Abstract
Abstract In 2017 April, the Event Horizon Telescope (EHT) observed the near-horizon region around the supermassive black hole at the core of the M87 galaxy. These 1.3 mm wavelength observations revealed a compact asymmetric ring-like source morphology. This structure originates from synchrotron emission produced by relativistic plasma located in the immediate vicinity of the black hole. Here we present the corresponding linear-polarimetric EHT images of the center of M87. We find that only a part of the ring is significantly polarized. The resolved fractional linear polarization has a maximum located in the southwest part of the ring, where it rises to the level of ∼15%. The polarization position angles are arranged in a nearly azimuthal pattern. We perform quantitative measurements of relevant polarimetric properties of the compact emission and find evidence for the temporal evolution of the polarized source structure over one week of EHT observations. The details of the polarimetric data reduction and calibration methodology are provided. We carry out the data analysis using multiple independent imaging and modeling techniques, each of which is validated against a suite of synthetic data sets. The gross polarimetric structure and its apparent evolution with time are insensitive to the method used to reconstruct the image. These polarimetric images carry information about the structure of the magnetic fields responsible for the synchrotron emission. Their physical interpretation is discussed in an accompanying publication.
Highlights
The Event Horizon Telescope (EHT) Collaboration has recently reported the first images of the event-horizon-scale structure around the supermassive black hole in the core of the massive elliptical galaxy M87, one of its two main targets.130 The EHT images of M87ʼs core at 230 GHz (1.3 mm wavelength) revealed a ring-like structure whose diameter of 42 μas, brightness temperature, shape, and asymmetry are interpreted as synchrotron emission from relativistic electrons gyrating around magnetic field lines in close vicinity to the event horizon
In Appendix D we present several validation tests of our intra-site baseline D-term estimation method carried out to motivate the use of band-averaged data products, comparisons to independent polarimetric source properties measured from simultaneous interferometric-Atacama Large Millimeter/submillimeter Array (ALMA) observations (Goddi et al 2021) near-in-time interferometric-Submillimeter Array (SMA) leakage estimates, and comparisons to results from a model fitting approach
Fiducial Polarimetric Images of M87 In Figure 6, we present the fiducial M87 linear-polarimetric images produced by each method from the low-band data on all four observing days
Summary
The Event Horizon Telescope (EHT) Collaboration has recently reported the first images of the event-horizon-scale structure around the supermassive black hole in the core of the massive elliptical galaxy M87, one of its two main targets.130 The EHT images of M87ʼs core at 230 GHz (1.3 mm wavelength) revealed a ring-like structure whose diameter of 42 μas, brightness temperature, shape, and asymmetry are interpreted as synchrotron emission from relativistic electrons gyrating around magnetic field lines in close vicinity to the event horizon. The Event Horizon Telescope (EHT) Collaboration has recently reported the first images of the event-horizon-scale structure around the supermassive black hole in the core of the massive elliptical galaxy M87, one of its two main targets.130. In this Letter, we present the first polarimetric analysis of the 2017 EHT observations of M87 and the first images of the linearly polarized radiation surrounding the M87 black hole shadow. These polarimetric images provide essential new information about the NASA Hubble Fellowship Program, Einstein Fellow. The other primary target being the black hole in Sgr A* in the center of the Milky Way
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