An extreme particle accelerator in the Galactic plane: HESS J1826-130

The unidentified very-high-energy (VHE; E > 0.1 TeV) γ-ray source, HESS J1826-130, was discovered with the High Energy Stereoscopic System (HESS) in the Galactic plane. The analysis of 215 h of HESS data has revealed a steady γ-ray flux from HESS J1826-130, which appears extended with a half-width of 0.21° ± 0.02<SUB>stat</SUB>° ± 0.05<SUB>sys</SUB>°. The source spectrum is best fit with either a power-law function with a spectral index Γ = 1.78 ± 0.10<SUB>stat</SUB> ± 0.20<SUB>sys</SUB> and an exponential cut-off at 15.2<SUB>-3.2</SUB><SUP>+5.5</SUP> TeV, or a broken power-law with Γ<SUB>1</SUB> = 1.96 ± 0.06<SUB>stat</SUB> ± 0.20<SUB>sys</SUB>, Γ<SUB>2</SUB> = 3.59 ± 0.69<SUB>stat</SUB> ± 0.20<SUB>sys</SUB> for energies below and above E<SUB>br</SUB> = 11.2 ± 2.7 TeV, respectively. The VHE flux from HESS J1826-130 is contaminated by the extended emission of the bright, nearby pulsar wind nebula, HESS J1825-137, particularly at the low end of the energy spectrum. Leptonic scenarios for the origin of HESS J1826-130 VHE emission related to PSR J1826-1256 are confronted by our spectral and morphological analysis. In a hadronic framework, taking into account the properties of dense gas regions surrounding HESS J1826-130, the source spectrum would imply an astrophysical object capable of accelerating the parent particle population up to ≳200 TeV. Our results are also discussed in a multiwavelength context, accounting for both the presence of nearby supernova remnants, molecular clouds, and counterparts detected in radio, X-rays, and TeV energies.