Kavli Affiliate: Norbert Schulz
| First 5 Authors: Graciela Sanjurjo-Ferrín, Jose Miguel Torrejón, Konstantin Postnov, Michael Nowak, Jose Joaquín Rodes-Roca
| Summary:
4U 0114+65 is a high-mass X-ray binary system formed by the luminous
supergiant B1Ia, known as V{*} V662 Cas, and one of the slowest rotating
neutron stars (NS) with a spin period of about 2.6 hours. This fact provides a
rare opportunity to study interesting details of the accretion within each
individual pulse of the compact object. In this paper, we analyze 200 ks of
Chandra grating data, divided into 9 uninterrupted observations around the
orbit. The changes in the circumstellar absorption column through the orbit
suggest an orbital inclination of $sim$ $40^{circ}$ with respect to the
observer and a companion mass-loss rate of $sim$ 8.6 10$^{-7}$ solar masses
yr$^{-1}$. The peaks of the NS pulse show a large pulse-to-pulse variability.
Three of them show an evolution from a brighter regime to a weaker one. We
propose that the efficiency of Compton cooling in this source fluctuates
throughout an accumulation cycle. After significant depletion of matter within
the magnetosphere, since the settling velocity is $sim times$ 2 times lower
than the free-fall velocity, the source gradually accumulates matter until the
density exceeds a critical threshold. This increase in density triggers a
transition to a more efficient Compton cooling regime, leading to a higher mass
accretion rate and consequently to an increased brightness.
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