arXiv subjects

Maxim Lyutikov

Publications and source records attributed to Maxim Lyutikov.

At least 37 records · Page 2Linked to original sources

arXiv2024

3D Relativistic MHD simulations of the gamma-ray binaries

In gamma-ray binaries neutron star is orbiting a companion that produces a strong stellar wind. We demonstrate that observed properties of "stellar wind"-"pulsar wind" interaction depend both on the overall wind thrust ratio, as well as more subtle geometrical factors: the relative direction of the pulsar's spin, the plane of the orbit, the direction of motion, and the instantaneous line of sight. Using fully 3D relativistic magnetohydrodynamical simulations we find that the resulting intrinsic morphologies can be significantly orbital phase-dependent: a given system may change from tailward-open to tailward-closed shapes. As a result, the region of unshocked pulsar wind can change by an order of magnitude over a quarter of the orbit. We calculate radiation maps and synthetic light curves for synchrotron (X-ray) and Inverse-Compton emission (GeV-TeV), taking into account $γ-γ$ absorption. Our modeled light curves are in agreement with the phase-dependent observed light curves of LS5039.

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arXiv2024

Dissecting the Crab Nebula with JWST: Pulsar wind, dusty filaments, and Ni/Fe abundance constraints on the explosion mechanism

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 IFU 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 iron-core-collapse supernova, even though an electron-capture explosion cannot be ruled out.

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arXiv2024

Linear to circular conversion in the polarized radio emission of a magnetar

Radio emission from magnetars provides a unique probe of the relativistic, magnetized plasma within the near-field environment of these ultra-magnetic neutron stars. The transmitted waves can undergo birefringent and dispersive propagation effects that result in frequency-dependent conversions of linear to circularly polarized radiation and vice-versa, thus necessitating classification when relating the measured polarization to the intrinsic properties of neutron star and fast radio burst (FRB) emission sites. We report the detection of such behavior in 0.7-4 GHz observations of the P = 5.54 s radio magnetar XTE J1810$-$197 following its 2018 outburst. The phenomenon is restricted to a narrow range of pulse phase centered around the magnetic meridian. Its temporal evolution is closely coupled to large-scale variations in magnetic topology that originate from either plastic motion of an active region on the magnetar surface or free precession of the neutron star crust. Our model of the effect deviates from simple theoretical expectations for radio waves propagating through a magnetized plasma. Birefringent self-coupling between the transmitted wave modes, line-of-sight variations in the magnetic field direction and differences in particle charge or energy distributions above the magnetic pole are explored as possible explanations. We discuss potential links between the immediate magneto-ionic environments of magnetars and those of FRB progenitors.

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arXiv2024

Free electron laser in magnetically dominated regime: simulations with ONEDFEL code

Using the ONEDFEL code we perform Free Electron Laser simulations in the astrophysically important guide-field dominated regime. For wigglers' (Alfven waves) wavelengths of tens of meters and beam Lorentz factor $\sim 10^3$, the resulting coherently emitted waves are in the centimeter range. Our simulations show a growth of the wave intensity over fourteen orders of magnitude, over the astrophysically relevant scale of $\sim$ few kilometers. The signal grows from noise (unseeded). The resulting spectrum shows fine spectral sub-structures, reminiscent of the ones observed in Fast Radio Bursts (FRBs).

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arXiv2023

Jump-starting relativistic flows, and the M87 jet

We point out the dominant importance of plasma injection effects for relativistic winds from pulsars and black holes. We demonstrate that outside the light cylinder the magnetically dominated outflows while sliding along the helical magnetic field move in fact nearly radially with very large Lorentz factors $γ_0 \gg 1 $, imprinted into the flow during pair production within the gaps. Only at larger distances, $r \geq γ_0 (c/Ω)$, the MHD acceleration $Γ\propto r$ takes over. As a result, Blandford-Znajek (BZ) driven outflows would produce spine-brightened images. The best-resolved case of the jet in M87 shows both bright edge-brightened features, as well as weaker spine-brightened feature. Only the spine-brightened component can be BZ-driven/originate from the BH's magnetosphere.

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arXiv2023

Unveiling the white dwarf in J191213.72-441045.1 through ultraviolet observations

J191213.72-441045.1 is a binary system composed of a white dwarf and an M-dwarf in a 4.03-hour 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 an effective temperature of 11485+/-90 K and mass of 0.59+/-0.05 solar masses. 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 crystallisation 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 crystallisation 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.

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arXiv2023

Escaping of Fast Radio Bursts

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 nonlinear absorption. Sufficiently strong surface fields, $\geq 10\%$ 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 (CME). 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: (i) for propagation across magnetic field, the O-mode suffers much smaller dissipation than the X-mode; (ii) quasi-parallel propagation suffers minimal dissipation; (iii) initial mildly relativistic radial plasma flow further reduces losses; (iv) for oblique propagation of a pulse with limited transverse size, the leading part of the pulse would ponderomotively sweep the plasma aside.

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arXiv2023

Relativistic coronal mass ejections from magnetars

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 over-laying magnetic field. At later stages, sufficiently powerful CMEs may experience ``detonation" and lead to opening of the magnetosphere beyond some equipartition radius $r_{eq}$, where the energy of the CME becomes larger than the decreasing external magnetospheric energy. Post-CME magnetosphere relaxes via formation of a plasmoid-mediated current sheet, initially at $\sim r_{eq}$ and slowly reaching the light cylinder (this transient stage has much higher spindown rate and may produce an ``anti-glitch''). Both the location of the foot-point shear and the global magnetospheric configuration affect the frequent-and-weak versus rare-and-powerful CME dichotomy - to produce powerful flares the slow shear should be limited to field lines that close near the star. After the creation of a topologically disconnected flux tube, the tube quickly (at $\sim$ 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 Alfven waves lead to opening of the magnetosphere (which later recovers similarly to the slow shear case). At distances much larger than the light cylinder, the resulting shear Alfven waves propagate through the wind non-dissipatively. Implications to Fast Radio Bursts are discussed.

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arXiv2023

Centrifugal barriers in magnetospheric accretion

We reconsider the dynamics of accretion flows onto magnetized central star. For dipolar magnetically aligned case, the centrifugal barrier is at $R_{cb} = (2/3)^{1/3} R_c = 0.87 R_c$, where $R_c= ( G M/Ω^2)^{1/3}$ is the corotation radius. For oblique dipole direct accretion from the corotation radius $R_c$ is possible only for magnetic obliquity satisfying $\tan θ_μ\geq 1/( 2 \sqrt{3}) $ ($θ_μ\geq 16.1^\circ $). The accretion proceeds in a form of funnel flows - along two streams centered on the $μ-Ω$ plane, with azimuthal opening angle $ \cos (Δϕ) = { \cot^ 2 {θ_μ} }/{12} $. For the magnetosphere distorted by the diamagnetic disk, the centrifugal barrier can be at as small radius as $R_{cb}= 0.719 R_c$ for the fully confined dipole, extending out to $R_{cb} \sim R_c$ for the magnetically balanced case. Type-II X-ray bursts in accreting neutron stars may be mediated by the centrifugal barrier; this requires nearly aligned configuration. Centrifugally-barriered material trapped in the magnetosphere may lead to periodic obscuration ("dips") in the light curve of the host star, e.g., as observed in accreting young stellar objects and X-ray binaries.

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arXiv2022

Electromagnetic draping of merging neutron stars

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.

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arXiv2022

Radius-to-frequency mapping and FRB frequency drifts

We build a model of radius-to-frequency mapping in magnetospheres of neutron stars and apply it to frequency drifts observed in Fast Radio Bursts. We assume that an emission patch propagates along the dipolar magnetic field lines producing coherent emission with frequency, direction and polarization defined by the local magnetic field. The observed temporal evolution of the frequency depends on relativistic effects of time contraction and the curvature of the magnetic field lines. The model generically produces linear scaling of the drift rate, $\dotω \propto - ω$, matching both numerically and parametrically the rates observed in FBRs; a more complicated behavior of $\dotω $ is also possible. Fast rotating magnetospheres produce higher drifts rates for similar viewing parameters than the slowly rotating ones. In the case of repeaters same source may show variable drift pattens depending on the observing phase. We expect rotational of polarization position angle through a burst, though by smaller amount than in radio pulsars. All these findings compare favorably with properties of FBRs, strengthening their possible loci in the magnetospheres of neutron stars.

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arXiv2022

Coherent emission in pulsars, magnetars and Fast Radio Bursts: reconnection-driven free electron laser

We develop a model of the generation of coherent radio emission in the Crab pulsar, magnetars and Fast Radio Bursts (FRBs). Emission is produced by a reconnection-generated beam of particles via a variant of Free Electron Laser (FEL) mechanism, operating in a weakly-turbulent, guide-field dominated plasma. We first consider nonlinear Thomson scattering in a guide-field dominated regime, and apply to model to explain emission bands observed in Crab pulsar and in Fast Radio Bursts. We consider particle motion in a combined fields of the electromagnetic wave and thee lectromagnetic (Alfvenic) wiggler. Charge bunches, created via a ponderomotive force, Compton/Raman scatter the wiggler field coherently. The model is both robust to the underlying plasma parameters and succeeds in reproducing a number of subtle observed features: (i) emission frequencies depend mostly on the length $λ_t$ of turbulence and the Lorentz factor of the reconnection generated beam, $ω\sim γ_b^2 ( c/λ_t) $ - it is independent of the absolute value of the underlying magnetic field. (ii) The model explains both broadband emission and the presence of emission stripes, including multiple stripes observed in the High Frequency Interpulse of the Crab pulsar. (iii) The model reproduces correlated polarization properties: presence of narrow emission bands in the spectrum favors linear polarization, while broadband emission can have arbitrary polarization. (iv) The mechanism is robust to the momentum spread of the particle in the beam. We also discuss a model of wigglers as non-linear force-free Alfven solitons (light darts).

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arXiv2022

FRB-periodicity: mild pulsars in tight O/B-star binaries

Periodicities observed in two Fast Radio Burst (FRB) sources (16 days in FRB 180916.J0158+65 and 160 days in FRB 121102) are consistent with that of tight, stellar mass binary systems. In the case of FRB 180916.J0158+65 the primary is an early OB-type star with mass loss rate $\dot{M} \sim 10^{-8}- 10^{-7} M_\odot$ yr$^{-1}$, and the secondary a neutron star. The observed periodicity is not intrinsic to the FRB's source, but is due to the orbital phase-dependent modulation of the absorption conditions in the massive star's wind. The observed relatively narrow FRB activity window implies that the primary's wind dynamically dominates that of the pulsar, $η= L_{sd}/(\dot{M} v_w c) \leq 1$, where $L_{sd} $ is pulsar spin-down, $\dot{M}$ is the primary's wind mass loss rate and $v_w$ is its velocity. The condition $η\leq 1$ requires mildly powerful pulsar with $L_{sd} \lesssim 10^{37}$ erg $s^{-1}$. The observations are consistent with magnetically-powered radio emission originating in the magnetospheres of strongly magnetized neutron stars, the classical magnetars.

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arXiv2022

On the nature of Fast Blue Optical Transients

Short rise times of Fast Blue Optical Transients (FBOTs) require very light ejected envelopes, $M_{ej} \leq 10^{-1} M_\odot$, much smaller than of a typical supernova. Short peak times also mean that FBOTs should be hydrodynamically, not radioactively powered. The detection by Chandra of X-ray emission in AT2020mrf of $L_X \sim 10^{42} $ erg s$^{-1}$ after 328 days implies total, overall dominant, X-ray energetics at the Gamma Ray Bursts (GRBs) level of $\sim 6 \times 10^{49}$ erg. We further develop a model of Lyutikov & Toonen (2019), whereby FBOTs are the results of a late accretion induced collapse (AIC) of the product of super-Chandrasekhar double white dwarf (WD) merger between ONeMg WD and another WD. Small ejecta mass, and the rarity of FBOTs, result from the competition between mass loss from the merger product to the wind, and ashes added to the core, on time scale of $\sim 10^3-10^4$ years. FBOTs occur only when the envelope mass before AIC is $\leq 10^{-1} M_\odot$. FBOTs proper come from central engine-powered radiation-dominated forward shock as it propagates through ejecta. FBOTs' duration is determined by the diffusion time of photons produced by the NS-driven forward shock within the expanding ejecta. All the photons produced by the central source deep inside the ejecta escape almost simultaneously, producing a short bright event. The high energy emission is generated at the highly relativistic and highly magnetized termination shock, qualitatively similar to Pulsar Wind Nebulae. The X-ray bump observed in AT2020mrf by SRG/eROSITA, predicted by Lyutikov & Toonen (2019), is coming from the break-out of the engine-powered shock from the ejecta into the preceding wind. The model requires total energetics of just few $\times 10^{50}$ ergs, slightly above the observed X-rays. We predict that the system is hydrogen poor.

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arXiv2022

Radial diffusion in corotating magnetosphere of Pulsar PSR J0737-3039B

Rich observational phenomenology associated with Pulsar B in PSR J0737$-$3039A/B system resembles in many respects phenomena observed in the Earth and Jupiter magnetospheres, originating due to the wind-magnetosphere interaction. We consider particle dynamics in the fast corotating magnetosphere of Pulsar B, when the spin period is shorter than the third adiabatic period. We demonstrate that trapped particles occasionally experience large radial variations of the L-parameter (effective radial distance) due to the parametric interaction of the gyration motion with the large scale electric fields induced by the deformations of the magnetosphere, in what could be called a betatron-induced diffusion. The dynamics of particles from the wind of Pulsar A trapped inside Pulsar B magnetosphere is governed by Mathieu's equation, so that the parametrically unstable orbits are occasionally activated; particle dynamics is not diffusive per se. The model explains the high plasma density on the closed field lines of Pulsar B, and the fact that the observed eclipsing region is several times smaller than predicted by the hydrodynamic models.

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arXiv2022

Faraday conversion in pair-symmetric winds of magnetars and Fast Radio Bursts

We consider 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 $\propto B^2$ 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, $ω, \, ω_p \ll ω_B$, the corresponding rotation rates are independent of the magnetic field. A plasma screen with dispersion measure DM $\sim 10^{-6}$ pc cm$^{-3}$ can induce large polarization changes, including large effective Rotation Measure (RM). The frequency scaling of the (generalized) RM, $ \propto 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) large circular polarization component observed in FRBs, with right-left switching; (ii) large RM, with possible sign changes; (iii) time-depend variable polarization. Relatively dense and slow wind is needed - the corresponding effect in regular pulsars is small.

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arXiv2022

Faraday rotation in fast radio bursts

Fast Radio Bursts (FBRs) show highly different polarization properties: high/small RMs, high/small circular/linear fractions. We outline a complicated picture of polarization propagation in the inner parts of the magnetars' winds, at scales $\sim$ few to hundreds of light cylinder radii. The key point is the Faraday rotation of linear polarization in highly magnetized symmetric pair plasma, a $\propto B^2$ effect. Position angle (PA) rotation rate is maximal for propagation across the magnetic field and disappears only for parallel propagation. In the highly magnetized regime, $ω\ll ω_B$, it becomes independent of the magnetic field. Very specific properties of PA($λ$) (scaling of the rotation angle with the observed wavelength $λ$) can help identify/sort out the propagation effects. Two basic regimes in pair plasma predict PA $\propto λ$ and $\propto λ^3$ (depending on the magnetic dominance); both are different from the conventional plasma's PA = RM $ λ^2$. This is the main prediction of the model. A number of effects, all sensitive to the underlying parameters, contribute to the observed complicated polarization patterns: streaming of plasma along magnetic field lines near the light cylinder, Faraday depolarization, effects of limiting polarization, the associated effect of linear-circular conversion, and synchrotron absorption.

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arXiv2022

Relativistic magnetic explosions

Many explosive astrophysical events, like magnetars' bursts and flares, are magnetically driven. We consider dynamics of such magnetic explosions - relativistic expansion of highly magnetized and highly magnetically over-pressurized clouds. The corresponding dynamics is qualitatively different from fluid explosions due to the topological constraint of the conservation of the magnetic flux. Using analytical, relativistic MHD as well as force-free calculations, we find that the creation of a relativistically expanding, causally disconnected flow obeys a threshold condition: it requires sufficiently high initial over-pressure and sufficiently quick decrease of the pressure in the external medium (the pre-explosion wind). In the subcritical case the magnetic cloud just "puffs-up" and quietly expands with the pre-flare wind. We also find a compact analytical solution to the Prendergast's problem - expansion of force-free plasma into vacuum.

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