  The key point of studying AXPs/SGRs (anomalous X-ray pulsars/soft gamma-ray
repeaters) is relevant to the energy budget. Historically, rotation was thought
to be the only free energy of pulsar until the discovery of accretion power in
X-ray binaries. AXPs/SGRs could be magnetars if they are magnetism-powered, but
would alternatively be quark-star/fallback-disk systems if more and more
observations would hardly be understood in the magnetar scenario.
