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  • 1
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    Online Resource
    Broadband Multi-wavelength Properties of M87 during the 2017 Event Horizon Telescope Campaign
    American Astronomical Society ; 2021
    In:  The Astrophysical Journal Letters Vol. 911, No. 1 ( 2021-04-01), p. L11-
    Details
    In: The Astrophysical Journal Letters, American Astronomical Society, Vol. 911, No. 1 ( 2021-04-01), p. L11-
    Abstract: In 2017, the Event Horizon Telescope (EHT) Collaboration succeeded in capturing the first direct image of the center of the M87 galaxy. The asymmetric ring morphology and size are consistent with theoretical expectations for a weakly accreting supermassive black hole of mass ∼6.5 × 10 9 M ⊙ . The EHTC also partnered with several international facilities in space and on the ground, to arrange an extensive, quasi-simultaneous multi-wavelength campaign. This Letter presents the results and analysis of this campaign, as well as the multi-wavelength data as a legacy data repository. We captured M87 in a historically low state, and the core flux dominates over HST-1 at high energies, making it possible to combine core flux constraints with the more spatially precise very long baseline interferometry data. We present the most complete simultaneous multi-wavelength spectrum of the active nucleus to date, and discuss the complexity and caveats of combining data from different spatial scales into one broadband spectrum. We apply two heuristic, isotropic leptonic single-zone models to provide insight into the basic source properties, but conclude that a structured jet is necessary to explain M87’s spectrum. We can exclude that the simultaneous γ -ray emission is produced via inverse Compton emission in the same region producing the EHT mm-band emission, and further conclude that the γ -rays can only be produced in the inner jets (inward of HST-1) if there are strongly particle-dominated regions. Direct synchrotron emission from accelerated protons and secondaries cannot yet be excluded.
    Type of Medium: Online Resource
    ISSN: 2041-8205 , 2041-8213
    URL: Article
    DOI: 10.3847/2041-8213/abef71
    Language: Unknown
    Publisher: American Astronomical Society
    Publication Date: 2021
    detail.hit.zdb_id: 7233-3
    detail.hit.zdb_id: 2006858-X
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  • 2
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    Event Horizon Telescope imaging of the archetypal blazar 3C 279 at an extreme 20 microarcsecond resolution
    EDP Sciences ; 2020
    In:  Astronomy & Astrophysics Vol. 640 ( 2020-08), p. A69-
    Details
    In: Astronomy & Astrophysics, EDP Sciences, Vol. 640 ( 2020-08), p. A69-
    Abstract: 3C 279 is an archetypal blazar with a prominent radio jet that show broadband flux density variability across the entire electromagnetic spectrum. We use an ultra-high angular resolution technique – global Very Long Baseline Interferometry (VLBI) at 1.3 mm (230 GHz) – to resolve the innermost jet of 3C 279 in order to study its fine-scale morphology close to the jet base where highly variable γ -ray emission is thought to originate, according to various models. The source was observed during four days in April 2017 with the Event Horizon Telescope at 230 GHz, including the phased Atacama Large Millimeter/submillimeter Array (ALMA), at an angular resolution of ∼20  μ as (at a redshift of z  = 0.536 this corresponds to ∼0.13 pc  ∼ 1700 Schwarzschild radii with a black hole mass M BH  = 8 × 10 8   M ⊙ ). Imaging and model-fitting techniques were applied to the data to parameterize the fine-scale source structure and its variation. We find a multicomponent inner jet morphology with the northernmost component elongated perpendicular to the direction of the jet, as imaged at longer wavelengths. The elongated nuclear structure is consistent on all four observing days and across different imaging methods and model-fitting techniques, and therefore appears robust. Owing to its compactness and brightness, we associate the northern nuclear structure as the VLBI “core”. This morphology can be interpreted as either a broad resolved jet base or a spatially bent jet. We also find significant day-to-day variations in the closure phases, which appear most pronounced on the triangles with the longest baselines. Our analysis shows that this variation is related to a systematic change of the source structure. Two inner jet components move non-radially at apparent speeds of ∼15  c and ∼20  c (∼1.3 and ∼1.7  μ as day −1 , respectively), which more strongly supports the scenario of traveling shocks or instabilities in a bent, possibly rotating jet. The observed apparent speeds are also coincident with the 3C 279 large-scale jet kinematics observed at longer (cm) wavelengths, suggesting no significant jet acceleration between the 1.3 mm core and the outer jet. The intrinsic brightness temperature of the jet components are ≲10 10 K, a magnitude or more lower than typical values seen at ≥7 mm wavelengths. The low brightness temperature and morphological complexity suggest that the core region of 3C 279 becomes optically thin at short (mm) wavelengths.
    Type of Medium: Online Resource
    ISSN: 0004-6361 , 1432-0746
    URL: Article
    DOI: 10.1051/0004-6361/202037493
    RVK:
    UA 1000
    RVK:
    US 1090
    Language: English
    Publisher: EDP Sciences
    Publication Date: 2020
    detail.hit.zdb_id: 626-9
    detail.hit.zdb_id: 1458466-9
    SSG: 16,12
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  • 3
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    First M87 Event Horizon Telescope Results. II. Array and Instrumentation
    American Astronomical Society ; 2019
    In:  The Astrophysical Journal Letters Vol. 875, No. 1 ( 2019-04-10), p. L2-
    Details
    In: The Astrophysical Journal Letters, American Astronomical Society, Vol. 875, No. 1 ( 2019-04-10), p. L2-
    Abstract: The Event Horizon Telescope (EHT) is a very long baseline interferometry (VLBI) array that comprises millimeter- and submillimeter-wavelength telescopes separated by distances comparable to the diameter of the Earth. At a nominal operating wavelength of ∼1.3 mm, EHT angular resolution ( λ / D ) is ∼25 μ as, which is sufficient to resolve nearby supermassive black hole candidates on spatial and temporal scales that correspond to their event horizons. With this capability, the EHT scientific goals are to probe general relativistic effects in the strong-field regime and to study accretion and relativistic jet formation near the black hole boundary. In this Letter we describe the system design of the EHT, detail the technology and instrumentation that enable observations, and provide measures of its performance. Meeting the EHT science objectives has required several key developments that have facilitated the robust extension of the VLBI technique to EHT observing wavelengths and the production of instrumentation that can be deployed on a heterogeneous array of existing telescopes and facilities. To meet sensitivity requirements, high-bandwidth digital systems were developed that process data at rates of 64 gigabit s −1 , exceeding those of currently operating cm-wavelength VLBI arrays by more than an order of magnitude. Associated improvements include the development of phasing systems at array facilities, new receiver installation at several sites, and the deployment of hydrogen maser frequency standards to ensure coherent data capture across the array. These efforts led to the coordination and execution of the first Global EHT observations in 2017 April, and to event-horizon-scale imaging of the supermassive black hole candidate in M87.
    Type of Medium: Online Resource
    ISSN: 2041-8205 , 2041-8213
    URL: Article
    DOI: 10.3847/2041-8213/ab0c96
    Language: Unknown
    Publisher: American Astronomical Society
    Publication Date: 2019
    detail.hit.zdb_id: 7233-3
    detail.hit.zdb_id: 2006858-X
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  • 4
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    Online Resource
    First M87 Event Horizon Telescope Results. I. The Shadow of the Supermassive Black Hole
    American Astronomical Society ; 2019
    In:  The Astrophysical Journal Letters Vol. 875, No. 1 ( 2019-04-10), p. L1-
    Details
    In: The Astrophysical Journal Letters, American Astronomical Society, Vol. 875, No. 1 ( 2019-04-10), p. L1-
    Abstract: When surrounded by a transparent emission region, black holes are expected to reveal a dark shadow caused by gravitational light bending and photon capture at the event horizon. To image and study this phenomenon, we have assembled the Event Horizon Telescope, a global very long baseline interferometry array observing at a wavelength of 1.3 mm. This allows us to reconstruct event-horizon-scale images of the supermassive black hole candidate in the center of the giant elliptical galaxy M87. We have resolved the central compact radio source as an asymmetric bright emission ring with a diameter of 42 ± 3 μ as, which is circular and encompasses a central depression in brightness with a flux ratio ≳10:1. The emission ring is recovered using different calibration and imaging schemes, with its diameter and width remaining stable over four different observations carried out in different days. Overall, the observed image is consistent with expectations for the shadow of a Kerr black hole as predicted by general relativity. The asymmetry in brightness in the ring can be explained in terms of relativistic beaming of the emission from a plasma rotating close to the speed of light around a black hole. We compare our images to an extensive library of ray-traced general-relativistic magnetohydrodynamic simulations of black holes and derive a central mass of M  = (6.5 ± 0.7) × 10 9 M ⊙ . Our radio-wave observations thus provide powerful evidence for the presence of supermassive black holes in centers of galaxies and as the central engines of active galactic nuclei. They also present a new tool to explore gravity in its most extreme limit and on a mass scale that was so far not accessible.
    Type of Medium: Online Resource
    ISSN: 2041-8205 , 2041-8213
    URL: Article
    DOI: 10.3847/2041-8213/ab0ec7
    Language: Unknown
    Publisher: American Astronomical Society
    Publication Date: 2019
    detail.hit.zdb_id: 7233-3
    detail.hit.zdb_id: 2006858-X
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  • 5
    Online Resource
    Online Resource
    First M87 Event Horizon Telescope Results. IV. Imaging the Central Supermassive Black Hole
    American Astronomical Society ; 2019
    In:  The Astrophysical Journal Letters Vol. 875, No. 1 ( 2019-04-10), p. L4-
    Details
    In: The Astrophysical Journal Letters, American Astronomical Society, Vol. 875, No. 1 ( 2019-04-10), p. L4-
    Abstract: We present the first Event Horizon Telescope (EHT) images of M87, using observations from April 2017 at 1.3 mm wavelength. These images show a prominent ring with a diameter of ∼40 μ as, consistent with the size and shape of the lensed photon orbit encircling the “shadow” of a supermassive black hole. The ring is persistent across four observing nights and shows enhanced brightness in the south. To assess the reliability of these results, we implemented a two-stage imaging procedure. In the first stage, four teams, each blind to the others’ work, produced images of M87 using both an established method (CLEAN) and a newer technique (regularized maximum likelihood). This stage allowed us to avoid shared human bias and to assess common features among independent reconstructions. In the second stage, we reconstructed synthetic data from a large survey of imaging parameters and then compared the results with the corresponding ground truth images. This stage allowed us to select parameters objectively to use when reconstructing images of M87. Across all tests in both stages, the ring diameter and asymmetry remained stable, insensitive to the choice of imaging technique. We describe the EHT imaging procedures, the primary image features in M87, and the dependence of these features on imaging assumptions.
    Type of Medium: Online Resource
    ISSN: 2041-8205 , 2041-8213
    URL: Article
    DOI: 10.3847/2041-8213/ab0e85
    Language: Unknown
    Publisher: American Astronomical Society
    Publication Date: 2019
    detail.hit.zdb_id: 7233-3
    detail.hit.zdb_id: 2006858-X
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  • 6
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    First M87 Event Horizon Telescope Results. III. Data Processing and Calibration
    American Astronomical Society ; 2019
    In:  The Astrophysical Journal Letters Vol. 875, No. 1 ( 2019-04-10), p. L3-
    Details
    In: The Astrophysical Journal Letters, American Astronomical Society, Vol. 875, No. 1 ( 2019-04-10), p. L3-
    Abstract: We present the calibration and reduction of Event Horizon Telescope (EHT) 1.3 mm radio wavelength observations of the supermassive black hole candidate at the center of the radio galaxy M87 and the quasar 3C 279, taken during the 2017 April 5–11 observing campaign. These global very long baseline interferometric observations include for the first time the highly sensitive Atacama Large Millimeter/submillimeter Array (ALMA); reaching an angular resolution of 25 μ as, with characteristic sensitivity limits of ∼1 mJy on baselines to ALMA and ∼10 mJy on other baselines. The observations present challenges for existing data processing tools, arising from the rapid atmospheric phase fluctuations, wide recording bandwidth, and highly heterogeneous array. In response, we developed three independent pipelines for phase calibration and fringe detection, each tailored to the specific needs of the EHT. The final data products include calibrated total intensity amplitude and phase information. They are validated through a series of quality assurance tests that show consistency across pipelines and set limits on baseline systematic errors of 2% in amplitude and 1° in phase. The M87 data reveal the presence of two nulls in correlated flux density at ∼3.4 and ∼8.3 G λ and temporal evolution in closure quantities, indicating intrinsic variability of compact structure on a timescale of days, or several light-crossing times for a few billion solar-mass black hole. These measurements provide the first opportunity to image horizon-scale structure in M87.
    Type of Medium: Online Resource
    ISSN: 2041-8205 , 2041-8213
    URL: Article
    DOI: 10.3847/2041-8213/ab0c57
    Language: Unknown
    Publisher: American Astronomical Society
    Publication Date: 2019
    detail.hit.zdb_id: 7233-3
    detail.hit.zdb_id: 2006858-X
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  • 7
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    Online Resource
    First M87 Event Horizon Telescope Results. VI. The Shadow and Mass of the Central Black Hole
    American Astronomical Society ; 2019
    In:  The Astrophysical Journal Letters Vol. 875, No. 1 ( 2019-04-10), p. L6-
    Details
    In: The Astrophysical Journal Letters, American Astronomical Society, Vol. 875, No. 1 ( 2019-04-10), p. L6-
    Abstract: We present measurements of the properties of the central radio source in M87 using Event Horizon Telescope data obtained during the 2017 campaign. We develop and fit geometric crescent models (asymmetric rings with interior brightness depressions) using two independent sampling algorithms that consider distinct representations of the visibility data. We show that the crescent family of models is statistically preferred over other comparably complex geometric models that we explore. We calibrate the geometric model parameters using general relativistic magnetohydrodynamic (GRMHD) models of the emission region and estimate physical properties of the source. We further fit images generated from GRMHD models directly to the data. We compare the derived emission region and black hole parameters from these analyses with those recovered from reconstructed images. There is a remarkable consistency among all methods and data sets. We find that 〉 50% of the total flux at arcsecond scales comes from near the horizon, and that the emission is dramatically suppressed interior to this region by a factor 〉 10, providing direct evidence of the predicted shadow of a black hole. Across all methods, we measure a crescent diameter of 42 ± 3 μ as and constrain its fractional width to be 〈 0.5. Associating the crescent feature with the emission surrounding the black hole shadow, we infer an angular gravitational radius of GM / Dc 2  = 3.8 ± 0.4 μ as. Folding in a distance measurement of gives a black hole mass of . This measurement from lensed emission near the event horizon is consistent with the presence of a central Kerr black hole, as predicted by the general theory of relativity.
    Type of Medium: Online Resource
    ISSN: 2041-8205 , 2041-8213
    URL: Article
    DOI: 10.3847/2041-8213/ab1141
    Language: Unknown
    Publisher: American Astronomical Society
    Publication Date: 2019
    detail.hit.zdb_id: 7233-3
    detail.hit.zdb_id: 2006858-X
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  • 8
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    Online Resource
    First M87 Event Horizon Telescope Results. V. Physical Origin of the Asymmetric Ring
    American Astronomical Society ; 2019
    In:  The Astrophysical Journal Letters Vol. 875, No. 1 ( 2019-04-10), p. L5-
    Details
    In: The Astrophysical Journal Letters, American Astronomical Society, Vol. 875, No. 1 ( 2019-04-10), p. L5-
    Abstract: The Event Horizon Telescope (EHT) has mapped the central compact radio source of the elliptical galaxy M87 at 1.3 mm with unprecedented angular resolution. Here we consider the physical implications of the asymmetric ring seen in the 2017 EHT data. To this end, we construct a large library of models based on general relativistic magnetohydrodynamic (GRMHD) simulations and synthetic images produced by general relativistic ray tracing. We compare the observed visibilities with this library and confirm that the asymmetric ring is consistent with earlier predictions of strong gravitational lensing of synchrotron emission from a hot plasma orbiting near the black hole event horizon. The ring radius and ring asymmetry depend on black hole mass and spin, respectively, and both are therefore expected to be stable when observed in future EHT campaigns. Overall, the observed image is consistent with expectations for the shadow of a spinning Kerr black hole as predicted by general relativity. If the black hole spin and M87’s large scale jet are aligned, then the black hole spin vector is pointed away from Earth. Models in our library of non-spinning black holes are inconsistent with the observations as they do not produce sufficiently powerful jets. At the same time, in those models that produce a sufficiently powerful jet, the latter is powered by extraction of black hole spin energy through mechanisms akin to the Blandford-Znajek process. We briefly consider alternatives to a black hole for the central compact object. Analysis of existing EHT polarization data and data taken simultaneously at other wavelengths will soon enable new tests of the GRMHD models, as will future EHT campaigns at 230 and 345 GHz.
    Type of Medium: Online Resource
    ISSN: 2041-8205 , 2041-8213
    URL: Article
    DOI: 10.3847/2041-8213/ab0f43
    Language: Unknown
    Publisher: American Astronomical Society
    Publication Date: 2019
    detail.hit.zdb_id: 7233-3
    detail.hit.zdb_id: 2006858-X
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  • 9
    Online Resource
    Online Resource
    The Event Horizon General Relativistic Magnetohydrodynamic Code Comparison Project
    American Astronomical Society ; 2019
    In:  The Astrophysical Journal Supplement Series Vol. 243, No. 2 ( 2019-08-01), p. 26-
    Details
    In: The Astrophysical Journal Supplement Series, American Astronomical Society, Vol. 243, No. 2 ( 2019-08-01), p. 26-
    Abstract: Recent developments in compact object astrophysics, especially the discovery of merging neutron stars by LIGO, the imaging of the black hole in M87 by the Event Horizon Telescope, and high- precision astrometry of the Galactic Center at close to the event horizon scale by the GRAVITY experiment motivate the development of numerical source models that solve the equations of general relativistic magnetohydrodynamics (GRMHD). Here we compare GRMHD solutions for the evolution of a magnetized accretion flow where turbulence is promoted by the magnetorotational instability from a set of nine GRMHD codes: Athena++ , BHAC , Cosmos++ , ECHO , H-AMR , iharm3D , HARM-Noble , IllinoisGRMHD , and KORAL . Agreement among the codes improves as resolution increases, as measured by a consistently applied, specially developed set of code performance metrics. We conclude that the community of GRMHD codes is mature, capable, and consistent on these test problems.
    Type of Medium: Online Resource
    ISSN: 0067-0049 , 1538-4365
    URL: Article
    DOI: 10.3847/1538-4365/ab29fd
    RVK:
    UA 1000
    Language: Unknown
    Publisher: American Astronomical Society
    Publication Date: 2019
    detail.hit.zdb_id: 2961-0
    detail.hit.zdb_id: 2006860-8
    SSG: 16,12
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  • 10
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    Online Resource
    Monitoring the Morphology of M87* in 2009–2017 with the Event Horizon Telescope
    American Astronomical Society ; 2020
    In:  The Astrophysical Journal Vol. 901, No. 1 ( 2020-09-01), p. 67-
    Details
    In: The Astrophysical Journal, American Astronomical Society, Vol. 901, No. 1 ( 2020-09-01), p. 67-
    Abstract: The Event Horizon Telescope (EHT) has recently delivered the first resolved images of M87*, the supermassive black hole in the center of the M87 galaxy. These images were produced using 230 GHz observations performed in 2017 April. Additional observations are required to investigate the persistence of the primary image feature—a ring with azimuthal brightness asymmetry—and to quantify the image variability on event horizon scales. To address this need, we analyze M87* data collected with prototype EHT arrays in 2009, 2011, 2012, and 2013. While these observations do not contain enough information to produce images, they are sufficient to constrain simple geometric models. We develop a modeling approach based on the framework utilized for the 2017 EHT data analysis and validate our procedures using synthetic data. Applying the same approach to the observational data sets, we find the M87* morphology in 2009–2017 to be consistent with a persistent asymmetric ring of ∼40 μ as diameter. The position angle of the peak intensity varies in time. In particular, we find a significant difference between the position angle measured in 2013 and 2017. These variations are in broad agreement with predictions of a subset of general relativistic magnetohydrodynamic simulations. We show that quantifying the variability across multiple observational epochs has the potential to constrain the physical properties of the source, such as the accretion state or the black hole spin.
    Type of Medium: Online Resource
    ISSN: 0004-637X , 1538-4357
    URL: Article
    DOI: 10.3847/1538-4357/abac0d
    RVK:
    UA 1000
    Language: Unknown
    Publisher: American Astronomical Society
    Publication Date: 2020
    detail.hit.zdb_id: 2960-9
    detail.hit.zdb_id: 1473835-1
    SSG: 16,12
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