The MeerKAT Pulsar Timing Array: first data release

We present the first 2.5 yr of data from the MeerKAT Pulsar Timing Array (MPTA), part of MeerTime, a MeerKAT Large Surv e y Project. The MPTA aims to precisely measure pulse arri v al 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 gra vitational wa ves as part of the International Pulsar Timing Array. This project makes use of the MeerKAT telescope and operates with a typical observing cadence of 2 weeks using the L-band receiver that records data from 856 to 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 arri v al times and the initial timing ephemerides, noise models, and the frequency-dependent standard templates (portraits) used to derive pulse arri v al times. After accounting for detected noise processes in the data, the frequenc y-av eraged residuals of 67 of the pulsars achieved a root-mean-square residual precision of < 1 mu s. We also present a no v el reco v ery 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 arri v al times, standards, and full Stokes parameter-calibrated pulsar timing archives are publicly available.