A revised view of the linear polarization in the subparsec core of M87 at 7 mm

Abstract

The linear polarization images of the jet in the giant elliptical galaxy M87 have previously been observed with Very Long Baseline Array at 7 mm. They exhibit a complex polarization structure surrounding the optically thick and compact subparsec-scale core. However, given the low level of linear polarization in the core, it is required to verify that this complex structure does not originate from residual instrumental polarization signals in the data. We have performed a new analysis of the same data sets observed in four epochs by using the Generalized Polarization CALibration pipeline (GPCAL). This novel instrumental polarization calibration pipeline overcomes the limitations of LPCAL, a conventional calibration tool used in the previous M87 studies. The resulting images show a compact linear polarization structure with its peak nearly coincident with the total intensity peak, which is significantly different from the results of previous studies. The core linear polarization is characterized as fractional polarization of $\sim 0.2-0.6$% and polarization angles of $\sim 66-92^{\circ }$, showing moderate variability. We demonstrate that, based on tests with synthetic data sets, LPCAL using calibrators having complex polarization structures cannot achieve sufficient calibration accuracy to obtain the true polarization image of M87 due to a breakdown of the "similarity approximation". We find that GPCAL obtains more accurate D-terms than LPCAL by using observed closure traces of calibrators that are insensitive to both antenna gain and polarization leakage corruptions. This study suggests that polarization imaging of very weakly polarized sources has become possible with the advanced instrumental polarization calibration techniques.

arXiv comment22 pages, 13 figures, 4 tables, accepted for publication in ApJ

References in corpus (83)

• First M87 Event Horizon Telescope Results. I. The Shadow of the Supermassive Black Hole
• Observational Evidence of AGN Feedback
• First M87 Event Horizon Telescope Results. VI. The Shadow and Mass of the Central Black Hole
• First M87 Event Horizon Telescope Results. IV. Imaging the Central Supermassive Black Hole
• First M87 Event Horizon Telescope Results. V. Physical Origin of the Asymmetric Ring
• Efficient Generation of Jets from Magnetically Arrested Accretion on a Rapidly Spinning Black Hole
• First M87 Event Horizon Telescope Results. II. Array and Instrumentation
• General Relativistic Magnetohydrodynamic Simulations of Magnetically Choked Accretion Flows around Black Holes
• First M87 Event Horizon Telescope Results. III. Data Processing and Calibration
• Relativistic Jets in Active Galactic Nuclei
• Magnetically Arrested Disk: An Energetically Efficient Accretion Flow
• Polarimetric Observations of 15 Active Galactic Nuclei at High Frequencies: Jet Kinematics from Bimonthly Monitoring with the Very Long Baseline Array
• First M87 Event Horizon Telescope Results. VIII. Magnetic Field Structure near The Event Horizon
• General Relativistic Magnetohydrodynamic Simulations of Jet Formation and Large-Scale Propagation from Black Hole Accretion Systems
• The ACS Fornax Cluster Survey. V. Measurement and Recalibration of Surface Brightness Fluctuations and a Precise Value of the Fornax--Virgo Relative Distance
• First M87 Event Horizon Telescope Results. VII. Polarization of the Ring
• The Black-Hole Mass in M87 from Gemini/NIFS Adaptive Optics Observations
• Magnetic acceleration of ultra-relativistic jets in gamma-ray burst sources
• Magnetic acceleration of relativistic AGN jets
• Kinematics of Parsec-Scale Jets of Gamma-Ray Blazars at 43~GHz within the VLBA-BU-BLAZAR Program
• The Structure and Dynamics of the Sub-parsec Scale Jet in M87 Based on 50 VLBA Observations Over 17 Years at 43 GHz
• MOJAVE: Monitoring of Jets in AGN with VLBA Experiments - I. First-Epoch 15 GHz Linear Polarization Images
• The M87 Black Hole Mass from Gas-dynamical Models of Space Telescope Imaging Spectrograph Observations
• The Structure of the M87 Jet: A Transition from Parabolic to Conical Streamlines
• MOJAVE: XV. VLBA 15 GHz Total Intensity and Polarization Maps of 437 Parsec-Scale AGN Jets From 1996-2017
• Simulations of Ultrarelativistic Magnetodynamic Jets from Gamma-ray Burst Engines
• Revisiting the radio interferometer measurement equation. I. A full-sky Jones formalism
• Kinematics of the jet in M87 on scales of 100 -- 1000 Schwarzschild radii
• High Resolution Linear Polarimetric Imaging for the Event Horizon Telescope
• Radio Imaging of the Very-High-Energy Gamma-Ray Emission Region in the Central Engine of a Radio Galaxy
• MOJAVE: Monitoring of Jets in Active Galactic Nuclei with VLBA Experiments. VIII. Faraday rotation in parsec-scale AGN jets
• Interferometric Imaging Directly with Closure Phases and Closure Amplitudes
• Magnetic Driving of Relativistic Outflows in Active Galactic Nuclei. I. Interpretation of Parsec-Scale Accelerations
• The Inner Jet of the Radio Galaxy M87
• Asymptotic structure of Poynting dominated jets
• Energy, momentum and mass outflows and feedback from thick accretion discs around rotating black holes
• The limb-brightened jet of M87 down to 7 Schwarzschild radii scale
• Complex Faraday depth structure of Active Galactic Nuclei as revealed by broadband radio polarimetry
• Multiwaveband Polarimetric Observations of 15 Active Galactic Nuclei at High Frequencies: Correlated Polarization Behavior
• Optical and Radio Polarimetry of the M87 Jet at 0.2" Resolution
• High-Sensitivity 86GHz (3.5mm) VLBI Observations of M87: Deep Imaging of the Jet Base at a 10 Schwarzschild-Radius Resolution
• Two-temperature, Magnetically Arrested Disc simulations of the jet from the supermassive black hole in M87
• Parabolic Jets from the Spinning Black Hole in M87
• High Frequency VLBI Imaging of the Jet Base of M87
• Active Galactic Nuclei Feedback in an Elliptical Galaxy with the Most Updated AGN Physics (I): Low-angular Momentum Case
• The Inner Halo of M87: A First Direct View of the Red-Giant Population
• The Parabolic Jet Structure in M87 as a Magnetohydrodynamic Nozzle
• Broadband Multi-wavelength Properties of M87 during the 2017 Event Horizon Telescope Campaign
• Polarimetric properties of Event Horizon Telescope targets from ALMA
• Three dimensional magnetic field structure of six parsec-scale active galactic nuclei jets
• Discovery of Sub- to Superluminal Motions in the M87 Jet: An Implication of the Acceleration from Sub-relativistic to Relativistic Speeds
• The Next Generation Virgo Cluster Survey (NGVS). XVIII. Measurement and Calibration of Surface Brightness Fluctuation Distances for Bright Galaxies in Virgo (and Beyond)
• The stratified two-sided jet of Cygnus A. Acceleration and collimation
• Faraday rotation in the jet of M87 inside the Bondi radius: indication of winds from hot accretion flows confining the relativistic jet
• Collimation, Acceleration and Recollimation Shock in the Jet of Gamma-Ray-emitting Radio-Loud Narrow-Line Seyfert 1 Galaxy 1H 0323+342
• rPICARD: A CASA-based Calibration Pipeline for VLBI Data
• Faraday Rotation Measures in the Parsec-Scale Jets of the Radio Galaxies M87, 3C 111, and 3C 120
• Kinematics of the M87 jet in the collimation zone: gradual acceleration and velocity stratification
• Closure statistics in interferometric data
• Pilot KaVA monitoring on the M87 jet: confirming the inner jet structure and superluminal motions at sub-pc scales
• A strong radio brightening at the jet base of M87 during the elevated very-high-energy gamma-ray state in 2012
• The X-ray Jet in Centaurus A: Clues on the Jet Structure and Particle Acceleration
• Broadband, radio spectro-polarimetric study of 100 radiative-mode and jet-mode AGN
• Optical Proper Motion Measurements of the M87 Jet: New Results from the Hubble Space Telescope
• Jet collimation and acceleration in the giant radio galaxy NGC 315
• Spatially resolved origin of mm-wave linear polarization in the nuclear region of 3C 84
• Steady General Relativistic Magnetohydrodynamic Inflow/Outflow Solution along Large-Scale Magnetic Fields that Thread a Rotating Black Hole
• Broadband radio spectro-polarimetric observations of high Faraday rotation measure AGN
• Linear polarization in the nucleus of M87 at 7 mm and 1.3 cm
• Parsec-scale Faraday rotation and polarization of 20 active galactic nuclei jets
• MOJAVE XVI: Multi-Epoch Linear Polarization Properties of Parsec-Scale AGN Jet Cores
• Evidence for nuclear radio jet and its structure down to <100 Schwarzschild radii in the center of the Sombrero galaxy (M 104, NGC 4594)
• Enhanced Polarized Emission from the One-Parsec-Scale Hotspot of 3C 84 as a Result of the Interaction with Clumpy Ambient Medium
• Polarization structure in the core of 1803+784: a signature of recollimation shocks?
• Polarization calibration techniques for new-generation VLBI
• Properties of Trans-fast Magnetosonic Jets in Black Hole Magnetospheres
• Closure Traces: Novel Calibration-Insensitive Quantities for Radio Astronomy
• Revealing the Nature of Blazar Radio Cores through Multi-Frequency Polarization Observations with the Korean VLBI Network
• A D-term Modeling Code (DMC) for simultaneous calibration and full-Stokes imaging of very long baseline interferometric data
• GPCAL: a generalized calibration pipeline for instrumental polarization in VLBI data
• Ejection of Double knots from the radio core of PKS 1510--089 during the strong gamma-ray flares in 2015
• Low optical polarisation at the core of the optically-thin jet of M87
• rPICARD: A CASA-based Calibration Pipeline for VLBI Data. Calibration and imaging of 7 mm VLBA observations of the AGN jet in M87