A microquasar shot out from its birth place

Abstract

We show that the microquasar LSI+61° 303 is running away from its birth place in a young complex of massive stars. The supernova explosion that formed the compact object shot out the X-ray binary with a linear momentum of 430 ± 140 M⊙ km s-1, which is comparable to the linear momenta found in solitary runaway neutron stars and millisecond pulsars. The properties of the binary system and its runaway motion of 27±6 km s-1 imply that the natal supernova was asymmetric and that the upper limit for the mass that could have been suddenly ejected in the explosion is ∼2 M⊙. The initial mass of the progenitor star of the compact object that is inferred depends on whether the formation of massive stars in the parent stellar cluster was coeval or a sequential process.