[Paper Review] Electromagnetic Cascade Emission from Neutrino-Coincident Tidal Disruption Events

Chengchao Yuan, Walter Winter|arXiv (Cornell University)|Jan 1, 2023

Astrophysics and Cosmic Phenomena5 references1 citations

TL;DR

This paper models electromagnetic (EM) cascade emission from neutrino-coincident tidal disruption events (TDEs), specifically AT2019dsg and AT2019fdr, by solving time-dependent transport equations for particle interactions. It finds that Fermi γ-ray upper limits constrain the radiation zone size and proton maximum energy, predicting fewer than 0.1 neutrino events per TDE, with EM cascades potentially detectable in X-rays if pγ interactions are efficient.

ABSTRACT

The potential association between Tidal Disruption Events (TDEs) and high-energy astrophysical neutrinos implies the acceleration of cosmic rays. These accelerated particles will initiate electromagnetic (EM) cascades spanning from keV to GeV energies by the processes related to neutrino production. We model the EM cascade and neutrino emissions by numerically solving the time-dependent transport equations and discuss the implications for AT2019dsg and AT2019fdr in the X-ray and $\gamma$-ray bands. We show that the $\gamma$-ray constraints from \emph{Fermi} can constrain the size of the radiation zone and the maximum energy of injected protons, and that the corresponding expected neutrino event numbers in follow-up searches are limited to be less than about 0.1. Depending on the efficiency of $p\gamma$ interactions, the X-ray and $\gamma$-ray signals can be expected closer to the peak of the optical-ultraviolet (OUV) luminosity, or to the time of the neutrino production.

Motivation & Objective

• To investigate the connection between high-energy neutrinos and TDEs by modeling electromagnetic cascade emission from particle interactions.
• To determine the time-dependent behavior of EM cascades in TDEs, particularly in relation to neutrino production and observed X-ray/γ-ray emissions.
• To constrain source parameters—such as radiation zone size and maximum proton energy—using Fermi γ-ray upper limits and neutrino event rates.
• To assess the detectability of EM cascade signals in X-ray and γ-ray bands for TDEs like AT2019dsg and AT2019fdr.
• To provide a template for multi-messenger studies of TDEs using coherent lepto-hadronic modeling of EM cascades and neutrino emission.

Proposed method

• Numerically solves time-dependent transport equations for secondary particles (e±, γ, π±, π0) produced in pγ interactions within radiation zones of TDEs.
• Models electromagnetic cascade processes including electron/positron synchrotron and inverse Compton emission, γγ attenuation, and pion/muon decays.
• Uses the pγ interaction rate as a proxy for EM cascade development timescale, justified by secondary process rates being much faster.
• Applies the M-IR, M-OUV, and M-X scenarios to different TDEs, varying which photon field (IR, OUV, X-ray) dominates pγ interactions.
• Compares model predictions with observational data: X-ray light curves (Swift-XRT, XMM-Newton, NICER), Fermi γ-ray upper limits, and IceCube neutrino event times.
• Evaluates neutrino event rates via generalized follow-up (GFU) searches, estimating <0.1 expected events per TDE under model constraints.

Experimental results

Research questions

• RQ1 How do electromagnetic cascade emissions in TDEs evolve over time, and how do they relate to the observed neutrino production times?
• RQ2 What constraints do Fermi γ-ray upper limits place on the size of the radiation zone and the maximum energy of injected protons in TDEs?
• RQ3 Can EM cascade emission in X-rays or γ-rays be detected for neutrino-coincident TDEs like AT2019dsg and AT2019fdr?
• RQ4 To what extent can the time delay between OUV peaks and neutrino detections be explained by pγ interaction timescales?
• RQ5 How do different photon fields (IR, OUV, X-ray) influence the efficiency and timing of EM cascade and neutrino production?

Key findings

• Fermi γ-ray upper limits constrain the radiation zone to be pγ optically thin, limiting the source to a maximum proton energy of ~10^18–10^19 eV for AT2019dsg and AT2019fdr.
• The predicted neutrino event rate for each TDE is less than 0.1, consistent with the absence of significant detections in generalized follow-up searches.
• X-ray emission around 100 days post-OUV peak in AT2019dsg can be explained by EM cascade emission in the M-IR scenario, suggesting detectability by Swift-XRT, XMM-Newton, and NICER.
• The time delay between OUV peak and neutrino detection can be attributed solely to the pγ interaction timescale in the M-IR scenario, supporting a causal link between cascade development and neutrino production.
• Secondary processes such as muon and pion decay, synchrotron, and inverse Compton emission occur on timescales much faster than pγ interactions, validating the use of pγ rate as the cascade development timescale.
• The model provides a viable template for multi-messenger studies of TDEs, applicable to both jetted and quasi-isotropic TDEs through coherent lepto-hadronic modeling.