Roughly a 12 months in the past, astronomers introduced that they’d noticed an object that should not exist. Like a pulsar, it emitted usually timed bursts of radio emissions. However not like a pulsar, these bursts have been separated by over 20 minutes. If the 22 minute hole between bursts represents the rotation interval of the item, then it’s rotating too slowly to provide radio emissions by any identified mechanism.
Now, a number of the identical staff (together with new collaborators) are again with the invention of one thing that, if something, is appearing much more oddly. The brand new supply of radio bursts, ASKAP J193505.1+214841.0, takes practically an hour between bursts. And it seems to have three totally different settings, typically producing weaker bursts and typically skipping them solely. Whereas the researchers suspect that, like pulsars, that is additionally powered by a neutron star, it is not even clear that it is the identical class of object as their earlier discovery.
How pulsars pulse
Opposite to the part heading, pulsars do not really pulse. Neutron stars can create the phantasm by having magnetic poles that are not lined up with their rotational pole. The magnetic poles are a supply of fixed radio emissions however, because the neutron star rotates, the emissions from the magnetic pole sweep throughout house in a fashion just like the sunshine from a rotating lighthouse. If Earth occurs to be caught up in that sweep, then the neutron star will seem to blink on and off because it rotates.
The star’s rotation can also be wanted for the era of radio emissions themselves. If the neutron star rotates too slowly, then its magnetic discipline will not be robust sufficient to provide radio emissions. So, it is thought that if a pulsar’s rotation slows down sufficient (inflicting its pulses to be separated by an excessive amount of time), it is going to merely shut down, and we’ll cease observing any radio emissions from the item.
We do not have a transparent concept of how lengthy the time between pulses can get earlier than a pulsar will shut down. However we do know that it is going to be far lower than 22 minutes.
Which is why the 2023 discovery was so unusual. The thing, GPM J1839–10, not solely took a very long time between pulses, however archival pictures confirmed that it had been pulsing on and off since not less than 35 years in the past.
To determine what’s going on, we actually have two choices. One is extra and higher observations of the supply we learn about. The second is to search out different examples of comparable conduct. There’s an opportunity we now have a second object like this, though there are sufficient variations that it is not solely clear.
An enigmatic discover
The thing, ASKAPJ193505.1+214841.0, was found by chance when the Australian Sq. Kilometre Array Pathfinder telescope was used to carry out observations within the space attributable to detections of a gamma ray burst. It picked up a brilliant radio burst in the identical discipline of view, however unrelated to the gamma ray burst. Additional radio bursts confirmed up in later observations, as did just a few far weaker bursts. A search of the telescope’s archives additionally noticed a weaker burst from the identical location.
Checking the timing of the radio bursts, the staff discovered that they may very well be defined by an object that emitted bursts each 54 minutes, with bursts lasting from 10 seconds to simply below a minute. Checking further observations, nonetheless, confirmed that there have been usually situations the place a 54 minute interval wouldn’t finish with a radio burst, suggesting the supply typically skipped radio emissions solely.
Odder nonetheless, the photons within the robust and weak bursts appeared to have totally different polarizations. These variations come up from the magnetic fields current the place the bursts originate, suggesting that the 2 forms of bursts differ not solely in complete power, but in addition that the item that is making them has a special magnetic discipline.
So, the researchers recommend that the item has three modes: robust pulses, faint pulses, and an off mode, though they cannot rule out the off mode producing weak radio indicators which might be under the detection capabilities of the telescopes we’re utilizing. Over about eight months of sporadic observations, there isn’t any obvious sample to the bursts.
What is that this factor?
Checks at different wavelengths point out there is a magnetar and a supernova remnant within the neighborhood of the thriller object, however not on the identical location. There’s additionally a close-by brown dwarf at that time within the sky, however they strongly suspect that is simply an opportunity overlap. So, none of that tells us extra about what produces these erratic bursts.
As with the sooner discover, there appear to be two potential explanations for the ASKAP supply. One is a neutron star that is nonetheless managing to emit radiofrequency radiation from its poles regardless of rotating extraordinarily slowly. The second is a white dwarf that has an inexpensive rotation interval however an unreasonably robust magnetic discipline.
To get at this concern, the researchers estimate the energy of the magnetic discipline wanted to provide the bigger bursts and give you a worth that is considerably larger than any beforehand noticed to originate on a white dwarf. So that they strongly argue for the supply being a neutron star. Whether or not that argues for the sooner supply being a neutron star will depend upon whether or not you are feeling that the 2 objects characterize a single phenomenon regardless of their considerably totally different behaviors.
In any case, we now have two of those thriller slow-repeat objects to clarify. It is potential that we’ll be capable of be taught extra about this newer one if we are able to get some info as to what’s concerned in its mode switching. However then we’ll have to determine if what we be taught applies to the one we found earlier.
Nature Astronomy, 2024. DOI: 10.1038/s41550-024-02277-w (About DOIs).