Discovery of 30 Galactic radio transient pulsars with MeerTRAP

TL;DR

This work reports the discovery of 30 new Galactic radio transient sources from MeerTRAP, a commensal MeerKAT time-domain survey leveraging real-time single-pulse searches. It combines real-time detection, transient-buffer imaging for arcsecond localisation, and offline DM and period analyses, supplemented by Effelsberg follow-ups that reveal faint regular emission in several long-period sources. Periods are constrained for multiple sources (14 with estimated periods; one with a phase-connected solution), including a 17.5 s pulsar (PSR J2218+2902), and a notable microstructure signature with $P_{\mu} \approx 8.4$ ms in MTP0068, all while showing low duty cycles consistent with RRAT-like behaviour. The results expand the slow-rotator and RRAT populations, strengthen the links between RRATs, magnetars, and FRBs, and demonstrate MeerTRAP's effectiveness in discovering and characterising Galactic transients and informing the neutron-star population via timing, polarimetry, and microstructure analyses.

Abstract

We present the discovery of 30 new Galactic sources from the MeerTRAP project, a commensal fast radio transient search programme using the MeerKAT telescope. These sources were all identified via a single pulse search. Most of them are likely to be rotating radio transients (RRATs) given their low pulse rates. Using data captured in our transient buffer we have localised nine sources in the image domain to arcsecond precision. This facilitates the timing of these sources and further follow-up with other telescopes. Using the arrival times of single pulses, we have constrained the periods of 14 sources, ranging from 121ms to 7.623s, and derived a phase-coherent timing solution for one of them. Follow-up observations of the MeerTRAP sources (including those published previously) performed with the Effelsberg telescope have detected regular but faint emission from three sources, confirming their long rotation period, including PSR J2218+2902 with a period of 17.5s, the fourth slowest in the radio pulsar population. A few of the sources exhibit interesting emission features, such as periodic microstructure in PSR J1243-0435 and possible nulling in PSR J1911-2020 and PSR J1243-0435. We find that the duty cycles of the three newly discovered pulsars are very low and follow the general trend for the duty cycle with period of known pulsars.

Figures (12)

• Figure 1: The discovery pulses of the 30 Galactic MeerTRAP sources. Each panel shows the dynamic spectrum (bottom) and frequency-averaged pulse profile (top) from the filterbank data dedispersed to the best DM given in Table \ref{['tab:properties']}. The data of faint pulses have been donwsampled in frequency and time by a factor of up to 32 and 16. The source name (see Table \ref{['tab:detections']}) is given to each pulse in the top-left corner. Blank horizontal lines are either missing channels or flagged due to RFI. The plot of MTP0058 is affected by RFI and zero-DM flagging.
• Figure 2: Best-fit timing residuals of MTP0063/PSR J1817-1932 (left) and distribution of residuals (right).
• Figure 3: Fluence distributions of individual pulses for the MeerTRAP sources with imaging localisation and more than 20 pulse detections. MTP0055 is detected in both UHF (17 pulses) and L-band (9 pulses), while the other three sources are detected only in the L-band. The red line shows the best-fit lognormal distribution for the observed pulse fluences of each source.
• Figure 4: Polarisation profiles of bright pulses created from the transient buffer data. Each panel shows the PPA (top) and the frequency averaged pulse profile (bottom) for total intensity ($I$, black), linear polarisation ($L$, red) and circular polarisation ($V$, blue). The polarisation data are Faraday corrected to the RM values given in Table \ref{['tab:pol']}. Vertical error bars indicate the $1\sigma$ uncertainties in the PPA.
• Figure 5: The discovery pulse of MTP0068 at UTMOST. The top panel shows the frequency-averaged pulse profile, while the bottom panel shows the dynamic spectrum. The data have been dedispersed to the detection DM of $11.5\,\text{pc}\,\text{cm}^{-3}$.