In section 5. Galactic structure, stellar clusters and populations.
The compactness of the isolated neutron star RX J0720.4-3125
RX J0720.4-3125 (here referred to as J0720) is one of the "magnificent seven", the few isolated neutron stars to have been discovered by ROSAT. J0720 is one of the brightest and best studied (partly because it has been used to calibrate different X-ray telescopes). Pulsations at 8.39 s have been readily observed, establishing a connection with magnetars (i.e. highly magnetic neutron star). In this paper, Hambaryan and co-authors convincingly show that the true spin period is actually twice this reported value (i.e. 16.78 s), highlighting subtle variations in the light curve profile and energy spectrum from one (old) period to the following one. This configuration is achieved with a nearly orthogonal rotator with an angle between the magnetic and the rotation axis of 90 degrees.