From Douglas Dwyer
With Sarah Scoles’s report on radio bursts you show a graph of the delays between the first and last components of each to arrive, and these mysteriously appear in multiples of 187.5 (4 April, p 8). This looks to me like evidence of “stepped chirp” signals.
Radar designers, bats and whales all use “chirp” – varying the frequency of a signal during a pulse. This maximises the amount of information they can gain about the environment by looking at the reflections of many different frequencies instead.
A knowledge of the degree and nature of the dispersion can be used to de-chirp and thus increase sensitivity to reflected signals. So were the radio signals sent, with a chirp, by someone who hopes eventually to receive reflections?
Or do they result from a natural process, such as laser- or maser-like activity in the shells of old supernovae?
Northlew, Devon, UK
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