Internal dynamics and particle acceleration in Tycho's SNR

Aims. The consequences of a newly suggested value for the SN explosion energy Esn = 1.2 $\times$ 1051 erg are explored for the case of Tycho's supernova remnant (SNR). Methods. A nonlinear kinetic theory of cosmic ray (CR) acceleration in supernova remnants (SNRs) is employed to investigate the properties of Tycho's SNR and their correspondence to the existing experimental data. Results. It is demonstrated that the high mean ratio between the radii of the contact discontinuity and the forward shock is consistent with the very effective acceleration of nuclear energetic particles at the forward shock. It is also argued that consistency of the value Esn = 1.2 $\times$ 1051 erg with the gas dynamics, acceleration theory, and the existing γ-ray measurements requires the source distance ${ d}$ to be greater than 3.3 kpc. The corresponding ambient gas number density is lower than 0.4 cm-3. Since the expected γ-ray flux strongly depends on the source distance, $F_{\gamma}\propto d^{-7}$, a future experimental determination of the actual γ-ray flux from Tycho's SNR will make it possible to determine the values of the source distance ${ d}$ and of the mean ambient gas density. A simple inverse Compton model without a dominant population of nuclear CRs is not compatible with the present upper limit for the γ-ray emission for any reasonable ambient interstellar B-field. Conclusions. Given the consistency between acceleration theory and overall, as well as internal, gas dynamics, a future γ-ray detection would make the case for nuclear particle acceleration in Tycho's SNR incontrovertible in our view