WFC 3 TV 2 Testing : UVIS - 2 Read Noise

We examine the read noise of the spare UVIS-2 detector of the Wide Field Camera 3 during its second thermal vacuum campaign at the Goddard Space Flight Center. Only the frames acquired in the default readout mode are considered : a gain = 1.5 e/DN, a four amplifier readout (ABCD), and no on-chip binning. The read noise is calculated from the serial virtual overscan region of each quadrant. From a sample of ~600 frames at an operating temperature of -78 C, the read noise is 3.17± 0.02, 3.15± 0.08, 3.20 ± 0.03, and 3.27 ± 0.02 e for amplifiers A, B, C, and D, respectively. At a temperature of 81 C (and from a smaller sample), the read noise is lower by ~0.6% for amps A and B and by ~1.4% for amps C and D. A weak positive correlation is found between the read noise and the median level of the imaging areas for amps C and D, possibly from a nonperfect serial transfer of the charge. The variation is very small, roughly 0.05 e (1.5%) or less over a range of imaging levels of 10000 e to 60000 e. Similarly, a weak negative correlation is found for amplifiers A and B. The CEI specification of a read noise of < 4 e is easily met for an operating detector temperature of < -20 C. There is no difference in the read noise between instrument sides 1 and 2. In an appendix, we present and analyze the superbias frame. A weak residual odd/even effect is observed in each quadrant and the ovsercan regions. The peak-to-peak amplitude of the effect is 0.01-0.03 e for amps A,C,D and ~0.4 e for amp B. The presence of this pattern will be checked for the flight detector and if necessary, proper modifications to calwf3 will be explored to minimize its impact. Operated by the Association of Universities for Research in Astronomy, Inc., for the National Aeronautics and Space Administration