arXiv subjects

S. X. Yi

Publications and source records attributed to S. X. Yi.

16 recordsLinked to original sources

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

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.

astro-ph.CO↗

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

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↗

arXiv2023

Super-Eddington Accretion as a Possible Scenario to Form GW190425

On 2019 April 25, the LIGO/Virgo Scientific Collaboration detected a compact binary coalescence, GW190425. Under the assumption of the binary neutron star (BNS), the total mass of $3.4^{+0.3}_{-0.1}\, M_\odot$ lies five standard deviations away from the known Galactic population mean. In the standard common envelope scenario, the immediate progenitor of GW190425 is a close binary system composed of an NS and a He-rich star. With the detailed binary evolutionary modeling, we find that in order to reproduce GW190425-like events, super-Eddington accretion (e.g., $1,000\,\dot{M}_{\rm Edd}$) from a He-rich star onto the first-born NS with a typical mass of 1.33 $M_\odot$ via stable Case BB mass transfer (MT) is necessarily required. Furthermore, the immediate progenitors should potentially have an initial mass of $M_{\rm ZamsHe}$ in a range of $3.0-3.5$ $M_\odot$ and an initial orbital period of $P_{\rm init}$ from 0.08 days to 0.12 days, respectively. The corresponding mass accreted onto NSs via stable Case BB MT phase varies from $0.70\, M_\odot$ to $0.77\, M_\odot$. After the formation of the second-born NS, the BNSs are expected to be merged due to gravitational wave emission from $\sim$ 11 Myr to $\sim$ 190 Myr.

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arXiv2023

Revisiting the Properties of GW190814 and Its Formation History

GW190814 was reported during LIGO's and Virgo's third observing run with the most asymmetric component masses (a $\sim 23$ $M_{\odot}$ black hole and a $\sim2.6$ $M_{\odot}$ compact object). Under the assumption that this event is a binary black hole (BBH) merger formed through the isolated binary evolution channel, we reanalyze the publicly released data of GW190814 with the modified astrophysical priors on the effective spin $χ_{\rm eff}$, and further explore its formation history using detailed binary modeling. We show that GW190814 is likely to have been formed through the classical common envelope channel. Our findings show that the properties inferred using the modified astrophysical priors are consistent with those inferred by the uniform priors. With the newly-inferred properties of GW190814, we perform detailed binary evolution of the immediate progenitor of the BBH (namely a close binary system composed of a BH and a helium star) in a large parameter space, taking into account mass-loss, internal differential rotation, supernova kicks, and tidal interactions between the helium star and the BH companion. Our findings show that GW190814-like events could be formed in limited initial conditions just after the common envelope phase: a $\sim 23$ $M_{\odot}$ BH and a helium star of $M_{\rm ZamsHe}$ $\sim$ 8.5 $M_{\odot}$ at solar metallicity ($\sim$ 7.5 $M_{\odot}$ at 10\% solar metallicity) with an initial orbital period at around 1.0 day. Additionally, the inferred low spin of the secondary indicates that the required metallicity for reproducing GW190814-like events should not be too low (e.g., Z $\gtrsim$ 0.1 $Z_{\odot}$).

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arXiv2023

A simulation study on the constraints of the Hubble constant using sub-threshold GW observation on double neutron star mergers

Gravitational waves observation with electromagnetic counterparts provides an approach to measure the Hubble constant which is also known as the bright siren method. Great hope has been put into this method to arbitrate the Hubble tension. In this study, we apply the simulation tool \GWT\, and modeling of the aLIGO-design background to simulate the bright siren catalogues of sub-threshold double neutron star mergers with potential contamination from noise and dis-pairing between gravitational waves and electromagnetic counterparts. The Hubble constant and other cosmology parameters are thus inferred from the simulated catalogues with a Bayesian method. From our simulation study, we reach the following conclusions: 1) the measurement error of the $H_0$ decreases with a lower signal-to-noise ratio threshold (or equivalently the $P_{\rm astro}$) in the region where $P_{\rm astro} \gtrsim $ 0.1, while the inferred most probable $H_0$ trends to bias towards larger values; and 2) other higher order cosmological parameters such as $Ω_{m}$ remain unconstrained even with the sub-threshold catalogues. We also discuss adding the network of the gravitational wave detectors to the simulation tool and the electromagnetic counterparts follow-up efficiency simulation, which will improve our work in the future.

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arXiv2020

The rarity of repeating fast radio bursts from binary neutron star mergers

Fast radio bursts (FRBs) are extragalactic, bright pulses of emission at radio frequency with milliseconds duration. Observationally, FRBs can be divided into two classes, repeating FRBs and non-repeating FRBs. At present, twenty repeating FRBs have been discovered with unknown physical origins. Localization of the first repeating FRB 121102 and discovery of an associated persistent radio source support that FRBs are powered by young millisecond magnetars, which could be formed by core-collapses of massive stars or binary neutron stars mergers. These two formation channels can be distinguished by gravitational waves generated by binary neutron stars mergers. We first calculate the lower limit of the local formation rate of repeating FRBs observed by the Canadian Hydrogen Intensity Mapping Experiment (CHIME) . Then we show that only a small fraction ($6\%$) of repeating FRBs is produced by young magnetars from binary neutron star mergers, basing on the gravitational wave detections by the third observing run (O3) of Advanced LIGO/Virgo gravitational-wave detectors. Therefore, we believe that repeating FRBs are more likely produced by the magnetars newborn from the core-collapses of massive stars rather than the magnetars from the binary neutron stars mergers.

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arXiv2019

Modelling the multi-wavelength emissions from PSR B1259-63/LS 2883: the effects of the stellar disc on shock radiations

PSR B1259-63/LS 2883 is an elliptical pulsar/Be star binary and emits broadband emissions from radio to TeV $γ$-rays. The massive star possesses an equatorial disc, which is inclined with the orbital plane of the pulsar. The non-thermal emission from the system is believed to be produced by the pulsar wind shock and the double-peak profiles in the X-ray and TeV $γ$-ray light curves are related to the phases of the pulsar passing through the disc region of the star. In this paper, we investigate the interactions between the pulsar wind and stellar outflows, especially with the presence of the disc, and present a multi-wavelength modelling of the emission from this system. We show that the double-peak profiles of X-ray and TeV $γ$-ray light curves are caused by the enhancements of the magnetic field and the soft photons at the shock during the disc passages. As the pulsar is passing through the equatorial disc, the additional pressure of the disc pushes the shock surface closer to the pulsar, which causes the enhancement of magnetic field in the shock, and thus increases the synchrotron luminosity. The TeV $γ$-rays due to the inverse-Compton (IC) scattering of shocked electrons with seed photons from the star is expected to peak around periastron which is inconsistent with observations. However, the shock heating of the stellar disc could provide additional seed photons for IC scattering during the disc passages, and thus produces the double-peak profiles as observed in the TeV $γ$-ray light curve. Our model can possibly be examined and applied to other similar gamma-ray binaries, such as PSR J2032+4127/MT91 213, HESS J0632+057, and LS I+61$^{\circ}$303.

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arXiv2014

Universal Behavior of X-ray Flares from Black Hole Systems

X-ray flares have been discovered in black hole systems, such as gamma-ray bursts, the tidal disruption event Swift J1644+57, the supermassive black hole Sagittarius A$^*$ at the center of our Galaxy, and some active galactic nuclei. Their occurrences are always companied by relativistic jets. However, it is still unknown whether there is a physical analogy among such X-ray flares produced in black hole systems spanning nine orders of magnitude in mass. Here we report the observed data of X-ray flares, and show that they have three statistical properties similar to solar flares, including power-law distributions of energies, durations, and waiting times, which both can be explained by a fractal-diffusive self-organized criticality model. These statistical similarities, together with the fact that solar flares are triggered by a magnetic reconnection process, suggest that all of the X-ray flares are consistent with magnetic reconnection events, implying that their concomitant relativistic jets may be magnetically dominated.

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arXiv2014

Similar radiation mechanism in gamma-ray bursts and blazars: evidence from two luminosity correlations

Active galactic nuclei (AGNs) and gamma-ray bursts (GRBs) are powerful astrophysical events with relativistic jets. In this Letter the broadband spectral properties are compared between GRBs and the well-observed blazars. The distribution of GRBs are consistent with the well-known blazar sequence including the $νL_ν(5\rm GHz)-α_{\rm RX}$ and $νL_ν(5\rm GHz)-ν_{\rm peak}$ correlations, where $α_{\rm RX}$ is defined as the broadband spectral slope in radio-to-X-ray bands, and $ν_{\rm peak}$ is defined as the spectral peak frequency. Moreover, GRBs occupy the low radio luminosity end of these sequences. These two correlations suggest that GRBs could have a similar radiation process with blazars both in the prompt emission and afterglow phases, i.e., synchrotron radiation.

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arXiv2014

X-Ray Afterglow Plateaus of Long Gamma-Ray Bursts: Further Evidence for Millisecond Magnetars

Many long-duration gamma-ray bursts (GRBs) were observed by {\it Swift}/XRT to have plateaus in their X-ray afterglow light curves. This plateau phase has been argued to be evidence for long-lasting activity of magnetar (ultra-strongly magnetized neutron stars) central engines. However, the emission efficiency of such magnetars in X-rays is still unknown. Here we collect 24 long GRB X-ray afterglows showing plateaus followed by steep decays. We extend the well-known relationship between the X-ray luminosity ${L_{\mathrm{X}}}$ and spin-down luminosity $L_{\mathrm{sd}}$ of pulsars to magnetar central engines, and find that the initial rotation period $P_{0}$ ranges from 1 ms to 10 ms and that the dipole magnetic field $B$ is centered around $10^{15}$ G. These constraints not only favor the suggestion that the central engines of some long GRBs are very likely to be rapidly rotating magnetars but also indicate that the magnetar plateau emission efficiency in X-rays is close to 100%.

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