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 four IGR sources: three 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 four 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 Gamma 0: 5 1: 1. While many previously studied IGR sources show high column densities (N-H similar to 10(23)-10(24) cm(-2)), only IGR J16195-4945 has a column density that could be as high as 10(23) cm(-2). Using optical and IR sky survey catalogs and our own photometry, we have obtained identifications for all four 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, suggesting that these are not HMXBs.