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Polarization the Central

Calibration of Pixel of ALFA

Hands-on Project AO-6

Outline

Motivation Observational Setup Calibration Data Analysis Results Future W ork

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M o ti v a ti o n
Determine the flux and % polarization of 3C286 Determine instrumental polarization of ALFA beam zero without assumi ng source parameters Characterize i nstrumental polarization so that it can be removed i n future observations Determine instrumental parameters as a function of frequency

Observations

Source: 3C286 (polarized quasar) Receiver: ALFA, beam 0 Back end: W APPs Central Frequency: 1385 MHz Bandwidth: 100 MHz Sampling time: 1 ms

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Observations (cont'd)

91 on-source scans: Integration time per scan: 20 sec Total rotation of feed: 180 degrees Rotation per scan: 2 degrees Off-source scan: Integration time ~100 s, drifting

Calibration #1
25 Hz hot winking cal duri ng both ON and OFF source observations Accounts for gain and phase difference between two polarization channels after noise is injected Tcal( ) is known across bandpass Used Vcal( ) Tcal( ) to put on- and off- source observations on same temperature scale

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Calibration #1

Tcal versus Frequency



Vcal

Tcal

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Calibration 2

Ton source - Toff source Removes receiver temperature (effects from before noise injection) Otherwise, differences between the two pol. chans can lead to pseudo-polarization

Data Analysis
Observed combi nations of Stokes parameters:

Gx, Gy are complex voltage gai ns i n each polarization channel is the complex mutual coupling factor

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Data Analysis

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Future W ork

Expand calibration of central pixel to the whole bandpass Calibrate the other ALFA pixels

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