57 research outputs found
The polarized image of a synchrotron-emitting ring of gas orbiting a black hole
High Energy Astrophysic
The variability of the black hole image in M87 at the dynamical timescale
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.https://iopscience.iop.org/article/10.3847/1538-4357/ac332e/pdfPublished versio
Broadband multi-wavelength properties of M87 during the 2017 Event Horizon Telescope campaign
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 × 109Me. 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.http://iopscience.iop.org/2041-8205am2022Physic
Constraints on black-hole charges with the 2017 EHT observations of M87*
InstrumentationHigh Energy Astrophysic
A universal power-law prescription for variability from synthetic images of black hole accretion flows
Instrumentatio
Event Horizon Telescope observations of the jet launching and collimation in Centaurus A
InstrumentationLarge scale structure and cosmolog
Characterizing and mitigating intraday variability: reconstructing source structure in accreting black holes with mm-VLBI
Instrumentatio
First sagittarius A* Event Horizon Telescope results. IV. Variability, morphology, and black hole mass
Galaxie
First sagittarius A* Event Horizon Telescope results. VI. Testing the black hole metric
Galaxie
Millimeter light curves of sagittarius A* observed during the 2017 Event Horizon Telescope campaign
Galaxie
- …