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Infrared identification of 2XMM J191043.4+091629.4

Here we report the infrared identification of the X-ray source 2XMM J191043.4+091629.4, which was detected by XMM-Newton/EPIC in the vicinity of the Galactic supernova remnant W49B. The aim of this work is to establish the nature of the X-ray source 2XMM J191043.4+091629.4 studying both the infrared photometry and spectroscopy of the companion. We analyse UKIDSS images around the best position of the X-ray source, and obtain spectra of the best candidate using NICS in the 3.5 m TNG telescope. We present both photometric and spectroscopic TNG analysis of the infrared counterpart of the X-ray source identifying emission lines in the K-band. H-band spectra does not present any significant feature. We have showed that Brackett gamma H I, at 2.165 micrometre, and He I, at 2.184 micrometre and at 2.058 micrometre, are present significantly in the infrared spectrum. The CO bands are also not present in our spectrum. Based on these results and the X-ray characteristics of the source we conclude that the infrared counterpart is an early B-type supergiant star with an E(B-V)= 7.6 +/- 0.3 at a distance of 16.0 +/- 0.5 kpc. This would be, therefore, the first high-mass X-ray binary in the Outer Arm at galactic longitudes between 30 and 60 degrees.