Small‐Scale Structure of the SN 1006 Shock withChandraObservations

Abstract

The northeast shell of SN 1006 is the most probable acceleration site of high-energy electrons (up to $100 TeV) with the Fermi acceleration mechanism at the shock front. We resolved nonthermal filaments from thermal emission in the shell with the excellent spatial resolution of Chandra. The thermal component is extended over $100 00 (about 1 pc at 1.8 kpc distance) in width, consistent with the shock width derived from the Sedov solution. The spectrum is fitted with a thin thermal plasma of kT ¼ 0:24 keV in nonequilibrium ionization, typical for a young supernova remnant. The nonthermal filaments are likely thin sheets with scale widths of $4 00 (0.04 pc) and $20 00 (0.2 pc) upstream and downstream, respectively. The spectra of the filaments are fitted with a power-law function of index 2.1-2.3, with no significant variation from position to position. In a standard diffusive shock acceleration model, the extremely small scale length in the upstream region requires the magnetic field nearly perpendicular to the shock normal. The injection efficiency () from thermal to nonthermal electrons around the shock front is estimated to be $1 Â 10 À3 under the assumption that the magnetic field in the upstream region is 10 lG. In the filaments, the energy densities of the magnetic field and nonthermal electrons are similar to each other, and both are slightly smaller than that of thermal electrons. These results suggest that the acceleration occurs in more compact regions with larger efficiency than suggested by previous studies. Subject headings: acceleration of particles -ISM: individual (SN 1006) -shock wavessupernova remnants -X-rays: ISM

Geometry of the non-thermal emission in SN 1006

“…This is compatible with the Chandra data, as shown by Berezhko et al (2003). Bamba et al (2003) reported a much smaller scale height upstream, but this was based on the mistaken assumption that there should be no emissivity jump at the shock. Berezhko et al (2002) argue that the bright limbs are polar caps where the magnetic field (far upstream) is parallel to the shock speed.…”

“…This is supported by the very thin filaments observed by Chandra (Bamba et al 2003), whose width is probably limited by radiative losses.…”

“…For a reasonable ordered magnetic field (<10 µG) this is at odds with the polarisation measurements (Reynolds & Gilmore 1993) which require that 20% of the magnetic energy be in the ordered field. However it explains naturally why the X-ray emission decreases as sharply downstream as observed by Chandra (20 scale height, Bamba et al 2003). The precursor should have a very similar scale height upstream.…”

“…We did not attempt to deconvolve it to reach the 3-D structure. Bamba et al (2003) applied the same SRCUT + thermal model to Chandra data of the northeast rim, with two important differences. First they do not fix the normalisation of the non-thermal component on radio data (there is no adequate radio map at their spatial resolution), but let it free.…”

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.…”