Discovery and modelling of a flattening of the positive cyclotron line/luminosity relation in GX 304−1 with RXTE. Issue 3 (12th December 2016)

• Record Type: Journal Article
• Authors: Rothschild, Richard E.; Kühnel, Matthias; Pottschmidt, Katja; Hemphill, Paul; Postnov, Konstantin; Gornostaev, Mikhail; Shakura, Nikolai; Fürst, Felix; Wilms, Jörn; Staubert, Rüdiger; Klochkov, Dmitry
• Is Part Of: Monthly notices of the Royal Astronomical Society. Volume 466:Issue 3(2017)
• Page Start: 2752
• Page End: 2779
• Publication Date: 2016-12-12
• Subjects: magnetic fields -- stars: neutron -- pulsars: individual: GX 304−1 -- X-rays: binaries -- X-rays: individual: GX 304−1; Astronomy -- Periodicals; Periodicals; 520.5
• DOI: 10.1093/mnras/stw3222
• Languages: English
• ISSNs: 0035-8711

Abstract

Abstract: The Rossi X-ray Timing Explorer ( RXTE ) observed four outbursts of the accreting X-ray binary transient source, GX 304−1 in 2010 and 2011. We present results of detailed 3–100 keV spectral analysis of 69 separate observations, and report a positive correlation between cyclotron line parameters, as well as other spectral parameters, with power-law flux. The cyclotron line energy, width and depth versus flux, and thus luminosity, correlations show a flattening of the relationships with increasing luminosity, which are well described by quasi-spherical or disc accretion that yield the surface magnetic field to be ∼5 × 10 12 Gauss. Since HEXTE (High Energy X-ray Timing Experiment) cluster A was fixed aligned with the Proportional Counter Array field of view and cluster B was fixed viewing a background region 1 $_{.}^{\circ}$ 5 off of the source direction during these observations near the end of the RXTE mission, the cluster A background was estimated from cluster B events using HEXTEBACKEST . This made possible the detection of the ∼55 keV cyclotron line and an accurate measurement of the continuum. Correlations of all spectral parameters with the primary 2–10 keV power-law flux reveal it to be the primary driver of the spectral shape. The accretion is found to be in the collisionless shock braking regime.