Magnetised spinning neutron star at heart of brightest explosion
31 January 2014
Gamma-Ray Bursts (GRBs) are by far the most luminous events in the cosmos we are aware of. These stellar explosions emit the amount of energy the whole Milky Way galaxy releases in ten years, and they do so in a few tens of a second. To the question which engine is able to produce these spectacular explosions, the astronomy community has long identified two possible scenarios, and as often the case when extreme physics is involved, compact objects are the usual suspects.
One scenario is the fall (or accretion) of material onto a black hole of a few solar masses, the other invokes a class of neutron stars known as "magnetars". If some (if not all) GRBs had their origin in this highly magnetised and fast spinning neutron stars, we would have a simple solution to a long standing issue – which an international research team tested in a recent publication, co-authored by CAASTRO member Dr Davide Burlon (University of Sydney). Around one in six GRBs show emission prior to the main explosion, sometimes recurring in a few episodes – a phenomenon known as "precursor" emission. A consistent fraction of GRBs also shows a peculiar behaviour in the light-curve of the afterglow in the days following the main explosion. The presence of an accreting magnetar consistently gives a natural explanation for all these features.
Using this method of fitting the light-curve of the X-ray afterglow with the aforementioned model the researchers propose that also a very famous explosion, known as GRB 130427A, could be due to an accreting magnetar. This GRB is per se a standard-long GRB, with the exception of being very close –in astrophysical terms – to Earth, allowing an unprecedented campaign of follow-up with several telescopes. This makes it possible for scientists all over the world to test their models with high-quality data across the whole electromagnetic spectrum.
by D. Burlon