Unraveling the nature of the TeV source HESS J1857+026 with a pulsar wind nebula scenario

HESS J1857+026 has an energy-dependent morphology in the energy range of 10–500 GeV, and is spatially coincident with the energetic pulsar PSR J1856+0245. We have reanalyzed the GeV emission from the HESS J1857+026 region using ~16.7 years of Fermi Large Area Telescope observations. The γ-ray spectrum is best described by a single power-law model with an index of 1.95 ± 0.12 in the energy range of 0.03–1 TeV, and could connect smoothly with the TeV γ-ray spectrum. Given the uncertainty regarding the origin of this emission, we conducted a theoretical analysis to explore the possibility that the multiwavelength emission from HESS J1857+026 originates from a pulsar wind nebula (PWN). Using a time-dependent one-zone model, we found that the observed γ-ray fluxes can be adequately reproduced under the assumption that particles with broken power-law energy distribution are continuously injected into the nebula. This result indicates that it is reasonable to attribute the multiband non-thermal emission from this source to the PWN powered by PSR J1856+0245. Furthermore, the magnetic field strength in the nebula is constrained to approximately 2.6 μG.