Astronomers Measure The Direct Distance To A Magnetar For The First Time

Artist's conception of a magnetar releasing a powerful burst of radiowaves.  Sophia Dagnello, NRAO/AUI/NSF

Researchers have finally managed to measure the direct distance of a magnetar in the Milky Way from Earth. Magnetars are neutron stars where the collapsed core has gone supernova with incredibly strong magnetic fields, hence the name.

As reported in the Monthly Notices of the Royal Astronomical Society, the team used the parallax method to measure the distance. The team took measurements from January to November of 2019, then again during March and April of 2020. This allowed them to measure its position in the sky when the Earth was at opposite places in its orbit in order to detect the shift in the magnetar's apparent position relative to other objects in the background. Thanks to simple geometry, the team was able to estimate that magnetar XTE J1810-197 is located 8,100 light-years from Earth.

Parallax is a way for astronomers to directly calculate the distance to a celestial body using geometry. In this case, a magnetar within our own Milky Way galaxy. The illustration is not to scale. Sophia Dagnello, NRAO/AUI/NSF

“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,” lead author Hao Ding, a graduate student at the Swinburne University of Technology in Australia, said in a statement.

The team used the Very Long Baseline Array (VLBA), a network of radio telescopes extending in longitude from the Virgin Islands to Hawaii, with several sites across the contiguous United States. The team hopes to use the VLBA to determine the distance of more of these peculiar objects, which might provide insight into the still-mysterious fast radio bursts (FRBs).

FRBs are incredibly short, powerful emissions of radio waves. A few extragalactic FRBs have been followed back to their galaxy of origin and researchers believe that magnetars might be involved in those emissions. Just a few months ago, researchers reported the first FRB from within our own galaxy. 

“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,” explained Adam Deller, also of Swinburne University. “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."

XTE J1810-197 is a rare magnetar known to emit radio pulses. It was detected doing so from its discovery in 2003 through 2008. Then mysteriously, it stopped for a decade. It started emitting bright radio pulses again in December 2018. 

“We know that pulsars, such as the one in the famous Crab Nebula, emit ‘giant pulses,’ much stronger than their usual ones. Determining the distances to magnetars will help us understand this phenomenon, and learn if maybe FRBs are the most extreme example of giant pulses,” Ding explained.

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