The initial spin period of magnetar-like pulsar PSR J1846-0258 in Kes 75

While the origin of the ultra-strong surface magnetic fields believed to be present in magnetars is unknown, one of the leading theories is that magnetars are born spinning very rapidly, with initial spin periods on the order of 2 ms. Unfortunately, it has not been possible to directly measure the initial spin-period due to the lack of detected pulsar wind nebulae around these neutron stars. The recent detection of magnetar-like X-ray flares from PSR J1846-0258 in SNR Kes 75 suggests this neutron star, which powers a well-studied pulsar wind nebula, is a magnetar. I will present an estimate of the initial spin period of this neutron star from a detailed study of its pulsar wind nebula, and discuss its implications for the formation of magnetars.