The Persistent Radio Sources and Multi-wavelength Counterparts of Fast Radio Bursts in Massive Binary Systems

Abstract

Fast radio bursts (FRBs) are millisecond-duration pulses originating from cosmological distances. Multi-wavelength counterparts associated with FRBs are important for unveiling their physical origins. Recent observations provide strong evidence that the sources of some active FRBs are residing in massive star binaries. In this paper, we study the electromagnetic counterparts of FRBs, including the persistent radio sources (PRSs) and the bow shock radiation from wind collisions for FRBs residing in magnetar - massive star binaries. We find that the PRSs with luminosity $10^{38}-10^{39}$ erg s$^{-1}$ can be generated by young magnetar wind nebulae (MWN). The age of magnetars is a few decades. The observed long-term variation of flux density for PRSs can be explained by the internal magnetic field decay of magnetars. The bow shock radiation can account for the less luminous PRS of FRB 20201124A. The multi-wavelength emission arising from synchrotron radiation and inverse-Compton scattering in the bow shock can be the electromagnetic counterpart of FRBs. The emission at keV, GeV and TeV bands from the binary model can be detected at the distances of $\sim10-100$ Mpc, $\sim 1-10$ Mpc and $\sim0.1$ Mpc by current instruments, respectively.

Figures (12)

• Figure 1: Schematic diagram of repeating FRBs' environments. a, The magnetar/massive star binary is embedded in a supernova remnant. b, The case of a stronger magnetar wind ($\eta \gg 1$), the shock bends back to the star. The magnetar wind will propagate freely, especially in the direction perpendicular to the orbital plane. As the free expanding magnetar wind interacts with the outer SN ejecta, it generates an MWN at a distance much greater than the orbit separation. The observed luminous PRSs are produced by the synchrotron radiation of the MWN. c, The case of a stronger companion wind ($\eta \ll 1$), the shock bends back to the magnetar. The magnetar wind will be terminated by the stellar wind at the standoff distance $r_{\mathrm{s}}$. The high-energy emission (keV to TeV) arising from synchrotron radiation and inverse-Compton scattering in the bow shock, which can be the multiwavelength counterpart of FRBs. The binary systems are unlikely to be responsible for generating bright PRSs, but they may account for some faint sources, such as FRB 20201124A and FRB 20181030A. Although the magnetar wind is typically stronger than the stellar wind in binary systems containing a young magnetar and a massive star, the wind interaction still occurs within the orbital plane.
• Figure 2: The value of $L_{\mathrm{syn}}$ for different companion mass $M_{\star}$ and orbital periods $P$. The magnetization parameter $\sigma =0.01$ is adopted in our calculation. The free–free absorption optically thick regions for $\nu=1$ GHz have been excluded (shown in gray). The blue, red and cyan lines represent the PRS with luminosity $\nu L_{\nu}=10^{35}$ erg s$^{-1}$ (FRB 20181030A-like), $\nu L_{\nu}=10^{38}$ erg s$^{-1}$ (FRB 20201124A-like) and $\nu L_{\nu}=10^{39}$ erg s$^{-1}$ (FRB 20121102A-like), respectively. For bright PRS with the luminosity $\nu L_{\nu}>10^{39}$ erg s$^{-1}$, the viable parameter space is virtually nonexistent. For binary systems with orbital periods of several hundred days and companion masses greater than 10 $M_\odot$, the observed faint PRSs can be produced. This is consistent with the results obtained by DM and RM fitting Wang2025.
• Figure 3: The synchrotron SEDs (panels (1a)-(3a)) and light curves (panels (1b)-(3b)) of the rotation-powered nebula. The left panels show the spectrum for ages $t_{\mathrm{age}} = 1$ yr (blue lines), 10 yr (red lines), and 100 yr (green lines). For the initial spin period $P_{\mathrm{i}}=2$ ms, the final accelerated expanding velocity of the nebula is $v_{\mathrm{n}}=2.5\times 10^9$ cm/s (solid line). For the cases of $P_{\mathrm{i}}=20$ ms, the nebula is not accelerated, and the expanding velocity is $v_{\mathrm{n}}=v_{\mathrm{ej}}=1\times 10^9$ cm/s (dashed lines). The right panels show the light curves at frequencies $\nu=1.5$ GHz (blue lines), $\nu=3$ GHz (red lines), and $\nu=10$ GHz (green lines). Panel (1a-1b): for $B_{\mathrm{dip}}=10^{14}$ G and $\chi=1$. Panel (2a-2b): for $B_{\mathrm{dip}}=10^{15}$ G and $\chi=1$. For the case of a higher dipolar magnetic field, the synchrotron luminosity is 1–2 orders of magnitude lower. The shorter spin-down timescale means the faster decay of the luminosity. Panel (3a-3b): for $B_{\mathrm{dip}}=10^{14}$ G and $\chi=0.1$. A smaller radiation region results in higher peak frequency and lower luminosity synchrotron radiation at the same age.
• Figure 4: Same as Figure \ref{['fig:rot']}, but for the magnetic-powered model. Compared to rotational energy, the internal magnetic energy of magnetars has a longer decay timescale, which allows the luminosity of MWNs to remain stable over a period of $1-100$ yr.
• Figure 5: The spectra of synchrotron radiation (blue lines), SSC (green lines), and EIC scattering radiation (orange lines) from the bow shock of rotation-powered models ($\Gamma=10^5$ and $\sigma=0.01$). For simplicity, we assume that the luminosity of the central engine is constant ($\dot{E}=10^{40}$ erg/s) and that the binary systems are in circular orbits. The period of the binary system is $P=100$ d. The typical massive star and stellar wind parameters are used in our calculation: $M_{\odot}=30M_{\odot}, R_{\odot}=10R_{\odot},T_{\mathrm{eff}}=2\times 10^4$ K, $\dot{M}=5\times 10^{-7} M_{\odot}$ yr$^{-1}$ and $v_{\mathrm{w}}=3\times 10^{8}$ cm/s. The synchrotron radiation of nonthermal electrons in the bow shock is mainly in the keV X-ray band and can be detected by Chandra and XMM-Newton at the luminosity distance of $D_{\mathrm{L}}\sim 10$ Mpc (left panel). The SSC and EIC scattering radiation is mainly at the GeV band, which can be detected by Fermi-LAT at the luminosity distance of $D_{\mathrm{L}}\sim 1$ Mpc (middle panel). At a closer distance (e.g., $D_{\mathrm{L}}\lesssim 0.1$ Mpc), the TeV $\gamma$-ray emission from the IC scattering process can be detected by CAT and LHAASO (right panel).