I\'ve been reading up on some pulsar emission theory (admittedly written in the

Question

I've been reading up on some pulsar emission theory (admittedly written in the 70's and 80's, but I figured that's a good place to start), namely this review by Curtis Michel as well as the book Black Holes, White Dwarves and Neutron Stars - Shapiro and Teukolsky.

They both mention that a pulsar predominantly emits radiation from it's magnetic poles, even though it has a dipolar magnetic field. In the case of a charged plasma-filled magnetosphere, I understand that the charged particles (electrons/positrons) are pulled out from the surface due to the large electric field, and this causes them to radiate in the direction of the magnetic pole, but why don't they radiate while circulating around the magnetic field lines?

Surely since the field lines are curving themselves, they will provide acceleration to the charged particles causing them to radiate? Or am I missing something?

Explanation / Answer

First, Shapiro and Teukolsky is gospel---it will never be outdated.

Regarding your question: are you asking why emission doesn't come from the entire magnetic field region? I.e. why doesn't emission come from everywhere along the field-lines connecting the poles?

The most important answer is that there is radiation from the particules trapped along the closed field-lines --- it's just not where the strongest emission comes from. The strength of the emission is roughly proportional to the square of the magnetic field strength, ?B2, and remembder that magnetic field strength corresponds to the density of field-lines in a depiction like the one above. Clearly the field-lines are most dense at the poles, and thus the strongest fields, and the strongest radiation come from there.

When you're looking at x-ray emission, it also becomes important that the electrons can actually escape the system from the open field lines, allowing them to compton scatter photons.

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