高能暂现源 · 每日文献综述

The multimessenger observations of GW170817 provided strong evidence that binary neutron star mergers are a site of heavy-element production through the rapid neutron capture process. The decay of unstable r-process nuclei produces a significant number of gamma-rays, which not only power the associated kilonova, but may also be observable in current and future gamma-ray observatories, providing a direct probe of the nuclei synthesized. Current models of the emitted gamma rays link a nuclear reaction network with individual decay spectra. Typically, only the population of the ground state of the nuclei is tracked in the reaction network, and rapid deexcitation of the daughter nuclei is assumed when calculating the decay spectra. This may not be accurate in nuclei where there are longer-lived, high-energy nuclear isomers. In this work, we relax these assumptions, modeling the dynamic behavior of nuclear isomers for a select list of nuclei. These isomers are included as independent states in the network, with temperature-dependent effective transition rates between ground and isomeric states and β-feeding probabilities calculated using the nuclear level structure. We estimate the gamma-ray flux from isomeric transitions, finding that the 743.3 keV line of Nb-97m and the 555.6 keV line of Y-91m may be detectable in gamma-ray observatories such as COSI, AMEGO, and LOX at Galactic distances. These results, calculated for a small fraction of nuclei with isomers, highlight the need for the robust inclusion of nuclear isomers in nuclear reaction networks, as well as careful modeling of the resultant gamma-ray spectroscopy to characterize observational signals.

Fast radio bursts (FRBs) are millisecond-duration radio transients of extragalactic origin, while ultra-high-energy cosmic rays (UHECRs; <inline-formula><mml:math><mml:semantics><mml:mrow><mml:mi>E</mml:mi><mml:mo>≳</mml:mo><mml:msup><mml:mn>10</mml:mn><mml:mn>18</mml:mn></mml:msup></mml:mrow></mml:semantics></mml:math></inline-formula> eV) remain among the most important unresolved problems in astroparticle physics. This review examines the viability of FRBs and their central engines as sources of UHECRs within a comprehensive multi-messenger framework. We summarize the observational constraints on UHECR source populations imposed by the energy spectrum, nuclear composition, anisotropy measurements, diffuse <inline-formula><mml:math><mml:semantics><mml:mi>γ</mml:mi></mml:semantics></mml:math></inline-formula>-ray background, and high-energy neutrino observations, which, together, favor source classes capable of accelerating heavy nuclei with hard injection spectra, modest cosmological evolution, and sufficiently high source densities. We then review the current landscape of FRB progenitor and engine models, including magnetars, supramassive neutron stars, compact-object mergers, and accretion-powered systems, emphasizing their energetics, environments, and particle-acceleration capabilities through relativistic shocks, magnetic reconnection, magnetar wind nebulae, and direct electromagnetic acceleration by ultra-relativistic FRB pulses. We discuss how these scenarios are constrained by neutrino and <inline-formula><mml:math><mml:semantics><mml:mi>γ</mml:mi></mml:semantics></mml:math></inline-formula>-ray observations from IceCube, KM3NeT, and Fermi-LAT, as well as by large-scale UHECR anisotropy measurements from the Pierre Auger Observatory and Telescope Array. Finally, we examine the observational tests that will become possible in the coming decade through large samples of localized FRBs, composition-resolved UHECR measurements, next-generation neutrino observatories, and wide-field <inline-formula><mml:math><mml:semantics><mml:mi>γ</mml:mi></mml:semantics></mml:math></inline-formula>-ray facilities. We emphasize that FRB dispersion and rotation measures provide unique probes of the baryonic and magnetic environments relevant for UHECR acceleration and propagation, enabling a new form of multi-messenger tomography of cosmic-ray source environments and allowing the FRB─UHECR connection to become a quantitatively testable astrophysical framework.