HESS J1832$-$085: evidence for a new gamma-ray binary candidate

Abstract

The Galactic plane survey conducted by the High Energy Stereoscopic System (H.E.S.S.) has revealed numerous teraelectronvolt (TeV) sources, many of which remain unidentified. HESS~J1832$-$085 is a point-like TeV source lacking a confirmed multiwavelength (MWL) counterpart. In this paper, we present evidence that HESS~J1832$-$085 is likely a gamma-ray binary. We aim to investigate the nature of HESS~J1832$-$085 using {\it Fermi}-LAT and X-ray data, complemented by broadband radiative modeling, to assess its classification as a potential gamma-ray binary. We analyzed $\sim$17.3~yr of {\it Fermi}-LAT data between 0.1 and 500~GeV to establish the gigaelectronvolt (GeV) counterpart of HESS~J1832$-$085, including performing spectral, spatial, and periodicity analyses. Archival X-ray observations were examined to search for a counterpart and to characterize its spectrum and potential variability. The broadband emission was interpreted using models commonly applied to gamma-ray binaries. We detect a point-like GeV gamma-ray source spatially consistent with HESS~J1832$-$085, with spectral properties compatible with known gamma-ray binaries. No significant GeV periodic modulation is detected. A potential X-ray counterpart is identified in archival X-ray data, exhibiting a hard, absorbed spectrum and moderate variability. The broadband spectral energy distribution is reproduced by the adopted binary radiative model. Our results indicate that HESS~J1832$-$085 is likely a gamma-ray binary candidate, motivating dedicated MWL follow-up observations to confirm the source nature.

Figures (5)

• Figure 1: H.E.S.S. significance map of the region centered at HESS J1832$-$085. The colorbar signifies the $\rm \sqrt{TS}$ value of the region. The white circle denotes the spectral extraction region of HESS J1832-085. The cyan and magenta circles signify the GeV counterpart 4FGL J1832.4$-$0847 and SNR G23.11+0.18. The radio pulsar PSR J1832$-$0827 and millisecond pulsar PSR J1832$-$0836 are shown as red and green stars. The blue circle denotes the intermediate polar AX J1832.3$-$0840, and the teal square marks the radio point source in the region. The XMM-Newton detected X-ray source is shown with a black cross.
• Figure 2: XMM-Newton MOS2 image depicting the source region with a circle of $30^{\prime\prime}$ in green ($l = 23.2390621^{\circ}, b = 0.3090542^{\circ}$). This coordinate is close to the analysis of aktekin25 with much better constraint owing to a better spatial resolution of XMM-Newton detectors compared to that of Suzaku. The white circle, denoting the 95$\%$ positional uncertainty, is centered on HESS J1832-085 centroid hess18 and has a radius of $0.05^{\circ}$. The image is smoothed with a Gaussian kernel for visual purposes.
• Figure 3: The spectra and residual of the source with a simple absorbed power-law fit to the XMM-Newton observation. pn, MOS1, and MOS2 are depicted with black, red, and green, respectively. Spectra are rebinned for visual purposes.
• Figure 4: Long term unabsorbed $2.0 \hbox{--} 10.0$ keV flux variation over time from different observatories, depicting a flux variability in the source.
• Figure 5: Broadband SED of HESS J1832$-$085, along with the model synchrotron and IC emission. The X-ray, GeV, and TeV data for HESS J0632+057 hinton_09Li_17 and HESS J1832$-$093 Eger_16Mart_2020 are also shown in all purple and all blue, respectively, for comparison.