Is the remnant of SN1006 composed of iron?

Abstract

The remnant of the supernova explosion of AD 1006 (the brightest in recorded history) has a shell-like appearance at both radio and X-ray wavelengths. Einstein X-ray observations by Pye et al.¹ show a soft (photon energy ε ≲ ¼ keV) filled interior surrounded by a harder (ε ≳ 1 keV) unresolved ring of emission of radius ∼15 arc min. Superficially it appears to be similar to most supernova remnants for which many studies have shown that the X-ray emission is thermal radiation from gas shock-heated by high-velocity ejecta. The spectrum² of parts of the edge of the remnant in the range 0.75 ≲ ε ≲ 10 keV shows, however, no evidence for line emission. The spectral shape is consistent with a power-law perhaps due to a non-thermal mechanism. Moreover, the total mass of gas¹ required exceeds ∼10M_⊙ if it is of normal cosmic abundance. This is much greater than that expected for a remnant several hundred parsecs above the galactic plane. As no pulsar (or Crab-like morphology) is evident in the remnant of SN1006, Reynolds and Chevalier³ have proposed that relativistic particles are being efficiently accelerated in shocked gas, and provide the major source of X rays through synchrotron emission. SN1006 is then an important region for the study of such acceleration processes. Here we reinvestigate a thermal interpretation and show that the element abundances associated with a Type I supernova^4–7 may provide an alternative explanation.