A likely detection of γ-ray emission from the region of Kepler’s Supernova Remnant (SNR) is reported by analyzing ∼12 yr of Pass 8 data of the Fermi Large Area Telescope. Its photon flux is (4.85 ± 0.60) × 10−10 ph cm−2 s−1 with ∼4σ significance in 0.2−500 GeV. Moreover, our results show that there is no significant variability in the light curve of ∼12 yr, and its position can well overlap with the observation result of Chandra in hard X-ray band with a good spatial resolution of 0.″5, so the source is likely to be the GeV γ-ray counterpart of Kepler’s SNR. The spectral energy distribution of γ-rays from Kepler’s SNR favors a hadronic origin in GeV band. Through analyzing multi-band data from radio to γ-ray and surveying the distribution from the surrounding CO molecules cloud, we found that if this γ-ray emission is from Kepler’s SNR, then it may originate from interactions between the relativistic protons escaping from the shock of Kepler’s SNR and surrounding CO gas molecules. However, more observation data are necessary to firmly confirm the association between the γ-ray source and Kepler’s SNR in the future.

We report the likely GeV γ-ray emission from the composite supernova remnant (SNR) COMP G327.1+1.1 by analyzing ∼12.2 yr of the Fermi Large Area Telescope (Fermi-LAT) Pass 8 data. We found the features of its spectrum and luminosity are well consistent with those of the observed COMP SNRs in the Milky Way. Moreover, the position of the source matches those in radio and TeV energy bands; we propose that the γ-ray source is likely to be a GeV counterpart of COMP G327.1+1.1. Considering the case of the association from COMP G327.1+1.1 and the γ-ray source, we interpreted its broadband spectral energy distribution (SED) by using three simple stationary models including one-zone and two-zone leptonic models and a one-zone leptohadronic model. We found that the simple two-zone model dominated by leptons can better explain its SED. More high-energy data are expected to firmly confirm the association between the γ-ray source and COMP G327.1+1.1 in the future.

A new γ-ray source with a significance level of approximately 5σ was reported in the region of the supernova remnant (SNR) G272.2–3.2 by analyzing the approximately 12.4 yr of observation data from the Fermi Large Area Telescope. Its γ-ray spatial distribution did not show an extended feature, and it had a soft spectrum with a spectral index of 2.56 ± 0.01 in the power-law model. No significant variability of its light curve with 10 time bins was identified, and its spatial positions in the X-ray and GeV bands overlapped. We suggest that the new γ-ray source is a likely counterpart of SNR G272.2–3.2. Analyzing its spectrum, we discussed the likely origins of the γ-ray emission.

The unknown γ-ray excess in the northwest region of Arp 220 was revisited by analyzing ∼11.8 years of the Fermi Large Area Telescope (Fermi-LAT) data in this study. We found that its photon flux was approximately three times higher than that of the previous study in the 0.2–100 GeV band, and the corresponding significance level ∼ 8.15σ was approximately four times higher than before. The light curves of 15 and 45 time bins from the whole time all showed two active periods, and the variability of the second period was more significant than that of the first period. The spectral indices from the two active periods were not statistically different and were close to the range of γ-ray flat-spectrum radio quasars observed by Fermi-LAT. Because the position of CRATES J153246+234400 was consistent with the best-fit position of our analysis, we suggest that CRATES J153246+234400 is more likely a γ-ray counterpart for the variational region. For Arp 220, there was no significant variability in the γ-ray emission.

In this work, we reanalyzed 11 years of spectral data from the Fermi Large Area Telescope (Fermi-LAT) of currently observed starburst galaxies (SBGs) and star-forming galaxies (SFGs). We used a one-zone model provided by NAIMA and the hadronic origin to explain the GeV observation data of the SBGs and SFGs. We found that a protonic distribution of a power-law form with an exponential cutoff can explain the spectra of most SBGs and SFGs. However, it cannot explain the spectral hardening components of NGC 1068 and NGC 4945 in the GeV energy band. Therefore, we considered the two-zone model to well explain these phenomena. We summarized the features of two model parameters, including the spectral index, cutoff energy, and proton energy budget. Similar to the evolution of supernova remnants (SNRs) in the Milky Way, we estimated the protonic acceleration limitation inside the SBGs to be the order of 102 TeV using the one-zone model; this is close to those of SNRs in the Milky Way.