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 \Gamma = 0.5 –1.1 .
While many previously studied IGR sources show high column densities ( N _ { H } \sim 10 ^ { 23 - 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 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 .