AARTFAAC

The Amsterdam-ASTRON Radio Transient Facility And Analysis Centre (AARTFAAC) is a part of the LOw Frequency Array (LOFAR) located in the Netherlands. The primary science goal of AARTFAAC is to search the entire visible sky for very short duration transients, bright bursts of light coming from extreme astronomical events, like the mergers of neutron stars, Galactic centre burps, fast radio bursts, or any other as of yet unexplained or unobserved phenomena.

AARTFAAC observes at low frequencies, typically 60 MHz where our sensitivity peaks, however this particular observation was at 36.7 MHz, near the lowest limit in our frequency range. These images were made during the peak of the perseids meteor shower, Aug 11-13 2017. At low radio frequencies the tails of meteors can glow brightly for up to a couple minutes, briefly outshining the brightest objects in the sky. This is the result of extreme heating by friction as the meteor smashes through the atmosphere. The hot gas is ionized, causing it to glow, and reflect radio waves.

Brief flashes of light on the horizon, around the edge of the sky, are bright flashes of human made radio frequency interference.

As the sky rotates above you’ll notice point sources of light. However, unlike the stars you see in optical wavelengths, these bright objects are mostly Quasars, super massive black accreting matter at the centre of distant galaxies.

The milky way can be seen to rotate over head. Along the plane of our Galaxy the brightest objects, which appear slightly bigger in size, are nearby Super Nova Remnants. After the death of a massive star, a tremendous explosion expels hot gas outward. This hot ionized gas also glows brightly at low frequencies.

When the sky stops rotating, we slow down for a moment to watch the twinkling of these distant galaxies. Similar to how stars twinkly due to the turbulence of the atmosphere, low frequency radio source fluctuate due to the turbulence in the ionosphere. This is the top layer of gas in the atmosphere, which is ionized by the bombardment of solar radiation. This ionized gas has a greater and greater influence at lower frequencies. Unfortunately below 10 MHz the ionosphere becomes completely opaque, and observations from the ground are impossible.