Discovery of a Bow Shock around Vela X-1

Abstract

We report the discovery of a symmetric bow shock around thewell-known high-mass X-ray binary (HMXB) Vela X-1. Wind bow shocksare a ubiquitous phenomenon around OB-runaway stars, but now such astructure is found around an HMXB. The presence of a bow shock indicatesthat the system has a high (supersonic) velocity with respect to theinterstellar medium. From the symmetry of the bow shock, the direction ofmotion and, moreover, the origin and age of the system can be derived.Our observation supports Blaauw's scenario for the formation of anOB-runaway star by the supernova explosion of the binary companion.