Science Alerts with Gaia

Gaia is before all a survey mission designed to observe the sky in a continuous manner. The sky coverage results from the spin of the satellite over a period of 6h, combined with a much slower motion of the spin axis, allowing after six months complete sky coverage. The CCD counts are stored on-board and sent to the ground station every day during the visibility period of the spacecraft by the ground antenna. The satellite design has been optimized for a survey mission, with ground treatment and not for an immediate access to the data, let alone to some scientifically immediately usable information. The processing comprises several more or less independent pipelines, each involving some sort of global processing requiring the accumulation of a substantial amount of data over several weeks or months. However, it remains possible to carry out a quick, but crude in regard of the accuracy achievable on a longer term, analysis of the data stream arriving on the ground to detect transient phenomena, like photometric burst or fast motion of solar system objects. This dedicated processing, largely distinct from the general processing, and the associated validation systems put in place, is referred to as Science Alerts within the DPAC community.