Commissioning of a 4k x 4k CCD mosaic and the new ESO FIERA CCD controller at the SUSI-2 imager of the NTT

We present the characteristics of the new CCD imager, SUSI2, installed at the ESO 3.5m NTT. The instrument shares the Nasmyth focus A with the new infrared imager-spectrograph SOFI. The focal plane array of SUSI2 is a mosaic of 2 EEV44-82, 2k x 4k, 15 mu m pixels, thinned, anti-reflection coated CCDs, which are placed at the direct focus of the telescope (scale 0.08 arcsec/pixel, field of view 5.5 x 5.5 arcmin). The average QE for the two devices is 76, 90, 85, 80, 68, 49, 23% at 350, 400, 500, 600, 700, 800 900 nm respectively. The overall instrument efficiency, including the three mirrors of the telescope and the detector but without filters, is computed to be 46, 55, 51 and 48% at the central wavelengths of the U, B, V and R bands. The CCDs are driven by the new ESO CCD controller FIERA. The system performance was measured during the commissioning of the instrument at the telescope in February 98. The mosaic is read in 16 seconds in the standard operating mode (2 x 2 binning of the CCDs) with a read-out-noise of 4.7 e(-)/pixel. The other CCD parameters such as CTE, dark current and linearity, were also found to comply with the requirements. The FWHM of stellar sources in images obtained in good seeing conditions were measured to be 0.49 arcsec, with no significant variation over the field of view.