The bright star VFTS 399 turned out to be more interesting than its not-so-catchy name suggests. While classified as “apparent single star”, it stood out by its rapid rotation and, as turned out when inspecting data from the Chandra Satellite, by its exceptionally bright in X-rays. In this paper lead by Simon Clark, we conclude this VFTS399 is most likely the secondary star in a binary system. It is about 20 times more massive than the sun, rapidly rotating and probably shedding material from its equator by the centrifugal effect. Its companion star is now gone and left a neutron star when it exploded as a supernova. The neutron star appears to be the second pulsar in this region. The other neutron star is about 200 light years away.
The VLT-FLAMES Tarantula survey XX. The nature of the X-ray bright emission line star VFTS 399, Clark et al. 2015, accepted for publication in Astronomy and Astrophysics, http://arxiv.org/abs/1503.00930