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Early-time UV observations are sensitive to the outermost layers of the ejecta (and least affected by the explosion itself) and show the most diversity for SNe Ia. This makes the UV bandpass an excellent probe to solve these open questions about the nature of these cosmological distance indicators. To achieve this science, we present UVIa, a CubeSat that will be reactive and have simultaneous optical, Near-UV (NUV), and Far-UV (FUV) coverage, takes advantage of state-of-the-art UV coatings, UV-enhanced silicon detectors with whitelight rejection filter, and autonomous observing scheduling, updated regularly based on newly discovered SNe Ia from modern transient surveys.
The Coronagraph Instrument (CGI) will be required to operate with low signal flux for long integration times, demanding all noise sources are kept to a minimum. The Electron Multiplication (EM)-CCD has been baselined for both the imaging and spectrograph cameras due its ability to operate with sub-electron effective read noise values with appropriate multiplication gain setting. The presence of other noise sources, however, such as thermal dark signal and Clock Induced Charge (CIC), need to be characterized and mitigated. In addition, operation within a space environment will subject the device to radiation damage that will degrade the Charge Transfer Effciency (CTE) of the device throughout the mission lifetime. Irradiation at the nominal instrument operating temperature has the potential to provide the best estimate of performance degradation that will be experienced in-flight, since the final population of silicon defects has been shown to be dependent upon the temperature at which the sensor is irradiated.
Here we present initial findings from pre- and post- cryogenic irradiation testing of the e2v CCD201-20 BI EMCCD sensor, baselined for the WFIRST coronagraph instrument. The motivation for irradiation at cryogenic temperatures is discussed with reference to previous investigations of a similar nature. The results are presented in context with those from a previous room temperature irradiation investigation that was performed on a CCD201-20 operated under the same conditions. A key conclusion is that the measured performance degradation for a given proton fluence is seen to measurably differ for the cryogenic case compared to the room temperature equivalent for the conditions of this study.
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