Tile 107, or “the Outlier” as it is known, is one of 256 tiles of the MWA located 1.5km from the … [+]
Pete Wheeler, ICRAR
Sensational headlines invoking beamed ‘signals’ from an object in our own Milky Way aside, an Australian-led team of astronomers has detected what is most likely an ultra-long period magnetar. No, it’s not aliens! But it is most probably a heretofore unknown class of magnetar, a highly magnetized neutron star with a magnetic field about a trillion times larger than that of Earth.
The observations, made by the Murchison Widefield Array (MWA) in Western Australia, were detailed this week in a paper appearing in the journal Nature. The detection certainly caught the Curtin University-led team in Perth by surprise but paves the way for even more extreme magnetars to be discovered by the MWA.
The source, dubbed GLEAM-XJ 162759.5-523504.3, is located only 4000 light years away within our own galaxy and is the most luminous example of its kind, the authors note. “Our analysis reveals that the source pulses every 18.18 minutes and an exhaustive of MWA’s archive yielded 71 pulses spanning January to March 2018,” the authors write.
As it spins on its axis, this putative magnetar releases a giant burst of energy three times an hour, sending out a beam of radiation that just happens to cross earth’s line of sight. And as a result, for three times each hour, was observed to be one of the brightest radio sources in the sky, says Curtin University.
“This object was appearing and disappearing over a few hours during our observations,” Hurley-Walker said in a statement. “That was completely unexpected.”
No one has ever observed a source that repeats at this period and persists for so long, Natasha Hurley-Walker, the paper’s lead author and an astrophysicist at Curtin University in Perth, told me.
But the MWA has enabled these observations as it already has 8.5 years of observations in its archive and covers a large 1000 square degree field of view.
“So, I was able to search and find 71 pulses, giving us excellent leverage to measure the periodicity very precisely,” said Hurley-Walker.
If this indeed is a magnetar, how does it convert its magnetic energy into radio waves?
There are about 30 magnetars known, and six of them do sometimes produce radio waves, says Hurley-Walker. Astronomers think that some kind of starquake or accretion event causes their magnetic field to become twisted, she says. As it untwists, it generates radio waves, and once it is finished, the radio waves stop. Known magnetars rotate every 1—10 seconds, she notes.
Hurley-Walker is now monitoring the object with the MWA to see if it switches back on, Curtin University reports. “If it does, there are telescopes across the Southern Hemisphere and even in orbit that can point straight to it,” she said in a statement.
What puzzles Hurley-Walker most about these observations?
“I am absolutely astonished that no one has ever detected a source like this,” said Hurley-Walker. “We have been mapping the sky with radio waves for about 80 years, so how did we never see these objects before?”
What’s next?
If we find more, we can start to understand this population: we can follow them up quickly while they are still active, getting information at higher time resolution, and at other wavelengths, says Hurley-Walker. If we find enough, the distributions of their properties will help us build a better picture of what they actually are, she says.
