The Circinus Galaxy Revisited with 10 yr Fermi-LAT Data

The Circinus galaxy is a nearby composite starburst/active galactic nucleus (AGN) system. In this work we re-analyze the GeV emission from Circinus with 10 yr of Fermi-LAT Pass 8 data. In the energy range of 1?500 GeV, the spectrum can be well fitted by a power-law model with a photon index of ?;=;2.20;;0.14, and its photon flux is (5.90;;1.04);;10(?10) photons cm(?2) s(?1). Our 0.1?500 GeV flux is several times lower than that reported in previous literature, which is roughly in compliance with the empirical relation for star-forming and Local Group galaxies and might be reproduced by the interaction between cosmic rays and the interstellar medium. The ratio between the ?-ray luminosity and the total infrared luminosity is near the proton calorimetric limit, indicating that Circinus may be a proton calorimeter. However, marginal evidence for variability of the ?-ray emission is found in the timing analysis, which may indicate the activity of an AGN jet. More Fermi-LAT data and future observation of CTA are required to fully reveal the origin of its ?-ray emission.