On the detectability of CO molecules in the Interstellar Medium via X-ray spectroscopy

Katerine Joachimi (1), Efraín Gatuzz (1,2), Javier A. Garcia (3), Timothy R. Kallman (4)

(1) Escuela de Física, Facultad de Ciencias, Universidad Central de Venezuela, PO Box 20632, Caracas 1020A, Venezuela. (2) Max-Planck-Institut fur Astrophysik, 85741 Garching bei Munchen, Germany. (3) Harvard-Smithsonian Center for Astrophysics, Cambridge, MA, 02138, USA. (4) NASA Goddard Space Flight Center, Greenbelt, MD 20771, USA.

We present a study of the detectability of CO molecules in the Galactic interstellar medium using high-resolution X-ray spectra obtained with the XMM-Newton Reflection Grating Spectrometer. We analyzed 10 bright low mass X-ray binaries (LMXBs) to study the CO contribution in their line-of-sights. A total of 25 observations were fitted with the ISMabs X-ray absorption model which includes photoabsorption cross-sections for O I, O II, O III and CO. We performed a Monte-Carlo (MC) simulation analysis of the goodness of fit in order to estimate the significance of the CO detection. We determine that the statistical analysis prevents a significant detection of CO molecular X-ray absorption features, except for the lines-of-sight toward XTE J1718-330 and 4U 1636-53. In the case of XTE J1817-330, this is the first report of the presence of CO along its line-of-sight. Our results reinforce the conclusion that molecules have a minor contribution to the absorption features in the O K-edge spectral region. We estimate a CO column density lower limit to perform a significant detection with XMM-Newton of N(CO) > 6×10^{16} cm-2 for typical exposure times.

Article –> http://arxiv.org/abs/1606.02285


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