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The proper motion of the magnetar J1550-5418 measured with VLBI

Submitter: Adam Deller
Description: Whilst "ordinary" neutron stars exhibit extraordinarily strong magnetic fields (typically one million million times stronger than that of the Earth!), magnetars are even more extreme - up to a thousand times stronger again. When the existence of magnetars was first proposed, they were expected to possess extremely high velocities of 1000 km/s or more, a consequence of an extremely strong “kick” during the supernova formation process. However, testing this hypothesis has proved difficult, since most magnetars exhibit transitory radio and x-ray emission and so are difficult to follow for long enough to measure their proper motion across the sky.

Using the Long Baseline Array (LBA) in Australia, a team led by ASTRON researcher Adam Deller was able to measure the proper motion for the radio magnetar J1550-5418, and constrain its velocity to be between 160 and 410 km/s. The results were recently published in the Astrophysical Journal Letters (here). The positional changes in right ascension and declination over the course of two years is shown in the image above, along with the fitted proper motion. This measurement was extremely challenging, as the source is deep in the Galactic plane and highly scattered, and its radio emission was generally weak and/or highly variable. Several triggered Target of Opportunity observations with the LBA were required to complete the observing program. This was just the second measurement of a transverse velocity for a magnetar - the first being 200 km/s for the object XTE J1810-197, made with the Very Long Baseline Array in the US in 2007. Taken together, these two velocity measurements argue strongly against large birth kicks for magnetars - if all magnetars had a 3D space velocity of 1000 km/s, the probability of obtaining the two measurements so far is just 0.1%.

Further information: http://adsabs.harvard.edu/abs/2012ApJ...748L...1D
Copyright: Adam Deller
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