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V1741 Sgr (= SPICY 71482/Gaia22dtk) is a Classical T Tauri star on theoutskirts of the Lagoon Nebula. After at least a decade of stability, inmid-2022, the optical source brightened by ~3 mag over two months, remainedbright until early 2023, then dimmed erratically over the next four months.This event was monitored with optical and infrared spectroscopy and photometry.Spectra from the peak (October 2022) indicate an EX Lup-type (EXor) accretionoutburst, with strong emission from H I, He I, and Ca II lines and CO bands. Atthis stage, spectroscopic absorption features indicated a temperature of T ~4750 K with low-gravity lines (e.g., Ba II and Sr II). By April 2023, with theoutburst beginning to dim, strong TiO absorption appeared, indicating a coolerT ~ 3600 K temperature. However, once the source had returned to itspre-outburst flux in August 2023, the TiO absorption and the CO emissiondisappeared. When the star went into outburst, the source's spectral energydistribution became flatter, leading to bluer colours at wavelengths shorterthan ~1.6 microns and redder colours at longer wavelengths. The brighteningrequires a continuum emitting area larger than the stellar surface, likely fromoptically thick circumstellar gas with cooler surface layers producing theabsorption features. Additional contributions to the outburst spectrum mayinclude blue excess from hotspots on the stellar surface, emission lines fromdiffuse gas, and reprocessed emission from the dust disc. Cooling of thecircumstellar gas would explain the appearance of TiO, which subsequentlydisappeared once this gas had faded and the stellar spectrum reemerged.

The 2022-2023 accretion outburst of the young star V1741 Sgr