Revealing the state transition of Cen X-3 at high spectral resolution with Chandra

Kavli Affiliate: Norbert Schulz

| First 5 Authors: Graciela Sanjurjo-Ferrín, Jose Miguel Torrejón, Lida Oskinova, Konstantin Postnov, Jose Joaquín Rodes-Roca

| Summary:

Cen X-3 is a compact, high-mass X-ray binary (HMXRB), likely powered by Roche
lobe overflow. We present a phase-resolved X-ray spectral and timing analysis
of a target of opportunity textit{Chandra} observation made during a low-flux
to high-flux transition. The high-resolution spectra allow us to delve into the
events that occurred during this episode. The spectrum is described by a single
black body absorbed by a local column density of the order of $10^{23-24}$
cm$^{-2}$, which is one to two orders of magnitude higher than found for
previous analyses of data taken at similar orbital phases. Such a large column
produces a Compton shoulder in the Fe K$alpha$ line. The transition appears to
be caused by the onset of efficient cooling, which cools the plasma by 10
million degrees in just 10 ks, allowing matter to enter the magnetosphere. This
happens after a major disturbance, probably the arrival of a train of wind
clumps with individual masses in the range $10^{19-20}$ g. This train moves
ballistically in an eccentric orbit around the NS, producing a distinctive
Doppler modulation in the ion{Fe}{xxv} line.

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