High-Energy Neutrino and Gamma-Ray Emission from Tidal Disruption Events

Abstract: Tidal disruption events (TDE) have been considered as cosmic-ray and neutrino sources for a decade. We suggest two classes of new scenarios for high-energy multi-messenger emission from TDEs that do not have to harbor powerful jets. First, we investigate high-energy neutrino and gamma-ray production in the core region of a supermassive black hole. In particular, we show that about 1-100 TeV neutrinos and MeV gamma-rays can efficiently be produced in hot coronae around an accretion disk. We also study the consequences of particle acceleration in radiatively inefficient accretion flows (RIAFs). Second, we consider possible cosmic-ray acceleration by sub-relativistic disk-driven winds or interactions between tidal streams, and show that subsequent hadronuclear and photohadronic interactions inside the TDE debris lead to GeV-PeV neutrinos and sub-GeV cascade gamma-rays. We demonstrate that these models should be accompanied by soft gamma-rays or hard X-rays as well as optical/UV emission, which can be used for future observational tests. Although this work aims to present models of non-jetted high-energy emission, we discuss the implications of the TDE AT2019dsg that might coincide with the high-energy neutrino IceCube-191001A, by considering the corona, RIAF, hidden sub-relativistic wind, and hidden jet models. It is not yet possible to be conclusive about their physical association and the expected number of neutrinos is typically much less than unity. We find that the most optimistic cases of the corona and hidden wind models could be consistent with the observation of IceCube-191001A, whereas jet models are unlikely to explain the multi-messenger observations.

High-Energy Neutrino and Gamma-Ray Emission from Tidal Disruption Events

This paper by Murase et al. discusses potential scenarios for high-energy neutrino and gamma-ray emission associated with tidal disruption events (TDEs) without requiring the presence of relativistic jets. The study proposes two main models: the core model, focusing on activities in the vicinity of a supermassive black hole, and a hidden wind model, involving sub-relativistic flows interacting with TDE debris.

Core Models: Potential Neutrino Sources

Corona Model

The corona model suggests that high-energy neutrinos and gamma-rays can efficiently be produced in hot coronae surrounding accretion disks. The corona acts as a region for particle acceleration via mechanisms such as turbulence and magnetic reconnection, possibly leading to effective neutrino emission. In this model, reactions such as $pp$ and $p\gamma$ are integral to neutrino production, with the proton acceleration specifications largely dependent on the mass of the SMBH and the Eddington ratio.

Radiatively Inefficient Accretion Flow (RIAF) Model

This model explores scenarios where accretion falls below a critical rate, pushing the state of the disk to a RIAF, conducive for efficient neutrino production via $pp$ interactions. Here, the effective optical depth is a crucial parameter, allowing CR interactions without substantial gamma-ray production, making these sources “gamma-ray hidden.” Nevertheless, challenges exist in reconciling observed UV emission with expected emission from RIAFs.

Hidden Wind Model: Expanding the Scope

The hidden wind model considers CR acceleration in sub-relativistic disk-driven winds or interactions within TDE debris. This scenario markedly differs from TDE models requiring active jet mechanisms, offering an alternative perspective on high-energy emission. CRs can undergo hadronuclear and photohadronic interactions, leading to observable neutrinos and potentially traceable gamma-rays below the GeV range, making observational tests feasible with current and next-generation instruments such as Fermi-LAT, e-ASTROGAM, and AMEGO.

Implications for TDE Observations

The events around AT2019dsg and the lone detection of a high-energy neutrino (IceCube-191001A) present a complex puzzle. While the paper explores multiple models, including the possibility of coincidental emission with minimal detection probability, it illustrates that explaining this singular detection is challenging across all models. However, the corona model presents a feasible mechanism under certain conditions, potentially providing insights into the formation and nature of TDE emission.

Contributions to Diffuse Neutrino Flux

The studied models, despite challenges in explaining individual neutrino detections, indicate that TDEs may contribute to a portion of the observed diffuse neutrino flux. Yet, constraints based on cumulative source densities and emission rates suggest that TDEs are unlikely dominant contributors. The investigations in this paper thus demonstrate the nuanced contributions various astrophysical phenomena might offer to diffuse neutrino background.

Conclusion and Future Directions

Murase et al.'s exploration into non-jetted mechanisms for TDE emissions provides significant insights, though concrete associations with observed neutrino events remain tentative. Future work, particularly observational, is crucial to test these models and refine our understanding of TDE phenomena. Enhanced MeV gamma-ray and hard X-ray missions promise to deliver critical tests that could validate or challenge the predictions laid out concerning core and hidden wind models, offering new realms to investigate the particle acceleration in complex cosmic environments.