Multiband lightcurves of tidal disruption events (1008.4589v2)

Abstract: Unambiguous detection of the tidal disruption of a star would allow an assessment of the presence and masses of supermassive black holes in quiescent galaxies. It would also provide invaluable information on bulge scale stellar processes (such as two-body relaxation) via the rate at which stars are injected into the tidal sphere of influence of the black holes. This rate, in turn, is essential to predict gravitational radiation emission by compact object inspirals. The signature of a tidal disruption event is thought to be a fallback rate for the stellar debris onto the black hole that decreases as $t^{-5/3}$. This mass flux is often assumed to yield a luminous signal that decreases in time at the same rate. In this paper, we calculate the monochromatic lightcurves arising from such an accretion event. Differently from previous studies, we adopt a more realistic description of the fallback rate and of the super-Eddigton accretion physics. We also provide simultaneous lightcurves in optical, UV and X-rays. We show that, after a few months, optical and UV lightcurves scale as $t^{-5/12}$, and are thus substantially flatter than the $t^{-5/3}$ behaviour, which is a prerogative of the bolometric lightcurve, only. At earlier times and for black hole masses $< 10^7 M_{\sun}$, the wind emission dominates: after reaching a peak of $10^{41}-10^{43}$ erg/s at roughly a month, the lightcurve decreases steeply as $\sim t^{-2.6}$, until the disc contribution takes over. The X-ray band, instead, is the best place to detect the $t^{-5/3}$ "smoking gun" behaviour, although it is displayed only for roughly a year, before the emission steepens exponentially.

Multiband Lightcurves of Tidal Disruption Events

In the paper by Lodato and Rossi, titled "Multiband lightcurves of tidal disruption events," the authors present an analytical and numerical paper focused on the lightcurves produced by tidal disruption events (TDEs) across multiple wavelengths. TDEs hold significant importance in astrophysics as they can unambiguously signal the presence and quantify the masses of supermassive black holes (SMBHs) in quiescent galaxies. Moreover, they facilitate an understanding of bulge-scale stellar dynamics, particularly two-body relaxation processes, which play a critical role in stellar injection rates into the tidal sphere proximate to SMBHs, thereby influencing the predictions for gravitational wave emissions from compact object inspirals.

The authors recalibrate the theoretical framework traditionally associated with the fallback rate of stellar debris during TDEs, often assumed to decrease as $t^{-5/3}$. This framework provides a cornerstone for interpreting observed luminous signals emanating from such events. However, contrary to previous conclusions, this paper presents a more sophisticated analysis that incorporates a realistic depiction of fallback rates, alongside considerations of super-Eddington accretion physics, resulting in modifications to the expected lightcurve phenomena across varied frequency bands.

Key Findings

1. Fallback Rate and Monochromatic Lightcurves:
   • The paper elucidates that monochromatic lightcurves diverge from a uniform $t^{-5/3}$ decline. Specifically, optical and ultraviolet (UV) lightcurves demonstrate a scaling behavior able to be characterized by $t^{-5/12}$ after several months, showcasing a substantially flatter profile compared to the bolometric lightcurve behavior.
   • The X-ray emissions, in contrast, exhibit the anticipated $t^{-5/3}$ decline, but this characteristic manifests over approximately one year before steepening into an exponential decay.
2. Wind Emission Effects:
   • For SMBHs with masses less than $10^7 M_{\odot}$, an initial phase dominated by wind emission occurs, marked by steep declines until contributions from the accretion disc surpass wind effects. Here, wind emissions peak at $10^{41}-10^{43}$ erg/s about a month post-event, decreasing sharply at $\sim t^{-2.6}$.

Implications and Future Directions

This paper reveals critical insights into emission profiles across several bands, enhancing our understanding of the dynamic processes underpinning TDEs. Practically, it presents a sophisticated framework requisite for the analysis of observational data concerning star-black hole interaction events. The research postulates deviations from earlier models suggesting oversimplified assumptions regarding accretion rates and luminosities that highlight the necessity for refined models incorporating super-Eddington physics.

The discovery challenges customary groundwork models, fostering inquiries into the complex interplay between fallback rates and accretion processes of disrupted material. Future developments could explore a greater granularity within TDE simulation environments to deliver more precise evolutionary paths of fallback rates and their subsequent influence on emitted light curves.

Such advancements could fundamentally support the identification and characterization of SMBHs in non-AGNs, while also acting as a primer for gravitational wave experiments envisaging extreme mass ratio inspirals. Enhanced detection methodologies within various wavebands might emerge, utilizing theoretical feedback from these findings, optimizing probing strategies for SMBHs.

Ultimately, this paper significantly contributes to the theoretical understanding of TDE luminosity profiles, challenging existing perceptions while proposing nuanced mechanisms that underscore subtle departures from traditional theoretical characterizations. Such research paves the way for the establishment of robust multimodal astrophysical investigations of SMBH activity in quiescent galaxies.