2022ApJ...928...89H

There have been substantial improvements on Fermi Large Area Telescope (LAT) data and analysis tools since the last analysis by Auchettl et al. on the intermediate-aged supernova remnant (SNR) Kes 79. Recent multiwavelength studies confirmed its interaction with molecular clouds. About 0.°36 north from Kes 79, a powerful pulsar, PSR J1853+0056, also deserves our attention. In this work, we analyze the 11.5 yr Fermi-LAT data to investigate the γ-ray feature in/around this complex region. Our result shows a more significant detection (∼34.8σ in 0.1-50 GeV) for this region. With >=5 GeV data, we detect two extended sources: Src-N (the brighter one; radius ≃0.°31) concentrated at the north of the SNR while enclosing PSR J1853+0056, and Src-S (radius ≃0.°58) concentrated at the south of the SNR. Their spectra have distinct peak energies (∼1.0 GeV for Src-N and <=0.5 GeV for Src-S), suggesting different origins for them. In our hadronic model that includes the leaked cosmic rays (CRs) from the shock-cloud collision, even with extreme values of parameters, SNR Kes 79 can by no means provide enough CRs reaching clouds at Src-N to explain the local GeV spectrum. We propose that the Src-N emission could be predominantly reproduced by a putative pulsar wind nebula powered by PSR J1853+0056. On the other hand, our same hadronic model can reproduce a majority of the GeV emission at Src-S with typical values of parameters, while the three known pulsars inside Src-S release a total power that is too low to account for half of its γ-ray emission.