More Like this

1. Nonthermal Signatures of Radiative Supernova Remnants

   https://doi.org/10.3847/1538-4357/ad74f0  

   Diesing, Rebecca; Guo_郭, Minghao 明浩; Kim, Chang-Goo; Stone, James; Caprioli, Damiano (October 2024, The Astrophysical Journal)

   Abstract The end of supernova remnant (SNR) evolution is characterized by a so-called “radiative” stage, in which efficient cooling of the hot bubble inside the forward shock slows expansion, leading to eventual shock breakup. Understanding SNR evolution at this stage is vital for predicting feedback in galaxies, since SNRs are expected to deposit their energy and momentum into the interstellar medium at the ends of their lives. A key prediction of SNR evolutionary models is the formation at the onset of the radiative stage of a cold, dense shell behind the forward shock. However, searches for these shells via their neutral hydrogen emission have had limited success. We instead introduce an independent observational signal of shell formation arising from the interaction between nonthermal particles accelerated by the SNR forward shock (cosmic rays) and the dense shell. Using a semi-analytic model of particle acceleration based on state-of-the-art simulations coupled with a high-resolution hydrodynamic model of SNR evolution, we predict the nonthermal emission that arises from this interaction. We demonstrate that the onset of the radiative stage leads to nonthermal signatures from radio to gamma rays, including radio and gamma-ray brightening by nearly 2 orders of magnitude. Such a signature may be detectable with current instruments, and will be resolvable with the next generation of gamma-ray telescopes (namely, the Cherenkov Telescope Array). 

   more » « less
2. Radiative energy and mass shifts of quantum cyclotron states

   https://doi.org/10.1140/epjd/s10053-025-00982-3  

   Jentschura, U D (April 2025, The European Physical Journal D)

   AbstractWe discuss relativistic and radiative corrections to the energies of quantum cyclotron states. In particular, it is shown analytically that the leading logarithmic radiative (self-energy) correction to the bound-state energy levels of quantum cyclotron states is state independent and must be interpreted as a magnetic field-dependent correction to the electron’s mass in a Penning trap. Graphical abstract 

   more » « less
3. Stochastic Averaging of Radiative Transfer Coefficients for Relativistic Electrons

   https://doi.org/10.3847/1538-4357/ad4636  

   Mościbrodzka, Monika; Gammie, Charles F (June 2024, The Astrophysical Journal)

   Abstract Synchrotron emissivities, absorptivities, and Faraday rotation and conversion coefficients are needed in modeling a variety of astrophysical sources, including Event Horizon Telescope (EHT) sources. We develop a method for estimating transfer coefficients that exploits their linear dependence on the electron distribution function, decomposing the distribution function into a sum of parts each of whose emissivity can be calculated easily. We refer to this procedure as stochastic averaging and apply it in two contexts. First, we use it to estimate the emissivity of an isotropicκdistribution function with a high-energy cutoff. The resulting coefficients can be evaluated efficiently enough to be used directly in ray-tracing calculations, and we provide an example calculation. Second, we use stochastic averaging to assess the effect of subgrid turbulence on the volume-averaged emissivity and along the way provide a prescription for a turbulent emissivity. We find that for parameters appropriate to EHT sources turbulence reduces the emissivity slightly. In the infrared, turbulence can dramatically increase the emissivity. 

   more » « less
4. Magnetic Webs in Stellar Radiative Zones

   https://doi.org/10.3847/2041-8213/adefda  

   Skoutnev, Valentin A; Beloborodov, Andrei M (August 2025, The Astrophysical Journal Letters)

   Abstract Rotational evolution of stellar radiative zones is an old puzzle. We argue that angular momentum transport by turbulent processes induced by differential rotation is insufficient, and propose that a key role is played by “magnetic webs.” We define magnetic webs as stable magnetic configurations that enforce corotation of their coupled mass shells, and discuss their resistance to differential torques that occur in stars. Magnetic webs are naturally expected in parts of radiative zones that were formerly convective, retaining memory of extinguished dynamos. For instance, red giants with moderate massesM ≳ 1.3M_⊙likely contain a magnetic web deposited on the main sequence during the retreat of the central convective zone. The web couples the helium core to the hydrogen envelope of the evolving red giant and thus reduces spin-up of the contracting core. The magnetic field and the resulting slower rotation of the core are both consistent with asteroseismic observations, as we illustrate with a stellar evolution model with mass 1.6M_⊙. Evolved massive stars host more complicated patterns of convective zones that may leave behind many webs, transporting angular momentum toward the surface. Efficient web formation likely results in most massive stars dying with magnetized and slowly rotating cores. 

   more » « less
5. Monster Radiative Shocks in the Perturbed Magnetospheres of Neutron Stars

   https://doi.org/10.3847/1538-4357/acf659  

   Beloborodov, Andrei M (December 2023, The Astrophysical Journal)

   Abstract Magnetospheres of neutron stars can be perturbed by star quakes, interaction in a binary system, or sudden collapse of the star. The perturbations are typically in the kilohertz band and excite magnetohydrodynamic waves. We show that compressive magnetospheric waves steepen into monster shocks, possibly the strongest shocks in the Universe. The shocks are radiative, i.e., the plasma energy is radiated before it crosses the shock. As the kilohertz wave with the radiative shock expands through the magnetosphere, it produces a bright X-ray burst. Then, it launches an approximately adiabatic blast wave, which will expand far from the neutron star. These results suggest a new mechanism for X-ray bursts from magnetars and support the connection of magnetar X-ray activity with fast radio bursts. Similar shocks may occur in magnetized neutron-star binaries before they merge, generating an X-ray precursor of the merger. Powerful radiative shocks are also predicted in the magnetosphere of a neutron star when it collapses into a black hole, producing a bright X-ray transient. 

   more » « less