Theory of cosmic ray and $\gamma$-ray production in the supernova remnant RX J0852.0-4622 (Vela Jr.)

Abstract

Explicitly time-dependent, nonlinear kinetic theory of cosmic ray (CR) acceleration in supernova remnants (SNRs) has been used to investigate the properties of the very large SNR RX J0852.0-4622. The available observations do not clearly distinguish between a ``nearby'' (at $\sim 200$ pc) and a ``distant'' (at $\sim 1$ kpc) source scenario. Therefore two correspondingly different models were analyzed. While the 200 pc solution can not be a priory excluded, the 1 kpc solution turns out to be clearly preferable for physical reasons. It requires a core collapse supernova (SN) with a massive progenitor in a molecular cloud $\sim 4000$ yrs ago. The overall synchrotron spectrum and the filamentary structures in hard X-rays both consistently lead to an amplified magnetic field $B > 100 \mu$G in the SNR interior. This implies a suppression of the leptonic TeV $\gamma$-ray emission to about 1 percent of the flux measured by the H.E.S.S. telescope system which therefore must be hadronic, consistent with the theoretical solution. Up to the present the 1 kpc solution has already converted $\sim 10$ percent of the explosion energy into nonthermal energy, as expected for a Galactic CR source. Also the derived $\gamma$-ray morphology is consistent with the H.E.S.S. measurements. For the ``nearby'' solution the leptonic and hadronic $\gamma$ ray fluxes are in the ratio 1:10 which means that this case is also hadronically dominated. However, the magnetic field strength, consistent with the overall synchrotron spectrum, differs significantly from that derived from the X-ray filaments. Finally, the total mechanical energy released amounts to only $1.8 \times 10^{50}$ erg, uncomfortably low even for a core collapse event.