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Erratic pulsar baffles astronomers

The European Space Agency reports that new observations of a pulsar using its XMM-Newtown are baffling astronomers. This particular pulsar, who radio emission is known to “switch on and off” periodically, exhibits the same twitchy behavior when observed at X-ray wavelengths. The space agency notes that these observations have renewed the debate about the mechanisms powering the emission from pulsars.

Astronomers contend that pulsars might top the list of puzzling astronomical objects. They were first identified as flickering sources of radio waves and soon after understood as spinning stars. Despite the discovery of several thousand pulsars since the first one was identified in 1967, astronomers still lack a good understanding of the mechanisms that power them.

“There is a general agreement about the origin of the radio emission from pulsars: It is caused by highly energetic electrons, positrons and ions moving along the field lines of the pulsar’s magnetic field, and we see it pulsate because the rotation and magnetic axes are misaligned,” says Wim Hermsen from SRON, the Netherlands Institute for Space Research in Utrecht, The Netherlands. “How exactly the particles are stripped off the neutron star’s surface and accelerated to such high energy, however, is still largely unclear.”

Hermsen and his colleagues examined a particular pulsar known as PSR B0943+10. Observations of this pulsar were made with the ESA’s XMM-Newtown and several ground-based radio telescopes. Hermsen says that the results of his study challenge all existing models for pulsar emission.

“Many pulsars have a rather erratic behavior  in the space of a few seconds, their emission becomes weaker or even disappears for a while, just to go back to the previous level after some hours,” says Hermsen. “We do not know what causes such a switch, but the fact that the pulsar keeps memory of its previous state and goes back to it suggests that it must be something fundamental.”

Astronomers note that in order for the radio emission to vary so completely on the short timescales observed, the pulsar’s global environment must undergo a very quick – and reversible – transformation.

Since the switch between a pulsar’s bright and quiet states links phenomena that occur on local and global scales, a thorough understanding of this process could clarify several aspects of pulsar physics. Unfortunately, we have not yet been able to explain it,” adds Hermsen.

Hermsen and his team set out to look for a similar pattern in X-rays to determine what causes this puzzling behavior. PSR B0943+10 seemed like an ideal candidate because of its erratic behavior at radio wavelengths and for its X-ray emission. Hermsen says that this pulsar’s X-ray emission is rather bright for its age. Young pulsars shine brightly in X-rays, but this pulsar is five million years old. Astronomers think that the X-ray emission comes from the magnetic poles.

After analyzing the XMM-Newtown data, astronomers made a baffling discovery.

“The X-ray emission of pulsar PSR B0943+10 beautifully mirrors the switches that are seen at radio wavelengths but, to our surprise, the correlation between these two emissions appears to be inverse: when the source is at its brightest in radio waves, it reaches its faintest in X-rays, and vice versa,” says Hermsen.

Astronomers also found that the astronomical object pulsates in X-rays only during the X-ray-bright phase.

Hermsen says that later in 2013, his team hopes to repeat the same study for another pulsar, which also exhibits similar radio emission properties, but has a different geometrical configuration.

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