The Kilonova-Chasing Gravitational-Wave Optical Transient Observer is About to be Watching the Complete Sky

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The Kilonova-Chasing Gravitational-Wave Optical Transient Observer is About to be Watching the Whole Sky

Recently there has been a surge of interest in gravitational waves. After the first official discovery at LIGO / Virgo in 2015, data is available that shows how common these once theoretical phenomena actually are. Usually they are caused by inconceivably violent events, such as a merging pair of black holes. Such events also tend to emit another type of phenomenon – light. So far it has been difficult to observe any optical events associated with these gravitational wave emission events. However, a research team hopes to change this with the full implementation of the GOTO (Gravitation-Wave Optical Transient Observer) telescope.

The GOTO project is specifically designed to find and monitor the parts of the sky that other instruments such as LIGO capture gravitational waves from. The original incarnation, known as the GOTO-4 prototype, went online in 2017. This prototype in La Palma on the Canary Islands consisted of four "Unit Telescopes" (UTs), which were housed in an 18-foot dome. In 2020 this prototype was upgraded to 8 UTs to allow for a much larger view of the sky.

Image of the GOTO prototype as work.
Photo credit: GOTO project

The wide field of view is necessary for the detection of optical phenomena on the basis of gravitational waves, since the directivity of gravitational waves is known to be difficult to determine. The larger a telescope's field of view, the more likely it is to detect an event that is occurring.

For this reason, the operators of GOTO started an upgrade plan in 2020. These upgrades included an additional 8 UT in a separate dome on the same observatory to be added in early 2021. More ambitiously, the team is planning to recreate the two -array array in La Palma at the Siding Spring Observatory in New South Wales, Australia. With these telescopes on opposite sides of the world, GOTO will "enable near-24-hour observation and ensure that GOTO will be able to respond to warnings whenever they occur," according to a recently published paper.

The campus of the observatory of the University of Warwick on La Palma in the Canary Islands.University of Warwick observatory in the Canary Islands with the GOTO domes on the right.
Photo credit: GOTO project

These warnings are an extremely important part of GOTO's observation planning. They come from NASA's Gamma-Ray Coordination Network (GCN), a warning system that monitors not only gravitational waves, but other phenomena that could generate interesting optical data, such as kilonovas or gamma-ray bursts.

GOTO monitors this network via its software package, which is also a key component for the entire system operation. The GOTO Telescope Control System (G-TeCS) is a custom Python script that monitors for signals of interest, calculates which signal has the highest priority, and then physically moves the telescopes to an observation position. All of this is also possible in less than 30 seconds, which allows an extremely fast turnaround to observe these temporary phenomena of interest.

Screenshot of the GOTO software package.Screenshot of the GOTO software with a potential candidate.
Photo credit: GOTO project

Once the telescopes are in position, G-TeCS can also collect and analyze images. It compares all captured images with a calibration image and uses a type of artificial intelligence known as a "convolutional neural network" to assign a rating to the likelihood that a signal of interest was detected. As with so much AI-powered research, humans are the last part of the analysis chain. The researchers use a tool called GOTO Marshall to individually validate highly interesting targets and can also schedule follow-up observations with other telescopes in the region.

The employees of the GOTO Observatory come from 3 different continents and 5 different countries.
Photo credit: GOTO project

The entire software system is remotely controlled at the University of Warwick, which leads the GOTO project, which includes 9 other institutions from Great Britain, Australia, Thailand, Spain and Finland. As they continue to implement their planned improvements and continue to receive data, we will be able to visualize the catastrophic events associated with some of the most violent phenomena in the universe.

Learn more:
arXiv: The optical gravitational wave transient observer (GOTO)
University of Warwick: Optical Transient Gravitational Wave Observatory

Lead Image Credit: The prototype of the GOTO telescope. Photo credit: GOTO project

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