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.

Signal lost!

When doing observations, it sometimes happens that things just won’t collaborate, one way or the other, making it impossible to get any good data. This is true for all areas of astronomy, where you can have clouds, high water vapor, light pollution, radio frequency interference or equipment malfunction of various sorts. Sometimes the reasons for not getting observations are tricky, but in other cases they are fairly obvious… Or so you would think.

Doing a pulsar survey one night at the Parkes Observatory, an undergrad student observer doesn’t seem to be getting any good data from the 64m radio telescope. In fact, he’s not even getting bad data, he’s getting no data at all. As much as it is annoying getting bad data, getting zero data is just immensely frustrating. The bad data would at least get you something that could potentially be useful. But having gone through all the planning and work associated with observations, for zero gain, is just painful.

After long hours that no doubt involved pulling out hairs and being frustrated, the relief, which happens to be the supervisor of the undergrad student, enters the observing tower at 4am. He’d apparently been keeping an eye out for things on the ground on the way there, as he had found a receiver lying on the ground outside. His immediate reaction was along the lines of “Huh, I wonder what that’s doing here? I better pick that up and bring it in with me.” The receiver was then brought to the control room, after which the supervisor continued to try and get some observations going, with very limited success.

At sunrise, one of the staff members arrive, to meet what was no doubt a very frustrated astronomer, who had not gotten any useful data at all that night. Upon seeing the receiver in the control room, he casually pointed out that there was a very nice receiver-shaped hole in the radio dish. In fact, it looked suspiciously like the receiver the supervisor had picked up during the night, would fit exactly there. Which of course provided an immediate explanation as to why no data was received. One can only wonder, why this had not come to mind earlier. I suppose it’s like when you are looking for your glasses while already wearing them. You just don’t see what’s right in front of you.

The Parkes Radio Telescope from the air Credit: Shaun Amy, CSIRO

The Parkes Radio Telescope from the air. Credit: Shaun Amy, CSIRO

Apparently, the receiver had recently been changed, and whoever was putting the receiver in, had not tightened the bolts sufficiently, so as the telescope was turning, the receiver had gotten loose and fallen to the ground. I suppose that the lesson here is: If you find a fairly essential piece of your instrument in a weird place, that might be a good place to start, when trying to figure out why nothing is working. In addition to that, some safety advice; Always wear a hard hat when observing. Even if in the middle of nowhere, with no tall things around, you never know what might hit you.