Discovery of a possible X-ray counterpart to HESS J1804-216

Aya Bamba, Katsuji Koyama, Junko S. Hiraga, John Hughes, Takayoshi Kohmura, Motohide Kokubun, Yoshitomo Maeda, Hironori Matsumoto, Atsushi Senda, Tadayuki Takahashi, Yohko Tsuboi, Shigeo Yamauchi, Takayuki Yuasa

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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 γ-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 × 1022 cm-2 for Src 1, and 1.7 -1.0+1.4 and 1.1-0.6+1.0 × 1023cm-2 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 × 1032(d/5kpc)2 erg s-1 (Src 1) and 1.3 × 1033(d/5kpc)2 erg s-1 (Src 2), where d is the source distance. Among the handful of TeV sources with known X-ray counterparts, HESS J1804-216 has the largest ratio of TeV γ-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.

Original languageEnglish (US)
JournalPublications of the Astronomical Society of Japan
Issue number1 SPEC. ISS.
StatePublished - Apr 11 2007


All Science Journal Classification (ASJC) codes

  • Astronomy and Astrophysics
  • Space and Planetary Science


  • Acceleration of particles
  • ISM: individual (HESS J1804-216)
  • X-rays: ISM
  • X-rays: individual (Suzaku J1804-2142, Suzaku J1804-2140)

Cite this

Bamba, A., Koyama, K., Hiraga, J. S., Hughes, J., Kohmura, T., Kokubun, M., Maeda, Y., Matsumoto, H., Senda, A., Takahashi, T., Tsuboi, Y., Yamauchi, S., & Yuasa, T. (2007). Discovery of a possible X-ray counterpart to HESS J1804-216. Publications of the Astronomical Society of Japan, 59(1 SPEC. ISS.).