arXiv subjects

Chenyuan Xu

Publications and source records attributed to Chenyuan Xu.

3 recordsLinked to original sources

arXiv2026

Spectro-Polarimetric Properties of CHIME FRB Sources

Fast radio bursts (FRBs) are enigmatic millisecond-duration radio transients whose polarization properties offer crucial insights into their origins and environments. In particular, low-frequency depolarization---quantified by the parameter $\sigma_{\mathrm{RM}}$---probes the complex magneto-ionic medium surrounding the progenitor, and has been observed across a population of repeating FRBs. We present a systematic spectro-polarimetric analysis of repeating and non-repeating FRBs using observations from the Canadian Hydrogen Intensity Mapping Experiment (CHIME). For 28 repeating FRBs, we measure $\sigma_{\mathrm{RM}}$, expanding the known sample from 14 to 36 sources (an increase by a factor of 2.6). The kernel density estimate (KDE) of the repeating population peaks at $1.3\ \mathrm{rad\,m^{-2}}$, with approximately 70\% of the sources showing $\sigma_{\mathrm{RM}} \gtrsim 1\ \mathrm{rad\,m^{-2}}$, implying that most reside in complex magneto-ionic environments. For 70 non-repeating FRBs, we investigate four spectro-polarimetric models; no source exhibits significant depolarization with $\sigma_{\mathrm{RM}} \gtrsim 5\ \mathrm{rad\,m^{-2}}$. Roughly half of the non-repeaters are consistent with a constant linear polarization fraction across frequency. We caution, however, that these results may be affected by the limited frequency coverage of CHIME. Future ultra-wideband polarimetry, spanning widely separated frequencies, will overcome current observational biases, enable precise $\sigma_{\mathrm{RM}}$ measurements, and substantially deepen our understanding of FRB environments.

astro-ph.HE↗

arXiv2026

The Real and Pseudo Dispersion Measures of FRB~20220912A

Fast radio bursts (FRBs) are millisecond-duration radio transients. As they propagate through the interstellar medium, they interact with free electrons, resulting in dispersion. The corresponding dispersion measure (DM) is referred to as the real DM (DM$_{\rm real}$). In practice, however, the dispersion measure derived from modeling (DM$_{\rm model}$) is often contaminated by intrinsic burst morphology, giving rise to a pseudo DM component (DM$_{\rm pseudo} = {\rm DM}_{\rm model} - {\rm DM}_{\rm real}$). In this work, we focus on the highly active repeating FRB~20220912A and utilize its microshots -- extremely short-duration (typically tens of microseconds), broadband emissions -- to investigate its DM$_{\rm real}$ and DM$_{\rm pseudo}$. We adopt two assumptions: first, that FRB~20220912A resides in a non-magneto-ionic environment and that its DM$_{\rm real}$ variation is smaller than $10^{-2}$\,pc\,cm$^{-3}$ over a few years; and second, that microshots have a negligible intrinsic morphological time delay. By identifying two new microshots and combining them with previously reported ones, we find that all four microshots exhibit remarkably consistent DM values over a one-month timescale, with an average of $219.380 \pm 0.004\,\mathrm{pc\,cm^{-3}}$. We define this value as the DM$_{\rm real}$ of FRB~20220912A. We further show that bright, narrow bursts with a width of less than 2\,ms also yield DM estimates consistent with the microshot-based DM$_{\rm real}$. A survey of five repeating FRBs reveals that DM$_{\rm pseudo}$ is a common phenomenon, with variations typically spanning a range of approximately $10\,\mathrm{pc\,cm^{-3}}$ at 1.2\,GHz. These findings highlight the importance of accounting for morphological contributions in DM interpretation and demonstrate that microshots and narrow bursts are powerful tools for probing DM$_{\rm real}$.

astro-ph.HE↗

arXiv2025

Refined Constraints on the Hubble Constant from Localized FRBs with Assessment of Systematic Effects

The dispersion measure-redshift relation of fast radio bursts (FRBs) provides a valuable cosmological probe for constraining the Hubble constant, offering an independent measurement that could help resolve the ongoing Hubble tension. In this paper, we begin with a sample of 117 localized FRBs and use 95 of them to constrain $H_0$ to $71.28^{+1.90}_{-2.08}$ km s$^{-1}$ Mpc$^{-1}$ within the standard Lambda Cold Dark Matter ($Λ$CDM) model. The resulting statistical uncertainty is below 2.8\%, improving previous FRB-based measurements and highlighting the promise of larger future samples. Beyond statistical improvements, we note that different parameter choices have been adopted in previous studies and some results show discrepancies in $H_0$. To address this issue, we perform a systematic assessment of modeling uncertainties that can affect the inferred value of $H_0$, including Galactic electron density models, the contribution of the Galactic halo, outliers such as FRB~20190520B located in extreme environments, and the other parameter selections. We also discuss possible approaches to mitigate these sources of uncertainty, emphasizing both the challenges and prospects of using FRBs as reliable cosmological tools.

astro-ph.CO↗