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ABSTRACT We reconsider the escape of high-brightness coherent emission of fast radio bursts (FRBs) from magnetars’ magnetospheres, and conclude that there are numerous ways for the powerful FRB pulse to avoid non-linear absorption. Sufficiently strong surface magnetic fields, $$\ge 10{{\ \rm per\ cent}}$$ of the quantum field, limit the waves’ non-linearity to moderate values. For weaker fields, the electric field experienced by a particle is limited by a combined ponderomotive and parallel-adiabatic forward acceleration of charges by the incoming FRB pulse along the magnetic field lines newly opened during FRB/coronal mass ejection. As a result, particles surf the weaker front part of the pulse, experiencing low radiative losses, and are cleared from the magnetosphere for the bulk of the pulse to propagate. We also find that initial mildly relativistic radial plasma flow further reduces losses. 

Abstract We point out the dominant importance of plasma injection effects of relativistic winds from pulsars and black holes. We demonstrate that outside the light cylinder, the magnetically dominated outflows sliding along the helical magnetic field move nearly radially with very large Lorentz factors,γ₀≫ 1, imprinted into the flow during pair production within the gaps. Only at larger distances,r≥γ₀(c/Ω), does MHD acceleration Γ ∝rtake over. As a result, Blandford–Znajek (BZ)-driven outflows produce spine-brightened images. The best-resolved case of the jet in M87 shows both edge-brightened features, as well as weaker spine-brightened features. Only the spine-brightened component can be BZ driven/originate from the black hole's magnetosphere. 

We first derive a set of equations describing general stationary configurations of relativistic force-free plasma, without assuming any geometric symmetries. We then demonstrate that electromagnetic interaction of merging neutron stars is necessarily dissipative due to the effect of electromagnetic draping—creation of dissipative regions near the star (in the single magnetized case) or at the magnetospheric boundary (in the double magnetized case). Our results indicate that even in the single magnetized case we expect that relativistic jets (or "tongues") are produced, with correspondingly beamed emission pattern. 

ABSTRACT We study dynamics of relativistic coronal mass ejections (CMEs), from launching by shearing of foot-points (either slowly – the ‘Solar flare’ paradigm, or suddenly – the ‘star quake’ paradigm), to propagation in the preceding magnetar wind. For slow shear, most of the energy injected into the CME is first spent on the work done on breaking through the overlaying magnetic field. At later stages, sufficiently powerful CMEs may lead to the ‘detonation’ of a CME and opening of the magnetosphere beyond some equipartition radius req, where the decreasing energy of the CME becomes larger than the decreasing external magnetospheric energy. Post-CME magnetosphere relaxes via the formation of a plasmoid-mediated current sheet, initially at ∼req, and slowly reaching the light cylinder. Both the location of the foot-point shear and the global magnetospheric configuration affect the frequent/weak versus rare/powerful CME dichotomy – to produce powerful flares, the slow shear should be limited to field lines that close in near the star. After the creation of a topologically disconnected flux tube, the tube quickly (at ∼ the light cylinder) comes into force-balance with the preceding wind and is passively advected/frozen in the wind afterward. For fast shear (a local rotational glitch), the resulting large amplitude Alfvén waves lead to the opening of the magnetosphere (which later recovers similarly to the slow shear case). At distances much larger than the light cylinder, the resulting shear Alfvén waves propagate through the wind non-dissipatively. 

ABSTRACT J191213.72 − 441045.1 is a binary system composed of a white dwarf and an M-dwarf in a 4.03-h orbit. It shows emission in radio, optical, and X-ray, all modulated at the white dwarf spin period of 5.3 min, as well as various orbital sideband frequencies. Like in the prototype of the class of radio-pulsing white dwarfs, AR Scorpii, the observed pulsed emission seems to be driven by the binary interaction. In this work, we present an analysis of far-ultraviolet spectra obtained with the Cosmic Origins Spectrograph at the Hubble Space Telescope, in which we directly detect the white dwarf in J191213.72 − 441045.1. We find that the white dwarf has a temperature of Teff = 11485 ± 90 K and mass of 0.59 ± 0.05 M⊙. We place a tentative upper limit on the magnetic field of ≈50 MG. If the white dwarf is in thermal equilibrium, its physical parameters would imply that crystallization has not started in the core of the white dwarf. Alternatively, the effective temperature could have been affected by compressional heating, indicating a past phase of accretion. The relatively low upper limit to the magnetic field and potential lack of crystallization that could generate a strong field pose challenges to pulsar-like models for the system and give preference to propeller models with a low magnetic field. We also develop a geometric model of the binary interaction which explains many salient features of the system. 

Abstract We present JWST observations of the Crab Nebula, the iconic remnant of the historical SN 1054. The observations include NIRCam and MIRI imaging mosaics plus MIRI/MRS spectra that probe two select locations within the ejecta filaments. We derive a high-resolution map of dust emission and show that the grains are concentrated in the innermost, high-density filaments. These dense filaments coincide with multiple synchrotron bays around the periphery of the Crab's pulsar wind nebula (PWN). We measure synchrotron spectral index changes in small-scale features within the PWN’s torus region, including the well-known knot and wisp structures. The index variations are consistent with Doppler boosting of emission from particles with a broken power-law distribution, providing the first direct evidence that the curvature in the particle injection spectrum is tied to the acceleration mechanism at the termination shock. We detect multiple nickel and iron lines in the ejecta filaments and use photoionization models to derive nickel-to-iron abundance ratios that are a factor of 3–8 higher than the solar ratio. We also find that the previously reported order-of-magnitude higher Ni/Fe values from optical data are consistent with the lower values from JWST when we reanalyze the optical emission using updated atomic data and account for local extinction from dust. We discuss the implications of our results for understanding the nature of the explosion that produced the Crab Nebula and conclude that the observational properties are most consistent with a low-mass Fe core-collapse supernova, even though an electron-capture explosion cannot be ruled out. 

Abstract We consider the propagation of polarization in the inner parts of pair-symmetric magnetar winds, close to the light cylinder. Pair plasmas in magnetic field is birefringent, a ∝ B 2 effect. As a result, such plasmas work as phase retarders: Stokes parameters follow a circular trajectory on the Poincare sphere. In the highly magnetized regime, ω , ω p ≪ ω B , the corresponding rotation rates are independent of the magnetic field. A plasma screen with dispersion measure DM ∼ 10 −6 pc cm −3 can induce large polarization changes, including large effective rotation measures (RMs). The frequency scaling of the (generalized) RM, ∝ λ α , mimics the conventional RM with α = 2 for small phase shifts, but can be as small as α = 1. In interpreting observations, the frequency scaling of polarization parameters should be fitted independently. The model offers explanations for (i) the large circular polarization component observed in FRBs, with right–left switching; (ii) large RM, with possible sign changes (when the observation bandwidth is small); and (iii) time-dependent variable polarization. A relatively dense and slow wind is needed—the corresponding effect in regular pulsars is small. 

Abstract Magnetars, the likely sources of Fast Radio Bursts (FRBs), produce both steady highly relativistic magnetized winds, and occasional ejection events. We demonstrate that the requirement of conservation of the magnetic flux dominates the overall dynamics of magnetic explosions. This is missed in conventional hydrodynamic models of the ejections as expanding shell with parametrically added magnetic field, as well as one-dimensional models of magnetic disturbances. Magnetic explosions from magnetars come into force balance with the pre-flare wind close to the light cylinder. They are then advected quietly with the wind, or propagate as electromagnetic disturbances. No powerful shock waves are generated in the wind. 

ABSTRACT We find a class of twisted and differentially rotating neutron star magnetospheres that do not have a light cylinder, generate no wind, and thus do not spin-down. The magnetosphere is composed of embedded differentially rotating flux surfaces, with the angular velocity decreasing as Ω ∝ 1/r (equivalently, becoming smaller at the foot-points closer to the axis of rotation). For each given North–South self-similar twist profile there is a set of self-similar angular velocity profiles (limited from above) with a ‘smooth’, dipolar-like magnetic field structure extending to infinity. For spin parameters larger than some critical value, the light cylinder appears, magnetosphere opens up, and the wind is generated. 

Abstract We consider topological configurations of the magnetically coupled spinning stellar binaries (e.g., merging neutron stars or interacting star–planet systems). We discuss conditions when the stellar spins and the orbital motion nearly “compensate” each other, leading to very slow overall winding of the coupled magnetic fields; slowly winding configurations allow gradual accumulation of magnetic energy, which is eventually released in a flare when the instability threshold is reached. We find that this slow winding can be global and/or local. We describe the topology of the relevant space F = T 1 S 2 as the unit tangent bundle of the two-sphere and find conditions for slowly winding configurations in terms of magnetic moments, spins, and orbital momentum. These conditions become ambiguous near the topological bifurcation points; in certain cases, they also depend on the relative phases of the spin and orbital motions. In the case of merging magnetized neutron stars, if one of the stars is a millisecond pulsar, spinning at ∼10 ms, the global resonance ω 1 + ω 2 = 2Ω (spin-plus beat is two times the orbital period) occurs approximately one second before the merger; the total energy of the flare can be as large as 10% of the total magnetic energy, producing bursts of luminosity ∼10 44 erg s −1 . Higher order local resonances may have similar powers, since the amount of involved magnetic flux tubes may be comparable to the total connected flux.