Probing the Origin of the Unidentified TeV Γ-Ray Source HESS J1702–420 Via the Surrounding Interstellar Medium

The unidentified TeV gamma-ray source HESS J1702-420 has no firm associations with any counterparts at other wavelengths. We present an analysis of the interstellar medium using results from the Mopra Southern Galactic Plane CO survey and archival HI data from the Southern Galactic Plane Survey. We find significant components of molecular and atomic gas overlapping the TeV gamma-ray source at several velocities along the line of sight, with masses similar to 10(2)-10(4) M-circle dot and densities up to similar to 10(3) cm(-3). Potentially interesting and favourable morphological correspondences between the ISM and the TeV gamma-ray emission were found, and in a hadronic scenario, we find that cosmic ray (CR) enhancement values of similar to 100 times the local solar values are required to produce the TeV gamma-rays. We investigate the separate scenarios in which HESS J1702-420 is powered by the nearby SNR G344.7-0.1, PSRJ1702-4128, and an unknown accelerator. No evidence in the ISM was found to link the SNR with the TeV source. While themorphology of the gas located at the dispersion distance of PSRJ1702-4128 (5.2 kpc, v(LSR) similar to-70 km s(-1)) did not discount the possibility of a leptonic origin, the required energetics and the broad and hard TeV spectrum would likely disfavour such a scenario. Given the presence of potentially favourable ISM overlapping HESS J1702-420, we additionally speculate on the plausibility of scenarios involving undetected CR accelerators.