A precessing Be disk as a possible model for occultation events in GX 304-1

• Published in: arXiv.org 2017-06
• Main Authors: Kühnel, Matthias, Rothschild, Richard E, Okazaki, Atsuo T, Müller, Sebastian, Pottschmidt, Katja, Ballhausen, Ralf, Choi, Jieun, Kreykenbohm, Ingo, Fürst, Felix, Marcu-Cheatham, Diana M, Hemphill, Paul, Sagredo, Macarena, Kretschmar, Peter, Martínez-Núñez, Silvia, José Miguel Torrejón, Staubert, Rüdiger, Wilms, Jörn
• Format: Article
• Language: English
• Subjects: Accretion disks; Density; Deposition; Light curve; Neutron stars; Occultation; Outbursts; Three dimensional models
• ISSN: 2331-8422
• DOI: 10.48550/arxiv.1706.09657

We report on the RXTE detection of a sudden increase in the absorption column density, \(N_\mathrm{H}\), during the 2011 May outburst of GX 304-1. The \(N_\mathrm{H}\) increased up to \({\sim}16\times 10^{22}\) atoms cm\(^{-2}\), which is a factor of 3-4 larger than what is usually measured during the outbursts of GX 304-1 as covered by RXTE. Additionally, an increase in the variability of the hardness ratio as calculated from the energy resolved RXTE-PCA light curves is measured during this time range. We interpret these facts as an occultation event of the neutron star by material in the line of sight. Using a simple 3D model of an inclined and precessing Be disk around the Be type companion, we are able to qualitatively explain the \(N_\mathrm{H}\) evolution over time. We are able to constrain the Be-disk density to be on the order of \(10^{-11}\) g cm\(^{-3}\). Our model strengthens the idea of inclined Be disks as origin of double-peaked outbursts as the derived geometry allows accretion twice per orbit under certain conditions.