Fermi-LAT Detected Gamma-Ray Emission Likely Associated with SNR Kes 78

Abstract We have analyzed the GeV gamma-ray emission in the region of the supernova remnant (SNR) Kes 78 using ∼16.7 yr of Fermi-LAT observations and found that the catalog sources 4FGL J1852.4+0037e and 4FGL J1851.8−0007c are better represented as two extended sources modeled as 2Ext . One of them, designated as E2, is located at R.A. = 282 <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mover> <mml:mrow> <mml:mo>.</mml:mo> </mml:mrow> <mml:mrow> <mml:mtext>°</mml:mtext> </mml:mrow> </mml:mover> </mml:math> 86, decl. = −0 <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mover> <mml:mrow> <mml:mo>.</mml:mo> </mml:mrow> <mml:mrow> <mml:mtext>°</mml:mtext> </mml:mrow> </mml:mover> </mml:math> 11 with the 68% containment radius R 68 = 0 <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mover> <mml:mrow> <mml:mo>.</mml:mo> </mml:mrow> <mml:mrow> <mml:mtext>°</mml:mtext> </mml:mrow> </mml:mover> </mml:math> 31, and is detected with a significance of 15.2 σ in the 0.2–500 GeV energy range. The gamma-ray emission of source E2 is well described by a log-parabola (LogP) spectral model with spectral index Γ = 1.2 and curvature β = 0.3. The fitting with electron–proton number ratio K ep = 0.01 indicates that the GeV emission of source E2 is dominated by hadronic emission. Given the dense molecular environment surrounding the middle-aged SNR Kes 78, the hadronic scenario provides a natural explanation for the observed GeV emission. The extended source E2 can also be replaced with two point sources. One of them, designated as PTS1, is coincident with the newly discovered pulsar (PSR) J1852−0002g within the 68% positional uncertainty circle, indicating a possible gamma-ray contribution from this PSR. The gamma-ray spectrum of source PTS1 can be well described by a LogP spectral shape. The synchro-curvature radiation model provides a satisfactory spectral fit for source PTS1, suggesting that some of the GeV emission from the Kes 78 region might possibly originate from the magnetosphere of PSR J1852−0002g.