Accretion and jet launching around massive stars

Neutron stars residing in a binary system with a normal star, can accrete and then eject material from their companion star. In their most extreme form, these ejections take the form of radio jets, which are launched from the close vincinity of the neutron star and can reach relativistic velocities. As such, these jets probe to complex interaction between the infalling material and the neutron star's strong gravitational field, extreme magnetic field, and fast rotation. The power of the jets impact the environment of the binary and may accelerate particles to extreme energies. My work focuses on the radio jets of the most strongly-magnetized neutron stars: this field was kickstarted by our discovery that their extreme fields to not prevent jet formation, that was published in Nature. Below, I highlight several of my projects on this topic.

The radio jet of 1A 0535+262

After the discovery of a radio jet launched by a strongly-magnetized accretion neutron star, we were able to repeat this observational campaign for another source. This result, importantly, shows that these jets are not unique to one target, nor to the super-Eddington accretion regime. It also allowed us to extend the relation between inflow and jets across a large range of X-ray luminosities. The full paper is available here.

A radio census of accreting neutron stars

Combining an enormous amount of radio observations of neutron stars, we published a new radio census of accretion neutron stars in 2021. We approximately doubled the sample of radio observated systems, and for the first time included a large number of high-mass X-ray binary systems as well. The full paper can be accessed here.

The discovery of jets from neutron star high-mass X-ray binaries

The neutron stars in high-mass X-ray binaries, i.e. those with massive stars as their companions, are extremely strongly magnetized (>1000 times stronger than their siblings with low-mass companions) and spin relatively slowly. For decades, these sources were not seen with radio telescopes, leading to the conjecture that their strong magnetic fields prevented to launching of jets. We disproved this paradigm when we discovered radio jets during an extremely bright outburst of Swift J0243.6+6124: a system consisting of a neutron star and a high-mass Be donor star. We published three detailed studies of the outburst: the discovery of the radio jet, its rapid evolution during the outburst's decay, and the possible detection of an ultra-fast X-ray outflow simultaneous with the jet.

The first hints of unexpected jets

Before we discovered the radio jets of Swift J0243.6+6124, we already detected radio emission from GX 1+4 and Hercules X-1. These tho peculiar X-ray binaries also host a strongly-magnetized neutron star, but our observational data was insufficient to conclude that we observed a jet. It did, however, spur our observations that lead to the later jet discoveries.