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4/27/17: SO/NOAO Joint Colloquium Series: Simon Hodgkin, Cambridge

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Title: Mapping the Transient Sky with Gaia

Gaia is an ESA cornerstone mission, delivering precision photometry, astrometry, spectrophotometry, and spectroscopy, all based on regular image-scanning the sky through two telescopes and the largest focal-plane array (1Gpixel) yet launched. This by design makes the time-domain the heart of Gaia's scientific requirements and capabilities. Gaia is monitoring the sky with cadences of seconds (between CCDs), hours (between fields-of-view) and weeks (between visits), with real-time source detection implemented by a fixed, available, and well-understood on-board algorithm. Every Gaia source obtains near-simultaneous (delay a few seconds) spectrophotometry. The selection effects which are most difficult to understand in ground-based transient surveys - seeing variations and the low fraction of sources which obtain spectroscopic follow-up - are substantially reduced for Gaia.

The GaiaAlerts system has been running routinely and reliably for over a year, publishing 6 transients per day (see, using well-defined selection criteria. We scan the whole sky exploring into the Galactic plane and crowded regions which are typically hard to do from the ground. In this talk, I will give an overview of the spacecraft, its instruments and the data management. I will describe the challenges we face in searching through half a billion CCD measurements every day to identify and publish Gaia’s transient events. I will discuss the properties of the alerts published to date and highlight some of our most interesting discoveries. I will examine the completeness and biases in our selection criteria, and look ahead to future improvements in the system, including making the most of Gaia’s astrometry.