O. Petruk

ROLE OF EJECTA CLUMPING AND BACK-REACTION OF ACCELERATED COSMIC RAYS IN THE EVOLUTION OF TYPE Ia SUPERNOVA REMNANTS

We investigate the role played by initial clumping of ejecta and by efficient acceleration of cosmic rays (CRs) in determining the density structure of the post-shock region of a Type Ia supernova remnant (SNR) through detailed three-dimensional MHD modeling. Our model describes the expansion of an SNR through a magnetized interstellar medium, including the initial clumping of ejecta and the effects on shock dynamics due to back-reaction of accelerated CRs. The model predictions are compared to the observations of SN 1006. We found that the back-reaction of accelerated CRs alone cannot reproduce the observed separation between the forward shock and the contact discontinuity unless the energy losses through CR acceleration and escape are very large and independent of the obliquity angle. On the contrary, the clumping of ejecta can naturally reproduce the observed small separation and the occurrence of protrusions observed in SN 1006, even without the need of accelerated CRs. We conclude that forward shock-contact discontinuity separation is a probe of the ejecta structure at the time of explosion rather than a probe of the efficiency of CR acceleration in young SNRs.

Some properties of synchrotron radio and inverse-Compton gamma-ray images of supernova remnants

The synchrotron radio maps of supernova remnants (SNRs) in a uniform interstellar medium and interstellar magnetic field (ISMF) are analysed, allowing for different ‘sensitivity’ of the injection efficiency to the obliquity of the shock. The very-high-energy γ -ray maps arising from inverse Compton processes are also synthesized. The properties of images in these different wavelength bands are compared, with particular emphasis on the location of the bright limbs in bilateral SNRs. Recent High-Energy Stereoscopic System (HESS) observations of SN 1006 show that the radio and inverse Compton γ -ray limbs coincide, and we found that this may happen if (i) injection is isotropic but the variation of the maximum energy of electrons is rather fast to compensate for differences in the magnetic field, or (ii) the obliquity dependence of injection (either quasi-parallel or quasi-perpendicular) and the electron maximum energy are strong enough to dominate the magnetic field variation. In the latter case, the obliquity dependences of the injection and the maximum energy should not be opposite. We argue that the position of the limbs alone, and even their coincidence in radio, X-rays and γ -rays, as discovered by HESS in SN 1006, cannot be conclusive as regards the dependence of the electron injection efficiency, the compression/amplification of the ISMF and the electron maximum energy on the obliquity angle.

Post-adiabatic supernova remnants in an interstellar magnetic field: parallel and perpendicular shocks

Gamma-rays from hadronic collisions are expected from supernova remnants (SNRs) located near molecular clouds. The temperature on the shock interacting with the dense environment quickly reaches

Constraints on magnetic field strength in the remnant SN 1006 from its non-thermal images

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Hadronic γ-ray images of Sedov supernova remnants

K. The radiative losses of plasma become essential in the evolution of SNRs. They decrease the thermal pressure and essentially increase the density behind the shock. The presence of ambient magnetic field may considerably alter the behavior of the post-adiabatic SNRs comparing to hydrodynamic scenario. In the present paper, the magneto-hydrodynamic simulations of radiative shocks in magnetic field are performed. High plasma compression due to the radiative losses results also in the prominent increase of the strength of the tangential component of magnetic field behind the shock and the decrease of the parallel one. If the strength of the tangential field before the shock is higher than about

Radio polarization maps of shell-type SNRs – II. Sedov models with evolution of turbulent magnetic field

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Post-adiabatic supernova remnants in an interstellar magnetic field: oblique shocks and non-uniform environment

it prevents formation of the very dense thin shell. The higher the strength of the tangential magnetic field the larger the thickness and the lower the maximum density in the radiative shell. Parallel magnetic field does not affect the distribution of the hydrodynamic parameters behind the shock. There are almost independent channels of energy transformations: radiative losses are due to the thermal energy, the magnetic energy increases by reducing the kinetic energy. The large density and high strength of the perpendicular magnetic field in the radiative shells of SNRs should result in considerable increase of the hadronic gamma-ray flux comparing to the leptonic one.

Bridging the gap between supernovae and their remnants through multi-dimensional hydrodynamic modeling

Images of SN 1006 have a number of important properties. For instance, the bright limbs coincide spatially in various bands, they have different brightness, and the contrast of brightness varies from radio to gamma-rays. The reasons of such properties and the role of the magnetic field strength are discussed. Simple, almost model-independent methods and analytical approximations for the derivation of the strength of magnetic field from the comparison of radio, X-rays and TeV images of SNR are presented. The methods require the TeV image to be well resolved and accurate, at least to the level of the radio and X-ray maps, in order to put reasonable constraints on magnetic field. If we apply it to the present HESS data, they limit the strength of magnetic field in limbs of SN 1006 to values lower than few hundreds micro Gauss. If applied to the Fermi-LAT band, the model predicts same position and same ratio of the surface brightness for GeV photons as for the radio band. We conclude that TeV and GeV future high-resolution data may be very informative about the MF of SN 1006.

Observational constraints on the modeling of SN1006

A number of modern experiments in high-energy astrophysics produce images of supernova remnants (SNRs) in the TeV and GeV gamma-rays. Either relativistic electrons (due to the inverse-Compton scattering) or protons (due to the pion decays) may be responsible for this emission. In particular, the broad-band spectra of SNRs may be explained in both leptonic and hadronic scenarios. Another kind of observational data, namely, images of SNRs, is an important part of experimental information. We present a method to model gamma-ray images of Sedov SNRs in uniform media and magnetic field due to hadronic emission. These γ-rays are assumed to appear as a consequence of meson decays produced in inelastic collisions of accelerated protons with thermal protons downstream of the shock – a model would be relevant for SNRs without firm confirmations of the shock-cloud interaction, as e.g. SN 1006. Distribution of surface brightness of the shell-like SNR is synthesized numerically for a number of configurations. An approximate analytical formula for azimuthal and radial variation of hadronic γ-ray brightness close to the shock is derived. The properties of images as well as the main factors determining the surface brightness distribution are determined. Some conclusions which would be relevant to SN 1006 are discussed.