The GeV γ -Ray Emission from the Pulsar Wind Nebula DA 495

Abstract We present an analysis of GeV γ -ray emission from the region of the pulsar wind nebula (PWN) DA 495, using 17 yr of PASS 8 data from the Fermi Large Area Telescope. In this region, we identify two point sources with markedly different spectra in the GeV band: one exhibits a soft γ -ray spectrum with an index of 3.26 ± 0.21, while the other shows a hard spectrum with an index of 1.54 ± 0.45 that aligns smoothly with the TeV spectrum of VER J2016+371, supporting its identification as the GeV counterpart of this TeV source. Given the difficulties in interpreting the entire system with a standard PWN model, we adopt a composite scenario in which a supernova remnant (SNR) shock is incorporated alongside the PWN to account for the multicomponent γ -ray emission. The soft GeV component is attributed to hadronic interactions between the SNR shock and the ambient gas. In contrast, VER J2016+371 with the hard GeV spectrum is well explained by a leptonic PWN model, where the multiwavelength data can be reproduced by a broken power-law electron distribution with parameters consistent with those of typical γ -ray PWNs. The compact X-ray emission is interpreted as arising from a separate population of electrons, described by a power-law energy distribution in a region of relatively high magnetic field strength. Deeper multiwavelength observations aimed at detecting the putative SNR shock, as well as future TeV observations with LHAASO and the Cherenkov Telescope Array, will be essential for clarifying the nature of the γ -ray emission and the overall structure of DA 495.