Roughly a yr in the past, astronomers introduced that they’d noticed an object that should not exist. Like a pulsar, it emitted commonly 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 thing, then it’s rotating too slowly to provide radio emissions by any recognized mechanism.
Now, a few of the similar crew (together with new collaborators) are again with the invention of one thing that, if something, is performing 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, generally producing weaker bursts and generally skipping them completely. Whereas the researchers suspect that, like pulsars, that is additionally powered by a neutron star, it is not even clear that it is the similar 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 be wanted for the era of radio emissions themselves. If the neutron star rotates too slowly, then its magnetic area 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’ll merely shut down, and we’ll cease observing any radio emissions from the thing.
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 article, 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 at the very least 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 find out 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 completely clear.
An enigmatic discover
The article, ASKAPJ193505.1+214841.0, was found accidentally when the Australian Sq. Kilometre Array Pathfinder telescope was used to watch the world attributable to detections of a gamma-ray burst. It picked up a brilliant radio burst in the identical area of view, however it was unrelated to the gamma-ray burst. Additional radio bursts confirmed up in later observations, as did a couple of 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 crew 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 extra observations, nevertheless, confirmed that there have been usually situations the place a 54-minute interval wouldn’t finish with a radio burst, suggesting the supply generally skipped radio emissions completely.
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 kinds of bursts differ not solely in complete power but in addition that the thing that is making them has a distinct magnetic area.
So, the researchers counsel that the thing has three modes: robust pulses, faint pulses, and an off mode, though they can not rule out the off mode producing weak radio indicators which are beneath 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 similar 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 area.
To get at this concern, the researchers estimate the energy of the magnetic area wanted to provide the bigger bursts and provide you with 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 rely on whether or not you’re 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 elucidate. It is potential that we’ll be capable to be taught extra about this newer one if we are able to get some data 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).