Accretion process at the Rapid Burster
The neutron star binary system MXB 1730-335, also known as the 'Rapid Burster', is a peculiar X-ray source, one of only two known to exhibit the elusive 'type-II' bursts. These bursts are sudden, erratic and extremely intense releases of X-rays that liberate enormous amounts of energy during periods otherwise characterised by very little emission occurring.
Observations of the Rapid Burster using three X-ray space telescopes – NASA's NuSTAR and Swift, and ESA's XMM-Newton – have revealed how the magnetic field regulates the accretion process before and during a type-II burst.
Before the burst, the fast spinning magnetic field of the neutron star (blue arrow) keeps the gas (white arrows) flowing from the companion star at bay, preventing it from reaching closer to the neutron star and effectively creating an inner edge at the centre of the disc. During this phase, only small amounts of gas leak towards the neutron star.
However, as the gas continues to flow and accumulate near this edge, it spins faster and faster, and eventually catches up with the spinning velocity of the magnetic field. The gas then hits the neutron star all at once, giving rise to the dramatic emission of type-II bursts.