Australian researchers have discovered a new type of gamma-ray burst (GRB) called radio faint GRB.
This is an artist’s impression of a gamma-ray burst. Image credit: NASA.
GRBs are flashes of gamma rays associated with explosions of massive stars in distant galaxies. Up until now, it was thought all GRBs were followed by a radio afterglow.
“But we were wrong. After studying an ultra-sensitive image of GRBs with no afterglow, we can now say the theory was incorrect and our telescopes have not failed us,” said Dr Paul Hancock of Curtin University, who is the lead author of the paper published in the Astrophysical Journal (arXiv.org).
“In our research paper we argue that there must be two distinct types of GRBs, likely linked to differences in the magnetic field of the exploding star.”
Exploding stars associated with the newly discovered type of GRBs ‘switch off’ their radio transmissions before collapsing into a black hole. They use all of their energy to emit one last strong beam of highly energetic radiation before they die.
“GRBs are thought to mark the birth of a black hole or neutron star – both of which have super-dense cores. But neutron stars have such strong magnetic fields that producing gamma-rays are more difficult. We think that those stars that collapse to form a neutron star have energy left over to produce the radio afterglow whereas those that become black holes put all their energy into one final powerful gamma-ray flash,” Dr Hancock said.
The new study is underway to test the theory and to see if there are other subtle ways in which the two types of GRBs differ.
“We now have to take a whole new look at gamma-ray bursts – so far this work has shown that being wrong is sometimes more interesting than being right,” Dr Hancock said.
______
Hancock PJ et al. 2013. Two populations of gamma-ray burst radio afterglows. ApJ, accepted for publication; arXiv: 1308.4766
