The GBOT Asteroid Survey (First years: Jan. 2015 - May 2018)

The GBOT group is in charge of the Ground Based Optical Tracking of the Gaia satellite. In concrete terms, since the launch of Gaia, our task is to take every night, using ground based medium-class telescopes, short sequences of $10$ or $20$ images of the Gaia satellite close to its meridian transit. For this purpose, we mainly use the VLT Survey Telescope and the Liverpool Telescope. In these images, taken close to the Sun's opposition - since Gaia is in L$_2$ - we observe many asteroids: between $30$ and $100$ asteroids every night, up to magnitude $22$. In order to extract the astrometric positions as well as the magnitudes of these asteroids, we have developed semi-automatic methods, strategies and tools tailored explicitly for this daily task. In only three and a half years of operation, this system has allowed us to send to the Minor Planet Center the position and the photometry for about $20,000$ asteroids, amongst which $9,000$ new objects. Here we describe all the aspects of the GBOT asteroid survey.