We report the discovery of a bow shock around the high-mass X-ray binary ( HMXB ) 4U 1907+09 using the Spitzer Space Telescope 24 \mu m data ( after Vela X-1 the second example of bow shocks associated with HMXBs ) .
The detection of the bow shock implies that 4U 1907+09 is moving through the space with a high ( supersonic ) peculiar velocity .
To confirm the runaway nature of 4U 1907+09 , we measured its proper motion , which for an adopted distance to the system of 4 kpc corresponds to a peculiar transverse velocity of \simeq 160 \pm 115 { km s ^ { -1 } } , meaning that 4U 1907+09 is indeed a runaway system and supporting the general belief that most of HMXBs possess high space velocities .
The direction of motion of 4U 1907+09 inferred from the proper motion measurement is consistent with the orientation of the symmetry axis of the bow shock , and shows that the HMXB is running away from the Galactic plane .
We also present the Spitzer images of the bow shock around Vela X-1 ( a system similar to 4U 1907+09 ) and compare it with the bow shock generated by 4U 1907+09 .