Astronomers make history in a split second with localization of fast radio burst | Hacker News Reader

Astronomers make history in a split second with localization of fast radio burst

news.ucsc.edu

132 pointsHooke37 comments

"Since ASKAP is an array of 36 dish antennas and the burst had to travel a slightly different distance to each dish, it reached each one at a slightly different time."

“From these tiny time differences—just a fraction of a billionth of a second—we identified the burst’s home galaxy and even its exact starting point..."

Simply amazing that they can get such precise measurements from so small a differential in distance.

I guess it's like any old heist movie:

The key is to synchronize your clocks beforehand!

Poincare has proven that it's impossible to synchronize clocks exactly

By the time you count your clocks, they've gone askew.

> Simply amazing that they can get such precise measurements from so small a differential in distance.

How do they know the billionths of a second differences aren't due to the radio waves travelling through pockets of air that have slightly different densities/temperatures/moisture/refraction properties?

That just seems like incredible error tolerance

With 36 antennas it would average out to some extent, but since propagation in air is very near that of vacuum already, I don't think a °C or two makes much of a difference.

There is a system in place to account for atmospheric effects on radio signals. Here's one example at the Very Large Array, which uses the GPS to measure (via interferometry) and correct for disturbances in the ionosphere: https://www.aanda.org/articles/aa/pdf/2001/06/aa10277.pdf

A lot of the atmospheric affects are on longer timescales than the sampling times, which means they can be calibrated out.

Most observations of this nature (interferometric observations) will point at a nearby calibrator source (usually a well characterized quasar or other "point source" star/object), and an atmospheric noise model will then be constructed based on this calibrator to apply to each dish to minimize/account for the atmospheric influence.

This is often repeated periodically to account for changing weather over time. And on top of that, a benefit of the location chosen for ASKAP was relatively dry air (being in the western desert climate of Australia).

That's really interesting! Would you be able to point me towards some resources to learn more about this?

A lot of it I learned when I studied Radio Astronomy in college (my major). I'm a little rusty now after about 7 years.

However, here's a few resources I remember and was able to dig up.

1) A presentation from Max Plank University, which has one of the strongest radio astro programs around: https://www.mpifr-bonn.mpg.de/3244052/IMPRS_BB_HRK5.pdf

2) Presentation from ASTRON, an interferometric array in the Netherlands, part of the Netherlands Institute for Radio Astronomy: https://www.eso.org/sci/meetings/2015/eris2015/L6_Heald_cali...

3) George Moellenbrock's slides from the 14th Synthesis Imaging Workshop (hosted by the National Radio Astronomy Observatory) is pretty detailed on calibration specifically: https://science.nrao.edu/science/meetings/2014/14th-synthesi...

There was at one time a video of the last link, but it appears the hosting site is no longer live. There are other lecture slides on radio interferometry available from the Synthesis Workshop site: https://science.nrao.edu/science/meetings/2014/14th-synthesi...

I'd assume they used some pretty solid statistical methods for reducing the atmospheric noise to a relatively negligible amount, based on covariance of their dish readings.

I don’t think that’s quite right. Light travels about one foot in a nanosecond. Unless the signal was directly overhead, the distance differential would surely be at least several feet, and thus the time differential comfortably more than a billionth of a second. Maybe they meant a millionth.

The wording is misleading. You need to compute the angle of incidence of the incoming wavefront to a high accuracy in order to localize the source.

The key quantity is not the absolute delay introduced by the absolute distance from antenna to antenna (which is tens of meters, http://www.atnf.csiro.au/projects/askap/ska.html). It's the differential delay as a function of incidence angle.

Ah yes. The difference in arrival time was many nanoseconds but it needed to be measured to within a fraction of a nanosecond to accurately localize the source.

A more interesting account by two of the members of the project that did the novel bit: https://theconversation.com/how-we-closed-in-on-the-location...

Also, the full science paper, might be decent too: https://science.sciencemag.org/content/early/2019/06/26/scie...

They made history in a split second, presumably after spending decades on building the infrastructure and gathering all the prerequisite knowledge.

The first observed binary black hole merge signal was probably also quite short (I'd wager less than a minute, possibly even less than a second), and many of us have read about how much effort that one took.

This has been happening since 1999 by the NAAPO (the same group who ran the "Big Ear"). They had a cluster of helix antennas being fed into a VA Linux Systems Hardware Cluster doing analysis on radio astronomy events:

http://www.naapo.org/Argus/docs/docsmenu.htm

I volunteered there from 2004-2008. I believe that the cluster is still active today.

That's great news- but I'm confused by the following analogy:

>> "It's like looking at the Earth from the Moon and not only knowing what house a person lived in, but what chair they were sitting in at the dining room table," Bannister said.

What are chairs and dining room tables by analogy to galaxies and in the context of fast radio bursts?

Could someone please clarify?

Further in the article they mentioned telescopes have to be placed certain distances apart to calculate differences in radio wave arrival by billionths of a second. These differences gives them granular placement within the galaxy (I'm assuming the analogy is referring to arms, stars, planets, etc.)

cached: https://webcache.googleusercontent.com/search?q=cache:89RLX_...

Amazing they can measure timing differences less than nanoseconds and use them to localize phenomena millions or billions of light years away. And I can't reliably measure whether I made my program 1% faster or not :(

I bet you could, but you need more measurements and statistical analysis. Keep in mind that a lot of these astrological measurements - and a more notable recent example is the black hole visualization - are not based on direct measurements, but statistical analysis on huge datasets.

It is spelled > astronomical < measurements, you squidface!

Well, it still stands as written, as long as you're one of those big-data astrology people.

Yep, astrological measurements require data going back all the way to the Sumerians...

If you're interested in astronomy, on the other hand, and dealing with a radio burst lasting a millisecond or less, relying on the wisdom of the ancients is not an option.

Fortunately enough though, you can go out and by off-the-shelf electronics capable of measuring distances at sub-cm level using the time of flight of photons. If you've ever used a (newer) Kinect, or a RealSense camera, you've already seen it in action:

https://www.pocket-lint.com/phones/news/147024-what-is-a-tim...

https://www.dronezon.com/learn-about-drones-quadcopters/best...

This as well as the recent imaging of the M87 black hole are both phenomenal feats of signal processing. Is this the new normal for astronomy?

Radio astronomy has always been pushing the frontier of signal processing. Gamma ray telescopes also need large amounts of data crunching. Until recently optical telescope where much more about instrumentation than data processing. But even that is changing, e.g. with small and mid-sized robotic telescopes that automatically search for transients and schedule their own follow-up observations.

One thing I don't understand from the article is whether they took into consideration galaxy movements. Given that this is a 3.6bn years old signal wouldn't it be safe to assume that the place we can pinpoint now as the originator might not be the same it was back then?

The radio signal is just as old as the light (both being EM), so they align (more or less).

Sure it's moved, but the light from the galaxy arriving now is the same age as the radio burst (they travel at practically the same speed).

Galaxy: Honey I'm 3.6 Billion light-years away.

Scientist: I'm getting mixed signals I don't know what to do anymore.

Amazing engineering

My confirmation bias says it's aliens. Who moved my car keys? Aliens.

Add it to the list. Alienses are here.

I find that to be highly doubtful.

If an Albecurrie Drive is feasible, could an FRB be a sign of operation?

Only if someone was around to hear it

Reply on news.ycombinator.com