The Event Horizon Telescope Image of the Quasar NRAO 530

Abstract

We report on the observations of the quasar NRAO 530 with the Event Horizon Telescope (EHT) on 2017 April 5−7, when NRAO 530 was used as a calibrator for the EHT observations of Sagittarius A*. At z = 0.902, this is the most distant object imaged by the EHT so far. We reconstruct the first images of the source at 230 GHz, at an unprecedented angular resolution of ∼20 μas, both in total intensity and in linear polarization (LP). We do not detect source variability, allowing us to represent the whole data set with static images. The images reveal a bright feature located on the southern end of the jet, which we associate with the core. The feature is linearly polarized, with a fractional polarization of ∼5%–8%, and it has a substructure consisting of two components. Their observed brightness temperature suggests that the energy density of the jet is dominated by the magnetic field. The jet extends over 60 μas along a position angle ∼ −28°. It includes two features with orthogonal directions of polarization (electric vector position angle), parallel and perpendicular to the jet axis, consistent with a helical structure of the magnetic field in the jet. The outermost feature has a particularly high degree of LP, suggestive of a nearly uniform magnetic field. Future EHT observations will probe the variability of the jet structure on microarcsecond scales, while simultaneous multiwavelength monitoring will provide insight into the high-energy emission origin.

First M87 Event Horizon Telescope Results. IX. Detection of Near-horizon Circular Polarization

“…In addition to the differences inherent in each approach as a result of the underlying method (CLEAN vs. raster fitting vs. geometric modeling, Bayesian exploration vs. fitting a single image), our methods face additional choices on how they deal with polarimetric leakage (D-terms) and residual gain ratios (G R/L ). Constraints on the D-terms were derived and discussed extensively in Paper VII; these constraints have been confirmed with analysis of EHT observations of AGNs in Issaoun et al (2022) and Jorstad et al (2023). As a result, some methods (DIFMAP, and m-ring modeling) chose to directly apply the Paper VII D-term results to the data and not treat polarimetric leakage further; in contrast, DMC and THEMIS fully explored uncertainties in the D-terms under flat priors as part of their Bayesian posterior exploration.…”

Atmospheric Limitations for High-frequency Ground-based Very Long Baseline Interferometry

“…In our models, M87 * and Sgr A * have long-baseline (∼30 Gλ) flux densities of ∼10 mJy and ∼20 mJy, respectively. Other sources observed with the EHT -including 3C 279 (Kim et al 2020), Centaurus A (Janssen et al 2021), J1924-2914 (Issaoun et al 2022), and NRAO 530 (Jorstad et al 2023)-exhibit flux densities between ∼100 and ∼500 mJy on ∼10 Gλ baselines. Furthermore, the brightness temperature maximum expected for synchrotron emission is ∼10 12 K (Kellermann & Pauliny-Toth 1969), corresponding (per Equation ( 18)) to correlated flux densities between ∼1 and ∼10 Jy on the longest baselines.…”

Key Science Goals for the Next-Generation Event Horizon Telescope

“…By observing with coordinated multi-wavelength campaigns, the ngEHT will provide decisive insights into the nature of the bright, compact "core" feature that is seen in many blazars (e.g., [150]). Current EHT images of blazars show complex, multi-component emission [16,18,19], so ngEHT observations extending over multiple months to study the evolution of these components will be imperative.…”

“…The Event Horizon Telescope (EHT) has produced the first images of the supermassive black holes (SMBHs) in the M87 galaxy ( [1][2][3][4][5][6][7][8], hereafter M87 * I-VIII) and at the center of the Milky Way ( [9][10][11][12][13][14], hereafter Sgr A * I-VI). Interpretation of the EHT results for Sgr A * and M87 * has relied heavily upon coordinated multi-wavelength campaigns spanning radio to gamma-rays ( [10], ETH MWL Science Working Group et al [15]) In addition, the EHT has made the highest resolution images to date of the inner jets of several nearby Active Galactic Nuclei (AGN), demonstrating the promise of millimeter VLBI in making major contributions to the studies of relativistic radio jets launched from SMBHs (Kim et al [16], Janssen et al [17], Issaoun et al [18], Jorstad et al [19]).…”