From Sky & Telescope: “Astronomers Pinpoint New Fast Radio Burst”

SKY&Telescope bloc

From Sky & Telescope

June 27, 2019
Monica Young

A next-gen Australian radio array has enabled astronomers to home in on the source of a mysterious fast radio burst — and the source is not what they expected.

The galaxy from which the burst originated was imaged by three of the world’s largest optical telescopes – Keck, Gemini South and the European Southern Observatory’s Very Large Telescope. The image combined with radio data shows that FRB 180924 lies on the outskirts of a massive “dead” galaxy.
CSIRO / Sam Moorfield

Keck Observatory, operated by Caltech and the University of California, Maunakea Hawaii USA, 4,207 m (13,802 ft)

Gemini/South telescope, Cerro Tololo Inter-American Observatory (CTIO) campus near La Serena, Chile, at an altitude of 7200 feet

ESO VLT at Cerro Paranal in the Atacama Desert, •ANTU (UT1; The Sun ),
•KUEYEN (UT2; The Moon ),
•MELIPAL (UT3; The Southern Cross ), and
•YEPUN (UT4; Venus – as evening star).
elevation 2,635 m (8,645 ft) from above Credit J.L. Dauvergne & G. Hüdepohl atacama photo,

If you could “listen” to the whole radio sky at once, you’d mostly hear a faint background hiss, like the static between radio stations. But roughly every 10 seconds, you’d pick up a downslurred whistle reminiscent of the Northern Cardinal’s song. This bright sound comes from so-called fast radio bursts (FRBs). Each one lasts only a small fraction of a second (hence “fast”), but in that time it carries some 10,000 times the energy of the Sun.

Since their discovery in 2007, FRBs have maintained an air of mystery. Astronomers have spotted 76 of the fleet emissions so far (and counting), but theories about their origins abound in part because they’re difficult to pin down. Until now, astronomers have only been able to localize one emission, FRB 121102, and that was only because it repeated often enough that astronomers could home in on its origin.

Now, Keith Bannister (CSIRO) and colleagues have used the 36-dish Australian Square Kilometer Array Pathfinder (ASKAP) to pinpoint the source of another FRB — one that doesn’t repeat. The feat, published on June 27th in Science, offers another avenue to understanding these puzzling sources.

Australian Square Kilometre Array Pathfinder (ASKAP) is a radio telescope array located at Murchison Radio-astronomy Observatory (MRO) in the Australian Mid West. ASKAP consists of 36 identical parabolic antennas, each 12 metres in diameter, working together as a single instrument with a total collecting area of approximately 4,000 square metres.

One of These Is Not Like the Other

When ASKAP captured the signal known as FRB 180924, an automated search pipeline triggered the receivers to save everything about the event. That information enabled ASKAP to not only detect the event, it also recorded enough information to pinpoint its source to within 0.12 arcsecond, in a massive galaxy whose light has traveled for 3.6 billion years to reach Earth.

Bannister’s team followed up with sensitive observations of the galaxy and its surroundings using the Very Large Telescope and the Gemini South Telescope in Chile and the Keck II Telescope in Hawai‘i. Images show the galaxy is a cross between an elliptical and a spiral. If it has any spiral arms around its big bulge, they’re tightly wound and difficult to see. Spectroscopic measurements show little to no evidence of star formation. If the burst really belongs to this galaxy, it’s in its anemic outer reaches.

This finding is in stark contrast to the home of the repeating burst FRB 121102. It appears to originate from within a radio-emitting nebula that’s part of a dwarf galaxy that’s birthing stars at a high rate. Given the plethora of new stars, astronomers think FRB 121102 is likely a highly magnetized kind of newborn neutron star known as a magnetar.

A composite image of the field around the first repeating fast radio burst, FRB 121102 (indicated), showed that the burst came from a star-forming dwarf galaxy.
Gemini Observatory / AURA / NSF / NRC

FRBs are known for having large dispersion measures, which means that the lower frequencies arrive much later than the higher-frequency ones. That’s what gives them the “sound” of a cardinal-like downslurred whistle. The longer-frequency photons are delayed by interacting with electrons, and in the case of FRB 121102, the whistle was so extended, it indicated that not only had the pulse traveled a long way, but that the source itself was probably embedded in highly magnetized plasma, which supports the magnetar scenario.

But are all FRBs magnetars? Astronomers have already been saying that even if the scenario pans out for FRB 121102, it might not explain FRBs as a population. The vast majority of these events, after all, don’t repeat.

“Basing models entirely on [FRB 121102’s] properties is dangerous, since the FRB population could be made up of different classes of sources,” says Victoria Kaspi (McGill University, Canada). Indeed, Bannister and colleagues’ localization of FRB 180924 in a galaxy that has retired from star formation suggests that this source has nothing to do with newborn stars, magnetars or otherwise.

“We now know that some FRBs originate from environments very different from that of FRB 121102,” says Kaspi, who was not involved in the study. “That is a very important finding!”

There’s another aspect of FRB 180924 that’s also telling: its dispersion measure. The distance to the source’s galaxy completely explains the dispersion measure so, unlike the repeater, this source doesn’t seem to be embedded in a highly magnetic plasma.

“If they are all like 121102 then yes, we’d expect the source itself to contribute [to the dispersion measure],” Kaspi notes. “But clearly, they are not all like FRB 121102!”

This single burst is likely the first of many that ASKAP will pinpoint, and other telescopes are working on that ability, too. The Canadian Hydrogen Intensity Mapping Experiment (CHIME) array, for example, could localize sources if it had outrigger telescopes, like “mini-CHIMES,” to provide additional information.

CHIME Canadian Hydrogen Intensity Mapping Experiment -A partnership between the University of British Columbia, the University of Toronto, McGill University, Yale and the National Research Council in British Columbia, at the Dominion Radio Astrophysical Observatory in Penticton, British Columbia, CA Altitude 545 m (1,788 ft)

That would be a boon for an instrument that’s already finding FRBs by the dozen. “Indeed we are planning CHIME outrigger telescopes right now,” Kaspi says.

For now, FRBs retain their mystery, but it’s only a matter of time before we unveil what unique physics is producing these events.

See the full article here .


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Sky & Telescope magazine, founded in 1941 by Charles A. Federer Jr. and Helen Spence Federer, has the largest, most experienced staff of any astronomy magazine in the world. Its editors are virtually all amateur or professional astronomers, and every one has built a telescope, written a book, done original research, developed a new product, or otherwise distinguished him or herself.

Sky & Telescope magazine, now in its eighth decade, came about because of some happy accidents. Its earliest known ancestor was a four-page bulletin called The Amateur Astronomer, which was begun in 1929 by the Amateur Astronomers Association in New York City. Then, in 1935, the American Museum of Natural History opened its Hayden Planetarium and began to issue a monthly bulletin that became a full-size magazine called The Sky within a year. Under the editorship of Hans Christian Adamson, The Sky featured large illustrations and articles from astronomers all over the globe. It immediately absorbed The Amateur Astronomer.

Despite initial success, by 1939 the planetarium found itself unable to continue financial support of The Sky. Charles A. Federer, who would become the dominant force behind Sky & Telescope, was then working as a lecturer at the planetarium. He was asked to take over publishing The Sky. Federer agreed and started an independent publishing corporation in New York.

“Our first issue came out in January 1940,” he noted. “We dropped from 32 to 24 pages, used cheaper quality paper…but editorially we further defined the departments and tried to squeeze as much information as possible between the covers.” Federer was The Sky’s editor, and his wife, Helen, served as managing editor. In that January 1940 issue, they stated their goal: “We shall try to make the magazine meet the needs of amateur astronomy, so that amateur astronomers will come to regard it as essential to their pursuit, and professionals to consider it a worthwhile medium in which to bring their work before the public.”