It is found that 1E 1207.4-5209 could be a low-mass bare strange star if its
small radius or low altitude cyclotron formation can be identified. The age
problems of five sources could be solved by a fossil-disk-assisted torque. The
magnetic dipole radiation dominates the evolution of PSR B1757-24 at present,
and the others are in propeller (or tracking) phases.Comment: ApJL accepted, or at
http://vega.bac.pku.edu.cn/~rxxu/publications/index_P.ht