PROPELLER EFFECT IN THE TRANSIENT X-RAY PULSAR SMC X-2

Abstract

We report the results of the monitoring campaign of the transient X-ray pulsar SMC X-2 performed with the Swift /XRT telescope over the period of 2015 September–2016 January during the Type II outburst. During this event, the bolometric luminosity of the source ranged from ≃10 39 down to several ×10 34 erg s −1 . Moreover, we discovered its dramatic drop by a factor of more than 100 below the limiting value of erg s −1 , which can be interpreted as a transition to the propeller regime. These measurements make SMC X-2 the sixth pulsating X-ray source where such a transition is observed and allow us to estimate the magnetic field of the neutron star in the system B  ≃ 3 × 10 12 G, which is in agreement with independent results of the spectral analysis.