Is there a propeller neutron star in $\gamma$ Cas?

Abstract

$\gamma$ Cas is the prototype of a small population of B0-B1.5 III-V classical Be (cBe) stars that emit anomalous and hard X-rays with a unique array of properties. $\gamma$ Cas is known to host, like other cBe stars, a decretion disk and also a low mass companion. Recently Postnov et al. have posited that this companion is a magnetized rapidly spinning neutron star that deflects direct gravitational accretion from a stellar/disk wind via the "propeller mechanism." These authors state that the key X-ray observations are "remarkably well produced" in this scenario. We reexamine this mechanism in detail and conclude that there are a number of fatal objections in its application to the $\gamma$ Cas case. Among other considerations these issues include the prediction under the propeller scenario of a much smaller population of $\gamma$ Cas stars than is observed and the lack of allowance for observed correlations of X-ray and UV and/or optical properties over a variety of timescales.

9 pages

References in corpus (7)

• Catalogue of high-mass X-ray binaries in the Galaxy ($4^{th}$ edition)
• Discovery of High-Energy Gamma-Ray Emission from the Binary System PSR B1259-63/LS 2883 Around Periastron with Fermi
• On the formation of Be stars through binary interaction
• Modeling interaction of relativistic and nonrelativistic winds in binary system PSR 1259-63/SS2883. I.Hydrodynamical limit
• A propelling neutron star in the enigmatic Be-star $\gamma$~Cassiopeia
• Discovery of Rapidly Moving Partial X-ray Absorbers within gamma Cassiopeiae
• Accretion regimes in the X-ray pulsar 4U 1901+03

Cited by in corpus (3)

• gamma Cas stars: Normal Be stars with disks impacted by the wind of a helium-star companion?
• The X-ray emission of Be+stripped star binaries
• Optical spectroscopy of Galactic field Classical Be stars