Hot
spots on neutron stars:
Phase variation in the X-ray emissions from three pulsars has been
examined using the EPIC instrument on XMM-Newton. In a paper published
this week in the Astrophysical Journal scientists reveal that analysis
of spectra over the pulsar rotation period has enabled them to track
hot spots on the surface of the neutron star.
The spectrum from an object such as a pulsar is made up from a
number of components such as:
1. Low temperature thermal emission
2. High temperature thermal emission
3. Non-thermal emission
Each of these components contributes in different amounts to make
up the overall spectrum profile. By scaling the relative contributions
from each element it is possible to derive the observed spectral
profile.
The animation above shows the phase variation of the X-ray emissions
detected from PSR 1055-52, a middle aged neutron star (~500 000
thousand years old), located at about 2000 light-years away from
us. The star rotates about five times every second.
The star emission has been divided in ten parts, corresponding
to one tenth of the star rotation, and spectra have been obtained
for each phase interval.
XMM-Newton data is shown in red, lower temperature emissions in
green, the higher temperature ‘hot spot’ emission is
in violet and non-thermal emissions in blue.
For almost half of the stars' rotation period the violet line disappears
as the hot spot region rotates onto the far side.
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