Discovery and modelling of a flattening of the positive cyclotron line/luminosity relation in GX 304−1 with RXTE

Date

2016-12-12

Department

Program

Citation of Original Publication

Richard E. Rothschild and others, Discovery and modelling of a flattening of the positive cyclotron line/luminosity relation in GX 304−1 with RXTE, Monthly Notices of the Royal Astronomical Society, Volume 466, Issue 3, April 2017, Pages 2752–2779, https://doi.org/10.1093/mnras/stw3222

Rights

This article has been accepted for publication in Monthly Notices of the Royal Astronomical Society ©: 2016Richard E. Rothschild, et al. Published by Oxford University Press on behalf of the Royal Astronomical Society. All rights reserved.

Subjects

Abstract

The Rossi X-ray Timing Explorer (RXTE) observed four outbursts of the accreting Xray 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 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.