Propeller effect in action in the ultraluminous accreting magnetar M82 X−2

We present here the first convincing observational manifestation of a magnetar-like magnetic field in an accreting neutron star in binary system – the first pulsating ultraluminous X-ray source X−2 in the galaxy M82. Using the Chandra X-ray observatory data, we show that the source exhibit the bimodal distribution of the luminosity with two well-defined peaks separated by a factor of 40. This behaviour can be interpreted as the action of the ‘propeller regime’ of accretion. The onset of the propeller in a 1.37 s pulsar at luminosity of ∼1040 erg s−1 implies the dipole component of the neutron star magnetic field of ∼1014 G.