RRAT-like behaviour of PSR B0656+14 observed with I-LOFAR

¹ Physics, School of Natural Sciences & Center for Astronomy, College of Science and Engineering, University of Galway, University Road, Galway H91 TK33, Ireland
² School of Physics, Trinity College Dublin, College Green, Dublin 2 D02 PN40, Ireland
³ Radio Astronomy Laboratory, University of California, Berkeley, CA, USA
⁴ ASTRON, The Netherlands Institute for Radio Astronomy, Oude Hoogeveensedijk 4, 7991 PD Dwingeloo, The Netherlands

^⋆ Corresponding author.

Received: 29 April 2025
Accepted: 4 July 2025

Abstract

Context. Single pulse studies offer vital insights into the emission physics of pulsars, particularly in the case of young, nearby sources where intrinsic variability is often pronounced. PSR B0656+14, known for its sporadic and sometimes intense pulses, provides an excellent opportunity to investigate such behaviour at low radio frequencies.

Aims. This study aims to characterise the single pulse behaviour of PSR B0656+14 using low-frequency observations at 110–190 MHz from the Irish LOFAR station. We focus on quantifying its pulse energy distribution, deriving precise dispersion measures (DMs) for both average and single pulses, analysing the temporal spacing (wait times) between subsequent pulses, and studying the spectral indices for single pulses.

Methods. We employed standard pulsar timing techniques to derive the highest possible DM precision using integrated profiles. Single-pulse extraction was performed, and individual pulse DMs were estimated to probe pulse-to-pulse dispersion variability. We also performed a wait-time analysis to understand the statistical nature of pulse occurrence, and estimated the spectral index from frequency-resolved flux density measurements. The pulse energy distribution was modelled using a combination of log-normal and power-law components.

Results. We report a DM of 14.053 ± 0.005 pc cm⁻³ for PSR B0656+14 at LOFAR HBA frequencies. A total of 41 pulses were detected in a 5-hour observation, allowing a wait-time distribution analysis that is well modelled by an exponential function, indicative of a Poisson process. A profile stability analysis indicates that a significant number of pulses (in excess of 47 500) are required to reach a stable average profile, which is unusual compared to many other pulsars. The single-pulse spectral index varies significantly from pulse to pulse, with a mean value of α = −0.5 and a standard deviation of Δα = 1.3. The pulse energy distribution shows a hybrid behaviour, consistent of a log-normal distribution and a power-law tail.

Conclusions. Our results confirm that PSR B0656+14 exhibits highly variable, memory-less emission at low frequencies, with characteristics that resemble the ones seen in some rotating radio transients (RRATs). The need for an unusually large number of pulses to reach profile stability highlights the complex nature of its emission. As solar-wind studies demand a high DM precision, this pulsar is insufficient for that purpose despite its proximity to the ecliptic plane; however, SKA-Low’s higher sensitivity could provide the required accuracy. While this study offers a detailed view of this pulsar’s behaviour at LOFAR frequencies, further observations – of both this source and others – are essential. If such variability proves to be widespread among pulsars, population synthesis models and survey yield predictions would need to incorporate this currently overlooked feature to ensure accuracy.