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.
Categories: astro-ph.HE