Prediction of Multi-Wavelength Afterglows Associated with FRB 20200120E and FRB 20201124A

TL;DR

This work addresses whether fast radio bursts (FRBs) in binary systems can produce detectable multi-wavelength afterglows. It develops a unified external-shock framework, inspired by gamma-ray burst afterglow theory, to predict radio, optical, and X-ray light curves as FRB ejecta interact with a wind-shaped circumbinary medium, including forward-shock synchrotron emission and a negligible reverse-shock contribution, with key parameters $E_k$, $\eta$, and the ambient density profile $n(r)$. Applying the model to FRB 20200120E and FRB 20201124A, the authors show that radio afterglows are the most promising detectables with instruments like the SKA or MeerKAT, while optical afterglows can be detectable only in dense environments and with high-cadence monitoring, and X-ray afterglows remain too faint for current telescopes. The results yield detectability maps in the $(E_k,\dot{M}_w)$ plane and provide practical guidance for targeted multi-wavelength follow-ups to probe FRB progenitors and their environments, offering a path to distinguish binary-enviroment scenarios from magnetar-only models. These insights highlight the role of the circumbinary medium in shaping FRB observables and the potential of multi-wavelength observations to constrain FRB central engines and surroundings.

Abstract

Fast radio bursts (FRBs) are mysterious radio transients with uncertain origins and environments. Recent studies suggest that some active FRBs may originate from compact objects in binary systems. In this work, we develop a unified theoretical framework to model the multi-wavelength afterglows of FRBs resided in binary systems and apply it to two representative repeaters, FRB 20200120E and FRB 20201124A. By solving the dynamics and radiation processes of FRB ejecta interacting with the surrounding medium, we compute afterglow light curves in the radio, optical, and X-ray bands. Our results show that radio afterglows offer the best prospects for detection, with their brightness highly sensitive to ejecta kinetic energy and ambient density. Future high-sensitivity radio telescopes, such as the Square Kilometre Array (SKA), could detect these signals. Optical afterglows, though short-lived and challenging to observe, may be significantly enhanced in dense environments, potentially making them detectable with facilities like the Large Synoptic Survey Telescope (LSST). In contrast, X-ray afterglows are predicted to be too faint for detection with current instruments. Our study highlights the potential of multi-wavelength afterglows as probes of FRB progenitors and their surrounding environments, offering crucial insights into the nature of these mysterious transients.

Figures (18)

• Figure 1: Temporal evolution of the bulk Lorentz factor $\Gamma(t)-1$ for the two FRB cases. Panel (a): FRB 20200120E with $\dot{M}_{\rm w} = 10^{-11}~M_{\odot}~\mathrm{yr}^{-1}$ . Panel (b): FRB 20201124A with $\dot{M}_{\rm w} = 10^{-10}~M_{\odot}~\mathrm{yr}^{-1}$.
• Figure 2: Time evolution of the spectral break frequencies. Panel (a): FRB 20200120E with $\dot{M}_{\rm w} = 10^{-11}~M_{\odot}~\mathrm{yr}^{-1}$ and $E_{\rm k} = 10^{42}~\mathrm{erg}$. Panel (b): FRB 20201124A with $\dot{M}_{\rm w} = 10^{-10}~M_{\odot}~\mathrm{yr}^{-1}$ and $E_{\rm k} = 10^{47}~\mathrm{erg}$.
• Figure 3: Multi-wavelength afterglow light curves of FRB 20200120E for different ejecta kinetic energies: $E_{\rm k} = 10^{41}~\mathrm{erg}$ (green), $10^{42}~\mathrm{erg}$ (blue), and $10^{43}~\mathrm{erg}$ (red). The stellar-wind mass-loss rate is fixed at $\dot{M}_{\rm w} = 10^{-11} M_{\odot} \mathrm{yr}^{-1}$ in all three panels. Panel (a): 1 GHz radio afterglow with SKA sensitivity limit (dotted purple; 2019arXiv191212699B). Panel (b): $R$-band optical afterglow with LSST sensitivity limit (dotted purple; 2014ApJ...792L..21Y). Panel (c): 1 keV X-ray afterglow with Swift/XRT sensitivity limit (dotted purple; Moretti2008MCAONP).
• Figure 4: Multi-wavelength afterglow light curves of FRB 20200120E for different stellar wind mass-loss rates: $\dot{M}_{\rm w} = 10^{-10}~M_{\odot}~\mathrm{yr}^{-1}$ (green), $10^{-9}~M_{\odot}~\mathrm{yr}^{-1}$ (blue), and $10^{-8}~M_{\odot}~\mathrm{yr}^{-1}$ (red). Panels as in Figure \ref{['fig:1']}. The ejecta kinetic energy is fixed at $E_{\rm k} = 10^{41} \mathrm{erg}$ in all three panels.
• Figure 5: Multi-wavelength afterglow light curves of FRB 20201124A for different ejecta kinetic energies: $E_{\rm k} = 10^{46}~\mathrm{erg}$ (green), $10^{47}~\mathrm{erg}$ (blue), and $10^{48}~\mathrm{erg}$ (red). Panels as in Figure \ref{['fig:1']}. The stellar-wind mass-loss rate is fixed at $\dot{M}_{\rm w} = 10^{-10} M_{\odot} \mathrm{yr}^{-1}$ in all three panels.