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Synchronous X-ray and Radio Mode Switches: a Rapid Transformation of the Pulsar Magnetosphere

Submitter: Joeri van Leeuwen & Jason Hessels
Description: Today an exciting result on chameleon-like behaviour in a radio/x-ray pulsar appears in Science. Pulsars are uniquely capable of producing emission from low-frequency radio waves all the way up to high-energy gamma-rays. We are, however, not sure where this emission is generated: close to the surface of the pulsar for the radio, and/or far out in the pulsar magnetosphere for the high-energy emission? Detecting changes in pulsar emission that happen simultaneously over multiple wavelengths is key to understanding the physical relationship between these emission sites. Now, through simultaneous observations with the LOFAR, XMM-Newton and GMRT telescopes, an international team led by Wim Hermsen (SRON) and including Jason Hessels and Joeri van Leeuwen (ASTRON) has detected synchronous switching in the radio and X-ray emission properties of PSR B0943+10.

Pulsar B0943+10 is extraordinarily bright at low radio frequency. It is special in that it has two distinct "personalities", or "radio modes". It can instantaneously switch between these modes, every few hours. In the left-hand plot, several of these modes changes can be easily seen in a 6-hr LOFAR observation. These are by far the most sensitive such observations to date. Through such simultaneous observations with LOFAR and GMRT, we were able to pinpoint all modes changes, down to a few seconds. The instrumental role LOFAR played is reflected by the inclusion of the LOFAR Pulsar Working Group and Builders List as paper authors. We next compared pulsar behaviour in radio and X-ray. To our surprise this produced the middle plot: whenever the pulsar is Bright in radio, there is no pulse profile in X-ray (top-left subpanel). But when the pulsar is Quiet in radio, it suddenly turns on in X-ray! The X-ray pulse profile is shown in the top-right subpanel.

These sudden changes in both radio and X-ray emission, which are thought to be produced very differently, mean that the entire pulsar magnetosphere must suddenly completely change state. So, through radio and X-ray `before' and `after' snapshots, we show that a magnetosphere ten times the size of Earth completely switches between two personalities, within a second -- like the two states on a flipping coin (right panel). These near-instant transformations challenge our current understanding of pulsar magnetospheres.

Copyright: ASTRON/SRON/JodrellBank/Rowe
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