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

Abstract

The unidentified very-high-energy (VHE; E $>$ 0.1 TeV) ${\hat{I}}^3$-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 ${\hat{I}}^3$-ray flux from HESS J1826$-$130, which appears extended with a half-width of 0.21${}^{\circ }$ $\pm$ 0.02${}_{\text{stat}}^{\circ }$ $\pm$ 0.05${}_{\text{sys}}^{\circ }$. The source spectrum is best fit with either a power-law function with a spectral index $\hat{I}“$ = 1.78 $\pm$ 0.10${}_{\text{stat}}$ $\pm$ 0.20${}_{\text{sys}}$ and an exponential cut-off at 15.2${}_{-3.2}^{+5.5}$ TeV, or a broken power-law with $\hat{I}{“}_1$ = 1.96 $\pm$ 0.06${}_{\text{stat}}$ $\pm$ 0.20${}_{\text{sys}}$, $\hat{I}{“}_2$ = 3.59 $\pm$ 0.69${}_{\text{stat}}$ $\pm$ 0.20${}_{\text{sys}}$ for energies below and above $E_{\mathrm{br}}$ = 11.2 $\pm$ 2.7 TeV, respectively. The VHE flux from HESS J1826$-$130 is contaminated by the extended emission of the bright, nearby pulsar wind nebula (PWN), HESS J1825$-$137, particularly at the low end of the energy spectrum. Leptonic scenarios for the origin of HESS J1826$-$130 VHE emission related to PSR J1826$-$1256 are confronted by our spectral and morphological analysis. In a hadronic framework, taking into account the properties of dense gas regions surrounding HESS J1826$-$130, the source spectrum would imply an astrophysical object capable of accelerating the parent particle population up to $\gtrsim$200 TeV. Our results are also discussed in a multiwavelength context, accounting for both the presence of nearby supernova remnants (SNRs), molecular clouds, and counterparts detected in radio, X-rays, and TeV energies.

9 Pages, 5 Figures