INTEGRAL plays decisive role in measuring the speed of the jets from an accreting neutron star
Relativistic jets are fast, collimated outflows that are observed from accreting
compact objects on all physical scales, from neutron stars or stellar-mass black
holes feeding on a nearby companion star (X-ray binaries), to supermassive black
holes at the centres of galaxies. These jets release huge amounts of energy, having
a profound impact on their surroundings. However, how jets are launched remains a
fundamental astrophysical question. Using X-ray observations from INTEGRAL and radio
observations from CSIRO's Australia Telescope Compact Array (ATCA), a remarkable new
connection between the accretion inflow and the outflowing jets has been discovered
that will provide a new and much needed tool to begin to solve the jet launching
problem.
Neutron stars that are accreting matter from a nearby companion can often display
extreme explosions on their surfaces as recently accreted material undergoes
thermonuclear burning. These bright bursts are visible in the X-ray band and
generally last a few to tens of seconds. During the X-ray bursts, the exploding
material interacts with the accretion flow, increasing the rate at which matter
falls onto the star by up to a factor of ten.
Using strictly simultaneous X-ray (INTEGRAL) observations to detect the X-ray
bursts and radio (ATCA) observations to track the jets, it was found that in the
minutes after every X-ray burst, a bright jet flare was observed. This flare was
a result of extra material being input into the jet due to the X-ray burst-induced
increase in accretion rate. Measuring the time delay between the X-ray bursts and
the jet flare at different radio frequencies (where different radio frequencies
probe different distances along the jet) allows the speed of the jet flow to be
measured. This was the very first time that such a measurement has been made for
a neutron star system.
Neutron stars act as ideal laboratories for jet studies, as they can have measurable
spin rates, well determined masses, and possibly even magnetic field strengths, all
of which are believed to be key ingredients for jet launching. This new and repeatable
study is now being expanded to explore how the jet speeds differ between neutron star
systems that have different properties, which can uniquely disentangle the key properties
responsible for the launching of the jets.
Image: Artist impression of the jets being launched from an accreting neutron star. An X-ray
burst causes a bright jet flare, revealing the speed of the matter in the jet stream.
Video: Artist impression of an X-ray burst and subsequent jet flare from an accreting neutron
star. Measuring the time delay between the burst and the jet flare revealed the rate
at which material travelled down the jet, for the very first time in a neutron star system.
Credits:
Image: D. Futselaar and N. Degenaar, Anton Pannekoek Institute, University of Amsterdam.
Video:: ESA media relations, media@esa.int
Acknowledgements: D. Futselaar and N. Degenaar, University of Amsterdam. Work performed by ATG Medialab under contract with ESA
