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A Sleeping Magnetar Star Just Woke Up

March 15, 2019
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A Sleeping Magnetar Star Just Woke Up

An odd magnetar star has woken up after a decade of radio silence. The spinning star is now spitting bright flashes of radio waves at us again.

A team of British/German astronomers has turned its telescopes toward a radio magnetar known as XTE J1810–197. This dense spinning star turned on in December 2018 after an almost decade-long period of dormancy.

Researchers have presented results of these observations in a paper published March 6 on arXiv.org.

Magnetars are neutron stars – remnants of larger stars the size of Manhattan – with extremely strong magnetic fields. These incredibly dense collapsed stars can generate magnetic fields that are around 1 quadrillion times more powerful than Earth’s.

XTE J1810–197 is one of only 23 magnetars and one of just four radio magnetars ever discovered.

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Astronomers discovered radio emission from this magnetar in 2004, a year after they’ve observed an X-ray outburst from this source. Then, in late 2008, it went dormant and no longer emitted radio waves. On Dec. 8, 2018, it woke up again.

“After spending almost a decade in a radio-quiet state, the Anomalous X-ray Pulsar XTE J1810–197 turned back on in early December 2018. We have observed this radio magnetar at 1.5 GHz with ∼daily cadence since the first detection of radio reactivation on December 8, 2018,” the astronomers wrote in the paper.

Interestingly, the profile of this new rhythm of radio waves shows some pretty big differences compared to previous observations.

“The pulse variations seen so far from the source have been significantly less dramatic, on timescales from hours to months, than seen in 2006,” the research team report.

The researchers report that the magnitude of the spin frequency of XTE J1810–197 has increased by a factor of 2.6 over the 48-day data set. The most rapid increase has occurred during the first 15 days.

The astronomers have also identified 50-millisecond oscillations seen in the pulse profile of the magnetar for about 10 days after it was re-detected. These oscillations have a characteristic frequency of 20 Hz. And are seen at different frequencies and different telescopes at the same time. The authors of the paper assume that such oscillations could be related to surface waves triggered in the neutron star crust with a wide spectrum of frequencies.

However, astronomers will continue observing XTE J1810–197 in order to find out whether or not the pulse profile of the magnetar will experience more variations over time.

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Thumbnail image: Artist’s conception of a powerful magnetar. Credit: ESO/L. Calçada.

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