Discovery of a retrogradely rotating neutron star in the X-ray pulsar GX 301$-$2

Abstract

We report on the analysis of the spin evolution of a slow X-ray pulsar GX 301$-$2 along the orbit using long-term monitoring by Fermi/GBM. Based on the observationally confirmed accretion scenario and an analytical model for the accretion of angular momentum we demonstrate that in this system, the neutron star spins retrogradely, that is, in a direction opposite to the orbital motion. This first-of-a-kind discovery of such a system proves the principal possibility of retrograde rotation in accreting systems with suitable accretion torque, and might have profound consequences for our understanding of the spin evolution of X-ray pulsars, estimates of their initial spin periods, and the ultimate result of their evolution.

arXiv comment5 pages, 2 figures, accepted by MNRAS

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Cited by in corpus (5)

• X-ray polarimetry of the accreting pulsar GX 301-2
• Timing and spectral variability of high mass X-ray pulsar GX 301--2 over orbital phases observed by Insight-HXMT
• X-ray reprocessing in accreting pulsar GX 301-2 observed with Insight-HXMT
• On the spin-up events and spin direction of the X-ray pulsar GX 301-2
• Evolution of eccentric high-mass X-ray binaries. The case of GX 301-2