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The Galactic TeV $gamma$-ray source HESS$,$J1804$-$216 is currently an unidentified source. In an attempt to unveil its origin, we present here the most detailed study of interstellar gas using data from the Mopra Southern Galactic Plane CO Survey, 7 and 12$,$mm wavelength Mopra surveys and Southern Galactic Plane Survey of HI. Several components of atomic and molecular gas are found to overlap HESS$,$J1804$-$216 at various velocities along the line of sight. The CS(1-0) emission clumps confirm the presence of dense gas. Both correlation and anti-correlation between the gas and TeV $gamma$-ray emission have been identified in various gas tracers, enabling several origin scenarios for the TeV $gamma$-ray emission from HESS$,$J1804$-$216. For a hadronic scenario, SNR$,$G8.7$-$0.1 and the progenitor SNR of PSR$,$J1803$-$2137 require cosmic ray (CR) enhancement factors of $mathord{sim} 50$ times the solar neighbour CR flux value to produce the TeV $gamma$-ray emission. Assuming an isotropic diffusion model, CRs from both these SNRs require a slow diffusion coefficient, as found for other TeV SNRs associated with adjacent ISM gas. The morphology of gas located at 3.8$,$kpc (the dispersion measure distance to PSR$,$J1803$-$2137) tends to anti-correlate with features of the TeV emission from HESS$,$J1804$-$216, making the leptonic scenario possible. Both pure hadronic and pure leptonic scenarios thus remain plausible.
We have analyzed three XMM-Newton observations of the central part of the unidentified TeV gamma-ray source HESS J1804-216. We focus on two X-ray sources 2XMMi J180442.0-214221 (Src 1) and 2XMMi J180432.5-214009 (Src 2), which were suggested to be th
We present a detailed analysis of the interstellar medium towards the TeV $gamma$-ray sources HESS J1640$-$465 and HESS J1641$-$463 using results from the Mopra Southern Galactic Plane CO Survey and from a Mopra 7 mm-wavelength study. The $gamma$-ray
HESS J1614$-$518 and HESS J1616$-$508 are two tera-electron volt (TeV) $gamma$-ray sources that are not firmly associated with any known counterparts at other wavelengths. We investigate the distribution of interstellar medium towards the TeV $gamma$
We report the detection, with the CANGAROO-III imaging atmospheric Cherenkov telescope array, of a very high energy gamma-ray signal from the unidentified gamma-ray source HESS J1614-518, which was discovered in the H.E.S.S. Galactic plane survey. Di
New generation TeV gamma-ray telescopes have discovered many new sources, including several enigmatic unidentified TeV objects. HESS J0632+057 is a particularly interesting unidentified TeV source since: it is a point source, it has a possible hard-s