Our next story looks at a neutron star with an extreme magnetic field that is located some 8,100 light-years away. Cataloged as XTE J1810-197, this tiny object regularly pulsed in the radio from 2003-2008. Then it stopped for ten years, only to begin pulsing again in December 2018. Since its reawakening, this system has been regularly observed by a global network of radio telescopes through the Very Long Baseline Array (VLBA). This includes observations from January to November 2019, and then roughly 6 months later, in March and April of 2020. 

The discovery of magnetars is relatively recent, and there are still a lot of unknowns about their physics. We know, thanks to an outburst in December 2004, that these objects can release so much energy that a magnetar on the other side of our galaxy can damage satellites here at Earth. 

When fast radio bursts (FRBs) were discovered in 2007, magnetars seemed to be a reasonable possible source of these millisecond bursts of energy, and on April 28 of this year, one magnetar, SGR 1935+2154 even emitted a brief radio burst that, while not as strong as a fast radio burst, was consistent enough with their behavior to make everyone take notice. One issue, however, has been that without actual distances to magnetars, we can only estimate the true luminosity of their outbursts.

This is where those high-resolution, six-months apart VLBA observations become important. The Earth’s change in location allows astronomers to measure the apparent change in position of XTE J1810-197 relative to background objects like quasars, and this gets a distance. According to Hao Ding, the first author on a new paper in Monthly Notices of the Royal Astronomical Society (MNRAS): This is the first parallax measurement for a magnetar, and shows that it is among the closest magnetars known — at about 8,100 light-years — making it a prime target for future study.

Coauthor Adam Deller goes on to state: Having a precise distance to this magnetar means that we can accurately calculate the strength of the radio pulses coming from it. If it emits something similar to an FRB, we will know how strong that pulse is. FRBs vary in their strength, so we would like to know if a magnetar pulse comes close or overlaps with the strength of known FRBs. 

This is only one magnetar, and it is only a starting point. More distances will need to be determined, so there is a greater chance that we’ll catch something bursting that we know the distance to. 

More Information

NRAO press release 

“A Magnetar Parallax,” H. Ding et al., 2020 Aug. 21, Monthly Notices of the Royal Astronomical Society (preprint on arxiv.org)