There has been new construction at the Green Bank Observatory of a uniquely shaped radio telescope, which is part of CHIME – Canadian Hydrogen Intensity Mapping Experiment.
Canadian astronomers began the experiment in 2017 with four antennas at the Dominion Radio Astrophysical Observatory in British Columbia, Canada. The project has now expanded to include a smaller version of the CHIME instrument at the GBO.
“In the last few years – I’d say in the last five years – there’s been a larger experiment in Canada that is CHIME,” GBO scientist Andrew Seymour said. “It was built to map hydrogen at a very far distance away, but during that time, there’s been a lot of development with mysterious objects called Fast Radio Bursts [FRB]. These are short-lived bursts that are only in ten milliseconds natively, but they have hallmarks of coming from other galaxies.”
With the discovery of the FRBs, the GBO CHIME instrument will track the bursts to attempt to locate their origin.
While the main CHIME project is an array of four large antennas shaped like a half-pipe, the GBO will have only one antenna.
“You’re trying to figure out what’s going on by taking a large number of samples,” Seymour said. “This really isn’t easy with the GBT or things like that because they have been designed to look at a very narrow spot – with great sensitivity – so we needed something different. This telescope, which is a fixed telescope that monitors the entire sky each day seemed to be the thing.
“So, it was adapted to search for these Fast Radio Bursts,” he continued. “Normally, during this time, there are probably twenty or thirty candidates. After CHIME came online, there are over five hundred, so it really changed the game of getting the candidates.”
Seymour refers to the possible FRBs as “candidates” and explains that it is like searching for a particular house in a particular neighborhood, but on the scale of the entire universe.
“We’re getting candidates, but we don’t know where they live,” he said. “We don’t know which galaxies they’re coming from.”
With the addition of the GBO as observers in the project, a baseline is created which increases the resolution in the sky. Going back to the neighborhood analogy, with just the CHIME in Canada, the astronomers weren’t able to locate with certainty where the FRBs originated. Adding the GBO observations, they will be able to narrow it down to a specific neighborhood.
“It covers the same portion of the sky and now you can take data from both locations, figure out where your candidates are coming from and be able to say, ‘yes, it lives in this neighborhood’ and then we can start studying the neighborhoods they live in and see if there is any commonality between all these events,” Seymour said.
The FRBs were initially discovered during the original experiment, which was designed to search for hydrogen. During those observations, the bright signals were unmistakable and led to the new experiment to search for FRBs.
“It was revamped to look for these Fast Radio Bursts which are really bright radio events, but they’re very short,” Seymour said. “They have what’s known as a sweep or a chirp and that gives it a distinct signature that it’s coming through a lot of material. Those are the events we’re looking for. We’re trying to figure out what’s causing these chirps, these large spikes in our data because for them to travel such distances, the energetics have to be extreme… astronomical if you will.”
The GBO antenna is still under construction and will be in operation for 10 years. The majority of the infrastructure was made in Canada, but has been assembled and stabilized by American contractors.
“They did a lot of the fabrication and design because they just took what they already had and the expertise they already had and redesigned it for here,” Seymour said. “But, as for the concrete and the footers and the actual building, that has been done locally.”
Two other observatories – a second one in Canada and one in California – will also have a smaller scale operation as part of the FRB project, but GBO is the farthest one away from the original CHIME.
“Those are relatively in the same type of time zone, so they don’t have as big a tilt and their baselines are probably about half the length of what our baseline is going to be,” Seymour said. “Ours was the most drastic that needed to be altered.”
After construction is complete and the receivers are connected, the observation will begin.
“A lot of the electronics and so forth have been paid for by the NSF [National Science Foundation] and that’s via WVU, so they will be coming down and doing a lot of the hardware, physical aspects of putting in the antennas, running the cables,” Seymour said. “Then a lot of astronomers from around the world who’ve been working on CHIME have the software that will go on to the computers and make sure this will talk nice with the other sites and be able to do everything that it’s supposed to do.”