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V. AllWISE Data Processing

V.3. Multiframe Pipeline Updates

V.3.d. Artifact Flagging

Identification and flagging of detections that are spurious detections of real detections contaminated by image artifacts produced by very bright sources is performed by the ARTID module in the WSDS Multiframe Pipeline. The general design and implementation of ARTID is described in section IV.4.g of the All-Sky Release Explanatory Supplement. Described here are modifications to ARTID made specifically for AllWISE Multiframe processing.

V.3.d.i. Coverage scaling

For Multiframe Pipeline processing, the artifact vs. magnitude models built for use with the Single-exposures are reused, but magnitudes undergo coverage scaling to account for greater sensitivity to artifacts relative to the background. The coverage used is usually from the w1m, w2m, w3m, or w4m column for the bright star's entry in the source extraction table. But as described in section of the All-Sky Release Supplement, off-field sources need to be modeled for on-field artifacts. Since these sources won't have entries in the Tile's detection table, no coverage estimate is available. In the All-Sky and 3-Band Cryo Releases, this resulted in a default coverage of 1 being used, which caused artifacts to be under-flagged. In AllWISE, an average coverage estimate derived (mostly) from the w1m, w2m, w3m and w4m columns of on-field bright sources is used to provide more realistic coverage modeling.

V.3.d.ii. Bright source upper limits

ARTID must always have a magnitude estimate for the parent source to use in its artifact models. For this reason, in the All-Sky and 3-Band Cryo releases, magnitude 95% confidence upper limits were used where necessary (sometimes very bright sources are assigned upper limits in some bands; c.f. II.2.e), leading to excessive flagging since the upper limits generally exceed the true magnitude of the source. In the AllWISE processing, a better estimate of the magnitudes is used by utilizing either data from the Bright Source List (c.f. in the All-Sky Release Supplement) or the quoted flux value for the source.

Last Updated: 22 November 2013

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