Maxim Lyutikov - Purdue University

Maxim Lyutikov
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Name
Maxim Lyutikov
Affiliation
Purdue University
City
West Lafayette
Country
United States

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High Energy Astrophysical Phenomena (48)
 
Physics - Plasma Physics (6)
 
General Relativity and Quantum Cosmology (6)
 
Solar and Stellar Astrophysics (4)
 
Earth and Planetary Astrophysics (1)
 
Physics - Space Physics (1)
 
Cosmology and Nongalactic Astrophysics (1)
 
Physics - Fluid Dynamics (1)
 
Physics - Computational Physics (1)
 
Instrumentation and Methods for Astrophysics (1)

Publications Authored By Maxim Lyutikov

We present a simple prescription for the rotation of polarization produced by a relativistically moving gravitational lens, applicable to arbitrary deflection angle and arbitrary velocity of the lens. When geometric optics is applicable, two independent components contribute to the total rotation of polarization: (i) in the frame of the lens the polarization vector experiences minimal rotation defined by the deflection angle (as measured by a set of remote observers, or no rotation if defined in terms of parallel-propagated tetrad); (ii) the effect of the motion of the lens on the polarization can be taken into account exactly using special relativistic Lorentz transformation of polarization. The effects of the gravitational lensing are thus parametrized by the deflection angle of the null geodesics (not necessarily small) and the motion of the lens (not necessarily with velocities much smaller than that of light). Read More

In our prior papers, we considered the non-relativistic linear stability analysis of magnetized jets that do not have current sheet at the boundary. In this paper, we extend our analysis to relativistic jets. In order to find the unstable modes of current sheet-free, magnetized relativistic jets, we linearize full relativistic magnetohydrodynamics equations and solve them numerically. Read More

2017Feb
Affiliations: 1Purdue University, 2Lebedev Physical Institute, Astro Space Center

We present a model of blazar variability that can both reproduce smooth large polarization angle swings, and at the same time allow for the seemingly random behaviour of synchrotron fluxes, polarization fraction and, occasionally, $\pi$/2 polarization jumps. We associate blazar flaring activity with a jet carrying helical magnetic fields and propagating along a variable direction (and possibly with a changing bulk Lorentz factor). The model predicts that for various jet trajectories (i) EVPA can experience large smooth temporal variations while at the same time polarization fraction ($\Pi$) can be highly variable; (ii) $\Pi \sim 0$ near sudden EVPA jumps of 90$^{\circ}$, but can also remain constant for large, smoother EVPA swings; (iii) the total angle of EVPA rotation can be arbitrary large; (iv) intensity I is usually maximal at points of fastest EVPA changes, but can have a minimum. Read More

We can probe observationally and reproduce theoretically intricate properties of the Crab Nebula nearest to the pulsar - The Inner Knot. The tiny knot is indeed a bright spot on the surface of a quasi-stationary magnetic relativistic shock that accelerates particles. It is required that the part of the wind that produces the Inner Knot has low magnetization; thus, it is not a site of gamma-ray flares. Read More

2017Jan
Authors: Maxim Lyutikov1
Affiliations: 1Purdue University, McGill University

We consider fluid dynamics of relativistic double explosion - when a point explosion with energy $E_1$ is followed by a second explosion with energy $E_2$ after time $t_d$ (the second explosion could be in a form of a long lasting wind). The primary explosion creates a self-similar relativistic blast wave propagating with \Lf\ $\Gamma_1(t)$. A sufficiently strong second explosion, with total energy $E_2 \geq 10^{-2} E_1$, creates a fast second shock in the external fluid previously shocked by the primary shock. Read More

2017Jan

We argue that the localization of the Repeating FRB at $\sim 1$ Gpc excludes rotationally-powered type of radio emission (e.g., analogues of Crab's giant pulses coming from very young energetic pulsars) as the origin of FRBs. Read More

2016Dec
Affiliations: 1Purdue University, 2Purdue University, Universidad Nacional de Colombia

We develop a model of early GRB afterglows with the dominant $X$-ray contribution from the reverse shock (RS) propagating in highly relativistic (Lorentz factor $\gamma_w \sim 10^6$) magnetized wind of a long-lasting central engine. The model reproduces, in a fairly natural way, the overall trends and yet allows for variations in the temporal and spectral evolution of early optical and $X$-ray afterglows. The high energy and the optical synchrotron emission from the RS particles occurs in the fast cooling regime; the resulting synchrotron power $L_s$ is a large fraction of the wind luminosity, $L_s \approx L_w/\sqrt{1+\sigma_w}$ ($L_w$ and $\sigma_w$ are wind power and magnetization). Read More

2016Oct
Affiliations: 1Purdue University, 2Lebedev Physical Institute, Astro Space Center

Knots (emission features in jets of active galactic nuclei) often show non-ballistic dynamics and variable emission/polarization properties. We model these features as emission pattern propagating in a jet that carries helical magnetic field and is launched along a changing direction. The model can reproduce a wide range of phenomena observed in the motion of knots: non-ballistic motion (both smooth and occasional sudden change of direction, and/or oscillatory behavior), variable brightness, confinement of knots' motion within an overlaying envelope. Read More

The direction of polarization produced by a moving source rotates with the respect to the rest frame. We show that this effect, induced by pulsar rotation, leads to an important correction to polarization swings within the framework of rotating vector model (RVM); this effect has been missed by previous works. We construct relativistic RVM taking into account finite heights of the emission region that lead to aberration, time-of-travel effects and relativistic rotation of polarization. Read More

2016May
Affiliations: 1Purdue University, 2West Virginia University

We discuss possible electromagnetic signals accompanying Fast Radio Bursts (FRBs) that are expected in the scenario where FRBs originate in neutron star magnetospheres. For models involving Crab-like giant pulses, no appreciable contemporaneous emission is expected at other wavelengths. Magnetar giant flares, driven by the reconfiguration of the magnetosphere, however, can produce both contemporaneous bursts at other wavelengths as well as afterglow-like emission. Read More

We develop a model of particle acceleration in explosive reconnection events in relativistic magnetically-dominated plasmas and apply it to explain gamma-ray flares from the Crab Nebula. The model relies on development of current-driven instabilities on macroscopic scales (not related to plasma skin depths). Using analytical and numerical methods (fluid and particle-in-cell simulations), we study a number of model problems in relativistic magnetically-dominated plasma: (i) we extend Syrovatsky's classical model of explosive X-point collapse to magnetically-dominated plasmas; (ii) we consider instability of two-dimensional force-free system of magnetic flux tubes; (iii) we consider merger of two zero total poloidal current magnetic flux tubes. Read More

2016Mar
Affiliations: 1Purdue University, 2Purdue University, 3Sternberg Astronomical Institute

We discuss possible association of fast radio bursts (FRBs) with supergiant pulses emitted by young pulsars (ages $\sim$ tens to hundreds of years) born with regular magnetic field but very short -- few milliseconds -- spin periods. FRBs are extra-Galactic events coming from distances $d \lesssim 100$ Mpc. Most of the dispersion measure (DM) comes from the material in the freshly ejected SNR shell; for a given burst the DM should decrease with time. Read More

In a prior paper (Kim et al. 2015) we considered the linear stability of magnetized jets that carry no net electric current and do not have current sheets. In this paper, in addition to physically well-motivated magnetic field structures, we also include the effects of jet shear. Read More

We argue that the physical constraints required by the association of the Fermi GBM signal contemporaneous with GW150914 - radiative power of $10^{49} $ erg s$^{-1}$, and corresponding magnetic fields on the black hole of the order of $10^{12}$ Gauss - are astrophysical highly implausible. Combined with the relatively high random probability of coincidence of 0.22 percents, we conclude that the electromagnetic signal is likely unrelated to the BH merger. Read More

2015Oct
Affiliations: 1Washington University in Saint Louis, Physics Department and McDonnell Center for the Space Sciences, 2Jet Propulsion Laboratory, 3California Institute of Technology, Cahill Center for Astronomy and Astrophysics, 4Washington University in Saint Louis, Physics Department and McDonnell Center for the Space Sciences, 5Washington University in Saint Louis, Physics Department and McDonnell Center for the Space Sciences, 6Washington University in Saint Louis, Physics Department and McDonnell Center for the Space Sciences, 7Washington University in Saint Louis, Physics Department and McDonnell Center for the Space Sciences, 8Washington University in Saint Louis, Physics Department and McDonnell Center for the Space Sciences, 9Washington University in Saint Louis, Physics Department and McDonnell Center for the Space Sciences, 10Anton Pannekoek Institute for Astronomy, 11California Institute of Technology, Cahill Center for Astronomy and Astrophysics, 12California Institute of Technology, Cahill Center for Astronomy and Astrophysics, 13Jet Propulsion Laboratory, 14Jet Propulsion Laboratory, 15Rice University, Department of Physics and Astronomy, 16Washington University in Saint Louis, Physics Department and McDonnell Center for the Space Sciences, 17Georgia College, Department of Chemistry, Physics, and Astronomy, 18Jet Propulsion Laboratory, 19Jet Propulsion Laboratory, 20North-West University, Centre for Space Research, 21Technical University of Denmark, DTU Space, National Space Institute, 22Yale University, Department of Astronomy, 23Washington University in Saint Louis, Physics Department and McDonnell Center for the Space Sciences, 24University of Virginia, Department of Astronomy, 25MPI for Extraterrestrial Physics Garching, 26Durham University, Centre for Extragalactic Astronomy, Department of Physics, 27Jet Propulsion Laboratory, 28North Carolina State University, Department of Physics, 29Jet Propulsion Laboratory, 30Cambridge, Institute of Astronomy, UK, 31Penn State University, Department of Astronomy and Astrophysics, 32Jet Propulsion Laboratory, 33University of California, Berkeley, Department of Physics, 34ASI Science Data Center, Italy, 35California Institute of Technology, Cahill Center for Astronomy and Astrophysics, 36Cambridge, Institute of Astronomy, UK, 37Jet Propulsion Laboratory, 38Purdue University, Department of Physics and Astronomy, 39Texas Tech University, Physics Department, 40Nagoya University, Center for Experimental Studies, Kobayashi-Maskawa Institute for the Origin of Particles and the Universe, 41University of Maryland, Physics Department, 42RIKEN, 43Univ. of Michigan in Ann Arbor, Astronomy Dept, 44Harvard-Smithsonian Center for Astrophysics, 45Istituto di Astrofisica e Planetologia Spaziali, INAF, 46Department of Astronomy/Steward Observatory, 47Lawrence Livermore National Laboratory, 48Jet Propulsion Laboratory, 49Department of Astronomy/Steward Observatory, 50NASA Goddard Space Flight Center, 51Tohoku University, Astronomical Institute, 52NASA Goddard Space Flight Center

This paper describes the Polarization Spectroscopic Telescope Array (PolSTAR), a mission proposed to NASA's 2014 Small Explorer (SMEX) announcement of opportunity. PolSTAR measures the linear polarization of 3-50 keV (requirement; goal: 2.5-70 keV) X-rays probing the behavior of matter, radiation and the very fabric of spacetime under the extreme conditions close to the event horizons of black holes, as well as in and around magnetars and neutron stars. Read More

We investigate the density-shear instability in Hall-MHD via numerical simulation of the full non-linear problem, in the context of magnetar activity. We confirm the development of the instability of a plane-parallel magnetic field with an appropriate intensity and electron density profile, in accordance with analytic theory. We find that the instability also appears for a monotonically decreasing electron number density and magnetic field, a plane-parallel analogue of an azimuthal or meridional magnetic field in the crust of a magnetar. Read More

2015Jun
Affiliations: 1Purdue University, 2The University of Leeds, 3The University of Leeds

We model the inner knot of the Crab Nebula as a synchrotron emission coming from the non-spherical MHD termination shock of relativistic pulsar wind. The post-shock flow is mildly relativistic; as a result the Doppler-beaming has a strong impact on the shock appearance. The model can reproduce the knot location, size, elongation, brightness distribution, luminosity and polarization provided the effective magnetization of the section of the pulsar wind producing the knot is low, $\sigma \leq 1$. Read More

In this paper we consider stability of magnetized jets that carry no net electric current and do not have current sheets (Gourgouliatos et al. 2012). The non-relativistic MHD equations are linearized around the background velocity and the magnetic field structure of the jet. Read More

We discuss properties of the ultra-luminous $X$-ray source in the galaxy M82, NuSTAR J095551+6940.8, containing an accreting neutron star. The neutron star has surface magnetic field $ B_{NS} \approx 1. Read More

We advance a "Solar flare" model of magnetar activity, whereas a slow evolution of the magnetic field in the upper crust, driven by electron MHD (EMHD) flows, twists the external magnetic flux tubes, producing persistent emission, bursts and flares. At the same time the neutron star crust plastically relieves the imposed magnetic field stress, limiting the strain $ \epsilon_t $ to values well below the critical strain $ \epsilon_{crit}$ of a brittle fracture, $ \epsilon_t \sim 10^{-2}\epsilon_{crit} $. Magnetar-like behavior, occurring near the magnetic equator, takes place in all neutron stars, but to a different extent. Read More

We discuss a novel instability in inertia-less electron magneto-hydrodynamics (EMHD), which arises from a combination of electron velocity shear and electron density gradients. The unstable modes have a lengthscale longer than the transverse density scale, and a growth-rate of the order of the inverse Hall timescale. We suggest that this density-shear instability may be of importance in magnetic reconnection regions on scales smaller than the ion skin depth, and in neutron star crusts. Read More

The double pulsar system PSR J0737-3039A/B offers exceptional possibilities for detailed probes of the structure of the pulsar magnetosphere, pulsar winds and relativistic reconnection. We numerically model the distortions of the magnetosphere of pulsar B by the magnetized wind from pulsar A, including effects of magnetic reconnection and of the geodetic precession. Geodetic precession leads to secular evolution of the geometric parameters and effectively allows a 3D view of the magnetosphere. Read More

I. There is growing evidence that pulsars' high energy emission is generated via Inverse Compton mechanism. II. Read More

We discuss three topics: (i) the dynamics of afterglow jet breaks; (ii) the origin of Fermi-LAT photons; (iii) the electromagnetic model of short GRBs Read More

(Abridged) We consider dynamics and turbulent interaction of whistler modes within the framework of inertialess electron MHD (EMHD). We argue there is no energy principle in EMHD: any stationary closed configuration is neutrally stable. We consider the turbulent cascade of whistler modes. Read More

2013Jun

We attribute the rapid spindown of magnetar 1E 2259+586 observed by Archibald et al. (2013), termed the "anti-glitch", to partial opening of the magnetosphere during the X-ray burst, followed by changes of the structure of the closed field line region. To account for the observed spin decrease during the X- ray flare all that is needed is the transient opening, for just one period, of a relatively small fraction of the magnetosphere, of the order of only few percent. Read More

2013May
Affiliations: 1Purdue University, 2University of Wisconsin

Astrophysical plasmas can have parameters vastly different from the more studied laboratory and space plasmas. In particular, the magnetic fields can be the dominant component of the plasma, with energy-density exceeding the particle rest-mass energy density. Magnetic fields then determine the plasma dynamical evolution, energy dissipation and acceleration of non-thermal particles. Read More

We present several models of the magnetic structure of solar coronal mass ejections (CMEs). First, we model CMEs as expanding force-free magnetic structures. While keeping the internal magnetic field structure of the stationary solutions, expansion leads to complicated internal velocities and rotation, while the field structures remain force-free. Read More

We observed the Crab pulsar with the 43-m telescope in Green Bank, WV over a timespan of 15 months. In total we obtained 100 hours of data at 1.2 GHz and seven hours at 330 MHz, resulting in a sample of about 95000 giant pulses (GPs). Read More

2012Sep
Authors: Maxim Lyutikov1
Affiliations: 1Purdue University and Osservatorio di Arcetri

The "no hair" theorem is not applicable to black holes formed from collapse of a rotating neutron star. Rotating neutron stars can self-produce particles via vacuum breakdown forming a highly conducting plasma magnetosphere such that magnetic field lines are effectively "frozen-in" the star both before and during collapse. In the limit of no resistivity, this introduces a topological constraint which prohibits the magnetic field from sliding off the newly-formed event horizon. Read More

2012Sep
Authors: Maxim Lyutikov1
Affiliations: 1Purdue University, Osservatorio Astrofisico di Arcetri

We discuss growing evidence that pulsar high energy is emission is generated via Inverse Compton mechanism. We reproduce the broadband spectrum of Crab pulsar, from UV to very high energy gamma-rays - nearly ten decades in energy, within the framework of the cyclotron-self-Compton model. Emission is produced by two counter-streaming beams within the outer gaps, at distances above ~ 20 NS radii. Read More

2012Aug
Authors: Maxim Lyutikov1
Affiliations: 1Purdue University, Osservatorio di Arcetri

We reproduce the broadband spectrum of Crab pulsar, from UV to very high energy gamma-rays - nearly ten decades in energy, within the framework of the cyclotron-self-Compton model. Emission is produced by two counter-streaming beams within the outer gaps, at distances above $\sim$ 20 NS radii. The outward moving beam produces UV-$X$-ray photons via Doppler-booster cyclotron emission, and GeV photons by Compton scattering the cyclotron photons produced by the inward going beam. Read More

The unusually short durations, high luminosities, and high photon energies of the Crab Nebula gamma-ray flares require relativistic bulk motion of the emitting plasma. We explain the Crab flares as the result of randomly oriented relativistic "minijets" originating from reconnection events in a magnetically dominated plasma. We develop a statistical model of the emission from Doppler boosted reconnection minijets and find analytical expressions for the moments of the resulting nebula light curve (e. Read More

We consider the dynamics of a mechanical failure induced by a shear stress in a strongly magnetized neutron-star crust. We show that even if the elastic properties of the crust allow the creation of a shear crack, the strongly sheared magnetic field around the crack leads to a back-reaction from the Lorentz force which does not allow large relative displacement of the crack surfaces. Instead, the global evolution of the crack proceeds on a slow resistive time scale, and is unable to release any substantial mechanical energy. Read More

We reanalyze the Fermi spectra of the Geminga and Vela pulsars. We find that the spectrum of Geminga above the break is exceptionally well approximated by a simple power law without the exponential cut-off, making Geminga's spectrum similar to that of Crab. Vela's broadband gamma-ray spectrum is equally well fit with both the exponential cut-off and the double power law shapes. Read More

Many short GRBs show prompt tails lasting up to hundreds of seconds that can be energetically dominant over the initial sub-second spike. In this paper we develop an electromagnetic model of short GRBs that explains the two stages of the energy release, the prompt spike and the prompt tail. The key ingredient of the model is the recent discovery that an isolated black hole can keep its open magnetic flux for times much longer than the collapse time and, thus, can spin-down electromagnetically, driving the relativistic wind. Read More

We derive a number of solution for one-dimensional dynamics of relativistic magnetized plasma that can be used as benchmark estimates in relativistic hydrodynamic and magnetohydrodynamic numerical codes. First, we analyze the properties of simple waves of fast modes propagating orthogonally to the magnetic field in relativistically hot plasma. The magnetic and kinetic pressures obey different equations of state, so that the system behaves as a mixture of gases with different polytropic indices. Read More

2011Sep
Affiliations: 1Purdue University, 2University of Notre Dame, 3University of Notre Dame

Very high energy gamma-ray flares from the Crab nebular detected by AGILE and Fermi satellites challenge our understanding of the pulsar wind nebulae. The short duration of the flares, only few days, is particularly puzzling since it is much shorter than the dynamical times scale of the nebular. In this work we investigate analytically and via numerical simulations the electromagnetic signatures expected from the large amplitude low frequency magnetosonic waves generated within the Crab nebular which induce the corrugation perturbations of the termination shock. Read More

2011Sep
Affiliations: 1Purdue University, 2Stanford University

The "no hair" theorem, a key result in General Relativity, states that an isolated black hole is defined by only three parameters: mass, angular momentum, and electric charge; this asymptotic state is reached on a light-crossing time scale. We find that the "no hair" theorem is not formally applicable for black holes formed from collapse of a rotating neutron star. Rotating neutron stars can self-produce particles via vacuum breakdown forming a highly conducting plasma magnetosphere such that magnetic field lines are effectively "frozen-in" the star both before and during collapse. Read More

The observations of gamma-ray emission from pulsars with the Fermi-LAT detector and the detection of the Crab pulsar with the VERITAS array of Cherenkov telescopes at energies above 100 GeV make it unlikely that curvature radiation is the main source of photons above GeV energies in the Crab and many other pulsars. We outline a model in which the broad UV-X-ray component and the very high energy \gamma-ray emission of pulsars are explained within the Synchrotron-Self-Compton (SSC) framework. We argue that the bulk of the observed radiation is generated by the secondary plasma, which is produced in cascades in the outer gaps of the magnetosphere. Read More

Expansion of non-spherical relativistic blast waves is considered in the Kompaneets (the thin shell) approximation. We find that the relativistic motion effectively "freezes out" the lateral dynamics of the shock front: only extremely strongly collimated shocks, with the opening angles $\Delta \theta \leq 1/\Gamma^2$, show appreciable modification of profiles due to sideways expansion. For less collimated profiles the propagation is nearly ballistic; the sideways expansion of relativistic shock becomes important only when they become mildly relativistic. Read More

We study the expansion of low density cavities produced by Active Galactic Nuclei jets in clusters of galaxies. The long term stability of these cavities requires the presence of linked magnetic fields. We find solutions describing the self-similar expansion of structures containing large-scale electromagnetic fields. Read More

The system PSR J0737-3039 is the only binary pulsar known to consist of two radio pulsars (PSR J0737-3039 A and PSR J0737-3039 B). This unique configuration allows measurements of spin orientation for both pulsars: pulsar A's spin is tilted from the orbital angular momentum by no more than 14 degrees at 95% confidence; pulsar B's by 130 +/- 1 degrees at 99.7% confidence. Read More

[Abridged] Electromagnetic emission can be produced as a precursor to the merger, as a prompt emission during the collapse of a NS and at the spin-down stage of the resulting BH. We demonstrate that the time evolution of the axisymmetric force-free magnetic fields can be expressed in terms of the hyperbolic Grad-Shafranov equation. We find exact non-linear time-dependent split-monopole structure of magnetosphere driven by spinning and collapsing NS in Schwarzschild geometry. Read More

We investigate the emission properties that a large-scale helical magnetic field imprints on AGN jet synchrotron radiation. A cylindrically symmetric relativistic jet and large-scale helical magnetic field produce significant asymmetrical features in transverse profiles of fractional linear polarization, intensity, Faraday rotation, and spectral index. The asymmetrical features of these transverse profiles correlate with one another in ways specified by the handedness of the helical field, the jet viewing angle (theta_ob), and the bulk Lorentz factor of the flow (Gamma). Read More

In situ measurements of ion charge states can provide unique insight into the heating and evolution of coronal mass ejections when tested against realistic non-equilibrium ionization modeling. In this work we investigate the representation of the CME magnetic field as an expanding spheromak configuration, where the plasma heating is prescribed by the choice of anomalous resistivity and the spheromak dynamics. We chose as a test case, the 19 May 2007 CME observed by STEREO and ACE. Read More

(Abridged) The motion of a Schwarzschild black hole with velocity $v_0 = \beta_0 c$ through a constant magnetic field $B_0$ in vacuum induces a component of the electric field along the magnetic field, generating a non-zero second Poincare electromagnetic invariant $ ^* F \cdot F \neq 0$. This will produce (e.g. Read More

We calculate the evolution of the prompt intrinsic Poynting power generated by merging black holes. Orbiting black holes induce rotation of the space-time. In a presence of magnetic field supported by an accretion disk outside of the orbit, this results in a generation of an electromagnetic outflow via the Blandford-Znajek-type process with luminosity $L_{EM} \sim G^3 M^3 B^2/(c^5 R_{orb}) $ and reaching a fairly low maximum values of $L_{EM} = 10^{37}-10^{39} m_6 $ erg s$^{-1}$ ($m_6$ is the masses of black holes in millions of Solar mass) at the time of the merger. Read More

We mode Solar coronal mass ejections (CMEs) as expanding force-fee magnetic structures and find the self-similar dynamics of configurations with spatially constant \alpha, where {\bf J} =\alpha {\bf B}, in spherical and cylindrical geometries, expanding spheromaks and expanding Lundquist fields correspondingly. The field structures remain force-free, under the conventional non-relativistic assumption that the dynamical effects of the inductive electric fields can be neglected. While keeping the internal magnetic field structure of the stationary solutions, expansion leads to complicated internal velocities and rotation, induced by inductive electric field. Read More

Progenitors of long GRBs, and core-collapse supernovae in general, may have two separate mechanisms driving the outflows: quasi-isotropic neutrino-driven supernova explosions followed by a highly collimated relativistic outflow driven by the GRB central engine, a black hole or a magnetar. We consider the dynamics of the second GRB-driven explosion propagating through expanding envelope generated by the passage of the primary supernova shock. Beyond the central core, in the region of steep density gradient created by the SN shock breakout, the accelerating secondary quasi-spherical GRB shock become unstable to corrugation and under certain conditions may form a highly collimated jet, a "chimney", when a flow expands almost exclusively along a nearly cylindrically collimated channel. Read More