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  • Print publication year: 2012
  • Online publication date: March 2012

13 Magnetars

Summary

The magnetars are a small group of neutron stars with extremely high effective dipole magnetic fields, comprising Anomalous X-ray Pulsars (AXPs) and Soft Gamma-ray Repeaters (SGRs). In both groups the rotation periods are long, and the slowdown rates are high, consistent with a high magnetic field and a short lifetime. The radiated energy is far higher than the rate of loss of rotational energy, and it is commonly assumed that the energy for the radiated X-rays and gamma-rays is derived from a decay of the magnetic field stored in the interior of the neutron star. The magnetars have been regarded as distinct from normal pulsars; it now appears that they may represent the extreme of a continuum.

The Soft Gamma-ray Repeaters (SGRs)

Cosmic gamma-ray bursts (GRBs) were first detected by satellites equipped with gamma-ray detectors, which were intended to monitor man-made nuclear explosions. The discovery was published in 1973 (Klebesadel, Strong & Olson 1973); since then some thousands of GRBs have been observed; many of these were measured from several satellites simultaneously, allowing positions to be determined from relative times of arrival. A typical GRB has a duration of some 10 s, and a rise time less than 1 s, but these are both widely variable; some bursts have structure within 1 ms.