Crab pulsar giant pulses
University of Toronto – Supervisor: Prof. Marten van Kerkwijk
(September 2025 - May 2026)
Neutron stars are some of the most extreme laboratories the universe offers in the study of physics. Their incredible density and magnetic fields offer environments that are inaccessible anywhere else. A subset of neutron stars – known as pulsars – emit radiation from their poles due to particularly strong magnetic fields accelerating charged particles. This emission is received on Earth in the form of brief pulses due to the pulsars rotation in the same way a lighthouse appears to pulse to a distant observer. However, certain pulsars have been found to produce a mysterious additional form of radiation known as giant pulses (GPs). These GPs are non-periodic but regular pulses whose emission ranges from long wavelength radio to high energy x-rays and demonstrate structure in their emission down to at least the nanosecond timescale; these fast components have been dubbed nanoshots.
Recent studies of giant pulses point to an emission mechanism in which a blob of plasma – or plasmoid – is ejected at relativistic velocities towards the observer. As it travels, the plasmoids are thought to produce the nanoshots which form the broader GP. However, this mechanism has not been thoroughly confirmed. Thus my work uses high frequency radio observations (11.5 - 16 GHz) from the Green Bank Telescope in an effort to confirm the proposed emission mechanism. By using higher frequency radio data, we are able to better resolve the nanoshot structure which enables analysis that is difficult at lower frequencies.
As the sole researcher under my supervisor, I was responsible for identifying the ~12 000 GPs in over 60 Tb of data. Through correlating the spectra of consecutive nanoshots I was able to probe the emission region of the GP. Given the relativistic velocities of the plamoids, we expect the spectra to shift and stretch in a predictable manner as consecutive emissions pass through adjacent regions of the scattering screen – in this case the crab nebula. Unfortunately, my results found spectral variations consistent with intergalactic scattering rather than nebular screen scattering. This implies our observations were taken at a time of very low nebular scattering which prevented us from drawing conclusions.
In the future, we will seek further GBT observations and will aim to use a telescope such as CHIME in tandem which observes the Crab pulsar daily to identify times of high scattering to make sure we avoid more ‘bad luck’. Additionally, we found that though there are benefits to using higher frequency observations as previously mentioned, the resulting reduced sample-size was a drawback. We will split the difference between high and low frequencies and aim to use observations in the ~5-10 GHz range instead.
