SJC - 109/29/05 IRAC Calibration Workshop

Status of IRAC Artifact Corrector

Sean Carey

SJC - 209/29/05 IRAC Calibration Workshop

imask Files

Reorder dmask flags, removing less than useful bits imask definition (tbs: to be set)

– Bit 0: reserved for boolean mask of data to mask– Bit 1: reserved– Bit 2: optical ghost (post-BCD, tbs)– Bit 3: stray light (post-BCD stray light masking sets this)– Bit 4: strong saturation (donut) detection (post-BCD, tbs) – Bit 5: muxbleed (post-BCD, set in prototype code)– Bit 6: banding (post-BCD, set in prototype code)– Bit 7: column pulldown (post-BCD, set in prototype code)– Bit 8: crosstalk (set in pipeline)– Bit 9: radhit (set in pipeline)– Bit 10: latent image (set in pipeline)– Bit 11: not flat-field corrected (set in pipeline)– Bit 12: data not linear (set in pipeline)– Bit 13: saturation (set in pipeline)– Bit 14: bad or missing data (set in pipeline)

Recommend using bits 3, 8-14 = 32520 in making mosaics, etc.

SJC - 309/29/05 IRAC Calibration Workshop

Muxbleed

Cause: Relaxation of multiplexer after observing bright source Present only in 3.6 and 4.5 m arrays Symptom: Trail of bright pixels in read direction (every 4th

column)

3.6 m 30 Doradus

Muxbleed

SJC - 409/29/05 IRAC Calibration Workshop

Muxstripes

Related to muxbleed

Symptom: Variation in level of column segments due to very bright source

Bright stars trigger and stop stripes

Muxstripe ends

Muxstripe starts

SJC - 509/29/05 IRAC Calibration Workshop

Column Pulldown

Symptom: Bias change in column containing bright source Strongest at 3.6 m, also present at 4.5 and 5.8 m Different above and below source - Fowler sampling dependent

SJC - 609/29/05 IRAC Calibration Workshop

Banding

Horizontal and vertical stripes produced by bright sources at 5.8 and 8.0 m

Partially electronic, also optical

Strength of banding can be different on opposite sides of triggering source

Weak banding may also be present in 3.6 and 4.5 m images

SJC - 709/29/05 IRAC Calibration Workshop

Optical Banding

Light scattered in array for Si:As arrays– Row and column bands– Diffuse component

Verified by ground tests on spare arrays

10-20% of incident flux scattered into bands

Diffuse scattering is 1.3 band flux

Banding has curvature

5.8 m

SJC - 809/29/05 IRAC Calibration Workshop

Electronic Artifact Mitigation Method

Artifact flagging– Cleaning up of mask files (dmask imask)– Identification of triggering pixels– Masking of affected data

Estimation of true sky under artifacts– Interpolation using nearby data– Gaussian kernel which mimics PRF

Modeling of artifacts– Fit to difference between data and estimation– Fit functional forms for each artifact

Correction of BCDs– Replace data with data - model– Update uncertainties

SJC - 909/29/05 IRAC Calibration Workshop

Artifact Flagging

Find triggering pixels based on unsaturated fluence (number of e-)

e- = MJy/sr * GAIN * EXPTIME / FLUXCONV HDR saturations

– Use short frame data to estimate fluence – Replace pixels if short > 100000 e- and long < 0.5 short

Full frametime saturations– Need additional data– Can estimate from 2MASS for most sources– Tool to PRF fit in testing

Muxbleed (3.6 and 4.5 m)– 30000, 60000, 150000 e- at 3.6 m to mask 32, 64, 192

samples– 55000, 160000, 250000 e- at 4.5 m to mask 32, 64, 128

samples Column pulldown (3.6 and 4.5 m)

– 30000 e- at 3.6 m– 110000 e- at 4.5 m

SJC - 1009/29/05 IRAC Calibration Workshop

3.6 m Flagging

MaskBCD

SJC - 1109/29/05 IRAC Calibration Workshop

5.8 and 8.0 m Flagging

Horizontal banding: 200000 e- (5.8 m), 55000 e- (8.0 m) Vertical banding: 80000 e- (5.8 m), 200000 e- (8.0 m)

5.8 m BCD 5.8 m mask

SJC - 1209/29/05 IRAC Calibration Workshop

Sky Estimation

Interpolate over masked pixels Use Gaussian kernel with FWHM of 1.44, 1.43, 1.49,

1.71 arcsec for 3.6, 4.5, 5.8, 8.0 m

3.6 m BCD 3.6 m sky estimate

SJC - 1309/29/05 IRAC Calibration Workshop

Model Fit

Fit corrective functions to BCD-sky_estimate difference Banding, pulldown : DC offset on either side of triggering

source– Linear fit may be appropriate for some data

Muxbleed: model derived from data in AOR– Fowler sampling dependent– Scaled and filtered muxbleed instances– Optionally, smooth with a polynomial fit

SJC - 1409/29/05 IRAC Calibration Workshop

Good 3.6 m Results

BCD Corrected BCD

SJC - 1509/29/05 IRAC Calibration Workshop

Poor 4.5 m Results

BCD Corrected BCD

SJC - 1609/29/05 IRAC Calibration Workshop

Good 8.0 m Results

BCD Corrected BCD

SJC - 1709/29/05 IRAC Calibration Workshop

Poor 8.0 m Results

BCD Corrected BCD

SJC - 1809/29/05 IRAC Calibration Workshop

Photometry?

BCD Corrected BCD

Source should be 2.0 ± 0.2Muxbleed source is 2.5 ± 0.5Pulldown source is 1.5 ± 0.4

SJC - 1909/29/05 IRAC Calibration Workshop

Future Improvements

Artifact thresholds as user-controlled input table Upper cutoff thresholds for artifacts Muxbleed model family as a function of triggering fluence Default muxbleed models for all frametimes Muxstripe corrector

– Detection of triggering pixel– Hot pixel map to determine end of effect– Median matching of outputs in affected subimage

Alternative background estimators– Morphlogical component analysis (Elad et al. 2005)