The first object within the Milky Way galaxy that emits rapid radio bursts is now officially repeater.
In a new peer-reviewed paper, SGR 1935 + 2154 describes spitting out two of the more powerful radio signals that have been observed from extragalactic sources.
The new signals, however, are not all equal strengths. This suggests that there may be more than one process inside the magnetors that are capable of generating these esoteric explosions – and that SGR 1935 + 2154 can be a dream come true, an excellent laboratory for understanding them.
Since his discovery in 2007, rapid radio burst has been a puzzle. They are extremely powerful bursts of energy only at radio frequencies that last only a millisecond. And there were many difficulties to find out what they were.
By April of this year, rapid radio bursts (FRBs) were detected only from outside the Milky Way, millions of light-years away – far from overcrowded, much like they would in a general area. Track galaxy on location. For most of them, however, we are not able to do so either.
And while some have been found to be repeating, most FRB sources have been detected to flare up only once, and without warning, which makes them incredibly difficult (but not impossible) to trace.
However, although a handful of FRBs were traced to an original galaxy, astronomers were not close to confirming a definitive source of the signals. SGR 1935 + to 2154.
On 28 April 2020, within our own galaxy, a dead, highly magnetized star just 30,000 light-years away, was recorded emitting radio waves over an incredibly powerful, millisecond period.
Once the signal was corrected for distance, astronomers found that it was not as powerful as the extragalactic FRB, but everything else about it conformed to the profile. The incident was officially confirmed as FRB earlier this month, and given a name – FRB 200428.
Since then, astronomers have been carefully tracking FRB 200428. And, adequately, on 24 May 2020, the Westerbork Synthesis Radio Telescope in the Netherlands caught two milliseconds long radio bursts from magnetism, 1.4 seconds apart.
The much larger FRB signal was detected on May 3 by the Five-Hundred Meter Aperture Spherical Radio Telescope (FAST) in China.
And already these three new signs are telling us a lot, as described in a paper led by astrophysicist Franz Kirsten of Chalmers University of Technology in Sweden.
From FRB 200428 the early April bursts were extremely bright – a combined flow of 700 kilogenski milliseconds. There were too many unconscious in the three follow-up signs.
In 60 milliseconds, Faust was the most unconscious. Westerbark’s two signs were 110 Janaki milliseconds and 24 Janasky milliseconds, respectively.
This is quite a limitation of signal strength, and it is unclear why.
“Assuming that a single emission mechanism is responsible for all reported radio bursts from SGR 1935 + 2154, it should be such that the burst rate is independent of the amount of energy emitted by more than seven orders of magnitude.” The researchers wrote in their paper.
“Alternatively, different parts of the emission cone may cross our line of sight if the beaming direction changes significantly over time.”
Magnetiers are fun animals. They are a type of neutron star – a small collapsed core of a dead star, which is about 1.1 to 2.5 times the mass of the Sun, but is enclosed in a circle about 20 kilometers (12 mi) across.
Magneters combine this into a highly powerful magnetic field – about 1,000 times more powerful than a normal neutron star, and a quadrillion times more powerful than Earth.
We do not really know how they are formed (recent evidence suggests that neutron stars may be the only way), but we know that they undergo 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 magnet. Two competing forces commonly seen in high-energy X-rays and gamma radiation are believed to produce instabilities, magnetar quakes and magnetar flares.
SGR 1935 + 2154 is known to undergo a period of X-ray activity; This is perfectly normal for a magnetor. But the first FRB – that 28 April one – was also an X-ray flare, something that had never been seen in the FRB before. However, the three new signals showed no signs of X-ray counterparts.
And, when the team worked in the opposite direction, studying X-ray data from the magnet and trying to relate it to their radio counterparts, they found nothing there.
“Therefore it seems that the majority of X-ray / gamma-ray bursts are not associated with pulsed radio emission,” the researchers wrote.
“The criteria and fluent we measure for X-ray bursts are consistent with the typical values observed for SGR 1935 + 2154, fitting with the idea that atypical, rather than radio bursts, are associated with harder-X-ray bursts. Huh.
And some questions remain. Some fast radio burst sources exhibit periodicity – a pattern – in their signals.
We have not seen with SGR 1935 + 2154. It is possible that we do not have enough data. It is possible that those periodic FRBs are in binary systems. And it is possible that magneters are only one source of FRBs, and others remain to be discovered.
But the magnet is not done yet.
On 8 October 2020, it was recorded to spit out three more radio bursts, over a period of three seconds. That data is still under analysis, but it marks the beginning of a good collection of signals that can help us look for patterns, or clue as to the behavior of magnets that spit them out ( A more recent paper suggests that magnetar quakes are responsible).
Researchers wrote in their paper, “Therefore SGR 1935 + 2154 is not an innocuous analogue of the extralactic FRB population. Nonetheless, magnetists can often explain the diverse phenomena observed from FRBs.”
“Probably far, periodically active FRB sources are brighter and more active because they are significantly lower than SGR 1935 + 2154 and because their magnetospheres are degraded by the ionized air of a nearby companion. Likewise, perhaps non- Repeated FRBs are older, non-inactivated and thus less active. Detailed characterization of the FRB local environment is important for investigating these possibilities. “
The research has been published in Nature Astronomy.