LIGO makes waves, Australian telescopes follow up

ASKAP and the MWA telescopes under a starry night sky. Credit: Alex Cherney (ASKAP) and Pete Wheeler (MWA).
ASKAP and the MWA telescpes - two of the four
radio telescopes involved in the LIGO/Virgo.
Click on the thumbnail for more.

The sky coverage that over 20 different facilities made for the follow-up observations.
Footprints of follow-up observations, showing
radio fields (red), optical/infrared fields (green),
and XRT fields (blue). Click on the thumbnail for more.

07 March 2016

Last month, physicists at LIGO made waves with the announcement that elusive gravitational waves – ripples in space time caused by a violent cosmic event taking place in the distant Universe – had finally been observed 100 years after Albert Einstein predicted their existence.

CSIRO’s ASKAP team played an exciting part in the follow-up observations, showcasing capabilities offered by the transient survey projects planned for the telescope.

A new scientific paper details the follow-up program that began soon after the possible gravitational wave candidate was first identified by LIGO in September 2015. Within two days of the trigger, 21 teams responded to the alert and began observations with satellites and ground-based telescopes around the world. Over the next three months, observations were performed using facilities spanning from radio to gamma-ray wavelengths.

The Australian radio telescopes involved in the EM follow-up are both located at CSIRO’s Murchison Radio-astronomy Observatory (MRO) – the Australian SKA Pathfinder (ASKAP) and the Murchison Widefield Array (MWA). Both instruments offer a wide field of view, high sensitivity and quick response times, and are complemented by high-speed supercomputing capabilities, making them valuable additions to the LIGO/Virgo collaboration.

The MWA was the first radio telescope in the world to respond to the call from LIGO to hunt down the source of the unconfirmed gravity wave detection. Soon after, ASKAP swung into action using the first of its antennas installed with phased array feed (PAF) receivers – a commissioning instrument also known as BETA, or the Boolardy Engineering Test Array. The team made multiple observations of the trigger region over the course of the following week.

The challenge of conducting follow-up gravitational wave surveys is that the source is located within a large region of sky and the positional error boxes for LIGO are therefore quite large. For telescopes with a wide field of view, like ASKAP and MWA, this is a great advantage.

“LIGO gives you two things: the area of sky to look at and the time the trigger started,” explains Keith Bannister, one of the CSIRO astronomers involved in the ASKAP follow-up, “With a wide field of view, good sensitivity and the 1 GHz observing frequency, ASKAP is an ideal instrument for finding EM counterparts. And, we now have the infrastructure in place so that when LIGO detects a trigger, we have the capability to do a follow-up observation.”

“We’re yet to detect anything, but just to be involved in this program is a great thrill,” he continues, “It’s exciting to think how much more we’ll be able to contribute with the full ASKAP telescope, when all 36 antennas are installed with Mk II PAFs.”

The MWA, through cooperative agreements with LIGO and other telescopes, is able to follow up time-critical astronomical events such as gravitational wave events and gamma-ray bursts. Having no moving parts, the MWA is very agile and can be observing the sky moments after receiving the alert.

“It’s been fantastic to follow-up this momentous event with the MWA,” says MWA Director Dr Randall Wayth of Curtin University (ICRAR), “The unique capabilities of the telescope really shone in this, allowing us to dominate with our coverage of the sky. The hardest part has been keeping this quiet for the last few months.”

The sentiment is echoed by ASKAP Project Scientist Lisa Harvey-Smith, who notes that two of the ASKAP Survey Science Projects, VAST and CRAFT, are dedicated to transient searches.

"It is very exciting for ASKAP to be involved in the international efforts to detect electromagnetic emission from this gravitational wave event. Our PAF receivers make ASKAP a very powerful instrument for detecting radio waves from these events, and our science teams are looking forward to continuing this work as part of the Early Science program that will start this year. "

Partner releases from the MWA telescope and the SKA telescope.

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