Synchrotron Emission from the Shell-Like Supernova Remnants and the Cosmic-Ray Origin

Hiroshi Tomida

We observed three shell-like supernova remnants (SNRs; G347.3-0.5, RCW86, and G156.2+5.7) with the ASCA satellite. With the spectroscopic and imaging analysis, we found both non-thermal and thermal X-rays from all of these SNRs.

The thermal emission of G347.3-0.5 is weak. This indicates that the SNR is either old, or very young with small swept-up matter. In RCW86, we found that the abundance pattern for each element is similar to that of SNR 0102-72.3 in the Small Magellanic Cloud. This suggests that RCW86 has type-II SN origin, and is consistent with the report that RCW86 resides in an OB star association. In G156.2+5.7, we found abundance concentration in the SNR center region. This is the second example among the middle-aged SNRs after Cygnus Loop. We suspect that some amount of ejecta still remains in the core region.

The non-thermal component is likely to be synchrotron emissions from extremely high-energy electrons. These discoveries of the synchrotron X-rays in shell-like SNRs follows those of SN1006, CasA, and IC443. Comparing the X-ray data with the radio results, we found that the synchrotron spectra break at 5-400eV. This indicates that the electron spectra break at (5-40)x10**12eV, which are higher than the break energy of the electron spectrum observed at the earth. The electron spectra are well described with the standard acceleration model. Neither SN-type nor direction of the magnetic field is essential for the acceleration efficiency. Using the model, we estimated the possible maximum energy of protons to be 10**14.5eV, which is close to so called 'knee' energy. We also estimated the total energy of electrons accelerated in SNRs to be 2x10 erg in average. We may approach to a goal to solve the long-standing problem of acceleration mechanism of the cosmic-ray, at least to energies less than 10**14.5 eV.