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First M87 Event Horizon Telescope Results. I. The Shadow of the Supermassive Black Hole

The Event Horizon Telescope Collaboration ; Akiyama, Kazunori ; Alberdi, Antxon ; [et al.]

American Astronomical Society ; 2019

In: The Astrophysical Journal Vol. 875, No. 1 ( 2019-04-10), p. L1-

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In: The Astrophysical Journal, American Astronomical Society, Vol. 875, No. 1 ( 2019-04-10), p. L1-

Type of Medium: Online Resource

ISSN: 2041-8213

URL: Article

DOI: 10.3847/2041-8213/ab0ec7

Language: Unknown

Publisher: American Astronomical Society

Publication Date: 2019

detail.hit.zdb_id: 2207648-7

detail.hit.zdb_id: 2006858-X

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Event Horizon Telescope imaging of the archetypal blazar 3C 279 at an extreme 20 microarcsecond resolution

Kim, Jae-Young ; Krichbaum, Thomas P. ; Broderick, Avery E. ; [et al.]

EDP Sciences ; 2020

In: Astronomy & Astrophysics Vol. 640 ( 2020-08), p. A69-

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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: 1458466-9

SSG: 16,12

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First M87 Event Horizon Telescope Results. II. Array and Instrumentation

The Event Horizon Telescope Collaboration ; Akiyama, Kazunori ; Alberdi, Antxon ; [et al.]

American Astronomical Society ; 2019

In: The Astrophysical Journal Vol. 875, No. 1 ( 2019-04-10), p. L2-

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In: The Astrophysical Journal, American Astronomical Society, Vol. 875, No. 1 ( 2019-04-10), p. L2-

Type of Medium: Online Resource

ISSN: 2041-8213

URL: Article

DOI: 10.3847/2041-8213/ab0c96

Language: Unknown

Publisher: American Astronomical Society

Publication Date: 2019

detail.hit.zdb_id: 2207648-7

detail.hit.zdb_id: 2006858-X

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First Sagittarius A* Event Horizon Telescope Results. I. The Shadow of the Supermassive Black Hole in the Center of the Milky Way

Event Horizon Telescope Collaboration ; Akiyama, Kazunori ; Alberdi, Antxon ; [et al.]

American Astronomical Society ; 2022

In: The Astrophysical Journal Letters Vol. 930, No. 2 ( 2022-05-01), p. L12-

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In: The Astrophysical Journal Letters, American Astronomical Society, Vol. 930, No. 2 ( 2022-05-01), p. L12-

Abstract: We present the first Event Horizon Telescope (EHT) observations of Sagittarius A* (Sgr A*), the Galactic center source associated with a supermassive black hole. These observations were conducted in 2017 using a global interferometric array of eight telescopes operating at a wavelength of λ = 1.3 mm. The EHT data resolve a compact emission region with intrahour variability. A variety of imaging and modeling analyses all support an image that is dominated by a bright, thick ring with a diameter of 51.8 ± 2.3 μ as (68% credible interval). The ring has modest azimuthal brightness asymmetry and a comparatively dim interior. Using a large suite of numerical simulations, we demonstrate that the EHT images of Sgr A* are consistent with the expected appearance of a Kerr black hole with mass ∼4 × 10 6 M ⊙ , which is inferred to exist at this location based on previous infrared observations of individual stellar orbits, as well as maser proper-motion studies. Our model comparisons disfavor scenarios where the black hole is viewed at high inclination ( i 〉 50°), as well as nonspinning black holes and those with retrograde accretion disks. Our results provide direct evidence for the presence of a supermassive black hole at the center of the Milky Way, and for the first time we connect the predictions from dynamical measurements of stellar orbits on scales of 10 3 –10 5 gravitational radii to event-horizon-scale images and variability. Furthermore, a comparison with the EHT results for the supermassive black hole M87* shows consistency with the predictions of general relativity spanning over three orders of magnitude in central mass.

Type of Medium: Online Resource

ISSN: 2041-8205 , 2041-8213

URL: Article

DOI: 10.3847/2041-8213/ac6674

Language: Unknown

Publisher: American Astronomical Society

Publication Date: 2022

detail.hit.zdb_id: 2207648-7

detail.hit.zdb_id: 2006858-X

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Monitoring the Morphology of M87* in 2009–2017 with the Event Horizon Telescope

Wielgus, Maciek ; Akiyama, Kazunori ; Blackburn, Lindy ; [et al.]

American Astronomical Society ; 2020

In: The Astrophysical Journal Vol. 901, No. 1 ( 2020-09-01), p. 67-

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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: 2207648-7

detail.hit.zdb_id: 1473835-1

SSG: 16,12

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First Sagittarius A* Event Horizon Telescope Results. II. EHT and Multiwavelength Observations, Data Processing, and Calibration

Event Horizon Telescope Collaboration ; Akiyama, Kazunori ; Alberdi, Antxon ; [et al.]

American Astronomical Society ; 2022

In: The Astrophysical Journal Letters Vol. 930, No. 2 ( 2022-05-01), p. L13-

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In: The Astrophysical Journal Letters, American Astronomical Society, Vol. 930, No. 2 ( 2022-05-01), p. L13-

Abstract: We present Event Horizon Telescope (EHT) 1.3 mm measurements of the radio source located at the position of the supermassive black hole Sagittarius A* (Sgr A*), collected during the 2017 April 5–11 campaign. The observations were carried out with eight facilities at six locations across the globe. Novel calibration methods are employed to account for Sgr A*'s flux variability. The majority of the 1.3 mm emission arises from horizon scales, where intrinsic structural source variability is detected on timescales of minutes to hours. The effects of interstellar scattering on the image and its variability are found to be subdominant to intrinsic source structure. The calibrated visibility amplitudes, particularly the locations of the visibility minima, are broadly consistent with a blurred ring with a diameter of ∼50 μ as, as determined in later works in this series. Contemporaneous multiwavelength monitoring of Sgr A* was performed at 22, 43, and 86 GHz and at near-infrared and X-ray wavelengths. Several X-ray flares from Sgr A* are detected by Chandra, one at low significance jointly with Swift on 2017 April 7 and the other at higher significance jointly with NuSTAR on 2017 April 11. The brighter April 11 flare is not observed simultaneously by the EHT but is followed by a significant increase in millimeter flux variability immediately after the X-ray outburst, indicating a likely connection in the emission physics near the event horizon. We compare Sgr A*’s broadband flux during the EHT campaign to its historical spectral energy distribution and find that both the quiescent emission and flare emission are consistent with its long-term behavior.

Type of Medium: Online Resource

ISSN: 2041-8205 , 2041-8213

URL: Article

DOI: 10.3847/2041-8213/ac6675

Language: Unknown

Publisher: American Astronomical Society

Publication Date: 2022

detail.hit.zdb_id: 2207648-7

detail.hit.zdb_id: 2006858-X

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The Variability of the Black Hole Image in M87 at the Dynamical Timescale

Satapathy, Kaushik ; Psaltis, Dimitrios ; Özel, Feryal ; [et al.]

American Astronomical Society ; 2022

In: The Astrophysical Journal Vol. 925, No. 1 ( 2022-01-01), p. 13-

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In: The Astrophysical Journal, American Astronomical Society, Vol. 925, No. 1 ( 2022-01-01), p. 13-

Abstract: The black hole images obtained with the Event Horizon Telescope (EHT) are expected to be variable at the dynamical timescale near their horizons. For the black hole at the center of the M87 galaxy, this timescale (5–61 days) is comparable to the 6 day extent of the 2017 EHT observations. Closure phases along baseline triangles are robust interferometric observables that are sensitive to the expected structural changes of the images but are free of station-based atmospheric and instrumental errors. We explored the day-to-day variability in closure-phase measurements on all six linearly independent nontrivial baseline triangles that can be formed from the 2017 observations. We showed that three triangles exhibit very low day-to-day variability, with a dispersion of ∼3°–5°. The only triangles that exhibit substantially higher variability (∼90°–180°) are the ones with baselines that cross the visibility amplitude minima on the u – v plane, as expected from theoretical modeling. We used two sets of general relativistic magnetohydrodynamic simulations to explore the dependence of the predicted variability on various black hole and accretion-flow parameters. We found that changing the magnetic field configuration, electron temperature model, or black hole spin has a marginal effect on the model consistency with the observed level of variability. On the other hand, the most discriminating image characteristic of models is the fractional width of the bright ring of emission. Models that best reproduce the observed small level of variability are characterized by thin ring-like images with structures dominated by gravitational lensing effects and thus least affected by turbulence in the accreting plasmas.

Type of Medium: Online Resource

ISSN: 0004-637X , 1538-4357

URL: Article

DOI: 10.3847/1538-4357/ac332e

RVK:

UA 1000

Language: Unknown

Publisher: American Astronomical Society

Publication Date: 2022

detail.hit.zdb_id: 2207648-7

detail.hit.zdb_id: 1473835-1

SSG: 16,12

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Comparison of Polarized Radiative Transfer Codes Used by the EHT Collaboration

Prather, Ben S. ; Dexter, Jason ; Moscibrodzka, Monika ; [et al.]

American Astronomical Society ; 2023

In: The Astrophysical Journal Vol. 950, No. 1 ( 2023-06-01), p. 35-

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In: The Astrophysical Journal, American Astronomical Society, Vol. 950, No. 1 ( 2023-06-01), p. 35-

Abstract: Interpretation of resolved polarized images of black holes by the Event Horizon Telescope (EHT) requires predictions of the polarized emission observable by an Earth-based instrument for a particular model of the black hole accretion system. Such predictions are generated by general relativistic radiative transfer (GRRT) codes, which integrate the equations of polarized radiative transfer in curved spacetime. A selection of ray-tracing GRRT codes used within the EHT Collaboration is evaluated for accuracy and consistency in producing a selection of test images, demonstrating that the various methods and implementations of radiative transfer calculations are highly consistent. When imaging an analytic accretion model, we find that all codes produce images similar within a pixel-wise normalized mean squared error (NMSE) of 0.012 in the worst case. When imaging a snapshot from a cell-based magnetohydrodynamic simulation, we find all test images to be similar within NMSEs of 0.02, 0.04, 0.04, and 0.12 in Stokes I , Q , U , and V , respectively. We additionally find the values of several image metrics relevant to published EHT results to be in agreement to much better precision than measurement uncertainties.

Type of Medium: Online Resource

ISSN: 0004-637X , 1538-4357

URL: Article

DOI: 10.3847/1538-4357/acc586

RVK:

UA 1000

Language: Unknown

Publisher: American Astronomical Society

Publication Date: 2023

detail.hit.zdb_id: 2207648-7

detail.hit.zdb_id: 1473835-1

SSG: 16,12

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First M87 Event Horizon Telescope Results. V. Physical Origin of the Asymmetric Ring

The Event Horizon Telescope Collaboration ; Akiyama, Kazunori ; Alberdi, Antxon ; [et al.]

American Astronomical Society ; 2019

In: The Astrophysical Journal Vol. 875, No. 1 ( 2019-04-10), p. L5-

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In: The Astrophysical Journal, American Astronomical Society, Vol. 875, No. 1 ( 2019-04-10), p. L5-

Type of Medium: Online Resource

ISSN: 2041-8213

URL: Article

DOI: 10.3847/2041-8213/ab0f43

Language: Unknown

Publisher: American Astronomical Society

Publication Date: 2019

detail.hit.zdb_id: 2207648-7

detail.hit.zdb_id: 2006858-X

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A Universal Power-law Prescription for Variability from Synthetic Images of Black Hole Accretion Flows

Georgiev, Boris ; Pesce, Dominic W. ; Broderick, Avery E. ; [et al.]

American Astronomical Society ; 2022

In: The Astrophysical Journal Letters Vol. 930, No. 2 ( 2022-05-01), p. L20-

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In: The Astrophysical Journal Letters, American Astronomical Society, Vol. 930, No. 2 ( 2022-05-01), p. L20-

Abstract: We present a framework for characterizing the spatiotemporal power spectrum of the variability expected from the horizon-scale emission structure around supermassive black holes, and we apply this framework to a library of general relativistic magnetohydrodynamic (GRMHD) simulations and associated general relativistic ray-traced images relevant for Event Horizon Telescope (EHT) observations of Sgr A*. We find that the variability power spectrum is generically a red-noise process in both the temporal and spatial dimensions, with the peak in power occurring on the longest timescales and largest spatial scales. When both the time-averaged source structure and the spatially integrated light-curve variability are removed, the residual power spectrum exhibits a universal broken power-law behavior. On small spatial frequencies, the residual power spectrum rises as the square of the spatial frequency and is proportional to the variance in the centroid of emission. Beyond some peak in variability power, the residual power spectrum falls as that of the time-averaged source structure, which is similar across simulations; this behavior can be naturally explained if the variability arises from a multiplicative random field that has a steeper high-frequency power-law index than that of the time-averaged source structure. We briefly explore the ability of power spectral variability studies to constrain physical parameters relevant for the GRMHD simulations, which can be scaled to provide predictions for black holes in a range of systems in the optically thin regime. We present specific expectations for the behavior of the M87* and Sgr A* accretion flows as observed by the EHT.

Type of Medium: Online Resource

ISSN: 2041-8205 , 2041-8213

URL: Article

DOI: 10.3847/2041-8213/ac65eb

Language: Unknown

Publisher: American Astronomical Society

Publication Date: 2022

detail.hit.zdb_id: 2207648-7

detail.hit.zdb_id: 2006858-X

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