Accurate polarization calibration of FAST spectral data for measurements of Zeeman splittings of OH megamasers in IRAS 02524+2046

Abstract

An accurate polarization calibration is essential for a spectral data analysis and Zeeman splitting measurements. Two anomalies challenge our understanding of OH megamasers in IRAS 02524+2046: an unexplained 1667/1665 MHz flux-ratio deviation, and complex Stokes V signatures. Well-calibrated sensitive polarization observations are required to understand them. We develop a polarization calibration solution for the L-band 19-beam receiver installed on the Five-hundred-meter aperture spherical radio telescope (FAST) to achieve a high calibration accuracy and thus enable accurate measurements of the OH megamaser properties in IRAS 02524+2046. We determined the Mueller matrix solution for spectral observations across the 1050-1450 MHz frequency range with an accuracy of about 0.01%-0.08% for circular polarization. We then applied it to FAST observational data of IRAS 02524+2046. Our results show narrower emission line components in the OH megamasers than previously reported, which are indistinguishable in the total power spectrum, but are detected in the circular polarization spectrum. The 1667 MHz OH megamaser emissions probably span a wide velocity range from ~54750 to ~53580 km/s, indicating greater complexity than previously recognized. Our fit of the total power and circular polarization spectra for IRAS 02524+2046 revealed ten line components with significant Zeeman splitting (>3sigma), indicating in situ magnetic fields with a strength of approximately -24.5 mG to +20.6 mG, most of which (8/10) have positive values.

15 pages, 9 figures, 3 tables, Accepted for publication in A&A

References in corpus (16)

• Molecular outflows in local ULIRGs: energetics from multi-transition OH analysis
• Calibrating High-Precision Faraday Rotation Measurements for LOFAR and the Next Generation of Low-Frequency Radio Telescopes
• Extragalactic Zeeman Detections in OH Megamasers
• An Early Transition to Magnetic Supercriticality in Star Formation
• The Effect of 53 micron IR Radiation on 18 cm OH Megamaser Emission
• Parsec-scale magnetic fields in Arp 220
• Peering into the Milky Way by FAST: II. Ionized gas in the inner Galactic disk revealed by the piggyback line observations of the FAST GPPS survey
• Peering into the Milky Way by FAST: IV. Identification of two new Galactic supernova remnants G203.1+6.6 and G206.7+5.9
• Peering into the Milky Way by FAST: I. Exquisite HI structures in the inner Galactic disk from the piggyback line observations of the FAST GPPS survey
• Distance of PSR B0458+46 indicated by FAST HI absorption observations
• Peering into the Milky Way by FAST: III. Magnetic fields in the Galactic halo and farther spiral arms revealed by the Faraday effect of faint pulsars
• The FAST Galactic Plane Pulsar Snapshot survey: IV. Discovery of five fast radio bursts
• A MeerKAT Polarization Survey of Southern Calibration Sources
• The radio properties of the OH megamaser galaxy IRAS 02524+2046
• Beam Measurements of Full Stokes Parameters for the FAST L-band 19-beam Receiver
• Radio continuum and OH line emission of high-z OH megamaser galaxies