Xray Transients Cool Fact
X-ray Transients
A large fraction of the MXRBs (massive X-ray binaries) which are seen to be transients have a Be star as the normal companion. Be stars were intensively studied in the 1930s by Otto Struve. The "e" stands for emission lines, which are seen to be present in their spectra with variable intensity over a wide range of timescales (hours to years).