An enigma, wrapped in a puzzle, surrounded by theoretical

[HysteryDiagnosis]

sleight of hand. Heh... they may have to dig deeper, until they hit rock bottom I imagine.

http://chandra.harvard.edu/photo/2010/sgr0418/


A slowly rotating neutron star with a weak surface magnetic field is giving off bursts of X-rays and gamma-rays.

This discovery may have implications for how some of the most powerful magnets in the cosmos evolve.

Several NASA telescopes including Chandra, Swift, RXTE, XMM-Newton and Fermi contributed to these results.


As neutron stars rotate, the radiation of low frequency electromagnetic waves or winds of high-energy particles carry energy away from the star, causing the rotation rate of the star to gradually decrease. Careful monitoring of SGR 0418 was possible because Chandra and XMM-Newton were able to measure its pulsation period even though it faded by a factor of 10 after the initial detection. What sets SGR 0418 apart from other magnetars is that careful monitoring over a span of 490 days has revealed no detectable decrease in its rotation rate.

The lack of rotational slowing implies that the radiation of low frequency waves must be weak, and hence the surface magnetic field must be much weaker than normal. But this raises another question: where does the energy come from to power bursts and the persistent X-ray emission from the source?

The generally accepted answer for magnetars is that the energy to power the X- and gamma-ray emission comes from an internal magnetic field that has been twisted and amplified in the turbulent interior of the neutron star, as depicted in the illustration above. Theoretical studies indicate that if the internal field becomes about ten or more times stronger than the surface field, the decay or untwisting of the field can lead to the production of steady and bursting X-ray emission through the heating of the neutron star crust or the acceleration of particles.

A crucial question is how large an imbalance can be maintained between the surface and interior fields. SGR 0418 represents an important test case. The observations already imply an imbalance of between 50 and 100. If further observations by Chandra push the surface magnetic field limit lower, then theorists may have to dig deeper for an explanation of this enigmatic object.

[Hardrada]

1. It's bad enough in the dental office.