Canada’s radio telescope has detected the second repeating fast radio burst (FRB). FRBs are short bursts of radio waves coming from far outside our Milky Way galaxy. Scientists believe FRBs emanate from powerful astrophysical phenomena billions of light years away.
The repeating FRB was one of 13 bursts detected over three weeks during the summer of 2018, while CHIME was in its pre-commissioning phase and running at only a fraction of its full capacity. Additional bursts from the repeating FRB were detected in following weeks by the telescope, which is located in British Columbia’s Okanagan Valley.
Before CHIME began to gather data, some scientists wondered if the range of radio frequencies the telescope had been designed to detect would be too low to pick up fast radio bursts. Most of the FRBs previously detected had been found at frequencies near 1400 MHz, well above the Canadian telescope’s range of 400 MHz to 800 MHz.
The CHIME team’s results – published January 9 in two papers in Nature and presented the same day at the American Astronomical Society meeting in Seattle – settled these doubts, with the majority of the 13 bursts being recorded well down to the lowest frequencies in CHIME’s range. In some of the 13 cases, the signal at the lower end of the band was so bright that it seems likely other FRBs will be detected at frequencies even lower than CHIME’s minimum of 400 MHz.
CHIME is a revolutionary new telescope, designed and built by Canadian astronomers. “CHIME reconstructs the image of the overhead sky by processing the radio signals recorded by thousands of antennas with a large signal processing system,” explains Perimeter Institute’s Kendrick Smith. “CHIME’s signal processing system is the largest of any telescope on Earth, allowing it to search huge regions of the sky simultaneously.”
CHIME is a collaboration of over 50 scientists led by the University of British Columbia, McGill University, University of Toronto, Perimeter Institute, and the National Research Council of Canada (NRC). The $16-million investment for CHIME was provided by the Canada Foundation for Innovation and the governments of British Columbia, Ontario and Quebec, with additional funding from the Dunlap Institute for Astronomy and Astrophysics, the Natural Sciences and Engineering Research Council and the Canadian Institute for Advanced Research. The telescope is located in the mountains of British Columbia’s Okanagan Valley at the NRC’s Dominion Radio Astrophysical Observatory near Penticton. CHIME is an official Square Kilometre Array (SKA) pathfinder facility.
Square Kilometer Array
The Square Kilometre Array (SKA) project is an international effort to build the world’s largest radio telescope, with eventually over a square kilometre (one million square metres) of collecting area.
The SKA will eventually use thousands of dishes and up to a million low-frequency antennas that will enable astronomers to monitor the sky in unprecedented detail and survey the entire sky much faster than any system currently in existence.
Its unique configuration will give the SKA unrivalled scope in observations, largely exceeding the image resolution quality of the Hubble Space Telescope.
It will also have the ability to image huge areas of sky in parallel a feat which no survey telescope has ever achieved on this scale with this level of sensitivity. With a range of other large telescopes in the optical and infra-red being built and launched into space over the coming decades, the SKA will perfectly augment, complement and lead the way in scientific discovery.
The SKA will be developed over a phased timeline. Pre-construction development started in 2012 and will last until the latter half of this decade, involving the detailed design, implementation, R&D work, and contract preparation needed to bring the SKA’s first phase to construction readiness. This first phase will involve testing the full system in a “proof of concept” manner.
In Australia, the SKA low-frequency telescope will comprise 512 stations in a large core and three spiral arms creating a maximum baseline of 65km. Each of the stations will contain around 250 individual antennas, meaning almost 130,000 will be installed on site in total.
Initially, 476 of these stations will be constructed with a maximum baseline of 40km. The further away antennas are from the core of the telescope, the more expensive they become, so slightly reducing the number in the early stages of construction will allow the SKA to stay within the budget available at the time construction begins. The remainder will be added when funding allows.
Unlike telescopes that take the form of one huge dish, the scalable nature of interferometers like the SKA means that more stations can simply be added to the array further down the line.
A similar situation will apply with the mid-frequency telescope in South Africa, where 133 antennas will be added to the existing the 64-dish MeerKAT precursor telescope, forming an array of nearly 200 dishes. Some of them will be arranged in three spiral arms with a maximum baseline of 150km.
Initially, 130 of these dishes will be constructed with a maximum baseline of 120km; the remaining three will be added later.
The ultimate goal is to expand the SKA further, to 10 times this size, with a million low-frequency antennas in Australia and some 2000 high and mid frequency dishes and aperture arrays extending into African partner countries across the continent.
The SKA will start conducting science observations in the mid-2020s with a partial array.
Chime’s Science Papers
Nature – A second source of repeating fast radio bursts
The discovery of a repeating fast radio burst (FRB) source FRB 121102, eliminated models involving cataclysmic events for this source. No other repeating FRB has hitherto been detected despite many recent discoveries and follow-ups suggesting that repeaters may be rare in the FRB population. Here we report the detection of six repeat bursts from FRB 180814.J0422+73, one of the 13 FRBs detected by the Canadian Hydrogen Intensity Mapping Experiment (CHIME) FRB project during its pre-commissioning phase in July and August 2018. These repeat bursts are consistent with originating from a single position on the sky, with the same dispersion measure, about 189 pc cm^−3. This traces approximately twice the expected Milky Way column density, and implies an upper limit on the source redshift of 0.1, at least a factor of about 2 closer than FRB 1211028. In some of the repeat bursts, we observe sub-pulse frequency structure, drifting, and spectral variation reminiscent of that seen in FRB 1211029, suggesting similar emission mechanisms and/or propagation effects. This second repeater, found among the first few CHIME/FRB discoveries, suggests that there exists—and that CHIME/FRB and other wide-field, sensitive radio telescopes will find—a substantial population of repeating FRBs.
Nature – Observations of fast radio bursts at frequencies down to 400 megahertz
ast radio bursts (FRBs) are highly dispersed millisecond-duration radio flashes probably arriving from far outside the Milky Way. This phenomenon was discovered at radio frequencies near 1.4 GHz and so far has been observed in one case at as high as 8 GHz, but not below 700 MHz in spite of significant searches at low frequencies. Here we report detections of 13 FRBs at radio frequencies as low as 400 MHz, on the Canadian Hydrogen Intensity Mapping Experiment (CHIME) using the CHIME/FRB instrument. They were detected during a telescope pre-commissioning phase, when our sensitivity and field-of-view were not yet at design specifications. Emission in multiple events is seen down to 400 MHz, the lowest radio frequency to which we are sensitive. The FRBs show various temporal scattering behaviours, with the majority significantly scattered, and some apparently unscattered to within measurement uncertainty even at our lowest frequencies. Of the 13 reported here, one event has the lowest dispersion measure yet reported, implying that it is among the closest yet known, and another has shown multiple repeat bursts, as described in a companion paper. The overall scattering properties of our sample suggest that FRBs as a class are preferentially located in environments that scatter radio waves more strongly than the diffuse interstellar medium in the Milky Way.
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