Detection of Gamma-Ray Emission with Fermi-LAT from Two Neighboring Galactic Supernova Remnants: G032.8-00.1 (Kes 78) and G032.4+00.1, and Their Adjacent PeVatron Candidate PWN G32.64+0.53

Abstract G032.8-00.1 (Kes 78) and G032.4+00.1 are two adjacent (in projection) supernova remnants (SNRs) with angular sizes of 0 . ° 47 × 0 . ° 26 and ∼0 . ° 15, respectively, apart by ∼0 . ° 4. Both show radio continuum shells—elongated for the former and spherical for the latter—and X-ray emission of different origin: center-filled thermal X-rays from shocked hot gas in Kes 78 and ringlike X-ray synchrotron radiation in G032.4+00.1. While both were previously linked to the gamma-ray source 2FGL J1850.7-0014c, this association was abandoned in the latest Fermi Large Area Telescope (LAT) catalogs. The current view supports a GeV gamma-ray excess from this location, though its origin remains uncertain. Using ∼16.2 yr of Fermi-LAT data, we investigate the gamma-ray emission from this region. Our morphological and spectral analysis identifies these SNRs as the most likely counterparts of the detected excess, which exhibits two distinct maxima. The emission is extended in both cases, indicating spatial association with each SNR. The curved GeV spectra, best described by a log-parabola model, together with likely interaction with nearby molecular gas, strongly support a hadronic origin, although leptonic contributions cannot be excluded. This is further supported by multiwavelength spectral energy distribution modeling. This discovery adds G032.4+00.1 to the select group of Galactic SNRs established as gamma-ray emitters with a dominant nonthermal X-ray component, of which only a handful are currently known. A statistically significant detection at the 4.5 σ level in the 10–100 GeV band is also obtained for the nearby PeVatron candidate pulsar wind nebula PWN G32.64+0.53 associated with PSR J1849–0001.