Identifications of FourINTEGRALSources in the Galactic Plane viaChandraLocalizations

Hard X-ray imaging of the Galactic plane by the INTEGRAL satellite isuncovering large numbers of 20-100 keV "IGR" sources. We present results fromChandra, INTEGRAL, optical, and IR observations of 4 IGR sources: 3 sources inthe Norma region of the Galaxy (IGR J16195-4945, IGR J16207-5129, and IGRJ16167-4957) 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 INTEGRALerror circle, and these are likely to be the soft X-ray counterparts of the IGRsources. They have hard 0.3-10 keV spectra with power-law photon indices of 0.5to 1.1. While many previously studied IGR sources show high column densities,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 haveobtained identifications for all 4 sources. The J-band magnitudes are in therange 14.9-10.4, and we have used the optical/IR spectral energy distributions(SEDs) to constrain the nature of the sources. Blackbody components withtemperature lower limits of >9400 K for IGR J16195-4945 and >18,000 K for IGRJ16207-5129 indicate that these are very likely High-Mass X-ray Binaries(HMXBs). However, for IGR J16167-4957 and IGR J17195-4100, low extinction andthe SEDs indicate later spectral types for the putative companions, indicatingthat these are not HMXBs.Comment: Accepted by the Astrophysical Journal after some reduction in the length of the paper and removal of one figur