Oral Presentation

Monitoring of the radio calibrator 3C 286 with ALMA and IRAM

Author(s): Minchul Kam (ASIAA), Hiroshi Nagai (NAOJ), Motoki Kino (NAOJ), Keiichi Asada (ASIAA), Ruediger Kneissl (ALMA), Ivan Agudo (IAA-CSIC), Sascha Trippe (SNU), Seiji Kameno (ALMA), Hojin Cho (Texas Tech), Richard Perley (NRAO), Bryan Butler (NRAO), Tomoki Matsuoka (ASIAA), Jongho Park (KHU), Carolina Casadio (IESL), Ioannis Myserlis (IRAM), Clemens Thum (IRAM), Wanchaloem Khwammai (SNU), Diego Alvarez (IESL), Juan Escudero (CfA)

Presenter: Minchul Kam (ASIAA)

We present the results of monitoring of the radio quasar 3C 286, conducted using three instruments: ALMA, the IRAM 30-m Telescope , and SMA. The total flux of 3C 286 has remained nearly constant throughout the monitoring period from 2006 to 2024, suggesting that it can be reliably used as a flux calibrator up to 343 GHz. The spectrum of 3C 286 steepens at higher frequencies, exhibiting a break at 67 GHz. This can be attributed to synchrotron cooling. The EVPA and fractional polarization of 3C 286 are stable at all frequencies. Notably, the EVPA gradually rotates as a function of wavelength squared, which is well described by a single power-law across all frequencies; we therefore propose using the theoretical EVPA values provided by the model curve for the purpose of absolute EVPA calibration between 5 and 343 GHz. Across the entire frequency range, the Faraday rotation measure increases proportional to the square of the frequency up to $\rm (3.0\pm1.5)\times10^4\ rad\ m^{-2}$. This is in agreement with core-shift caused by frequency-dependent jet plasma opacity. The fractional polarization gradually increases as a function of wavelength squared. This trend can be explained by a more ordered magnetic field in regions closer to the black hole, depolarization due to Faraday rotation, or a combination of both.