XMM-Newton and Suzaku spectroscopic studies of unidentified X-ray sources towards the Galactic bulge: 1RXS J180556.1-343818 and 1RXS J173905.2-392615
Abstract
With XMM-Newton and Suzaku observations, for the first time, we acquired broad-band spectra of two unidentified X-ray sources towards the Galactic bulge: 1RXS J180556.1-343818 and 1RXS J173905.2-392615. The 1RXS J180556.1-343818 spectrum in the 0.3-7 keV band was explained by X-ray emission that originated from an optically-thin thermal plasma with temperatures of 0.5 and 1.8 keV. The estimated absorption column density of NH ∼ 4 × 1020 cm-2 was significantly smaller than the Galactic H I column density towards the source. A candidate for its optical counterpart, HD 321269, was found within 4″. In terms of the X-ray properties and the positional coincidence, it is quite conceivable that 1RXS J180556.1-343818 is an active G giant. We also found a dim X-ray source that was positionally consistent with 1RXS J173905.2-392615. Assuming that the X-ray spectrum can be reproduced with an absorbed, optically-thin thermal plasma model with kT = 1.6 keV, the X-ray flux in the 0.5-8 keV band was 8.7 × 10-14 erg s-1 cm-2, fainter by a factor of ∼7 than that of 1RXS J173905.2-392615 during the ROSAT observation. The follow-up observations we conducted revealed that these two sources would belong to the Galactic disk, rather than the Galactic bulge.
- Publication:
-
Publications of the Astronomical Society of Japan
- Pub Date:
- June 2016
- DOI:
- 10.1093/pasj/psv142
- arXiv:
- arXiv:1512.08228
- Bibcode:
- 2016PASJ...68S..22M
- Keywords:
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- X-rays: individual (1RXS J173905.2-392615;
- 1RXS J180556.1-343818);
- X-rays: stars;
- Astrophysics - High Energy Astrophysical Phenomena
- E-Print:
- 9 pages, 5 figures, accepted for publication in PASJ