30th of April 2020 |
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Pulsar braking indices |
by Parthasarathy et al. |
Pulsars are rapidly rotating neutron stars. As they slowly lose energy,
they slow down and regular timing of pulsars allows the period derivative,
or frequency derivative to be measured.
The long-term spin-down of a pulsar can be approximated by relating
the frequency derivative to the frequency raised to the power n,
where n is referred to as the braking index.
The braking index describes the relationship between the braking
torque acting on a pulsar and its spin-frequency parameters,
and provides a probe into the physics determining pulsar temporal evolution.
For standard magnetic-dipole braking, the magnetic field
strength and the magnetic-dipole inclination angle are assumed
to be constant in time, with n=3.
Parthasarathy et al. have used ~10 years of timing observations from the Parkes radio-telescope to measure the braking index for 19 pulsars and demonstrate that the value of n can be significantly larger than the canonical value of 3. The figure above shows braking index detections (red points) and upper limits (blue points) for the complete sample of 85 pulsars. The possible implications of this finding are discussed the paper, published in Monthly Notices of the Royal Astronomical Society. |