Separating Thermal and Nonthermal X‐Rays in Supernova Remnants. I. Total Fits to SN 1006 AD

Abstract

The remnant of SN 1006 has an X-ray spectrum dominated by nonthermal emission, and pre-ASCA observations were well described by a synchrotron calculation with electron energies limited by escape. We describe the results of a much more stringent test: fitting spatially integrated ASCA GIS (0.6-8 keV) and RXTE PCA (3-10 keV) data with a combination of the synchrotron model sresc newly ported to XSPEC and a new thermal shock model vpshock. The new model can describe the continuum emission above 2 keV well, in both spatial distribution and spectrum. We find that the emission is dominantly nonthermal, with a small but noticeable thermal component: Mg and Si are clearly visible in the integrated spectrum. The synchrotron component rolls off smoothly from the extrapolated radio spectrum, with a characteristic rolloff frequency of 3.1 × 10 17 Hz, at which the spectrum has dropped about a factor of 6 below a powerlaw extrapolation from the radio spectrum. Comparison of TeV observations with new TeV model images and spectra based on the X-ray model fits gives a mean postshock magnetic field strength of about 9 µG, implying (for a compression ratio of 4) an upstream magnetic field of 3 µG, and fixing the current energy content in relativistic electrons at about 7 × 10 48 erg, resulting in a current electron-acceleration efficiency of about 5%. This total energy is about 100 times the energy in the magnetic field. The X-ray fit also implies that electrons escape ahead of the shock above an energy of about 30 TeV. This escape could result from an absence of scattering magnetohydrodynamic waves above a wavelength of about 10 17 cm. Our results indicate that joint thermal and nonthermal fitting, using sophisticated models, will be required for analysis of most supernova-remnant X-ray data in the future. Recent models of nonlinear shock acceleration (e.g., Berezhko Yelshin & Ksenofontov Berezhko

Geometry of the non-thermal emission in SN 1006

“…The azimuthal variations are very strong, much stronger than predicted in the escape model of Reynolds (1998) which Dyer et al (2001) used (which was an equatorial model incompatible with the geometrical test of Sect. 3.2 anyway).…”

“…Dyer et al (2001) have characterized the broad-band global spectrum of SN 1006 in terms of a power-law spectrum (cut-off at high frequency) plus a thermal spectrum. We used the same kind of approach, but locally.…”

“…The radio flux was extracted from the radio map in each region. The radio spectral index was fixed to 0.6 (Dyer et al 2001). The cut-off frequency was the only free parameter of the synchrotron component.…”

“…2, top right). On that basis, Reynolds (1996) and Dyer et al (2001) have proposed a model in which the asymmetry in SN 1006 is due solely to a large scale magnetic field aligned southeast to northwest and inclined at 60 • with respect to the line of sight, whereas the cosmic-rays are accelerated identically everywhere (up to a maximum energy limited by escape, independent of the magnetic field orientation). In their model, the maximum synchrotron emissivity is reached where the magnetic field is most compressed, i.e.…”

XMM–Newtonlarge programme on SN1006 – II. Thermal emission

“…5 (Vink et al 2000(Vink et al , 2003Dyer et al 2001;Allen et al 2001;Long et al 2003;Yamaguchi et al 2008;Uchida et al 2013;Broersen et al 2013). Compared to a similar n e t − kT diagram constructed with the high-resolution run (Paper I), the anti-correlation of n e t and kT caused by the degeneracy of these two parameters in spectral fitting is much less significant.…”