Context : 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 .

Aims : 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 .

Methods : We analysed UKIDSS images around the best position of the X-ray source and obtained spectra of the best candidate using NICS in the Telescopio Nazionale Galileo ( TNG ) 3.5-m telescope .
We present photometric and spectroscopic TNG analyses of the infrared counterpart of the X-ray source , identifying emission lines in the K -band .
The H -band spectra does not present any significant feature .

Results : We have shown that the Brackett \gamma H I at 2.165 \mu m , and He I at 2.184 \mu m and at 2.058 \mu m are significantly present in the infrared spectrum .
The CO bands are also absent from 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 \pm 0.3 at a distance of 16.0 \pm 0.5 kpc .
This would be , therefore , the first high-mass X-ray binary in the Outer Arm at galactic longitudes of between 30 ^ { \circ } and 60 ^ { \circ } .

Conclusions :