GAMMA-RAY BURSTS AND DECAY OF NEUTRON STAR MAGNETIC-FIELDS

The presence of cyclotron lines in the hard X-ray spectra of about 20 per cent of γ-ray bursts strongly supports the idea that at least some of these transient events originate from neutron stars with strong magnetic fields. The absence of a clear concentration of the γ-ray bursts towards the galactic plane suggests that the neutron stars which produce the γ-ray bursts are older than the average radio pulsar (whose sky distribution does show such a concentration), and this could indicate that the magnetic fields of neutron stars do not decay. I show here that the properties of the observed population of γ-ray burst sources are consistent with the idea that: (i) the magnetic fields of single neutron stars decay on a time-scale of about 107 yr, and (ii) all γ-ray bursts originate from neutron stars with magnetic fields in excess of a few 1011 G; they could, therefore, be rather young objects. © Royal Astronomical Society.