SKA precursor telescopes don ‘sunglasses’ to find brightest ever pulsar

BY RACHEL RAYNER (CSIRO)

An international research team has used a new observation technique to discover the brightest extragalactic pulsar known, and it could even be the most luminous one ever found. The findings have been published in The Astrophysical Journal.

A pulsar is a rapidly rotating neutron star – a remnant of a dead star - that emits two beams of circularly polarised radio light. As the beams flash across space they create a unique timing and polarisation signature. Around 3,000 pulsars have been detected inside our galaxy, while those in neighbouring galaxies, the Large Magellanic Cloud and Small Magellanic Cloud, only number around 30. This may be because they have fewer pulsars, being smaller dwarf galaxies compared to our own, but most pulsars would also be too faint for our telescopes to detect at that distance (around 200,000 light years away).

Traditional methods of finding pulsars look for the flickering time signature in telescope data but can miss those that are too fast or too slow.

The research team instead applied a new method of seeking out pulsars to CSIRO’s ASKAP radio telescope. By using the astronomical version of “sunglasses” to capture light that is polarised, they spotted an intriguing light source in the Large Magellanic Cloud. Follow-up observations by SARAO’s MeerKAT telescope in South Africa confirmed that researchers had found a never-before-seen pulsar that is 10 times brighter than any other detected outside our galaxy.

Collecting circularly polarised light is a highly specialised capability, which only a few of the world’s telescopes have the capacity to achieve. ASKAP and MeerKAT’s sophisticated engineering enables them to observe light that is linear or circularly polarised. By looking for light that is circularly polarised, pulsars outside the standard timing range can be found. The collaboration capitalised on the telescopes’ unique capabilities, namely ASKAP’s high survey speed and MeerKAT’s high resolution. ASKAP can scan large swathes of sky in this mode and then researchers, noticing anything unusual, can set MeerKAT to have a closer look.

With this team effort, new discoveries are being made. Before now, the bright spot in the radio data was overlooked as a distant galaxy.

Read the paper: https://iopscience.iop.org/article/10.3847/1538-4357/ac61dc

CSIRO acknowledges the Wajarri Yamatji as the traditional owners of the Murchison Radio-astronomy Observatory site where ASKAP is located.

A section of the Large Magellanic Cloud, captured under normal conditions by SARAO’s MeerKAT radio telescope. It is detecting all radio light, and the pulsar looks like just another source of radio light.

Credit: Yuanming Wang

The polarised light from a section of the Large Magellanic Cloud, as captured by SARAO’s MeerKAT radio telescope. In this field, MeerKAT was looking for sources that produced light that is circularly polarised. Very few objects in the sky produce this type of polarised light – pulsars being one of them.

Credit: Yuanming Wang