Fotis Gavriil: Review of Magnetar X-ray Observations

Fotis Gavriil gave a summary of X-ray (and some other wavelength!) observations of magnetars, which are neutron stars with extremely strong magnetic fields. There are now 4 confirmed Soft Gamma Repeaters (SGRs), with 1 candidate, and 10 confirmed Anomalous X-ray Pulsars (AXPs), with 1 candidate. Three of the confirmed sources, and one of the candidates, are associated with supernova remnants, implying that they are young stars. For an up to date summary of all known magnetars see this website.

Fotis gave a nice overview of all of the great things that we have learned about magnetars from X-ray observations with RXTE, including the persistent pulsations, the short repeating X-ray flares, the rare giant gamma-ray flares, and their long-term X-ray outbursts. Of particular interest is the high level of flux variability, and changes in pulse profile. Both types of source also show major timing noise (particularly the SGRs), and glitches have now been detected in all of the AXPs for which coherent timing is available. With regard to the short X-ray flares, he noted that the AXPs burst less often but can have much longer bursts (minutes as opposed to less than a second for the SGRs). He made a special point about the common statement that SGR bursts are more energetic, noting that this could just be because the SGRs are more prolific bursters, since high energy bursts are rarer.

Fotis also discussed in detail the emerging connections between the high field radio pulsars (one of which has now been found to show magnetar like X-ray flares) and the magnetars (some of which show transient radio pulsations). He argued that we now seem to be seeing a continuum of behavior, and pointed out that the high magnetic field radio pulsars have not been observed in X-ray very often, so we may have missed other transient magnetar like episodes. Something for future missions!

Wrapping up, he posed a number of questions for the future. How are magnetars born? What is the reason for their inherent variability? How common are they in the Galaxy? What is the source for their high energy emission? What is the connection between the magnetars and the rotation powered radio pulsars? And do other young, highly magnetized rotation powered pulsars exhibit magnetar like behavior?