EHT 2014

EHT 2014

 

 

Tuesday Nov 11, 2014
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The radio galaxy M87 is an excellent laboratory for investigating the formation process of the relativistic jet and the production mechanism of high energy particles and photons in the vicinity of super-massive black holes. VLBI observations at 1.3 mm can address at least two issues concerning the fundamental nature of M87. The first is the event-horizon-scale structure of the jet launching region, and another one is the production mechanism of very high energy (VHE; > 100 GeV) photons at there.

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Tuesday Nov 11, 2014
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Because of the existence of a prominent jet, M87 provides an ideal source with which the EHT can critically test current jet launching paradigms. The EHT has already placed weak limits on the black hole spin based on generic arguments regarding limits on the image size. However, careful modeling of the jet structure can produce much more stringent constraints on both the black hole properties and the mechanisms responsible for the generation of the observed radio emission.

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Tuesday Nov 11, 2014
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VLBI observations at the highest possible frequency penetrate the opacity barrier in the nuclear regions of radio-galaxies and blazars, which are synchrotron self-absorbed at longer wavelength. This facilitates a direct and sharper than ever view into the 'heart' of Active Galactic Nuclei (AGN), into region in which BH physics and general relativity effects become important and where radio jets are launched. Here we report on new results from global 3mm and 1.3mm VLBI observations adding the APEX and IRAM to the Event Horizon Telescope.

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Tuesday Nov 11, 2014
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Tuesday Nov 11, 2014
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Mass accretion rate on the SMBHs is one of the fundamental parameters used to investigate AGNs. Faraday Rotation Measure (RM) observations at mm/sub-mm wavelengths is one of the powerful methods to derive the mass accretion rate of hot accretion flows towards our galactic center, Sgr A* (e.g., Marrone et al. 2006). Based on this scheme, we conducted an SMA observation to apply this method to M 87, which is one of the primary target for our submm VLBI observations, in February 2013.

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Tuesday Nov 11, 2014
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The super-massive black hole in the center of the Milky Way, Sgr~A*, displays a nearly flat radio spectrum which is typical for jets in Active Galactic Nuclei. Indeed, time-dependent, magnetized models of radiatively inefficient accretion flows, which are commonly used to explain emission of Sgr A* also often produce jet-like outflows. However, the emission from these models so far has failed to reproduce the flat radio spectrum.

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Tuesday Nov 11, 2014
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Stellar dynamical measurements of black hole masses have become the de facto standard method. I will give a brief review of how this measurement method works, along with arguments for its overall reliability and caveats. Then I will turn my attention to the case of the black hole in M87. The black hole is undeniably large ? billions of solar masses ? but has a stellar dynamical mass measurement in disagreement with gas dynamical mass measurements at about the 2 sigma level.

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Tuesday Nov 11, 2014
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We examine the structure and dynamics of the M87 jet based on both multi-frequency observations and MHD jet theories. Millimeter (mm) VLBI cores are considered as innermost jet emissions. Resolved parabolic streamline may suggest that the jet collimation maintains in five orders of magnitude in the distance starting from the vicinity of the supermassive black hole (SMBH), less than 10 r_s where the VLBI core at 1.3 mm is located. Observed sub-to-superluminal motions may indicate an MHD acceleration takes place from non-relativistic to relativistic regimes.

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Tuesday Nov 11, 2014
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Both the continuum-fitting and Fe-line methods of measuring black hole spin will be discussed and compared, with attention to sources of systematic error. Both methods rely on estimating the inner radius of the black hole's accretion disk and identifying it with the radius of the ISCO. The Fe-line method is extremely important because of its dominant role in measuring the spins of supermassive black holes, which is problematic for the continuum-fitting method.

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Tuesday Nov 11, 2014
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There are good reasons to believe that relativistic jets of AGN are powered by rotating black holes via the Blandford-Znajek mechanism. Although the original mathematical solution, which demonstrated the possibility of such energy extraction, was found 37 years ago, its physical nature still remains a subject of debate.
I will give a brief review of some recent developments in this area with focus on the roles played by the EH and the Ergoregion in the Blandford-Znajek mechanism.

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