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Wide-field Infrared Survey Explorer

CdZnTe Substrate Photoluminescencein HgCdTe Arrays

A. Mainzer

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Wide-field Infrared Survey Explorer CdZnTe Behavior with Proton

Irradiation

• Analyzed 31 files from Ames/Bernie Rauscher containing full-frame darks from H1RG w/ 5 m detector material

• Data appear as 1024x1024x2 FITS cubes – a “signal” frame and a “noise” frame.

– Signal frame = average of 5 frames– Noise frame = standard deviation of 5 frames– Each frame has 8 samples (Fowler 4?)

• Easiest to spot CR strikes in noise frames, since hot/bad pixels don’t show up as much.

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Wide-field Infrared Survey Explorer

Example CR Hit + Glow

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Wide-field Infrared Survey Explorer

Two Examples

Hits seem to disappear after each frame, although these are 5 frames averaged together, so it’s not possible to check this. Persistence effect unknown on a single-frame basis.

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Wide-field Infrared Survey Explorer

Amplitudes in Noise Frame

• Median level in clean part of frame: ~0.0003

• Size of 5x noise region ~2400 pixels

• Size of 17x noise region~300 pixels

• Regions assymetric due to CR propagation thru substrate @ oblique angle

• Contours:– 0.001– 0.0015– 0.002– 0.005– 0.007– 0.010

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Wide-field Infrared Survey Explorer

Another Hit

• Median level in clean part of frame: 0.0003

• Size of 5x noise region ~510 pixels

• Size of 17x noise region~80 pixels

• Regions asymmetric due to CR propagation thru substrate @ oblique angle

• Contours:– 0.001– 0.0015– 0.002– 0.005– 0.007– 0.01– 0.05– 0.1

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Wide-field Infrared Survey Explorer

A Simulated WISE Frame

• Based on expected fluence of 1 hit/cm2/sec, we expect ~40 hits/frame.

• This image simulates the appearance of a typical WISE frame w/o substrate removal YUCK

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Wide-field Infrared Survey Explorer

Scientific Impacts - Sensitivity

• Based on an estimated 0.5 billion sources in the sky, we expect ~7000 point sources per WISE frame on average. Since most of sky is sparser, ~2400 is a reasonable.

• I added ~2400 fake stars w/ FWHM ~3 pixels to the simulated image & ran a simple aperture photometry routine w/ inner radius = 4 & sky apertures = 7-15 pixels.

• Measured in a clear (hit-free) region, the median SNR = 11.

• Median of entire image (including hits) was SNR = 5, due to irregular background and increased noise caused by CRs.

• 1/2400 sources was not detected due to inability of photometry routine to fit a Gaussian profile since source landed on CR

• Although this is only a single WISE frame, not a stack of 8, this is a significant hit to sensitivity. Asteroid science will be particularly impacted.

• Area affected is large enough that many sources will suffer from overlapping CR hits.

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Wide-field Infrared Survey Explorer

Scientific Impacts - Reliability

• Production of significant numbers of false faint sources would negatively impact brown dwarf science, as many candidates will be single-band detections in band 2 can’t use cross-band identification schemes

• An estimate of impact on reliability:– If ~2500 pixels are affected/CR, and we get ~30-50 CR/frame (based on 18

m pixels and 1 CR/cm2/sec fluence), we can expect ~10% of all pixels are affected per frame

– If we assume that a “source” must appear in 5/8 frames to be counted as a real detection, the probability of overlapping regions is 1e-5

– Multiply this by 1024x1024 pixels to get per pixel probability = 10– Now assume that we require a source to cover ~10 pixels to appear as a

point source 1 false source per set of 8– We survey 40,000 sq deg / (47 arcmin2 FOV) = 65,000 looks at the same

region There will be ~60,000 false sources detected– VERY rough calculation – lacking details of precise source extraction

algorithms