2022ApJ...938...94A

We have carried out a study of the interstellar medium (ISM) toward the shell-like supernova remnant (SNR) Puppis A using NANTEN CO and ATCA H I data. We synthesized a comprehensive picture of the SNR radiation by combining the ISM data with the gamma-ray and X-ray distributions. The ISM, both atomic and molecular gas, is dense and highly clumpy, and is distributed all around the SNR, but mainly in the northeast. The CO distribution revealed an enhanced line intensity ratio of CO(J = 2-1)/(J = 1-0) transitions as well as CO line broadening, which indicate shock heating/acceleration. The results support the assertion that Puppis A is located at 1.4 kpc, in the Local Arm. The ISM interacting with the SNR has a large mass of ∼10⁴M_⊙, which is dominated by H I, showing good spatial correspondence with the Fermi-LAT gamma-ray image. This favors a hadronic origin of the gamma-rays, while an additional contribution from a leptonic component is not excluded. The distribution of the X-ray ionization timescales within the shell suggests that the shock front ionized various parts of the ISM at epochs ranging over a few to ten thousand years. We therefore suggest that the age of the SNR is around 10⁴ yr as given by the largest ionization timescale. We estimate the total cosmic-ray energy W_p to be 10⁴⁷ erg, which is well placed in the cosmic-ray escaping phase of an age-W_p plot including more than ten SNRs.