Gamma-ray bursts powered by strongest magnetic fields in universe
By ANIThursday, November 4, 2010
WASHINGTON - Astronomers in the UK have seen the signature of a magnetar in 11 gamma-ray bursts (GRBs) observed by the Swift satellite.
The team, led by University of Leicester Professor Paul O’Brien, reported their results today at the GRB 2010 meeting in Annapolis, Maryland.
Gamma-ray bursts are the most luminous explosions in the Universe and come in two types: long and short.
The standard models for long- and short-duration GRBs involve the core-collapse of a rapidly-rotating massive star and the merger of a compact binary star system respectively.
It is usually assumed that a black hole forms immediately, which acts as the GRB power source.
But recent evidence from bursts observed with the Swift satellite indicates that in some cases, a rapidly rotating, highly magnetized millisecond pulsar, or magnetar, forms before the system collapses to a black hole.
Magnetars are neutron stars about the size of a city, which spin at hundreds of rotations per second and have enormously strong magnetic fields-more than a million billion times that of the Earth. When formed magnetars drive a thermal wind outwards, and that plus the strong magnetic field produces the GRB.
The rapidly-spinning magnetar is also a powerful source of rotational energy which prevents gravitational collapse to a black hole. If the rotational energy can be extracted it can lead to strong X-ray emission for a short period of time until the magnetar can no longer support itself against gravity. The X-ray emission would then rapidly disappear.
Professor O’Brien said, “A magnetar sounds like an object from science fiction, but they have all the properties required to power a GRB. We have now identified 11 GRBs which display a short-lived emission feature that looks exactly like what we would expect to see from a spinning-down magnetar.”
Antonia Rowlinson, lead author of the paper on the short GRB magnetar source, said, “Short-duration GRBs are poorly understood, so our observations provide clear evidence that in some cases you can merge two neutron stars and make an even bigger one which lives for a short period of time before forming a black hole”.
The results for both long- and short-duration GRBs have recently been published in papers in Monthly Notices of the Royal Astronomical Society. (ANI)
