Astronomy and Astrophysics – Astrophysics
Scientific paper
Apr 2002
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2002aps..apr.s7003c&link_type=abstract
American Physical Society, April Meeting, Jointly Sponsored with the High Energy Astrophysics Division (HEAD) of the American As
Astronomy and Astrophysics
Astrophysics
Scientific paper
Although these two peculiar classes of cosmic X-ray sources are discovered in very different ways, recent observations have revealed a growing blending of the timing properties and quiescent emission of the Soft Gamma Repeaters and Anomalous X-ray Pulsars. Their behavior is distinctly different from both classical radio pulsars and accreting neutron stars, and their birthrate is at least 10 percent of the total neutron star population. Both sources have been identified as magnetars -- neutron stars whose ultrastrong 10^14-10^15 G magnetic fields decay measureably even at the relatively young age of 10^4-10^5 yrs. The light curves and spectral properties of SGR flares are consistent with the cooling of a hot fireball confined by a super-QED magnetic field. The non-thermal persistent X-ray emission of the SGRs, the variations in their X-ray pulse profiles observed following outbursts, and their accelerated spindown and timing noise, can all be related to the presence of electrical currents flowing persistently through a 10^14-10^15 G magnetic field. The generally softer X-ray spectra and slower and steadier spindown of the AXPs point, in turn, to less active magnetic fields. I will present a simple model of a twisted, non-potential magnetosphere, developed with Lyutikov and Kulkarni, and show how the persistent X-ray emission is modified by multiple scattering at the ion and electron cyclotron resonances. The energetics of SGR flares suggests that the magnetic field is strongly wound up inside the star, and provides a hint that these sources were born rapidly rotating. Finally, I will show how calculations of magnetic field transport through the deep crust and core of the star, when contrasted with the observed lifetimes of the SGRs and AXPs as bright X-ray sources, can constrain their internal and surface composition, and shed some light on the possible connection with a growing class of nearby soft X-ray pulsars.
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