arXiv subjects

Zhen-Yin Zhao

Publications and source records attributed to Zhen-Yin Zhao.

9 recordsLinked to original sources

arXiv2026

Propagation Diagnostics of Supernova Remnant Environments around Young Repeating FRBs. I. Hydrodynamic Evolution of the Source-Local Dispersion Measure

Repeating fast radio bursts may reside in young supernova remnant (SNR) environments whose evolving plasma contributes to the observed dispersion measure (DM). We use two-dimensional axisymmetric hydrodynamic simulations to study the interaction between a continuous anisotropic wind from a young neutron star and homologously expanding supernova ejecta. We follow the evolution to approximately 160 yr and calculate the source-local DM along different viewing directions, using a passive tracer to separate wind and non-wind contributions. In the fiducial model, the strongly polar-focused wind inflates a low-density cavity, while the swept-up shell remains broadly rounded and the DM shows moderate angular variation. The DM is dominated by ejecta and swept-up non-wind material. The solid-angle-averaged ambient-subtracted excess DM declines throughout the evolution, approximately following $t_{\rm age}^{-2}$ during the first several tens of years and becoming modestly steeper later. Variations in wind and ejecta parameters modify the normalization, early evolution, and viewing-angle dependence, but the angle-averaged DM declines in all models, while different bipolar wind profiles produce similar long-term evolution. For FRB 20190520B, the fiducial model reaches a decline rate comparable to the source-frame value inferred from observations at approximately 20 yr, when the mean excess DM is approximately $1.8 \times 10^2$ pc cm$^{-3}$. Thus, such a young environment can retain a substantial electron column while producing a rapid secular decrease. Repeater diversity suggests that SNR-driven expansion may coexist with additional time-dependent plasma structures or ionization changes.

astro-ph.HE↗

arXiv2026

Periodic Emission Frequency Modulation in a Hyperactive Fast Radio Burst

Fast radio bursts (FRBs) are intense, short-duration radio transients of mysterious origin. They have been detected across a wide range of frequencies from 110 MHz to 8 GHz. Their spectral properties, remaining poorly understood, are essential for understanding the intrinsic radiation mechanism and propagation effects. Here, we report the discovery of a periodic modulation in the central emission frequency of FRB 20240114A, based on more than one thousand bursts collected by an ultra-wideband receiving system. The burst central frequencies reveals a significant modulation with a period of $\sim 112$ days. The statistical significance of this detected periodicity exceeds $6σ$ for both the Lomb-Scargle and phase-folding methods. Within a single period, the central emission frequency exhibits a systematic drift from lower to higher values. We evaluate several physical mechanisms for this unique spectral evolution. The free-free absorption together with cyclotron resonant absorption in a binary system or free precession models could potentially explain such behavior. The discovery of this periodic frequency modulation unveils a new layer of complexity in the underlying radiation mechanism and propagation effect of FRBs.

astro-ph.HE↗

arXiv2025

Two Periodic Activity Epochs in FRB 20201124A: Coincident with Critical RM Evolution Epochs and Its Implications

Recent observations of the repeating fast radio burst FRB 20201124A by the Five-hundred-meter Aperture Spherical radio Telescope (FAST) revealed a second-scale periodic modulation ($\sim$1.7\,s) in burst activity during two distinct observational windows. We find that these two periodic activity epochs temporally coincide with the transitional states of the source's Faraday rotation measure (RM), and the chance coincidence is only about 0.07$\%$. This correlation is can be understood within the magnetar/Be-star binary system framework. Considering that only the polar cap region can remain stable for such an extended period, we apply a coherent linear periodic evolution model to jointly constrain the initial burst period $ P_0 $ and the period derivative $ \dot{P} $ across both observation windows (MJD 59310 and MJD 59347). We obtain spin parameters consistent with blind search results: an initial spin period $P_0 = 1.7060155$\,s at the reference time and spin period derivative $\dot{P} = 6.1393 \times 10^{-10}$\,s\,s$^{-1}$. We conclude that during these two observational windows, the magnetar was just crossing the disk of the Be star. The disk-magnetar interaction at these two geometric positions may surpress the multi-polar magnetic fields at low latitudes of the magnetar, which enhances the dominance of the polar cap region emissions and makes the periodic activity detectable.

astro-ph.HE↗

arXiv2025

Structure Functions of Rotation Measures Revealing the Origin of Fast Radio Bursts

The structure function (SF) analysis is a powerful tool for studying plasma turbulence. Theoretically, the SF of Faraday rotation measure (RM) is expected to include a geometric component due to the relative orientation of sightlines through an ordered magnetic field. However, observational evidence for this component remains elusive. Here, we report that the SFs of the binary PSR B1744-24A and the repeating fast radio burst (FRB) 20201124A exhibit both a periodic geometric component, caused by binary orbital motion, and a flat statistical component. The statistical component, induced by stochastic fluctuations in electron density and magnetic field, aligns with RM scatter derived from pulse depolarization. These findings indicate that FRB 20201124A has a binary origin and suggest that the periodic geometric component can serve as a diagnostic tool to identify binary companions.

astro-ph.HE↗

arXiv2024

The physical origin of the periodic activity for FRB 20180916B

Fast radio bursts (FRBs) are transient radio signals with millisecond-duration, large dispersion measure (DM) and extremely high brightness temperature. Among them, FRB 20180916B has been found to have a 16-day periodically modulated activity. However, the physical origin of the periodicity is still a mystery. Here, we utilize the comprehensive observational data to diagnose the periodic models. We find that the ultra-long rotation model is the most probable one for the periodic activity. However, this model cannot reproduce the observed rotation measure (RM) variations. We propose a self-consistent model, i.e., a massive star binary containing a slowly rotational neutron star and a massive star with large mass loss, which can naturally accommodate the wealth of observational features for FRB 20180916B. In this model, the RM variation is periodic, which can be tested by future observations.

astro-ph.HE↗

arXiv2023

Fast Radio Bursts: Electromagnetic Counterparts to Extreme Mass Ratio Inspirals

Recent observations discovered that some repeating fast radio bursts (FRBs) show a large value and complex variations of Faraday rotation measures (RMs). The binary systems containing a supermassive black hole (SMBH) and a neutron star (NS) can be used to explain such RM variations. Meanwhile, such systems produce low-frequency gravitational wave (GW) signals, which are one of the primary interests of three proposed space-based GW detectors: the Laser Interferometer Space Antenna (LISA), Tianqin and Taiji. These signals are known as extreme mass ratio inspirals (EMRIs). Therefore, FRBs can serve as candidates of electromagnetic (EM) counterparts for EMRI signals. In this letter, we study the EMRI signals in this binary system, which can be detected up to $z\sim0.04$ by LISA and Tianqin for the most optimistic case. Assuming the cosmic comb model for FRB production, the total event rate can be as high as $\sim1$ Gpc$^{-3}$ yr$^{-1}$. EMRI signals associated with FRBs can be used to reveal the progenitor of FRBs. It is also a new type of standard siren, which can be used as an independent cosmological probe.

astro-ph.HE↗

arXiv2023

Temporal evolution of depolarization and magnetic field of FRB 20201124A

Fast radio bursts (FRBs) are energetic millisecond phenomena in radio band. Polarimetric studies of repeating FRBs indicate that many of these sources occupy extreme and complex magneto-ionized environments. Recently, a frequency-dependent depolarization has been discovered in several repeating FRBs. However, the temporal evolution of polarization properties is limited by the burst rate and observational cadence of telescopes. In this letter, the temporal evolution of depolarization in repeating FRB 20201124A is explored. Using the simultaneous variation of rotation measure and dispersion measure, we also measure the strength of a magnetic field parallel to the line-of-sight. The strength ranges from a few $μ{\rm G}$ to $10^3\ μ{\rm G}$. In addition, we find that the evolution of depolarization and magnetic field traces the evolution of rotation measure. Our result supports that the variation of depolarization, rotation measure and the magnetic field are determined by the same complex magneto-ionized screen surrounding the FRB source. The derived properties of the screen are consistent with the wind and the decretion disk of a massive star.

astro-ph.HE↗

arXiv2023

Tidal capture of an asteroid by a magnetar: FRB-like bursts, glitch and anti-glitch

Recently, remarkable anti-glitch and glitch accompanied by bright radio bursts of the Galactic magnetar SGR J1935+2154 were discovered. These two infrequent temporal coincidences between the glitch/anti-glitch and the fast radio burst (FRB)-like bursts reveal their physical connection of them. Here we propose that the anti-glitch/glitch and FRB-like bursts can be well understood by an asteroid tidally captured by a magnetar. In this model, an asteroid is tidally captured and disrupted by a magnetar. Then, the disrupted asteroid will transfer the angular momentum to the magnetar producing a sudden change in the magnetar rotational frequency at the magnetosphere radius. If the orbital angular momentum of the asteroid is parallel (or anti-parallel) to that of the spinning magnetar, a glitch (or anti-glitch) will occur. Subsequently, the bound asteroid materials fall back to the pericenter and eventually are accreted to the surface of the magnetar. Massive fragments of the asteroid cross magnetic field lines and produce bright radio bursts through coherent curvature radiation. Our model can explain the sudden magnetar spin changes and FRB-like bursts in a unified way.

astro-ph.HE↗

arXiv2021

FRB 190520B embedded in a magnetar wind nebula and supernova remnant: luminous persistent radio source, decreasing dispersion measure and large rotation measure

Recently, FRB 190520B with the largest extragalactic dispersion measure (DM), was discovered by the Five-hundred-meter Aperture Spherical radio Telescope (FAST). The DM excess over the intergalactic medium and Galactic contributions is estimated as $\sim 900$ pc cm$^{-3}$, which is nearly ten times higher than other fast radio bursts (FRBs) host galaxies. The DM decreases with the rate $\sim0.1$ pc cm$^{-3}$ per day. It is the second FRB associated with a compact persistent radio source (PRS). The rotation measure (RM) is found to be larger than $1.8 \times 10^{5} \mathrm{rad} ~\mathrm{m}^{-2}$. In this letter, we argue that FRB 190520B is powered by a young magentar formed by core-collapse of massive stars, embedded in a composite of magnetar wind nebula (MWN) and supernova remnant (SNR). The energy injection of the magnetar drives the MWN and SN ejecta to evolve together, and the PRS is generated by the synchrotron radiation of the MWN. The magnetar has the interior magnetic field $B_{\text{int}}\sim (2-4)\times 10^{16}$ G and the age $t_{\text{age}}\sim 14-22$ yr. The dense SN ejecta and the shocked shell contribute a large fraction of the observed DM and RM. Our model can naturally explain the luminous PRS, decreasing DM and extreme RM of FRB 190520B simultaneously.

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