On the patchiness of the individual pulse spectra at the very low radio frequencies

TL;DR

This study uses LOFAR observations to analyze the patchy and drifting spectral features of individual pulses from PSR B0809+74 at very low radio frequencies, revealing that these are caused by broadband signal enhancements rather than intrinsic pulsar properties.

Contribution

It demonstrates that spectral patchiness and drift observed at low frequencies are due to external broadband enhancements, not pulsar-intrinsic phenomena, impacting single-pulse analysis methods.

Findings

Spectral patches drift upwards in frequency over pulse sequences.

Broadband signal enhancements cause the observed spectral drift.

Phenomenon may influence analysis of high-dispersion pulses like Fast Radio Bursts.

Abstract

We have used sensitive LOw Frequency ARray (LOFAR) observations of PSR B0809+74 at 15--62 MHz to study the anomalously intensive pulses, first reported by Ulyanov et al. (2006) at 18--30MHz. Similarly to Ulyanov et al., we found that the spectra of strong pulses consist of distinct bright patches. Moreover, these spectral patches were spotted to drift upwards in frequency over the course of several pulse sequences. We established that this drift is not pulsar-intrinsic, but is caused by the broadband ~20 second-long enhancements of recorded signal, which influenced the dispersed tracks of several pulses at once. We speculate on the cause of such enhancements (i.e. propagation or telescope-related) and the ramifications they bring to the single-pulse studies at the very low radio frequencies. Depending on the origin, the phenomenon may also affect the analysis of highly dispersed single pulses at higher radio frequencies, e.g. Fast Radio Bursts.