Something’s cooking

As it sometimes happen in astronomy, very peculiar signals that could potentially represent a groundbreaking discovery turns out to come not from the far reaches of space, but from a much more local source, like the case of the potassium flaring stars. These incidents illustrate the rigorous testing and investigations that occurs when unexpected signals are present in the data, before a solid discovery can be claimed.

Another example of such a story involves the Parkes Observatory Radio Telescope and the search for fast radio bursts. Fast radio bursts are high-energy astrophysical signals lasting only a few milliseconds, and they are believed to originate from outside of the Milky Way. They were first observed in 2001 and to date only around 20 of these bursts have been detected. Their origin is still a mystery, but astronomers have proposed merging black holes, merging neuron stars, flaring magnetars or collapsing pulsars as the source of these bursts, but these explanations are all somewhat speculative. It is naturally of great interest to discover more of these bursts, to hopefully learn more about their origin.

When observing at radio frequencies, especially when looking for something as rare as fast radio bursts, it is important to rule out any kind of radio interference originating from Earth that could potentially mimic the astrophysical signal. A certain type of interference observed at Parkes has been labelled “perytons” after the mythological Peryton creature. They are short-lived burst of radiation at around 1.4GHz, with a shape that is somewhat similar to a bona fide fast radio burst signal.

While it was pretty clear to the astronomers that the perytons arose from some source on Earth (they were observed over a large field of view), it was not evident what was causing them. The radio astronomers at Parkes Observatory began a meticulous investigation to pin this down. One hint to the source was that they only appeared when the telescope was pointed in certain directions (towards the Visitors Center and the staff building). Furthermore, they mostly appeared between 9am and 6pm, clustering just around lunchtime.

The hunt then began for equipment localized in those two buildings that might emit signals in the right frequency range. Immediately, microwave ovens were suspected as the source, as the magnetron inside these operates at 2.4GHz. This is not too far from the 1.4GHz perytons detected with the radio dish. Several tests were performed, to see if there were malfunctioning microwave ovens that would emit at the right frequency. This initial effort did not produce any perytons, but by further experimentation it was found that if the door of the microwave was opened prematurely, a short 1.4GHz radio burst would escape from the oven. So something had definitely been cooking in the data. Take-away lesson: Save those microwave popcorn for when you’re not observing.

While this may seem like a silly investigation, it nevertheless underlines an important scientific principle, namely that when seeing a strange new signal, it is important to rule out sources of terrestrial origin, before a discovery can be claimed. This particular case also has the advantage that perytons have now been properly characterized and this can be used when trying to identify proper astrophysical signals. While peryton signals looks similar to fast radio bursts, they are not identical. Thus investigations like these helps astronomers in their search for more of these mysterious signals.

For the interested readers, a full paper describing the investigation of the perytons can be found here.