ArXiv Paper Digest

Fast radio bursts (FRBs) are widely considered to be associated with magnetars, motivated by the detection of an FRB-like radio burst from the Galactic magnetar SGR~1935+2154. However, constraining the magnetic field strength of extragalactic FRB sources remains challenging. In this work, we develop a Bayesian framework that models FRB time--energy sequences as a marked point process, combining burst waiting-time statistics with energy distributions to quantify the magnetic field strengths required to sustain the observed bursting activity under the magnetar powered scenario. Applying this method to a sample of repeating FRBs, we derive constraints on their magnetic fields by incorporating an empirical prior on the radio emission efficiency calibrated from the Galactic event. Under a conservative assumption for the activity duty cycle, most sources require magnetic energy reservoirs consistent with magnetar strength fields, with characteristic field strengths of order $10^{13}$--$10^{15}$ G, although the constraints remain sensitive to the poorly known efficiency and duty-cycle parameters. FRB~20200120E provides an interesting case with a substantially lower field requirement, highlighting the importance of source environment and evolutionary history in interpreting FRB activity. Our framework provides a statistical approach for connecting transient burst properties with magnetic energy reservoirs, with potential applications to FRBs and other magnetically powered transients.

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 \(σ_{\mathrm{RM}}\)---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 \(σ_{\mathrm{RM}}\), 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 \(σ_{\mathrm{RM}} \gtrsim 1\ \mathrm{rad\,m^{-2}}\), 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 \(σ_{\mathrm{RM}} \gtrsim 5\ \mathrm{rad\,m^{-2}}\). 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 \(σ_{\mathrm{RM}}\) measurements, and substantially deepen our understanding of FRB environments.

We use measurements of the time-dependent dispersion measure of the repeating FRB 121102, together with earlier radio observations of its associated persistent radio source (PRS), to derive stringent constraints on its underlying ``engine.'' The energy held by the relativistic PRS plasma is $>10^{49.5}$ erg, and its age is $\approx60$ yr, corresponding to an underlying source power exceeding $10^{40}$ erg s$^{-1}$. If the underlying source is a neutron star, this implies a rotational rather than a magnetic energy source, consistent with a $\sim10$ ms, $\sim10^{12.5}$ G neutron star. Alternatively, accretion may also be a viable energy source. The velocity and the kinetic energy of the cold plasma confining the relativistic PRS plasma are inconsistent with it being typical supernova ejecta (unless a significant fraction of the ejecta mass is carried by high-density clumps of $\approx10^{-2.5}$ fractional size)- its expansion speed is limited to a few hundred km/s, which also implies that it was ejected from the source more than $\approx 10^3$ yr preceding the onset of relativistic PRS plasma emission. These constraints may be satisfied by a white dwarf binary merger progenitor system, where a fraction of a solar mass was ejected at a slow speed during and after the merger, and a rapidly rotating neutron star was formed after $\sim10^3$ yr thermal evolution period of the merger remnant.

A significant fraction of millisecond pulsars (MSPs) in globular clusters (GCs) are observed as isolated objects, despite the widely accepted scenario in which MSPs are formed through recycling in compact binary systems. The origin of these isolated objects therefore remains an open problem. In this Letter, we propose a physically motivated encounter rate per binary, $Λ\propto n a/(σa_H)$, incorporating the local stellar density $n$, velocity dispersion $σ$, binary separation $a$, and the Heggie--Hills ionization radius $a_H$. Combined with companion ablation by the MSP, this rate successfully predicts the observed fraction of isolated MSPs in GCs, that is $\mathcal{F}_i \proptoΛ\propto a_H^{-1}$, establishing dynamical ionization as the primary channel for producing isolated MSPs. We quantitatively test this model against a null hypothesis in which $\mathcal{F}_i$ is independent of $a_H$, and find that the ionization-driven model is 220 times more likely than the null hypothesis. Our framework naturally explains the observed overabundance of isolated MSPs in $ω$ Centauri and establishes binary ionization as the primary mechanism responsible for the production of isolated MSPs in GCs.

We investigate potential sources of ultrahigh-energy cosmic rays (UHECRs) and their acceleration mechanisms, focusing on astrophysical phenomena associated with massive stellar deaths and supermassive black holes. These phenomena include gamma-ray bursts (GRBs), engine-driven supernovae/hypernovae, magnetars, newly born pulsars, binary neutron star mergers (BNS), tidal disruption events (TDEs), and active galactic nuclei (AGN). While high-luminosity GRBs (HL GRBs) are constrained as UHECR sources by high-energy neutrino observations, low-luminosity GRBs (LL GRBs) and engine-driven supernovae remain promising candidates, with intermediate-mass nuclei as the dominant components. Compact binary mergers and $r$-process nucleosynthesis in neutron-rich environments may also contribute to ultraheavy UHECRs. The composition of UHECRs from TDEs depends on the properties of the disrupted stars. AGN, particularly radio galaxies, remain promising sources, with acceleration occurring in their large-scale jets and lobes. Shear acceleration mechanisms have been proposed as a viable alternative for accelerating UHECRs, involving the re-acceleration of low-energy cosmic rays and being compatible with the observed spectrum and composition. Future multi-messenger observations, especially from upcoming observatories, are expected to provide critical data to refine our understanding of UHECR origins, test existing models, and explore new acceleration mechanisms.