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Supernova Kicks and Misaligned Microquasars

The low-mass X-ray binary microquasar GRO J1655-40 is observed to have a misalignment between the jets and the binary orbital plane. Since the current black hole spin axis is likely to be parallel to the jets, this implies a misalignment between the spin axis of the black hole and the binary orbital plane. It is likely the black holes formed with an asymmetric supernova which caused the orbital axis to misalign with the spin of the stars. We ask whether the null hypothesis that the supernova explosion did not affect the spin axis of the black hole can be ruled out by what can be deduced about the properties of the explosion from the known system parameters. We find that this null hypothesis cannot be disproved but we find that the most likely requirements to form the system include a small natal black hole kick (of a few tens of km/s) and a relatively wide pre-supernova binary. In such cases the observed close binary system could have formed by tidal circularisation without a common envelope phase.