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Outline Polarization Calibration of the Central Pixel of ALFA
Hands- on Pr oject AO-6 Motivation Observational Setup Calibr ation Data Analysis Results Futur e W ork

Motivation
Determine the flux and % polar ization of 3C286 Determine instrumental polar ization of ALFA beam zer o without assuming sourc e par ameters Char acterize instrumental polarization so that it can be r emoved in futur e obser vations Determine instrumental par ameters as a function of frequenc y

Observations

Sourc e: 3C286 ( polar ized quas ar) Receiver: ALFA, beam 0 Back end: W APPs Centr al Fr equency: 1385 MHz Bandwidth: 100 MHz Sampling time: 1 ms

Observations (cont'd)

Calibration #1
25 Hz hot winking c al during both ON and OFF source obser vations Accounts for gain and phas e differ enc e between two polarization channels after nois e is injected Tcal( ) is known acr oss bandpass Used Vcal( ) Tcal( ) to put on- and off- source obs er vations on s ame temper atur e scale


91 on-source scans: Integr ation time per scan: 20 sec Total r otation of feed: 180 degr ees Rotation per scan: 2 degr ees Off-source scan: Integr ation time ~100 s, drifting

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Calibration #1

Tcal versus Frequency

Calibration 2

Ton source - Toff source Removes r ec eiver temper atur e ( effects from bef or e noise injection) Otherwise, differences between the two pol. chans can lead to pseudo-polarization

Data Analysis



Vcal

T cal

Data Analysis
Observed c ombinations of Stokes par ameters:

Gx, G y ar e c omplex voltage gains in each polarization channel is the complex mutual coupling factor

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Future Work

Expand c alibr ation of centr al pixel to the whole bandpass Calibr ate the other ALFA pixels

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