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2018RAA....18..128C - Research in Astron. and astroph., 18, 128-128 (2018/October-0)

A striking confluence between theory and observations of high-mass X-ray binary pulsars.

CHRISTODOULOU D., LAYCOCK S. and KAZANAS D.

Abstract (from CDS):

We analyze the most powerful X-ray outbursts from neutron stars in eleven Magellanic high-mass X-ray binaries and three pulsating ultraluminous X-ray sources. Most of the outbursts rise to $L_max$ which is about the level of the Eddington luminosity, while the remaining more powerful outbursts also appear to recognize that limit when their emissions are assumed to be anisotropic and beamed toward our direction. We use the measurements of pulsar spin periods $P_S$ and their derivatives ${dot}P_S$ to calculate the X-ray luminosities $L_p$ in their faintest accreting ("propeller-line") states. In five cases with unknown ${dot}P_S$, we use the lowest observed X-ray luminosities, which only adds to the heterogeneity of the sample. Then we calculate the ratios $L_p/L_max$ and we obtain an outstanding confluence of theory and observations from which we conclude that work done on both fronts is accurate and the results are trustworthy: sources known to reside on the lowest Magellanic propeller line are all located on/near that line, whereas other sources jump higher and reach higher-lying propeller lines. These jumps can be interpreted in only one way, higher-lying pulsars have stronger surface magnetic fields in agreement with previous empirical results in which ${dot}P_S$ and $L_p$ values were not used.