Radio emission from a pulsar’s magnetic pole revealed by general relativity

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https://phys.org/news/2019-09-radio-emission-neutron-star-magnetic.html

Radio emission from a neutron star's magnetic pole revealed by General Relativity

by Max Planck Society

Representation of the precessing pulsar J1906+0746 (with the spin vector in red color) around the total angular momentum vector (blue vector). Two radio beams are emitted above the opposite magnetic poles of the pulsar, along the magnetic axis (grey arrow). As the radio beams cross through our line of sight, we can reconstruct the emission maps of the beams as shown with the circular maps at the edges of the two beams. Credit: Gregory Desvignes (MPIfR Bonn / Paris Observatory)

Pulsars in binary systems are affected by relativistic effects, causing the spin axes of each pulsar to change their direction with time. A research team led by Gregory Desvignes from the Max Planck Institute for Radio Astronomy in Bonn, Germany, has used radio observations of the source PSR J1906+0746 to reconstruct the polarised emission over the pulsar's magnetic pole and to predict the disappearance of the detectable emission by 2028. Observations of this system confirm the validity of a 50-year old model that relates the pulsar's radiation to its geometry. The researchers are also able to precisely measure the rate of change in spin direction and find an excellent agreement with the predictions of Einstein's general theory of relativity.

 

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the paper:

https://science.sciencemag.org/content/365/6457/1013

Radio emission from a pulsar’s magnetic pole revealed by general relativity:

General relativity reveals pulsar beams

Pulsars are rotating neutron stars that emit beams of radio waves along their magnetic poles, seen as regular pulses if the beam points toward Earth. Desvignes et al. monitored a pulsar for more than a decade, observing how its radio pulses vary. General relativity causes precession of the rotation axis, because of the influence of a binary companion. In 2005, two pulses per rotation were visible, one from each magnetic pole, but by 2018 one had precessed out of our line of sight and disappeared. Mapping the radio emission across the magnetic pole determines the beaming angle, the angular region in which a radio observer can detect a pulsar.

Science, this issue p. 1013

Abstract:

Binary pulsars are affected by general relativity (GR), causing the spin axis of each pulsar to precess. We present polarimetric radio observations of the pulsar PSR J1906+0746 that demonstrate the validity of the geometrical model of pulsar polarization. We reconstruct the (sky-projected) polarization emission map over the pulsar’s magnetic pole and predict the disappearance of the detectable emission by 2028. Two tests of GR are performed using this system, including the spin precession for strongly self-gravitating bodies. We constrain the relativistic treatment of the pulsar polarization model and measure the pulsar beaming fraction, with implications for the population of neutron stars and the expected rate of neutron star mergers.