arXiv subjects

F. Y. Wang

Publications and source records attributed to F. Y. Wang.

At least 19 recordsLinked to original sources

arXiv2026

The propagation-induced circular polarization of fast radio bursts in relativistic plasma

Although the physical origin of fast radio bursts (FRBs) remains unknown, magnetars are the most likely candidates. The polarization properties of FRBs offer crucial insights into their origins and radiation mechanisms. Significant circular polarization (CP) has been observed in some FRBs. CP may result from intrinsic radiation or propagation effects, both within and outside the magnetosphere. Recent observations indicate that polarization properties of FRB 20201124A can change over short timescales (about tens of milliseconds), challenging models that attribute CP to out-of-magnetosphere emission and propagation. Additionally, some magnetospheric radiation models predict that bursts with high CP produced by off-axis emission will be systematically fainter, which contradicts the observations. We propose that CP arises from magnetospheric propagation effects caused by relativistic plasma. We identify the conditions under which high CP occurs, finding it to be rare. Moreover, our model accounts for the more commonly observed low CP and the varying handedness of CP.

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arXiv2026

A unified model of active repeating fast radio bursts associated with persistent radio sources

Fast radio bursts (FRBs) are intense pulses with unknown origins. A subclass of repeating FRBs show some common features, such as associated compact persistent radio sources (PRSs), high burst rates, and large host-galaxy dispersion measures (DMs). Meanwhile, they show diverse DM and rotation measure (RM) variations, which cannot be explained by current models. A unified model urgently needs to be established. Here we show the first evidence for a supernova remnant surrounding the FRB 20190520B source. We then demonstrate that the five active repeating FRB sources associated with PRSs can be understood within a single model in which central objects are young magnetars in massive binary systems embedded in supernova remnants. This model naturally predicts distinct variations of DM and RM for repeating FRBs. Crucially, young magnetar wind nebulae can generate bright PRSs. As a magnetar becomes older, the luminosity of a PRS will fade, which can naturally explain less-luminous PRSs for some active FRBs. Our results support a unified population of active FRBs in dynamic magnetized environments.

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arXiv2026

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

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 persistent radio sources (PRSs) and multi-wavelength emission from magnetar wind nebulae (MWNe) or bow shocks in massive binary systems. We find that the PRSs with luminosity $10^{38}-10^{39}$ erg s$^{-1}$ can be generated by young 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 with the luminosity $\lesssim 10^{36}$ erg s$^{-1}$. Magnetically powered nebulae may yield detectable keV synchrotron self-Compton (SSC) X-rays out to $\lesssim 20$ Mpc, whereas rotation-powered systems mainly produce GeV SSC emission detectable only within $\lesssim 0.1$ Mpc. For active magnetars in massive binaries, enhanced wind interaction can generate synchrotron X-rays detectable within $\lesssim 50$ Mpc and GeV-TeV inverse-Compton emission detectable within $\lesssim 1-0.1$ Mpc.

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arXiv2026

An invariant energy release hierarchy in a repeating fast radio burst

Fast radio bursts (FRBs) are luminous millisecond radio transients whose physical origin remains unsettled. A key diagnostic is whether their burst-energy distributions retain characteristic physical scales that are intrinsic and temporally stable within an individual engine. Here we report a 3.2-year monitoring campaign of the hyperactive repeater FRB~20220529 with FAST and Parkes, yielding more than 1,300 bursts spanning nearly five orders of magnitude in spectral energy density. The cumulative burst-rate distribution is described by an exponential-plus-power-law (EXP+PL) form, linking a low-energy exponential component with characteristic scale (E_0) to a scale-free bright-end tail. This scale remains invariant despite the burst rate declining by more than an order of magnitude, revealing a stable dissipation scale decoupled from the source's macroscopic trigger activity. Within a magnetar interpretation, this phenomenology is consistent with localized sub-critical reconnection episodes coexisting with plasmoid-mediated magnetic avalanches in a twisted magnetosphere. The invariant (E_0) constrains the dissipation region to the inner-to-middle magnetosphere and reveals a robust energy-release hierarchy beneath the variable activity of repeating FRBs, providing an observational benchmark for relativistic reconnection in an ultra-magnetized neutron-star environment.

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arXiv2026

Locating the missing baryons in the warm-hot intergalactic medium with fast radio bursts and the Sunyaev-Zel'dovich effect

Traditional astronomical censuses in the late-time Universe can only account for a fraction of the baryonic matter budget. Hydrodynamical simulations predict that the missing baryons reside in the vast filamentary structures of the cosmic web as a highly diffuse, warm-hot intergalactic medium (WHIM). Observing the WHIM directly has remained a long-standing challenge due to its typical temperature. In this study, we report the first detection of spatial cross-correlations between the dispersion measures (DMs) of fast radio bursts (FRBs) from the second CHIME/FRB catalog and the thermal Sunyaev-Zel'dovich (tSZ) Compton-$y$ map from the Planck satellite. By masking virialized galaxy clusters to isolate the diffuse signal, we find a positive correlation with a probability $>99.77\%$ between FRBs and tSZ maps. Our joint parameter inference constrains the fraction of cosmic baryons in the WHIM to be $f_{\rm WHIM}=0.48$ with a $68\%$ confidence interval of $0.27<f_{\rm WHIM}<0.61$, anchored at a mean WHIM temperature of $2.4 \times 10^6\ {\rm K}$. More rigorous masking strategies confirm the signal originates from the WHIM instead of galaxy clusters. Our result demonstrates that the missing baryons are residing in the diffuse gas within the cosmic web, closing the cosmic baryon budget in the local Universe.

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arXiv2026

Utilizing Dispersion Measure of Fast Radio Bursts to Probe the Intergalactic Medium Turbulence

Extragalactic fast radio bursts (FRBs) have emerged as powerful probes of turbulence within the intergalactic medium (IGM), a phenomenon that plays a crucial role in various cosmological and astrophysical processes. In this study, we employ the structure function (SF) analysis on the dispersion measures (DMs) of over 3,000 FRBs, leveraging the recently released CHIME/FRB Catalog 2 alongside previously observed sources. By comparing our results with mock datasets generated from cosmological simulations, we find excellent agreement at large angular separations. At small angular scales, our findings reveal a potential scaling behavior consistent with a two-dimensional (2D) Kolmogorov power spectrum. From this scaling, we constrain the turbulence outer scale to be on the order of several Mpc, which aligns with theoretical expectations, independent observations of the low-redshift IGM, and cosmological simulations. Ultimately, to conclusively confirm this Kolmogorov-like turbulent cascade and overcome current small-sample statistical limitations, a larger sample of FRBs with sub-arcsecond localization is required.

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arXiv2026

Cosmological evolution of fast radio bursts and its rapid decline relative to star formation rate

Fast radio bursts (FRBs) are enigmatic millisecond-duration radio transients whose physical origins remain debated. To shed light on this, we analyze the CHIME/FRB Catalog 2. By using the probability distribution of dispersion measured (DM) derived from the IllustrisTGN simulation, we compute the pseudo-redshift with $1σ$ error for each FRB. To derive the FRB luminosity function and event rate, we employ a non-parametric statistical method. Building upon Efron-Petrosian method, we find strong luminosity evolution with redshift, well described by $L_0 \propto (1+z)^{6.38}$. After de-evolving this trend, we apply Lynden-Bell's $C^-$ method to derive the comoving FRB formation rate which is found to decline rapidly at high redshift, following $ρ(z) \propto (1+z)^{-5.38 \pm 0.02}$. We also test the robustness of our results by considering the upper and lower limits of pseudo-redshifts, and different flux limits of CHIME. Similar results are found. This steep decline is inconsistent with a direct tracing of the cosmic star formation rate, but closely resembles the redshift evolution of short gamma-ray bursts-systems linked to compact object mergers. Our results support that the origin of FRBs is associated with old populations, such as neutron stars and black holes.

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arXiv2026

The Role of Plasma Lensing in Fast Radio Bursts

Growing evidence indicates that some fast radio bursts (FRBs) reside in dense, magneto-ionic environments where extrinsic propagation effects can substantially reshape the observed signal. Within a 1D Gaussian plasma-lens framework, we show that small, monotonic variations in the incidence angle of the FRB wavefront naturally generate both downward and upward sub-burst frequency drifts. We further demonstrate that distinct lensed paths that probe different rotation measures (RMs), can produce orthogonal polarization-angle (PA) jumps at gigahertz frequencies. In this picture, a $\sim 90^\circ$ PA transition requires only a modest RM contrast of order a few $\times10~\rm{rad~m^{-2}}$ between the multiple images. The chromatic activity of FRB 20180916B-earlier and narrower activity windows at higher frequencies-can be explained as preferential magnification near the outer caustic. Finally, the intrinsic resolution of a plasma lens provides an upper limit on the transverse emission size: lenses located close to the source yield magnetospheric-scale constraints and offer a practical means of discriminating between inner- and outer-magnetospheric emission scenarios. These results suggest that plasma lensing could account for multiple complex observational features of FRBs and may play a non-negligible role in modulating their observable properties.

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arXiv2025

The Hubble Tension resolved by the DESI Baryon Acoustic Oscillations Measurements

The $Λ$ cold dark matter ($Λ$CDM) cosmological model provides a good description of a wide range of astrophysical and cosmological observations. However, severe challenges to the phenomenological $Λ$CDM model have emerged recently, including the Hubble constant tension and the significant deviation from the $Λ$CDM model reported by the Dark Energy Spectroscopic Instrument (DESI) collaboration. Despite many explanations for the two challenges have been proposed, the origins of them are still intriguing mysteries. Here, we investigate the DESI Baryon Acoustic Oscillations (BAOs) measurements to interpret the Hubble constant tension. Employing a non-parametric method, we find that the dark energy equation of state $w(z)$ evolves with redshift from DESI BAO data and type Ia supernovae. From the Friedmann equations, the Hubble constant ($H_0$) is derived from $w(z)$ model-independently. We find that the values of $H_0$ show a descending trend as a function of redshift, and can effectively resolve the Hubble constant tension. Our study finds that the two unexpected challenges to the $Λ$CDM model can be understood in one physical framework, e.g., dynamical dark energy.

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arXiv2025

A Unified Volumetric Rate-Energy Relation from Magnetar Radio Bursts to Fast Radio Bursts

Fast radio bursts (FRBs) are millisecond radio pulses with extremely high bright temperature. Their physical origin is still a mystery. The discovery of FRB 20020428 supports the idea that at least a portion of FRBs is generated by magnetars. However, FRB 20200428 and other radio bursts of SGR 1935+2154 are much less energetic than that of extragalactic FRBs. Thus, whether the progenitors of extragalactic FRBs are magnetars is still in controversy. Here, we investigate the volumetric rates of radio bursts from SGR 1935+2154, non-repeating FRBs and FRB 20180916B using the uniform samples detected by the Canadian Hydrogen Intensity Mapping Experiment (CHIME). We find that they share a similar relation between the volumetric rate $R$ and the burst energy $E$, i.e., $R\propto E^{-γ}$ with $γ=1.31\pm 0.13$ from $10^{29}$ erg to $10^{42}$ erg. Our results support the hypothesis that both repeating and non-repeating FRBs originate from magnetars.

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arXiv2025

Decadal evolution of a repeating fast radio burst source

The origin of fast radio bursts (FRBs), the brightest cosmic radio explosions, is still unknown. Bearing critical clues to FRBs' origin, the long-term evolution of FRBs has yet to be confirmed, since the field is still young and most FRBs were seen only once. Here we report clear evidence of decadal evolution of FRB~20121102A, the first precisely localized repeater. In conjunction with archival data, our FAST and GBT monitoring campaign since 2020 reveals a significant 7% decline of local dispersion measure (DM). The rotation measure (RM) of 30,755$\pm$16 $\mathrm{rad\,m^{-2}}$ detected in the last epoch represents a 70% decrease compared to that from December 2016. The $σ_{RM}$ parameter, which describes the complexity of the magneto-ionic environment surrounding the source, was shown to have decreased by 13%. These general trends reveal an evolving FRB environment, which could originate from an early-phase supernova associated with an enhanced pair wind from the FRB central engine.

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arXiv2025

Calibrating $\rm{DM_{IGM}}-z$ relation using host galaxies of FRBs

Fast radio bursts (FRBs) are extragalactic radio transients that offer valuable insight of intergalactic medium (IGM). However, the dispersion measure (DM) contributed by IGM ($\rm{DM_{IGM}}$) is degenerated with that from the host galaxy ($\rm{DM_{host}}$), necessitating calibration of the $\rm{DM_{IGM}}$$-z$ relation for cosmological applications. As $\rm{DM_{host}}$ is expected to correlate with host galaxy properties, it is feasible to estimate $\rm{DM_{host}}$ from observable host characteristics. In this study, we conduct spectral energy distribution (SED) and Sérsic model fittings to derive the parameters of FRB host galaxies. Then, we examine the correlations between the excess dispersion measure ($\rm{DM_{exc}}$) and host galaxy parameters, including star formation rate (SFR), stellar mass, specific star formation rate (sSFR), inclination angle, and projected area. A tight correlation between $\rm{DM_{exc}}$ and sSFR is found. This correlation is utilized to estimate the $\rm{DM_{host}}$ of FRBs, providing a method to calibrate the DM$_{\rm IGM}-z$ relation. This approach leads to a notable improvement in calibration performance.

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arXiv2025

Measuring Hubble constant using localized and unlocalized fast radio bursts

The Hubble constant ($H_0$) is one of the most important parameters in the standard $\rm ΛCDM$ model. The measurements given by the main two methods show a gap larger than $4σ$, which is known as Hubble tension. Fast radio bursts (FRBs) are extragalactic pulses with durations of milliseconds. They can be used as cosmological probes. We constrain $H_0$ using localized and nonlocalized FRBs. We first used 108 localized FRBs to constrain $H_0$ using the probability distributions of \DMhost and \DMIGM from the IllustrisTNG simulation. Then, we used a Monte Carlo sampling to calculate the pseudo-redshift distributions of 527 nonlocalized FRBs from CHIME observations. The 108 localized FRBs yield a constraint of $H_0=69.40_{-1.97}^{+2.14}$ ${\rm km\ s^{-1} Mpc^{-1}}$, which lies between the early- and late-time values. The constraint of $H_{0}$ from nonlocalized FRBs yields $H_0=68.81_{-0.68}^{+0.68}$ ${\rm km\ s^{-1} Mpc^{-1}}$. This result indicates that the uncertainty on the constraint of $H_0$ drops to $\sim1\%$ when the number of localized FRBs is increased to $\sim500$. These uncertainties only include the statistical error. The systematic errors are also discussed and play a dominant role in the current sample.

astro-ph.CO↗

arXiv2025

A universal break in energy functions of three hyperactive repeating fast radio bursts

Fast radio bursts (FRBs) are millisecond-duration pulses occurring at cosmological distances with a mysterious origin. Observations show that at least some FRBs are produced by magnetars. All magnetar-powered FRB models require some triggering mechanisms, among which the most popular is the crust cracking of a neutron star, which is called starquake. However, so far there has been no decisive evidence for this speculation. Here we report the energy functions of the three most active repeating FRBs, which show a universal break around $10^{38}$ erg. Such a break is similar to that of the frequency-magnitude relationship of earthquakes. The break and change of the power-law indices below and above it can be well understood within the framework of FRBs triggered by starquakes in the magnetar models. The seed of weak FRBs can grow both on the magnetar surface and in the deeper crust. In contrast, the triggering of strong FRBs is confined by the crustal thickness and the seed of strong FRBs can only grow on the surface. This difference in dimensionality causes a break in the scaling properties from weak to strong FRBs, occurring at a point where the penetration depth of starquakes equals the crustal thickness. Our result, together with the earthquake-like temporal properties of these FRBs, strongly supports that FRBs are triggered by starquakes, providing a new opportunity to study the physical properties of the neutron star crust.

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arXiv2025

Uncorrelated estimations of $H_0$ redshift evolution from DESI baryon acoustic oscillation observations

The Dark Energy Spectroscopic Instrument (DESI) collaboration recently released the first year data of baryon acoustic oscillations (BAOs). Based on the five different tracers, the cosmological constraint shows a hint of deviation from the standard $Λ$CDM model. In this letter, we combine the DESI BAOs with other cosmic probes to constrain the evolution of Hubble constant as a function of redshift in the flat $Λ$CDM model. The non-parametric method is used to estimate the value of Hubble constant at different redshift bins. The correlation among different bins are removed by diagonalizing the covariance matrix. The joint data sample demonstrate a decreasing trend of Hubble constant with a significance of $6.4 σ$, which can naturally resolve the Hubble tension. To avoid statistical effects caused by the binning methods, we tested other three different binning methods and also found a decreasing trend. It may be due to dynamical dark energy or modified gravity.

astro-ph.CO↗

arXiv2024

Hints of new physics for the Hubble tension: violation of cosmological principle

Discrepancy between the measurements of Hubble constant $H_{0}$ from the cosmic microwave background (CMB) and the local distance ladder is the most serious challenge to the standard $Λ$CDM model. Recent researches point out that it might be related with the violation of cosmological principle. Here, we investigate the impact of dipole-monopole correction on the constraints of $H_{0}$ utilizing the dipole fitting method based on the $Λ$CDM model and cosmography method. Our results show that the dipole-monopole correction can reduce the constraints of $H_{0}$ from a larger value consistent with SH0ES results to a smaller value consistent with Planck results. This finding can effectively alleviate the Hubble tension. Through making redshift tomography and model-independent analyses, we confirm that our findings are independent of redshift and cosmological model. In addition, the theoretical prediction of $H(z)/(1+z)$ reconstructed by the constraints of $Λ$CDM model with the dipole correction is in agreement with BAOs measurements including 5 DESI BAOs within 1$σ$ range except datapoint at z = 0.51. Our research suggests that the Hubble tension originates from new physics beyond the standard $Λ$CDM model, which might lead to a violation of the cosmological principle.

astro-ph.CO↗

arXiv2024

Sudden polarization angle jumps of the repeating fast radio burst FRB 20201124A

We report the first detection of polarization angle (PA) orthogonal jumps, a phenomenon previously only observed from radio pulsars, from a fast radio burst (FRB) source FRB 20201124A. We find three cases of orthogonal jumps in over two thousand bursts, all resembling those observed in pulsar single pulses. We propose that the jumps are due to the superposition of two orthogonal emission modes that could only be produced in a highly magnetized plasma, and they are caused by the line of sight sweeping across a rotating magnetosphere. The shortest jump timescale is of the order of one-millisecond, which hints that the emission modes come from regions smaller than the light cylinder of most pulsars or magnetars. This discovery provides convincing evidence that FRB emission originates from the complex magnetosphere of a magnetar, suggesting an FRB emission mechanism that is analogous to radio pulsars despite a huge luminosity difference between two types of objects.

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arXiv2024

The formation rate and luminosity function of fast radio bursts

Fast radio bursts (FRBs) are millisecond-duration flashes with unknown origins. Its formation rate is crucial for unveiling physical origins. However, the luminosity and formation rate are degenerated when directly fitting the redshift distribution of FRBs. In contrast to previous forward-fitting methods, we use the Lynden-Bell's $c^{-}$ method to derive luminosity function and formation rate of FRBs without any assumptions. Using the non-repeating FRBs from the first CHIME/FRB catalog, we find a relatively strong luminosity evolution, and luminosity function can be fitted by a broken power-law model with a break at $1.33\times10^{41}\ \mathrm{erg}\ \mathrm{s}^{-1}$. The formation rate declines rapidly as $(1+z)^{-4.9\pm0.3}$ with a local rate $1.13\times10^4\ \mathrm{Gpc}^{-3}\ \mathrm{yr}^{-1}$. This monotonic decrease is similar to the rate of short gamma-ray bursts. After comparing it with star formation rate and stellar mass density, we conclude that the old populations including neutron stars and black holes, are closely related to the origins of FRBs. Monte Carlo simulations are used to test our results. The distributions of mock sample are consistent with the observational data.

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