Our latest work is accepted for publication in ApJ. In this work, we have studied X-ray and gamma-ray properties of supernova remnants to evaluate their maximum attainable energies during lifetime. As most astrophysicists know, there are only a few supernova remnants which are accelerating particles up to PeV energies. We have evaluated this in a quantitative manner.
Still, supernova remnants can be PeVatrons if the ages when the maximum energies during lifetime are achieved are very young (< 10 yr), or if the observationally inferred maximum energies are biased and actual values are much larger. Additionally, we have found that the maximum energies during lifetime have a large variety of 1-2 orders of magnitude, which will be due to some environmental variety. We hope such ambiguities will be distinguished with future gamma-ray observations.