[ad_1]
The first object within the Milky Way galaxy captured by emitting fast radio bursts is now officially a repeater.
In a new peer-reviewed paper, SGR 1935 + 2154 was described to emit two more powerful radio signals consistent with those seen from extragalactic sources.
The new signals, however, are not all of the same strength. This suggests that there may be more than one process within the magnetars capable of producing these enigmatic explosions and that SGR 1935 + 2154 could be a dream come true, an excellent laboratory for understanding them.
Fast radio bursts have been an enigma since their discovery in 2007. They are extremely powerful bursts of energy only in radio frequencies, lasting only milliseconds at most. And there were many great difficulties in understanding what they were.
As of April of this year, fast radio bursts (FRBs) had only been detected from outside the Milky Way, millions of light years away, too far away to do more than, at most, track them to a general region. in another galaxy. For most of them, however, we haven’t even been able to do it.
And while some have been detected repeatedly, most FRB sources have only been detected once and without warning, making them incredibly difficult (but not impossible) to track down.
However, although a handful of FRBs had been traced to a galaxy of origin, astronomers were nowhere near confirming a definite source of the signals. Up to SGR 1935 + 2154.
On April 28, 2020, a dead and highly magnetized star within our galaxy, just 30,000 light years away, was recorded emitting an incredibly powerful burst of radio waves lasting milliseconds.
Once the signal was corrected for distance, the astronomers found that it was not as powerful as extragalactic FRBs, but everything else fit the profile. The event was officially confirmed as FRB earlier this month and given a name: FRB 200428.
Since then, astronomers have been keeping an eye on FRB 200428. And, sure enough, on May 24, 2020, the Westerbork synthesis radio telescope in the Netherlands captured two millisecond radio bursts from the magnetar, 1.4 seconds apart.
A much weaker FRB signal was also detected by the five hundred meter aperture spherical radio telescope (FAST) in China on May 3.
And these three new signals already tell us a lot, as described in an article led by astrophysicist Franz Kirsten of Chalmers University of Technology in Sweden.
The first April bursts from FRB 200428 were extremely bright – a combined fluence of 700 kilojansky milliseconds. The three follow-up signals were much weaker.
FAST’s was the weakest, with 60 millijansky milliseconds. The two signals from Westerbork were 110 jansky milliseconds and 24 jansky milliseconds respectively.
That’s a fairly wide range of signal strength and it’s not clear why.
“Assuming that a single emission mechanism is responsible for all the radio bursts reported by SGR 1935 + 2154, it must be of a type such that the burst rate is almost independent of the amount of energy emitted over more than seven orders of magnitude,” the researchers wrote in their paper.
“Alternatively, different parts of the emission cone could cross our line of sight if the direction of the beam changes significantly over time.”
Magnetars are funny beasts. They are a type of neutron star: the tiny collapsed core of a dead star, about 1.1 to 2.5 times the mass of the Sun, but encased in a sphere only 20 kilometers (12 miles) in diameter.
Magnetars add to this an 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 don’t really know how they form (recent evidence suggests that colliding neutron stars might be one way), but we do know that they go through periods of intense disruption 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 instabilities, magnetar earthquakes, and magnetar flare, usually seen in high-energy X-rays and gamma radiation.
It is known that SGR 1935 + 2154 goes through periods of X-ray activity; it is quite normal for a magnetar. But the first FRB – that of April 28 – was also accompanied by an X-ray flare, something that had never been seen in an FRB before. The three new signals, however, showed no signs of X-ray counterparts.
And, when the team worked in the opposite direction, studying the magnetar’s X-ray data to try to connect it to the radio counterparts, they found nothing there either.
‘Therefore it appears that most X-rays / gamma-ray bursts are not associated with pulsed radio emissions,’ the researchers wrote.
“The parameters and fluences we measure for the X-ray bursts are consistent with the typical values observed for SGR 1935 + 2154, in line with the idea that radio bursts are instead associated with atypical and harder X-ray bursts.
And some questions remain. Some fast radio burst sources exhibit periodicity – a pattern – in their signals.
We have not seen this with SGR 1935 + 2154. It is possible that we do not have sufficient data. It is possible that those periodic FRBs are in binary systems. And it is entirely possible that magnetars are just a source of FRB, and others remain to be discovered.
But the magnetar isn’t over yet.
On October 8, 2020, three more radio bursts were recorded, over a three-second period. This data is still being analyzed, but it marks the beginning of a good collection of signals that could help us look for patterns or clues about the magnetar-spitting behavior (another recent article suggests that magnetar earthquakes are responsible).
“So SGR 1935 + 2154 is not a flawless analogue of the extragalactic FRB population. However, magnetars can plausibly explain the different phenomena observed by FRBs,” the researchers wrote in their paper.
“Perhaps distant and periodically active FRB sources are brighter and more active because they are substantially younger than SGR 1935 + 2154 and because their magnetospheres are perturbed by the ionized wind of a nearby companion. Similarly, perhaps non-repetitive FRBs are more old, non-interaction and therefore less active. The detailed characterization of local FRB environments is fundamental to study these possibilities “.
The research was published in Nature Astronomy.
.
[ad_2]
Source link
