Identifications of Four Integral Sources in the Galactic Plane via Chandra Localizations

Hard X-ray imaging of the Galactic plane by the INTEGRAL satellite is uncovering large numbers of 20– 100 keV “IGR" sources. We present results from Chandra, INTEGRAL, optical, and IR observations of 4 IGR sources: 3 sources in the Norma region of the Galaxy (IGR J16195–4945, IGR J16207–5129, and IGR J16167– 4957) and one that is closer to the Galactic center (IGR J17195–4100). In all 4 cases, one relatively bright Chandra source is seen in the INTEGRAL error circle, and these are likely to be the soft X-ray counterparts of the IGR sources. They have hard 0.3–10 keV spectra with power-law photon indices of Γ = 0.5–1.1. While many previously studied IGR sources show high column densities (NH ∼ 1023−24 cm−2), only IGR J16195–4945 has a column density that could be as high as 1023 cm−2. Using optical and IR sky survey catalogs and our own photometry, we have obtained identifications for all 4 sources. The J-band magnitudes are in the range 14.9–10.4, and we have used the optical/IR spectral energy distributions (SEDs) to constrain the nature of the sources. Blackbody components with temperature lower limits of >9400 K for IGR J16195–4945 and >18,000 K for IGR J16207–5129 indicate that these are very likely High-Mass X-ray Binaries (HMXBs). However, for IGR J16167–4957 and IGR J17195–4100, low extinction and the SEDs indicate later spectral types for the putative companions, indicating that these are not HMXBs. Subject headings: stars: neutron — X-rays: stars — infrared: stars — stars: individual (IGR J16195–4945, IGR J16207–5129, IGR J16167–4957, IGR J17195–4100)