2007PASJ...59S.209B

Suzaku deep observations have discovered two highly significant nonthermal X-ray sources, Suzaku J1804-2142 (Src 1) and Suzaku J1804-2140 (Src 2), positionally coincident with the unidentified TeV g-ray source, HESS J1804-216. The X-ray sources are not time variable and show no counterpart in other wavebands, except for the TeV source. Src 1 is unresolved at Suzaku spatial resolution, whereas Src 2 is extended or composed of multiple sources. The X-ray spectra are highly absorbed, hard, and featureless, and are well fitted by absorbed power-law models with best-fit photon indices and absorption columns of -0.3_–0.5^+0.5 and 0.2_–0.2^+2.0 x 10²²/cm2 for Src 1, and 1.7_–1.0^+1.4 and 1.1_–0.6^+1.0 x 10²³/cm2 for Src 2. The measured X-ray absorption to the latter source is significantly larger than the total Galactic neutral hydrogen column in that direction. The unabsorbed 2-10keV band luminosities are 7.5 x 10³² (d/5 kpc)² erg/s (Src 1) and 1.3 x 10³³(d/5 kpc)² erg/s (Src 2), where d is the source distance. Among the handful of TeV sources with known X-ray counterparts, HESS J1804-216 216 has the largest ratio of TeV g-ray to hard X-ray fluxes. We discuss the nature of the emission and propose the Suzaku sources as plausible counterparts to the TeV source, although further observations are necessary to confirm this.