VLBA makes first direct distance measurement to magnetar
Work may help determine source of Fast Radio Bursts

Date:
September 18, 2020
Source:
National Radio Astronomy Observatory
Summary:
Using the VLBA, astronomers have made the first direct geometric
measurement of the distance to a magnetar. This precision
measurement to one of the most magnetic objects in the Universe
could help scientists determine if such objects are responsible
for generating the mysterious Fast Radio Bursts.



FULL STORY ========================================================================== Astronomers using the National Science Foundation's Very Long Baseline
Array (VLBA) have made the first direct geometric measurement of the
distance to a magnetar within our Milky Way Galaxy -- a measurement that
could help determine if magnetars are the sources of the long-mysterious
Fast Radio Bursts (FRBs).


========================================================================== 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 FRBs.

A magnetar called XTE J1810-197, discovered in 2003, 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.

A team of astronomers used the 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 8100 light-years --
making it a prime target for future study," said Hao Ding, a graduate
student at the Swinburne University of Technology in Australia.

On April 28, a different magnetar, called SGR 1935+2154, emitted a brief
radio burst that was the strongest ever recorded from within the Milky
Way. While not as strong as FRBs coming from other galaxies, this burst suggested to astronomers that magnetars could generate FRBs.



==========================================================================
Fast radio bursts were first discovered in 2007. They are very energetic,
and last at most a few milliseconds. Most have come from outside the
Milky Way.

Their origin remains unknown, but their characteristics have indicated
that the extreme environment of a magnetar could generate them.

"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,"
said 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," he added.

"A key to answering this question will be to get more distances to
magnetars, so we can expand our sample and obtain more data. The VLBA
is the ideal tool for doing this," said Walter Brisken, of the National
Radio Astronomy Observatory.

In addition, "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 said.

The ultimate goal is to determine the exact mechanism that produces FRBs,
the scientists said.

Ding, Deller, Brisken, and their colleagues reported their results in
the Monthly Notices of the Royal Astronomical Society.

The National Radio Astronomy Observatory is a facility of the National
Science Foundation, operated under cooperative agreement by Associated Universities, Inc.


========================================================================== Story Source: Materials provided by
National_Radio_Astronomy_Observatory. Note: Content may be edited for
style and length.


========================================================================== Journal Reference:
1. H Ding, A T Deller, M E Lower, C Flynn, S Chatterjee, W Brisken, N
Hurley-Walker, F Camilo, J Sarkissian, V Gupta. A magnetar parallax.

Monthly Notices of the Royal Astronomical Society, 2020; DOI:
10.1093/ mnras/staa2531 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2020/09/200918104236.htm

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