Using NSF’s Very Long Baseline Array, an international team of astronomers has made the direct geometric measurement of the distance to XTE J1810-197, a magnetar located in the constellation of Sagittarius.
An artist’s impression of a magnetar emitting a burst of radiation. Image credit: Sophia Dagnello, NRAO / AUI / NSF.
Magnetars are a variety of neutron stars — the superdense remains of massive stars that exploded as supernovae — with extremely strong magnetic fields.
A typical magnetar magnetic field is a trillion times stronger than the Earth’s magnetic field, making magnetars the most magnetic objects in the Universe.
They can emit strong bursts of X-rays and gamma rays, and recently have become a leading candidate for the sources of fast radio bursts (FRBs).
Discovered in 2003, XTE J1810-197 was the first of only six such objects found to emit radio pulses.
It did so from 2003 to 2008, then ceased for a decade. In December of 2018, it resumed emitting bright radio pulses.
Swinburne University of Technology astronomer Hao Ding and colleagues used the Very Long Baseline Array (VLBA) to regularly observe XTE J1810-197 from January to November of 2019, then again during March and April of 2020.
By viewing the magnetar from opposite sides of the Earth’s orbit around the Sun, they were able to detect a slight shift in its apparent position with respect to background objects much more distant.
This effect, called parallax, allows astronomers to use geometry to directly calculate the object’s distance.
“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,” Ding said.
“Having a precise distance to this magnetar means that we can accurately calculate the strength of the radio pulses coming from it,” said Dr. Adam Deller, also of Swinburne University.
“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.”
“A key to answering this question will be to get more distances to magnetars, so we can expand our sample and obtain more data,” said Dr. Walter Brisken, an astronomer at the National Radio Astronomy Observatory.
“The VLBA is the ideal tool for doing this.”
“We know that pulsars, such as the one in the famous Crab Nebula, emit ‘giant pulses,’ much stronger than their usual ones,” Ding said.
“Determining the distances to magnetars will help us understand this phenomenon, and learn if maybe FRBs are the most extreme example of giant pulses.”
The team’s paper was published in the Monthly Notices of the Royal Astronomical Society.
_____
H. Ding et al. A magnetar parallax. MNRAS, published online August 21, 2020; doi: 10.1093/mnras/staa2531
This article is based on text provided by the National Radio Astronomy Observatory.
