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Mapping and GALFA
Erasing striation with linked scans Linked scan options with ALFA A new gridding technique

Josh Goldston, ґ Carl Heiles & Snezana Stanimirovic


Two modes of `Linked Scanning'

Sept 2004 ALFA

June-August 2004 LBW


Least-square gain fitting using intersections is a success!
Continuum Maps with TW on LBW (Jun-Aug 2004) Before:

After:

Gridded with `AOGridzilla' (S. Stanimirovic) ґ


Drift

ALFA orientations depend upon scan method
dec RA

Basketweave (BW)

Typewriter (TW)


30°-1 : 1.06 sidereal

30° ALFA Basketweave mapping options
dec RA

30°-2 : 1.32 sidereal

30°-3 : 5.29 sidereal


0°-1 : 1.02 sidereal

0° ALFA Basketweave mapping options
dec RA

0°-2 : 1.53 sidereal

0°-3 : 3.09 sidereal


TW and BW techniques are useful for different mapping scenarios
Typewriter (TW)
-- Better for scanning near drift integration time (sidereal rate) -- Req's less timing precision -- Optimized for long R A regions

Basketweave (BW)
--Allows variable integration time (0.51x - 2.65x sidereal, 1.5 sq°/hr - 8 sq°/hr) -- Preserves beam pattern, giving higher comparison accuracy at crossing points -- Optimized for long dec regions


A few words about gridding:
-- Should `preserve information' -- Should handle non-simple beam patterns -- Should be independent of data-taking technique e.g. Tegmark 1997


Y = Time Ordered Data (TOD) X = Grid points A = Sparse Matrix to convert Grid to TOD

A·X = Y

X= A ·A

Least Squares Solution: -1 T T

·A ·Y


-- Linked scanning has been very successful! -- Both TW and BW are useful techniques -- BW scans are much more flexible w/ ALFA -- Advanced gridding techniques are available