Determination of the magnetic fields of Magellanic X-ray pulsars

Dimitris M. Christodoulou, Silas G. T. Laycock, Jun Yang, Samuel Fingerman


The 80 high-mass X-ray binary (HMXB) pulsars that are known to reside in the Magellanic Clouds (MCs) have been observed by the XMM-Newton and Chandra X-ray telescopes on a regular basis for 15 years, and the XMM-Newton and Chandra archives contain nearly complete information about the duty cycles of the sources with spin periods PS < 100 s. We have reprocessed the archival data from both observatories and we combined the output products with all the published observations of 31 MC pulsars with PS < 100 s in an attempt to investigate the faintest X-ray emission states of these objects that occur when accretion to the polar caps proceeds at the smallest possible rates. These states determine the so-called propeller lines of the accreting pulsars and yield information about the magnitudes of their surface magnetic fields. We have found that the faintest states of the pulsars segregate into five discrete groups which obey to a high degree of accuracy the theoretical relation between spin period and X-ray luminosity. So the entire population of these pulsars can be described by just five propeller lines and the five corresponding magnetic moments (0.29, 0.53, 1.2, 2.9 and 7.3, in units of 1030 G cm3).


Magellanic clouds — accretion, accretion disks — stars: magnetic field — stars: neutron — X-rays: binaries

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