100,000 Crab giant pulses at 215 MHz detected with an SKA-Low prototype station

TL;DR

This study reports the detection of approximately 95,000 Crab giant pulses at low frequencies using an SKA-Low prototype, revealing detailed fluence distributions, scattering effects, and implications for fast radio burst origins.

Contribution

First large-scale low-frequency Crab giant pulse sample analyzed with SKA-Low prototype, providing new insights into pulse fluence, scattering, and potential FRB connections.

Findings

Fluence distribution follows a single power law with index -3.17.

Scatter broadening time correlates with dispersion measure and varies over weeks.

Results support Crab-like pulsars as sources of some weak repeating FRBs.

Abstract

We report detection and analysis of the largest low-frequency (200 - 231.25 MHz) sample of Crab giant pulses (GPs) reported in the literature. In total about 95000 GPs were detected. The observations were performed in 2024/2025 with the EDA2, a prototype station of the SKA-Low telescope. The fluence distribution of GPs in the entire sample is very well characterised with a single power law (no flattening at higher fluences) N(F) $\propto$ F$^\alpha$, where $\alpha = -3.17\pm0.02$ for all GPs, and $\alpha_{MP} = -3.13\pm0.02$ and $\alpha_{IP} = -3.59\pm0.06$ for GPs at the phases of the main pulse and interpulse respectively. The index of the power law fluence distribution remained approximately constant over the observing period, but the normalisation of the distribution was strongly correlated with the scatter broadening time ($\tau$). As a result, the measured fluence distribution increased for lower ($\tau \approx$ 2 ms) and decreased for higher ($\tau \approx$ 5 ms) scatter broadening time $\tau$ causing the GP rate to vary between 3000 and 100 per hour respectively. The timescale of variations (weeks) indicates refractive scintillation as the root cause. We also observe a strong positive correlation between the scatter broadening time and dispersion measure. Our modelling favours the screen of the size $\sim10^{-5}$ pc and mean electron density $\sim 400$e$^{-}$cm$^{-3}$ located within 100 pc from the pulsar. The frequency scaling of the scattering broadening time ($\tau \propto \nu^{\beta}$) with $\beta \approx -3.6\pm0.1$ is in agreement with earlier measurements. Our results agree with the current views that GPs from extra-galactic Crab-like pulsars can be responsible for very weak repeating FRBs, but cannot explain the entire FRB population. Finally, these results demonstrate an enormous scientific potential of individual SKA-Low stations.