Accurate Polarization Calibration at 800 MHz with the Green Bank Telescope

Abstract

Polarization leakage of foreground synchrotron emission is a critical issue in HI intensity mapping experiments. While the sought-after HI emission is unpolarized, polarized foregrounds such as Galactic and extragalactic synchrotron radiation, if coupled with instrumental impurity, can mimic or overwhelm the HI signals. In this paper we present the methodology for polarization calibration at 700-900 MHz, applied on data obtained from the Green Bank Telescope (GBT). We use astrophysical sources, both polarized and unpolarized sources including quasars and pulsars, as calibrators to characterize the polarization leakage and control systematic effects in our GBT HI intensity mapping project. The resulting fractional errors on polarization measurements on boresight are well controlled to within 0.6%-0.8% of their total intensity. The polarized beam patterns are measured by performing spider scans across both polarized quasars and pulsars. A dominant Stokes I to V leakage feature and secondary features of Stokes I to Q and I to U leakages in the 700-900 MHz frequency range are identified. These characterizations are important for separating foreground polarization leakage from the HI 21 cm signal.

12 pages, 12 figures, accepted for publication in ApJ

References in corpus (6)

• PSRCHIVE and PSRFITS An Open Approach to Radio Pulsar Data Storage and Analysis
• Baryon Acoustic Oscillation Intensity Mapping as a Test of Dark Energy
• Measurement of 21 cm brightness fluctuations at z ~ 0.8 in cross-correlation
• Possibility of Precise Measurement of the Cosmological Power Spectrum With a Dedicated 21cm Survey After Reionization
• High-fidelity radio astronomical polarimetry using a millisecond pulsar as a polarized reference source
• Polarization observations of 100 pulsars at 774 MHz by the Green Bank Telescope

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• The MeerKAT Telescope as a Pulsar Facility: System verification and early science results from MeerTime
• Recovery of 21 cm intensity maps with sparse component separation
• Gaussian Process Regression for foreground removal in HI intensity mapping experiments
• The Global Magneto-Ionic Medium Survey: Polarimetry of the Southern Sky from 300 to 480 MHz
• Statistical recovery of the BAO scale from multipoles of the beam-convolved 21cm correlation function
• Eliminating polarization leakage effect for neutral hydrogen intensity mapping with deep learning
• Point Source C-Band Mueller Matrices for the Green Bank Telescope
• Exploring HI Galaxy Redshift Survey Strategies for the FAST Core Array Interferometry
• An Introduction to Single-Antenna Radio Astronomical Polarimetry
• Deep learning with hybrid frequency differencing and principal component analysis for 21-cm foreground and beam mitigation