AO helps detect Magnetar in the Cow

Artistic impression of the cosmic cow. Credit: Shanghai Astronomical Observatory, China.

The Arecibo Observatory was one of 21 telescopes involved in the large-scale European Very Large Baseline Interferometry (VLBI) Network (EVN) radio observations of the astronomical explosion AT2018cow ('the Cow'). AO, which has the largest collecting area of all of the participating telescopes, helped boost the sensitivity of the extended VLBI baselines to detect the radio signals, producing high-resolution images that enabled scientists to determine that the highly unique supernova resulted in the creation of a magnetar – a neutron star with a very strong magnetic field.

AT2018cow was initially detected on June 16, 2018 by the NASA-funded ATLAS-HKO telescope, located at the Haleakala Observatory in Hawaii and was over 10 times brighter than a typical supernova and approximately 8 times as bright as its host galaxy. The event occurred about 200 million lightyears away in the star-forming region CGCG 137-068, in the constellation Hercules.

This particular supernova caught the interest of the astronomical community because the event remained bright with a relatively constant spectrum at x-ray and UV wavelengths for nearly 3 weeks, which is unusual for a supernova. This indicated that there was likely a central engine at the core of the event, driving the explosion. Some attributed the powerful event to the tidal disruption of a star by an intermediate mass black hole, while others suggested that the core of the supernova had collapsed inward.

The explanation for the central engine was debated until the recent VLBI study, led by Dr. Prashanth Mohan, which consisted of 5 VLBI sessions lasting approximately one year. Arecibo observatory participated in the second VLBI session for the 5 GHz campaign, contributing about 4 hours of data.

From the follow-up VLBI observations, the team found that there were no relativistic jets, meaning that a supernova was a better explanation for AT2018cow. Of particular interest was how the radio signals faded from the central engine, which suggested that the supernova explosion had expanded into a dense, magnetized environment. This led the scientists to conclude that the central engine of AT2018cow is a magnetar.

Keywords: arecibo, observatory, cow, vlvi, at2018cow, magnetar, telescope, radio, astronomical, CGCG, EVN, NASA, ATLAS-HKO, supernova