Ok, end of day two of the 40 Years of Pulsars conference and what have we learned...
Well, pulsar emission mechanism is still a mystery; we still don't have a good handle on strong rotating magnetic fields, reconnection or field evolution; and, the population numbers for various pulsating neutron stars don't quite add up.
It is not quite as bad as I make it sound, a lot of work has been done, and the picture is coming together.
Chatting with a colleague, I get the impression that a lot of old, hard problems are close to solution, some just need an additional insight, or two, others just need a lot of hard detailed brute force slog work.
Had some fun at the end in the discussion session today, some discussion got going on modeling of magnetar spectra.
These are young, slowly rotating, very high magnetic field neutron stars, that emit a lot of high energy radiation and may undergo outbursts. Some also seem to have "hot spots" on their surface.
Looks like a new extreme magnetar may just have been found by Fernando et al - 2 second period, under 1000 year characteristic age.
Since the known magnetars are quite bright, they have pretty good x-ray spectral data, so people who like that sort of thing can do detailed model fitting.
Basically an emission function is assumed for the neutron star "surface" and the emitted flux is propagated through the neutron star atmosphere and plasma filled magnetosphere. Fits are for intensity as a function of wavelength, and polarization. There are a lot of free parameters, but also a lot of data.
Not all the physics are well known and a lot of effects that are usually small need to be calculated, in particular the magnetic fields are strong, possibly near the quantum "limit" magnetic field strengths where interesting things happen; but also approximations have to be made - the ab initio problem can not yet be done from first principles.
The calculations are interesting since knowing size (area), potential (radius) and cooling (internal structure) can put a lot of constraints on extreme physics.
So, the modelers got into a rather "free and frank" discussion; in particular as to whether it was possible to fit the observations assuming black body (one or two temperature) emission from the neutron star.
A neutron star is not, in reality, a good black body - but that does not preclude the possibility that it is an adequate approximation to start with a black body as a simple 1-2 parameter input, both because the output spectrum (over the observed spectral range) is heavily filtered by the transfer functions; and, because a lot of the time physics is robust and making incorrect assumptions will still give a correct answer (really!).
The moderator moderated, and suggested the kids go off and do something sensible like a head-to-head comparison of models fitting a consistent and real data set.
Of course these are multi-parameter models, so most of them should do just fine, for now.
Other important thing I learned, which I DID NOT KNOW before: this is why the Calvera compact object is so named
Apparently it did not come out favourably compared to the Magnificent Seven.