The cosmic cow explained - radio signals point to an explosion and a newborn magnetar | WPN World People News

Among short-lived sky phenomena, AT2018cow (The Cow) is an astronomical event like no other. First detected in 2018, it received its memorable name by chance according to alphabetical protocol to classify such events. However, it was not just its name that makes it memorable. AT2018cow was identified in a relatively nearby galaxy (about 200 million light years away). Its proximity, exceptionally brief brightness and unusually high temperature led to widespread attention upon discovery.

The cosmic cow explained - radio signals point to an explosion and a newborn magnetar

Originally discovered with optical telescopes, follow up observations were conducted across wavelengths from X-ray to radio. These observations indicated that there is a ‘central engine' which powered the event. This resulted in theories that the mysterious source could be a supernova - a star whose central core collapsed - or a Tidal Disruption Event (TDE), where a white dwarf star is being ripped apart as it approaches a massive black hole.

In the current study, an international team was led by Prashanth Mohan, astronomer at the Shanghai Astronomical Observatory, China.

"Both these theories suggested that the observed central engine would produce relativistic jets - a high energy expulsion of material. These jets, when aligned with our line of sight, would appear much brighter as ionised matter is accelerated close to the speed of light, and could be responsible for the exceptional brightness of the event. With a network of radio telescopes, we decided to test whether that was the case", explains Tao An.

The team monitored the radio afterglow to search for a relativistic jet from the Cow. They conducted five observations over the course of a year, using a total of 21 telescopes from the European VLBI Network (EVN). The high-resolution radio imaging provided by the EVN, led the team to a surprising conclusion: there was no sign of a relativistic jet.

"These most detailed images in the radio regime do not show any relativistic motion or expansion during this time period. That argues against a jet in the Cow, at least later in its evolution. Instead it seems that the Cow was intrinsically bright and originated from a star exploding as a supernova", says Jun Yang, astronomer at Onsala Space Observatory, Chalmers University of Technology in Sweden.

Further, the astronomers' observations reveal physical conditions that can only be explained by the presence of a neutron star with extremely strong magnetic fields (a magnetar), which was born in the explosion.

"We see signs that material from the explosion expanded into a dense, magnetized environment. The way the radio signals faded is just what we might expect if the Cow's "central engine" is a magnetar which formed from the collapse of a star's core" says Prashanth Mohan.

Such characteristics point to another intriguing possibility, the scientists suggest. Interaction of a magnetar with its strongly magnetized environment around it might also produce short enigmatic phenomena known as Fast Radio Bursts (FRBs).

"The EVN is the most sensitive standalone VLBI network in the world that has delivered cutting edge results in the field of transient science. It has by now provided the most accurate localizations of two FRBs. There is an intriguing possibility that there may be a link between FRBs and other type of transient sources (like the event that produced 2018ATcow), but this requires further studies", concludes Zsolt Paragi from the Joint Institute for VLBI ERIC (JIVE).

Source: Joint Institute for VLBI ERIC