The Crab nebula is widely used as a polarization angle calibrator for single-dish radio observations because of its brightness, high degree of linear polarization, and well-known polarization angle over a wide frequency range. However, the Crab nebula cannot be directly used as a polarization angle calibrator for single-dish observations with the Korean VLBI Network (KVN), because the beam size of the telescopes is smaller than the size of the nebula. To determine the polarization angle of the Crab nebula as seen by KVN, we use 3C 286, a compact polarized extragalactic radio source whose polarization angle is well-known, as a reference target. We observed both the Crab nebula and 3C 286 with the KVN from 2017 to 2021 and find that the polarization angles at the total intensity peak of the Crab nebula (equatorial coordinates (J2000) R.A. = 05h34m32.3804s and Dec = 22◦00′44.0982′′) are 154.2◦ ±0.3◦, 151.0◦ ±0.2◦, 150.0◦ ±1.0◦, and 151.3◦ ±1.1◦ at 22, 43, 86, and 94 GHz, respectively. We also find that the polarization angles at the pulsar position (RA = 05h34m31.971s and Dec = 22◦00′52.06′′) are 154.4◦ ±0.4◦, 150.7◦ ±0.4◦, and 149.0◦ ± 1.0◦ for the KVN at 22, 43, and 86 GHz. At 129 GHz, we suggest to use the values 149.0◦ ± 1.6◦ at the total intensity peak and 150.2◦ ± 2.0◦ at the pulsar position obtained with the Institute for Radio Astronomy in the Millimeter Range (IRAM) 30-meter Telescope. Based on our study, both positions within the Crab nebula can be used as polarization angle calibrators for the KVN single-dish observations.

Abstract
1. Introduction
2. Observations and Data Reduction
    2.1. KVN
    2.2. ALMA
3. Results
    3.1. The Stability of 3C 286
    3.2. The EVPA of the Crab NebulaGiven that the EVPA measured with circular
    3.3. The Fractional Polarization of the Crab Nebula
4. Discussion
    4.1. Angular Resolution
    4.2. Spectral Index
    4.3. Instrumental Polarization
    4.4. Faraday Rotation
5. Summary and Conclusions
Acknowledgments
Appendix A. The Stability of 3C 28
Appendix B. Fractional Polarization
References

• Minchul Kam(Department of Physics and Astronomy, Seoul National University)
• Sascha Trippe(Department of Physics and Astronomy, Seoul National University, SNU Astronomy Research Center, Seoul National University) Corresponding Author
• Do-Young Byun(Korea Astronomy and Space Science Institute)
• Jongho Park(Korea Astronomy and Space Science Institute, Institute of Astronomy and Astrophysics, Academia Sinica)
• Sincheol Kang(Korea Astronomy and Space Science Institute)
• Naeun Shin(Department of Physics and Astronomy, Seoul National University, Korea Astronomy and Space Science Institute)
• Sang-Sung Lee(Korea Astronomy and Space Science Institute)
• Taehyun Jung(Korea Astronomy and Space Science Institute)