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1

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Broadband Multi-wavelength Properties of M87 during the 2017 Event Horizon Telescope Campaign

Algaba, J. C. ; Anczarski, J. ; Asada, K. ; [et al.]

American Astronomical Society ; 2021

In: The Astrophysical Journal Letters Vol. 911, No. 1 ( 2021-04-01), p. L11-

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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: 2207648-7

detail.hit.zdb_id: 2006858-X

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2

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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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3

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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

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4

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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

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5

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Millimeter Light Curves of Sagittarius A* Observed during the 2017 Event Horizon Telescope Campaign

Wielgus, Maciek ; Marchili, Nicola ; Martí-Vidal, Iván ; [et al.]

American Astronomical Society ; 2022

In: The Astrophysical Journal Letters Vol. 930, No. 2 ( 2022-05-01), p. L19-

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In: The Astrophysical Journal Letters, American Astronomical Society, Vol. 930, No. 2 ( 2022-05-01), p. L19-

Abstract: The Event Horizon Telescope (EHT) observed the compact radio source, Sagittarius A* (Sgr A*), in the Galactic Center on 2017 April 5–11 in the 1.3 mm wavelength band. At the same time, interferometric array data from the Atacama Large Millimeter/submillimeter Array and the Submillimeter Array were collected, providing Sgr A* light curves simultaneous with the EHT observations. These data sets, complementing the EHT very long baseline interferometry, are characterized by a cadence and signal-to-noise ratio previously unattainable for Sgr A* at millimeter wavelengths, and they allow for the investigation of source variability on timescales as short as a minute. While most of the light curves correspond to a low variability state of Sgr A*, the April 11 observations follow an X-ray flare and exhibit strongly enhanced variability. All of the light curves are consistent with a red-noise process, with a power spectral density (PSD) slope measured to be between −2 and −3 on timescales between 1 minute and several hours. Our results indicate a steepening of the PSD slope for timescales shorter than 0.3 hr. The spectral energy distribution is flat at 220 GHz, and there are no time lags between the 213 and 229 GHz frequency bands, suggesting low optical depth for the event horizon scale source. We characterize Sgr A*’s variability, highlighting the different behavior observed just after the X-ray flare, and use Gaussian process modeling to extract a decorrelation timescale and a PSD slope. We also investigate the systematic calibration uncertainties by analyzing data from independent data reduction pipelines.

Type of Medium: Online Resource

ISSN: 2041-8205 , 2041-8213

URL: Article

DOI: 10.3847/2041-8213/ac6428

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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6

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First Sagittarius A* Event Horizon Telescope Results. III. Imaging of the Galactic Center Supermassive Black Hole

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. L14-

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In: The Astrophysical Journal Letters, American Astronomical Society, Vol. 930, No. 2 ( 2022-05-01), p. L14-

Abstract: We present the first event-horizon-scale images and spatiotemporal analysis of Sgr A* taken with the Event Horizon Telescope in 2017 April at a wavelength of 1.3 mm. Imaging of Sgr A* has been conducted through surveys over a wide range of imaging assumptions using the classical CLEAN algorithm, regularized maximum likelihood methods, and a Bayesian posterior sampling method. Different prescriptions have been used to account for scattering effects by the interstellar medium toward the Galactic center. Mitigation of the rapid intraday variability that characterizes Sgr A* has been carried out through the addition of a “variability noise budget” in the observed visibilities, facilitating the reconstruction of static full-track images. Our static reconstructions of Sgr A* can be clustered into four representative morphologies that correspond to ring images with three different azimuthal brightness distributions and a small cluster that contains diverse nonring morphologies. Based on our extensive analysis of the effects of sparse ( u , v )-coverage, source variability, and interstellar scattering, as well as studies of simulated visibility data, we conclude that the Event Horizon Telescope Sgr A* data show compelling evidence for an image that is dominated by a bright ring of emission with a ring diameter of ∼50 μ as, consistent with the expected “shadow” of a 4 × 10 6 M ⊙ black hole in the Galactic center located at a distance of 8 kpc.

Type of Medium: Online Resource

ISSN: 2041-8205 , 2041-8213

URL: Article

DOI: 10.3847/2041-8213/ac6429

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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7

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The Event Horizon Telescope Image of the Quasar NRAO 530

Jorstad, Svetlana ; Wielgus, Maciek ; Lico, Rocco ; [et al.]

American Astronomical Society ; 2023

In: The Astrophysical Journal Vol. 943, No. 2 ( 2023-02-01), p. 170-

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In: The Astrophysical Journal, American Astronomical Society, Vol. 943, No. 2 ( 2023-02-01), p. 170-

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 μ as, 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 μ as 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.

Type of Medium: Online Resource

ISSN: 0004-637X , 1538-4357

URL: Article

DOI: 10.3847/1538-4357/acaea8

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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8

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Resolving the Inner Parsec of the Blazar J1924–2914 with the Event Horizon Telescope

Issaoun, Sara ; Wielgus, Maciek ; Jorstad, Svetlana ; [et al.]

American Astronomical Society ; 2022

In: The Astrophysical Journal Vol. 934, No. 2 ( 2022-08-01), p. 145-

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In: The Astrophysical Journal, American Astronomical Society, Vol. 934, No. 2 ( 2022-08-01), p. 145-

Abstract: The blazar J1924–2914 is a primary Event Horizon Telescope (EHT) calibrator for the Galactic center’s black hole Sagittarius A*. Here we present the first total and linearly polarized intensity images of this source obtained with the unprecedented 20 μ as resolution of the EHT. J1924–2914 is a very compact flat-spectrum radio source with strong optical variability and polarization. In April 2017 the source was observed quasi-simultaneously with the EHT (April 5–11), the Global Millimeter VLBI Array (April 3), and the Very Long Baseline Array (April 28), giving a novel view of the source at four observing frequencies, 230, 86, 8.7, and 2.3 GHz. These observations probe jet properties from the subparsec to 100 pc scales. We combine the multifrequency images of J1924–2914 to study the source morphology. We find that the jet exhibits a characteristic bending, with a gradual clockwise rotation of the jet projected position angle of about 90° between 2.3 and 230 GHz. Linearly polarized intensity images of J1924–2914 with the extremely fine resolution of the EHT provide evidence for ordered toroidal magnetic fields in the blazar compact core.

Type of Medium: Online Resource

ISSN: 0004-637X , 1538-4357

URL: Article

DOI: 10.3847/1538-4357/ac7a40

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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9

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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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10

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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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