Cosmic‐Ray Acceleration at the Forward Shock in Tycho’s Supernova Remnant: Evidence fromChandraX‐Ray Observations

Abstract

We present evidence for cosmic ray acceleration at the forward shock in Tycho's supernova remnant (SNR) from three X-ray observables: (1) the proximity of the contact discontinuity to the forward shock, or blast wave, (2) the morphology of the emission from the rim of Tycho, and (3) the spectral nature of the rim emission. We determine the locations of the blast wave (BW), contact discontinuity (CD), and reverse shock (RS) around the rim of Tycho's supernova remnant using a principal component analysis and other methods applied to new Chandra data. The azimuthal-angle-averaged radius of the BW is 251 ′′ . For the CD and RS we find average radii of 241 ′′ and 183 ′′ , respectively. Taking account of projection effects, we find ratios of 1 : 0.93 : 0.70 (BW : CD : RS). We show these values to be inconsistent with adiabatic hydrodynamical models of SNR evolution. The CD:BW ratio can be explained if cosmic ray acceleration of ions is occurring at the forward shock. The RS:BW ratio, as well as the strong Fe Kα emission from the Tycho ejecta, imply that the RS is not accelerating cosmic rays. We also extract radial profiles from ∼34% of the rim of Tycho and compare them to models of surface brightness profiles behind the BW for a purely thermal plasma with an adiabatic shock. The observed morphology of the rim is much more strongly peaked than predicted by the model, indicating that such thermal -2emission is implausible here. Spectral analysis also implies that the rim emission is non-thermal in nature, lending further support to the idea that Tycho's forward shock is accelerating cosmic rays.

Prospects for Cherenkov Telescope Array Observations of the Young Supernova Remnant RX J1713.7−3946

“…This can lead to strong modifications of the shock structure and a nonlinear coupling between the shock flow and CR acceleration. Some observational results are consistent with the predictions of such nonlinear DSA (NLDSA) models (Bamba et al 2003(Bamba et al , 2005a2005b, Vink & Laming 2003Warren et al 2005;Uchiyama et al 2007;Helder et al 2009). However, whether these models can fully explain all aspects revealed by the accumulating multiwavelength observations still remains in doubt.…”

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

“…2-D simulations have confirmed these results (Blondin & Ellison 2001). These predictions are confirmed by X-ray observations of some young SNRs (Hughes, Rakowski & Decourchelle 2000;Decourchelle 2005;Warren et al 2005).…”

“…Thermal emission of the shocked ejecta at ≃ 1 keV usually dominates the overall spectrum while synchrotron emission essentially located at the shock dominates the 4-6 keV continuum. This is well exemplified by the deep Chandra observation of Tycho (Warren et al 2005).…”

The hydrodynamics of the supernova remnant Cassiopeia A

“…This is solely due to the presence of a clumpy shell. Although it is of no specific significance to our current investigation, there are other remnants in which similar features are also observed and explained by invoking cosmic ray acceleration at the forward shock (Warren et al 2005;Cassam-Chenaï et al 2008). While our models and results do not apply to these specific SNRs, the fact that a clumpy CS shell can have this effect might be of interest to those investigations.…”