Gaia21bja is a Gaia alerted young stellar object (YSO) that exhibits at least seven quasi-peridoic brightenings over a 20 year-long light curve with durations of 1.5-2 years and amplitudes up to ∼1.7 mag in the Gaia G-band. We analyze its optical and near-infrared photometry and spectra taken using the IRTF and VLT in its faint and bright states in order to characterize its physical properties. A Lomb-Scargle periodogram analysis results in a most significant period of 916±77 days. We derived the stellar parameters as R⋆=0.78±0.04R⊙, L⋆=(4.5±0.3)×10−2L⊙, and M⋆=0.16±0.03M⊙. The spectra taken during the burst are dominated by emission lines and are similar to those of EX Lupi-type eruptive young stars (EXors). We found that the accretion luminosity and mass accretion rate increased by a factor of 5.5−6 during the burst. Based on this, and the quasi-periodic bursts, we suggest that Gaia21bja is an eruptive YSO, and is most consistent with the `Periodic' category of the Outbursting YSOs Catalogue.
@article{arxiv.2605.19413,
title = {Gaia21bja: pre-main sequence star with quasi-periodic bursts},
author = {Ádám Mátéfy and Zsófia Nagy and Ágnes Kóspál and Péter Ábrahám and Fernando Cruz-Sáenz de Miera and Máté Szilágyi and Michał Siwak and Eleonora Fiorellino and Teresa Giannini and Mária Kun and László Szabados and Gábor Marton and Patrik Németh and Brunella Nisini and Zsófia Marianna Szabó},
journal= {arXiv preprint arXiv:2605.19413},
year = {2026}
}