties in this estimate. Future high-cadence transient searches may reveal these events. Some existing tidal disruption event candidates may originate from AGN SNe.

Long-term X-ray evolution of SDSS J134244.4+053056.1. A more than 18 year-old, long-lived IMBH-TDE candidate

SDSS J134244.4+053056 is a tidal disruption event candidate with strong temporal coronal line emitters and a long fading, mid-infrared dust echo. We present detailed analyses of X-ray emission from a Swift/XRT observation in 2009 and the most recent XMM-Newton/pn observation in 2020. The two spectra can be modeled with hard and soft components. While no significant variability is detected in the hard component above 2 keV between these two observations, the soft X-ray emission in 0.3–2 keV varies by a factor of ∼5. The luminosity of this soft component fades from ∼1.8 × 1041 to ∼3.7 × 1040 erg s−1 from the observation in Swift to that of XMM-Newton, which are 8 and 19 years after the outburst occurred, respectively. The evolution of luminosity matches with the t−5/3decline law well; there is a soft X-ray peak luminosity of 1044 erg s−1 at the time of the optical flare. Furthermore, the spectra of the soft component harden slightly in the decay phase, in which the photon index Γ varies from 4.8−0.9+1.2 to 3.7 ± 0.5, although they are consistent with each other if we consider the uncertainties. Additionally, by comparing the BH mass estimate between the M − σ correlation, the broad Hα emission, and the fundamental plane relation of BH accretion, we find that a value of ∼105 M⊙ is favored. If so, taking its X-ray spectral variation, luminosity evolution, and further support from theory into account, we suggest that SDSS J134244.4+053056 is a long-lived tidal disruption event candidate lasting more than 18 years with an intermediate-mass black hole.

Distinguishing Tidal Disruption Events from Impostors

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, there 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.

Spectroscopic Monitoring of the Candidate Tidal Disruption Event in F01004–2237

Abstract We present results of spectroscopic monitoring observations of the ultraluminous infrared galaxy F01004−2237. This galaxy was observed to undergo changes in its optical spectrum, detected by comparing a spectrum from 2015 with one from 2000. These changes were coincident with photometric brightening. The main changes detected in the optical spectrum are enhanced He ii λ4686 emission and the appearance of He i λ3898,λ5876 emission lines. The favored interpretation of these changes was that of a tidal disruption event (TDE) happening in 2010. However, subsequent work suggested that these changes are caused by another hitherto unknown effect related to variations in the accretion rate in the active galactic nucleus (AGN). Our optical spectroscopic monitoring observations show that the evolution of the He lines is in line with the evolution seen in TDEs and opposite of what is observed from reverberation-mapping studies of AGNs, renewing the discussion of the interpretation of the flare as a TDE.

AT 2019avd: a novel addition to the diverse population of nuclear transients

We report on SRG/eROSITA, ZTF, ASAS-SN, Las Cumbres, NEOWISE-R, and Swift XRT/UVOT observations of the unique ongoing event AT 2019avd, located in the nucleus of a previously inactive galaxy at z = 0.029. eROSITA first observed AT 2019avd on 2020-04-28 during its first all sky survey, when it was detected as an ultra-soft X-ray source (kT ~ 85 eV) that was ≳90 times brighter in the 0.2−2 keV band than a previous 3σ upper flux detection limit (with no archival X-ray detection at this position). The ZTF optical light curve in the ~450 days preceding the eROSITA detection is double peaked, and the eROSITA detection coincides with the rise of the second peak. Follow-up optical spectroscopy shows the emergence of a Bowen fluorescence feature and high-ionisation coronal lines ([Fe X] 6375 Å, [Fe XIV] 5303 Å), along with persistent broad Balmer emission lines (FWHM ~ 1400 km s−1). Whilst the X-ray properties make AT 2019avd a promising tidal disruption event (TDE) candidate, the optical properties are atypical for optically selected TDEs. We discuss potential alternative origins that could explain the observed properties of AT 2019avd, such as a stellar binary TDE candidate, or a TDE involving a super massive black hole binary.

An Extraordinary Response of Iron Emission to the Central Outburst in a Tidal Disruption Event Candidate

Abstract Understanding the origin of Fe ii emission is important because it is crucial to construct the main sequence of active galactic nuclei (AGNs). Despite several decades of observational and theoretical effort, the location of the optical iron emitting region and the mechanism responsible for the positive correlation between the Fe ii strength and the black hole accretion rate remain open questions. In this Letter, we report the optical Fe ii response to the central outburst in PS1-10adi, a candidate tidal disruption event taking place in an AGN at z = 0.203 that has aroused extensive attention. For the first time, we observe that the Fe ii response in the rising phase of its central luminosity is significantly more prominent than that in the decline phase, showing a hysteresis effect. We interpret this hysteresis effect as a consequence of the gradual sublimation of the dust grains situating at the inner surface of the torus into gas when the luminosity of the central engine increases. It is the iron element released from the sublimated dust that contributes evidently to the observed Fe ii emission. This interpretation, together with the weak response of the Hβ emission as we observe, naturally explains the applicability of relative Fe ii strength as a tracer of the Eddington ratio. In addition, optical iron emission of this origin renders the Fe ii time lag a potential “standard candle” with cosmological implications.

Application of The Wind-driven Model to a Sample of Tidal Disruption Events

Abstract An origin of the optical/ultraviolet (UV) radiation from tidal disruption events (TDEs) has recently been discussed for different scenarios, but observational support is generally lacking. In this Letter, we test the applicability of the “wind-driven model” for a sample of UV/optical TDEs. With the model, we aim to derive the physical properties of the optical/UV TDEs, such as mass-loss rates and characteristic radii. The model assumes optically thick continuous outflows like stellar winds, and one key question arises: how is the wind-launched radius connected to physical processes in TDEs? Here we propose one possibility: through a comparison between the escape velocities estimated from their black hole masses and the wind velocities estimated from observed line widths, the outflow is launched from the self-interaction radius (R SI) where the stellar debris stretched by the tidal force intersects. We show that the escape velocities at R SI are roughly consistent with the wind velocities. By applying the model to a sample of optical/UV TDE candidates, we find that explosive mass ejections (≳10 M ⊙ yr−1) from R SI (∼1014 cm) can explain the observed properties of TDEs around peak luminosity. We also apply the same framework to a peculiar transient, AT2018cow. This model suggests that AT2018cow is likely a TDE induced by an intermediate-mass black hole (M BH ∼ 104 M ⊙).

Eccentric tidal disruption event discs around supermassive black holes: dynamics and thermal emission

ABSTRACTAfter the tidal disruption event (TDE) of a star around a supermassive black hole (SMBH), if the stellar debris stream rapidly circularizes and forms a compact disc, the TDE emission is expected to peak in the soft X-ray or far ultraviolet (UV). The fact that many TDE candidates are observed to peak in the near UV and optical has challenged conventional TDE emission models. By idealizing a disc as a nested sequence of elliptical orbits that communicate adiabatically via pressure forces, and are heated by energy dissipated during the circularization of the nearly parabolic debris streams, we investigate the dynamics and thermal emission of highly eccentric TDE discs, including the effect of general-relativistic apsidal precession from the SMBH. We calculate the properties of uniformly precessing, apsidally aligned, and highly eccentric TDE discs, and find highly eccentric disc solutions exist for realistic TDE properties (SMBH and stellar mass, periapsis distance, etc.). Taking into account compressional heating (cooling) near periapsis (apoapsis), we find our idealized eccentric disc model can produce emission consistent with the X-ray and UV/optical luminosities of many optically bright TDE candidates. Our work attempts to quantify the thermal emission expected from the shock-heating model for TDE emission, and finds stream–stream collisions are a promising way to power optically bright TDEs.

AT 2017gbl: a dust obscured TDE candidate in a luminous infrared galaxy

ABSTRACT We present the discovery with Keck of the extremely infrared (IR) luminous transient AT 2017gbl, coincident with the Northern nucleus of the luminous infrared galaxy (LIRG) IRAS 23436+5257. Our extensive multiwavelength follow-up spans ∼900 d, including photometry and spectroscopy in the optical and IR, and (very long baseline interferometry) radio and X-ray observations. Radiative transfer modelling of the host galaxy spectral energy distribution and long-term pre-outburst variability in the mid-IR indicate the presence of a hitherto undetected dust obscured active galactic nucleus (AGN). The optical and near-IR spectra show broad ∼2000 km s−1 hydrogen, He i, and O i emission features that decrease in flux over time. Radio imaging shows a fast evolving compact source of synchrotron emission spatially coincident with AT 2017gbl. We infer a lower limit for the radiated energy of 7.3 × 1050 erg from the IR photometry. An extremely energetic supernova would satisfy this budget, but is ruled out by the radio counterpart evolution. Instead, we propose AT 2017gbl is related to an accretion event by the central supermassive black hole, where the spectral signatures originate in the AGN broad line region and the IR photometry is consistent with re-radiation by polar dust. Given the fast evolution of AT 2017gbl, we deem a tidal disruption event (TDE) of a star a more plausible scenario than a dramatic change in the AGN accretion rate. This makes AT 2017gbl the third TDE candidate to be hosted by a LIRG, in contrast to the so far considered TDE population discovered at optical wavelengths and hosted preferably by post-starburst galaxies.

A Tidal Disruption Event Candidate Discovered in the Active Galactic Nucleus SDSS J022700.77-042020.6

Abstract We report the discovery of a tidal disruption event (TDE) candidate occurring in the active galactic nucleus (AGN) SDSS J022700.77-042020.6. A sudden increase in flux from J0227-0420 during the second half of 2009 appears in the long-term optical, UV, and near-IR (NIR) light curves. A plateau phase, following an initial decline, is seen in the near-UV (NUV) and optical light curves. We find possible evidence that the plateau in the NUV band may lag behind the optical ones by ∼70–80 days with also a much shorter duration, that is, ∼7–15 days against ∼40–50 days. The long-term NUV/optical (after the plateau phase), NIR, and mid-infrared (MIR) light curves can be well characterized with a form of L(t) ∝ t −β , consistent with the expectation of a TDE. The plateaus can be explained if stellar streams collide with the preexisting disk at different radii. Though the overall fallback rate decreases, the material in the outer disk drifts inward and increases the local accretion rate in the inner region, producing the NUV/optical plateaus. The possible lag is then attributed to viscosity delay. The index β of the NIR J, H, and K s bands (∼1.4–3.3) is steeper than that of the UV/optical (∼0.7–1.3) and MIR bands (∼0.9–1.8), which may suggest that a certain fraction of the dust in the inner region of the torus may be sublimated during the TDE phase. Our results indicate that, due to collisions between stellar debris and the preexisting disk, the light curves of TDEs occurring in AGNs may show distinctive features, which may shed new light on the accretion process.

The Host Galaxies of Tidal Disruption Events

Recent studies of Tidal Disruption Events (TDEs) have revealed unexpected correlations between the TDE rate and the large-scale properties of the host galaxies. In this review, we present the host galaxy properties of all TDE candidates known to date and quantify their distributions. We consider throughout the differences between observationally-identified types of TDEs and differences from spectroscopic control samples of galaxies. We focus here on the black hole and stellar masses of TDE host galaxies, their star formation histories and stellar populations, the concentration and morphology of the optical light, the presence of AGN activity, and the extra-galactic environment of the TDE hosts. We summarize the state of several possible explanations for the links between the TDE rate and host galaxy type. We present estimates of the TDE rate for different host galaxy types and quantify the degree to which rate enhancement in some types results in rate suppression in others. We discuss the possibilities for using TDE host galaxies to assist in identifying TDEs in upcoming large transient surveys and possibilities for TDE observations to be used to study their host galaxies.

Multiwavelength Study of an X-Ray Tidal Disruption Event Candidate in NGC 5092

Abstract We present multiwavelength studies of a transient X-ray source, XMMSL1 J131952.3+225958, associated with the galaxy NGC 5092 at z = 0.023 detected in the XMM-Newton SLew survey (XMMSL). The source brightened in the band by a factor of in 2005 as compared with previous flux limits and then faded by a factor of >200 as observed with XMM-Newton in 2013 and with Swift in 2018. At the flaring state the X-ray spectrum can be modeled with a blackbody at a temperature of ∼60 eV and an overall luminosity of erg s−1. A UV flare and optical flare were also detected with the Galaxy Evolution Explorer and the Sloan Digital Sky Survey, respectively, within several months of the X-ray flare, whose nonstellar UV–optical spectrum can be described with a blackbody at a temperature of K and a luminosity of erg s−1. Interestingly, mid-infrared monitoring observations of NGC 5092 with the Wide-field Infrared Survey Explorer 5–13 yr later show a continuous flux decline. These dramatic variability properties, from the X-ray through UV and optical to infrared, appear to be orderly, suggestive of a stellar tidal disruption event (TDE) by a massive black hole, confirming the postulation by Kanner et al. This TDE candidate belongs to a rare sample with contemporaneous bright emission detected in the X-ray, UV, and optical, which are later echoed by dust-reprocessed light in the mid-infrared. The black hole has a mass of 10 , residing in a galaxy that is dominated by a middle-aged stellar population of 2.5 Gyr.

Polarimetry of relativistic tidal disruption event Swift J2058+0516

ABSTRACT A small fraction of candidate tidal disruption events (TDEs) show evidence of powerful relativistic jets, which are particularly pronounced at radio wavelengths, and likely contribute non-thermal emission at a wide range of wavelengths. A non-thermal emission component can be diagnosed using linear polarimetry, even when the total received light is dominated by emission from an accretion disc or disc outflow. In this paper, we present Very Large Telescope (VLT) measurements of the linear polarization of the optical light of jetted TDE Swift J2058+0516. This is the second jetted TDE studied in this manner, after Swift J1644+57. We find evidence of non-zero optical linear polarization, $P_{V}\sim 8{{\, \rm per\, cent}}$, a level very similar to the near-infrared polarimetry of Swift J1644+57. These detections provide an independent test of the emission mechanisms of the multiwavelength emission of jetted TDEs.

Evidence for rapid disc formation and reprocessing in the X-ray bright tidal disruption event candidate AT 2018fyk

ABSTRACT We present optical spectroscopic and Swift UVOT/XRT observations of the X-ray and UV/optical bright tidal disruption event (TDE) candidate AT 2018fyk/ASASSN–18ul discovered by ASAS–SN. The Swift light curve is atypical for a TDE, entering a plateau after ∼40 d of decline from peak. After 80 d the UV/optical light curve breaks again to decline further, while the X-ray emission becomes brighter and harder. In addition to broad H, He, and potentially O/Fe lines, narrow emission lines emerge in the optical spectra during the plateau phase. We identify both high-ionization (O iii) and low-ionization (Fe ii) lines, which are visible for ∼45 d. We similarly identify Fe ii lines in optical spectra of ASASSN–15oi 330 d after discovery, indicating that a class of Fe-rich TDEs exists. The spectral similarity between AT 2018fyk, narrow-line Seyfert 1 galaxies, and some extreme coronal line emitters suggests that TDEs are capable of creating similar physical conditions in the nuclei of galaxies. The Fe ii lines can be associated with the formation of a compact accretion disc, as the emergence of low-ionization emission lines requires optically thick, high-density gas. Taken together with the plateau in X-ray and UV/optical luminosity this indicates that emission from the central source is efficiently reprocessed into UV/optical wavelengths. Such a two-component light curve is very similar to that seen in the TDE candidate ASASSN–15lh, and is a natural consequence of a relativistic orbital pericentre.

Black hole masses of tidal disruption event host galaxies II

ABSTRACT We present new medium resolution, optical long-slit spectra of a sample of six ultraviolet (UV)/optical and 17 X-ray-selected tidal disruption event candidate host galaxies. We measure emission line ratios from the optical spectra, finding that the large majority of hosts are quiescent galaxies, while those displaying emission lines are generally consistent with star formation dominated environments; only three sources show clear evidence of nuclear activity. We measure bulge velocity dispersions using absorption lines and infer host black hole (BH) masses using the M – σ relation. While the optical and X-ray host BH masses are statistically consistent with coming from the same parent distribution, the optical host distribution has a visible peak near $M_{\rm BH} \sim 10^6 \, \mathrm{M}_\odot$, whereas the X-ray host distribution appears flat in MBH. We find a subset of X-ray-selected candidates that are hosted in galaxies significantly less luminous (Mg ∼ −16) and less massive (stellar mass ∼ 108.5–9 M⊙) than those of optical events. Using statistical tests we find suggestive evidence that, in terms of BH mass, stellar mass, and absolute magnitude, the hard X-ray hosts differ from the UV/optical and soft X-ray samples. Similar to individual studies, we find that the size of the emission region for the soft X-ray sample is much smaller than the optical emission region, consistent with a compact accretion disc. We find that the typical Eddington ratio of the soft X-ray emission is ∼ 0.01, as opposed to the optical events which have LBB ∼ LEdd. The latter seems artificial if the radiation is produced by self-intersection shocks, and instead suggests a connection to the supermassive black hole.

Tidal disruption events: Past, present, and future

The tidal disruption of a star by a nuclear supermassive black hole was predicted in the 1970s and first confirmed by soft X‐ray flares seen from quiescent galaxies in the ROSAT all‐sky survey. We report here on the discovery of a new candidate tidal disruption event, 1RXS J075908.8 + 074835, from the ROSAT bright source catalog, which faded by a factor > 100 in 20 years. Similar events have continued to be found in XMM‐Newton and Chandra data and more recently, flares in large‐area hard X‐ray, ultraviolet (UV) and optical transient surveys have also been attributed to the same phenomenon. Each of these spectral components, sometimes complemented by radio and IR activity, have their own timescale and possibly physical mechanism. Current models and simulations revolve around trying to explain how the energy released by the fall back of stellar debris in the gravitational well of the black hole is converted into radiation in each wave band. We look at the connection between optical, UV, and X‐ray emission and illustrate a dichotomy between X‐ray and optically dominated tidal disruption event (TDE), which is currently unexplained. We look at the observations that are needed to make further breakthroughs in the field and assess the optimum follow‐up strategies needed for events discovered in future large survey missions such as extended Roentgen Survey with an Imaging Telescope Array (eROSITA), the Einstein Probe, and Large Synoptic Survey Telescope (LSST). HIgh‐energy LIght‐curve GeneraTor (HILIGT), a useful new tool for comparing fluxes and upper limits between missions, is presented.

Stellar tidal disruption events in general relativity

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 $\sim 10^7 M_\odot$, 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 $\sim 10^8 M_\odot$ 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.

Tidal Disruption of a Main-sequence Star by an Intermediate-mass Black Hole: A Bright Decade

Abstract There has been suggestive evidence of intermediate-mass black holes (IMBHs; 103−5 M ⊙) existing in some globular clusters (GCs) and dwarf galaxies, but IMBHs as a population remain elusive. As a main-sequence star passes too close by an IMBH it might be tidally captured and disrupted. We study the long-term accretion and observational consequence of such tidal disruption events. The disruption radius is hundreds to thousands of the BH’s Schwarzschild radius, so the circularization of the falling-back debris stream is very inefficient due to weak general relativity effects. Due to this and a high mass fallback rate, the bound debris initially goes through a ∼10 yr long super-Eddington accretion phase. The photospheric emission of the outflow ejected during this phase dominates the observable radiation and peaks in the UV/optical bands with a luminosity of . After the accretion rate drops below the Eddington rate, the bolometric luminosity follows the conventional t −5/3 power-law decay, and X-rays from the inner accretion disk start to be seen. Modeling the newly reported IMBH tidal disruption event candidate 3XMM J2150-0551, we find a general consistency between the data and predictions. The search for these luminous, long-term events in GCs and nearby dwarf galaxies could unveil the IMBH population.

On the Missing Energy Puzzle of Tidal Disruption Events

Abstract For the majority of tidal disruption event (TDE) candidates, the observed energy in the optical/near-UV bands is of order 1051 erg. We show that this observed energy is smaller than the minimum bolometric energy for the radiative inefficient accretion flow model by a factor of 10–100. We argue that this discrepancy is because the majority of the energy released is in the extreme-UV (EUV) band and/or in the form of relativistic jets beamed away from the Earth. The EUV scenario is supported by existing mid-infrared data and should be further tested by future dust reverberation observations. The jet scenario is disfavored by radio observations of ASASSN-14li but may still be viable for other TDE candidates. We also provide evidence that, at least for some TDEs, most of the missing energy (in the EUV and/or in the form of jets) is released within a few times the orbital period of the most tightly bound material P min, which means (1) the circularization of the fallback stream may occur rapidly and (2) the luminosity of the accretion flow or the jet power may not be capped near the Eddington level when the fallback rate is super-Eddington. For most other TDEs, this energy-release timescale is currently not strongly constrained.