Spatially decomposed $\gamma$-ray features surrounding SNR Kes 79 & PSR J1853+0056

TL;DR

This study analyzes 11.5 years of Fermi-LAT data around SNR Kes 79 and PSR J1853+0056, revealing two distinct gamma-ray sources with different origins, and challenges previous hadronic models for cosmic-ray interactions.

Contribution

It introduces a spatially decomposed analysis of gamma-ray features around SNR Kes 79 and PSR J1853+0056, identifying two sources with different spectral characteristics and proposing new interpretations for their origins.

Findings

Detection of two extended gamma-ray sources with distinct spectra.

Src-N likely associated with a pulsar wind nebula powered by PSR J1853+0056.

Src-S emission can be explained by hadronic interactions with cosmic rays.

Abstract

There have been substantial improvements on Fermi Large Area Telescope (LAT) data and analysis tools since the last analysis on the mid-aged supernova remnant (SNR) Kes 79 (Auchettl et al. 2014). Recent multi-wavelength studies confirmed its interaction with molecular clouds. About $0.36\degr$ north from Kes 79, a powerful pulsar -- PSR J1853+0056 also deserves our attention. In this work, we analyse the 11.5-year Fermi-LAT data to investigate the $\gamma$-ray feature in/around this complex region. Our result shows a more significant detection ($\sim$34.8$\sigma$ in 0.1--50 GeV) for this region. With $\ge$5 GeV data, we detect two extended sources -- Src-N (the brighter one; radius $\approx0.31\degr$) concentrated at the north of the SNR while enclosing PSR J1853+0056, and Src-S (radius $\approx0.58\degr$) concentrated at the south of the SNR. Their spectra have distinct peak energies ($\sim$1.0 GeV for Src-N and $\lesssim$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 (PWN) 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 $\gamma$-ray emission.