The Blast Wave of Tycho’s Supernova Remnant

Abstract

We use the Chandra X-Ray Observatory to study the region in the Tycho supernova remnant between the blast wave and the shocked ejecta interface or contact discontinuity. This zone contains all the history of the shock-heated gas and cosmic-ray acceleration in the remnant. We present for the first time evidence for significant spatial variations of the X-ray synchrotron emission in the form of spectral steepening from a photon index of $2.6 right at the blast wave to a value of $3.0 several arcseconds behind. We interpret this result along with the profiles of radio and X-ray intensity using a self-similar hydrodynamical model including cosmic-ray back-reaction that accounts for the observed ratio of radii between the blast wave and contact discontinuity. Two different assumptions were made about the postshock magnetic field evolution: one where the magnetic field (amplified at the shock) is simply carried by the plasma flow and remains relatively high in the postshock region (synchrotron losses limited rim case), and another where the amplified magnetic field is rapidly damped behind the blast wave (magnetic damping case). Both cases fairly well describe the X-ray data; however, both fail to explain the observed radio profile. The projected synchrotron emission leaves little room for the presence of thermal emission from the shocked ambient medium. This can only be explained if the preshock ambient medium density in the vicinity of the Tycho supernova remnant is below 0.6 cm À3 .

Strong evidence for hadron acceleration in Tycho’s supernova remnant

“…account (Fig. 3), results in a bremsstrahlung emission peaked around 1.2 keV, which, at its maximum, contributes only about 6% of the total X-ray continuum emission only, in agreement with the findings of Cassam-Chenaï et al (2007). In the same energy range, there is however a non-negligible contribution from several emission lines, which increases their intensity moving inwards from the FS, where the X-ray emission is mainly nonthermal (Warren et al 2005).…”

“…The projected X-ray emission profile, computed at 1 keV, is shown in Fig. 9, where it is compared with the Chandra data in the region that Cassam-Chenaï et al (2007) call region W. The resulting radial profile, already convoluted with the Chandra PSF of about 0.5 arcsec, shows a remarkable agreement with the data. As widely stated above, the sharp decrease in the emission behind the FS is due to the rapid synchrotron losses of the electrons in a magnetic field as large as ∼300 μG.…”

A statistical approach to radio emission from shell-type SNRs

“…However, the mechanisms leading to both the magnetic field amplification and the electron injection at the SNR shock and their respective efficiencies remain poorly constrained. To investigate these processes observationally, there have been detailed studies, mostly in X-rays, of some selected SNRs (see e.g., Cassam-Chenaï et al 2007;Cassam-Chenaï et al 2008, and references therein). Relevant, complementary information should also be extracted from a statistical analysis of SNR data samples.…”

Supernova remnants, planetary nebulae and superbubbles: Prospects for new XMM‐Newton observations

“…Two interpretations have been proposed to account for this filamentary emission: either the magnetic field is large enough (≃ 100 µG) to induce strong radiative losses in the high energy electrons , or the magnetic field is damped at the shock (Pohl, Yan & Lazarian 2005). Both models predict different synchrotron morphologies and spectral shapes in X-rays (Cassam-Chenaï et al 2007).…”