The authors reported earlier two "fast transient" events with "precursors" of a few seconds duration separated from the "main" events by a few seconds. The origin of the precursors is unexplained to date. It is proposed that these events are due to a strong type I X-ray burst and that the observed burst profiles result from an expansion and subsequent contraction of the neutron star's photosphere. During the 1977 February 7 event, the photosphere expanded in about 4 s to a radius at least an order of magnitude larger than the neutron star's original radius. The subsequent contraction of the photosphere occurred on an approximately 50 s time scale. The gravitational redshift should change continuously during expansion and contraction.
No takes yet. Share an insight, caveat, or question.
Lewin et al. (1984) studied this question.