Magnetars and white dwarf pulsars

The anomalous X-ray pulsars (AXPs) and soft gamma-ray repeaters (SGRs) are a class of pulsars understood as neutron stars (NSs) with super strong surface magnetic fields, namely B greater than or similar to 10(14) G, and for that reason are known as magnetars. However, in the last years, some SGRs/AXPs with low surface magnetic fields B similar to (10(12)-10(13)) G have been detected, challenging the magnetar description. Moreover, some fast and very magnetic white dwarfs (WDs) have also been observed, and at least one showed X-ray energy emission as an ordinary pulsar. Following this fact, an alternative model based on WDs pulsars has been proposed to explain this special class of pulsars. In this model, AXPs and SGRs as dense and magnetized WDs can have surface magnetic field B similar to 10(7)-10(10) G and rotate very fast with frequencies Omega similar to 1 rad/s, consistent with the observed rotation periods P similar to (2-12) s.