Discovery and modelling of a flattening of the positive cyclotron line/luminosity relation in GX 304-1 with RXTE
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 × 1012 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 1.5° 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 <monospace>HEXTEBACKEST</monospace>. 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.
- Publication:
-
Monthly Notices of the Royal Astronomical Society
- Pub Date:
- April 2017
- DOI:
- 10.1093/mnras/stw3222
- arXiv:
- arXiv:1610.08944
- Bibcode:
- 2017MNRAS.466.2752R
- Keywords:
-
- magnetic fields;
- stars: neutron;
- pulsars: individual: GX 304-1;
- X-rays: binaries;
- X-rays: individual: GX 304-1;
- Astrophysics - High Energy Astrophysical Phenomena
- E-Print:
- 34 pages, 27 figures, 7 tables. Accepted for publication in the Monthly Notices of the Royal Astronomical Society