The MeerKAT Pulsar Timing Array: First Data Release

We present the first 2.5 years of data from the MeerKAT Pulsar Timing Array (MPTA), part of MeerTime, a MeerKAT Large Survey Project. The MPTA aims to precisely measure pulse arrival times from an ensemble of 88 pulsars visible from the Southern Hemisphere, with the goal of contributing to the search, detection and study of nanohertz-frequency gravitational waves as part of the International Pulsar Timing Array. This project makes use of the MeerKAT telescope, and operates with a typical observing cadence of two weeks using the L-band receiver that records data from 856-1712 MHz. We provide a comprehensive description of the observing system, software, and pipelines used and developed for the MeerTime project. The data products made available as part of this data release are from the 78 pulsars that had at least $30$ observations between the start of the MeerTime programme in February 2019 and October 2021. These include both sub-banded and band-averaged arrival times, as well as the initial timing ephemerides, noise models, and the frequency-dependent standard templates (portraits) used to derive pulse arrival times. After accounting for detected noise processes in the data, the frequency-averaged residuals of $67$ of the pulsars achieved a root-mean-square residual precision of $< 1 \mu \rm{s}$. We also present a novel recovery of the clock correction waveform solely from pulsar timing residuals, and an exploration into preliminary findings of interest to the international pulsar timing community. The arrival times, standards and full Stokes parameter calibrated pulsar timing archives are publicly available.