The first object in the Milky Way galaxy, caught emitting fast radio bursts, is now officially a repeater.
A new peer-reviewed article describes SGR 1935 + 2154, which emits two more powerful radio signals compatible with those observed from extragalactic sources.
However, the new signals are not equally strong. This suggests that there may be more than one process inside the magnetars that can cause these mysterious outbursts – and that SGR 1935 + 2154 could be a dream come true, an excellent laboratory for understanding them.
Fast radio bursts have been a puzzle since they were discovered in 2007. They are extremely powerful bursts of energy only at radio frequencies, lasting at most milliseconds. And there were a few major difficulties in figuring out what they were.
By April of this year, fast radio waves (FRBs) had been detected just outside the Milky Way, millions of light-years away, too far to do more than, at most, be traced to a common region in another galaxy. For most of them, however, we have not even been able to do so.
And although several of them have been repeated, most FRB sources have been detected only once and without warning, making them extremely difficult (but not impossible) to trace.
However, although a handful of FRBs were traced to a galaxy of origin, astronomers were no closer to confirming a specific source of signals. Until SGR 1
On April 28, 2020, a dead, highly magnetized star was recorded in our own galaxy, just 30,000 light-years away, emitting an incredibly powerful burst of radio waves lasting milliseconds.
After the distance-adjusted signal, astronomers found that it was not as powerful as the extragalactic FRBs, but everything else in it matched the profile. The event was officially confirmed as FRB earlier this month and was named FRB 200428.
Since then, astronomers have been closely monitoring FRB 200428. And, of course, on May 24, 2020, the Westerbork Synthesis Radio in the Netherlands captured two milliseconds of radio eruptions from the magnetar with an interval of 1.4 seconds.
A much weaker FRB signal was also detected by the 500-meter aperture spherical radio telescope (FAST) in China on May 3.
And now these three new signals tell us a lot, as described in an article led by astrophysicist Franz Kirsten of Chalmers University of Technology in Sweden.
The initial April bursts from FRB 200428 were extremely bright – a combined fluence of 700 kilojoule milliseconds. The three subsequent signals were much weaker.
FAST was the weakest, with 60 millionth milliseconds. The two signals from Westerbork were 110 jansky milliseconds and 24 jansky milliseconds, respectively.
This is a fairly large range of signal strength and it is not clear why.
“Assuming that a single emission mechanism is responsible for all reported radio bursts of SGR 1935 + 2154, it must be of such a type that the rate of explosion is almost independent of the amount of energy emitted for more than seven orders of magnitude,” they wrote. researchers in their report.
“Alternatively, different parts of the emission cone may cross our line of sight if the direction of emission changes significantly over time.”
Magnetars are fun animals. They are a neutron star type – the tiny collapsed core of a dead star, about 1.1 to 2.5 times the mass of the Sun, but packaged in a sphere only 20 kilometers (12 miles) away.
Magnetarians add to this insanely powerful magnetic field – about 1,000 times more powerful than a normal neutron star and a quadrillion times more powerful than Earth’s.
We really don’t know how they form (recent data suggest that colliding neutron stars may be one way), but we do know that they go through periods of intense destruction and activity.
As gravity pushes inward to try to hold the star together, the magnetic field pulls outward, distorting the shape of the magnetar. The two competing forces are thought to produce instability, magnetic tremors and magnetic eruptions, which are commonly seen with high-energy X-rays and gamma radiation.
It is known that SGR 1935 + 2154 goes through periods of X-ray activity; this is normal for a magnetar. But the first FRB – the one on April 28 – was also accompanied by an X-ray flash, something never seen before in the FRB. However, the three new signals show no signs of X-ray analogues.
And when the team worked in the opposite direction, studying X-ray data from the magnetar to try to connect them to radio signals, they also found nothing.
“Therefore, most X-rays / gamma rays do not appear to be associated with pulsed radio emission,” the researchers wrote.
“The parameters and fluences we measure for X-ray bursts are in line with the typical values observed for SGR 1935 + 2154, which fits the idea that radio waves are instead associated with atypical, harder X-ray bursts.
And some questions remain. Some sources of fast radio bursts show periodicity – pattern – in their signals.
We haven’t seen this with SGR 1935 + 2154. We may not have enough data. It is possible that these periodic FRBs are in binary systems. And it is extremely possible that magnetars are only one source of FRB, and others remain to be discovered.
But the magnetar is not over yet.
On October 8, 2020, the spitting of three more radio waves was recorded for a period of three seconds. These data are still being analyzed, but this marks the beginning of a good collection of signals that could help us look for patterns or clues to the behavior of the magnet that spits them out (another recent article suggests that earthquakes with a magnet are responsible).
“So SGR 1935 + 2154 is not a perfect analogue of the extragalactic population FRB. However, magnetars can credibly explain the various phenomena observed by FRB,” the researchers wrote in their report.
“Perhaps the distant periodically active sources of FRBs are brighter and more active because they are significantly younger than SGR 1935 + 2154 and because their magnetospheres are disturbed by the ionized wind of the nearby satellite. Similarly, perhaps the non-repeating FRBs are older, non-interacting and thus less active. Detailed characterization of the FRB local environment is crucial to explore these possibilities. “
The study was published in Natural astronomy.