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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 VelaX-1 the second example of bow shocks associated with HMXBs). The detection ofthe 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, wemeasured its proper motion, which for an adopted distance to the system of 4kpc corresponds to a peculiar transverse velocity of $\simeq 160 \pm 115$ km/s,meaning that 4U 1907+09 is indeed a runaway system and supporting the generalbelief that most of HMXBs possess high space velocities. The direction ofmotion of 4U 1907+09 inferred from the proper motion measurement is consistentwith the orientation of the symmetry axis of the bow shock, and shows that theHMXB is running away from the Galactic plane. We also present the Spitzerimages of the bow shock around Vela X-1 (a system similar to 4U 1907+09) andcompare it with the bow shock generated by 4U 1907+09.

4U 1907+09: a HMXB running away from the Galactic plane