From CAASTRO: “Solution to FRB conundrum also reveals clues about their origin”

CAASTRO bloc

CAASTRO ARC Centre of Excellence for All Sky Astrophysics

11 September 2015

Since first reported in 2007, the origin of the bright, millisecond-duration pulses known as Fast Radio Bursts (FRBs) has remained a mystery to astronomers. There have been more theories proposed to explain them than the 17 events so far detected. Where do they come from – our Solar System, our Galaxy, or beyond? The dispersion sweeps of FRBs (the delay of the pulse arrival time with wavelength caused by propagating through plasma in space) indicate that they have travelled through so much material on their way to Earth that they must be cosmological in origin. There just is not enough plasma in the interstellar medium of the Milky Way to explain their long dispersion sweeps.

1
Four recently detected “blitzars” (red stars) have revealed that these sources of fleeting radio bursts are much more distant than known pulsars (black dots) (Image: C. Ng/MPIfR)

Adding to the mystery, CAASTRO PhD student Emily Petroff (Swinburne University) and colleagues analysed the distribution of FRB detections across the sky and reported (in their 2014 paper) that their rate is about four times higher at high Galactic latitudes than close to the Galactic plane. This result is doubly puzzling because (a) the distribution of extragalactic pulses should not be related to their position with respect to the Galactic disk and (b) the rate of pulses of Galactic origin should be higher closer to the Galactic plane, the exact opposite of what is observed.

CAASTRO members Dr Jean-Pierre Macquart (Curtin University) and Prof Simon Johnston (CSIRO) now provide an explanation in their recent publication. Radio pulses received at the Earth have propagated through the turbulent interstellar medium of our own Galaxy irrespective of whether they were generated inside or outside of it. The density fluctuations in this medium can randomly amplify the amplitude of a pulse. This effect is equivalent to the Earth’s atmosphere causing an apparent twinkling of stars.

The intensity fluctuations change both with time and with observing frequency; and the more material, the more quickly they change with frequency. At low Galactic latitudes, FRBs propagate through so much turbulent Galactic material that the intensity fluctuations change very rapidly with frequency – so much so that radio telescopes average over many tens to hundreds of intensity fluctuations over the observing band. When averaged across the bandwidth of the telescope, the intensity is very close to the mean intensity of the pulse. However, at high Galactic latitudes the FRB radiation is subject to only one or two intensity fluctuations across the telescope observing band, and the observed radiation can be either greatly diminished or enhanced.

See the full article here .

Please help promote STEM in your local schools.

STEM Icon

Stem Education Coalition

Astronomy is entering a golden age, in which we seek to understand the complete evolution of the Universe and its constituents. But the key unsolved questions in astronomy demand entirely new approaches that require enormous data sets covering the entire sky.

In the last few years, Australia has invested more than $400 million both in innovative wide-field telescopes and in the powerful computers needed to process the resulting torrents of data. Using these new tools, Australia now has the chance to establish itself at the vanguard of the upcoming information revolution centred on all-sky astrophysics.

CAASTRO has assembled the world-class team who will now lead the flagship scientific experiments on these new wide-field facilities. We will deliver transformational new science by bringing together unique expertise in radio astronomy, optical astronomy, theoretical astrophysics and computation and by coupling all these capabilities to the powerful technology in which Australia has recently invested.

PARTNER LINKS

The University of Sydney
The University of Western Australia
The University of Melbourne
Swinburne University of Technology
The Australian National University
Curtin University
University of Queensland