6.3.3 Straylight background

The RVS straylight background is measured using the same principles as the BP/RP background model (see Section 5.3.1). All the RVS Virtual Objects from the first month of the mission (28 days Ecliptic Pole Scanning Law) were processed off-line. The median flux value of each VO, which contains 1260 samples, was computed, to avoid contamination by cosmic rays and stellar spectra. The row fraction coordinate (out of RVS CCD rows 4-7) and heliotropic spin phase were also calculated. All the virtual objects belonging to the same cell are averaged to obtain a median value, removing outliers. A straylight map was constructed for each of the three RVS CCD strips using a grid of 2160 cells in the spin direction and 50 cells in the AC direction covering the four RVS CCD rows (see Figure 6.3). This map is used to correct all the Gaia DR2 data, neglecting any temporal variation.

Figure 6.3: The straylight map used in the pipeline, for CCD strip 15, 16 and 17. The background map is dominated by the solar straylight. On the Y axis is the across scan direction plotted as CCD row number, in the X-axis is the Gaia solar-phase angle. The units are electrons pixel-1, integrated over the 4.4 s exposure time. Part of this figure, by Katja Janßen, is also presented in Sartoretti et al. (2018).