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DTSTART;TZID=Australia/Sydney:20211020T150000
DTEND;TZID=Australia/Sydney:20211020T160000
DTSTAMP:20260515T180112
CREATED:20250819T101933Z
LAST-MODIFIED:20250820T023820Z
UID:14989-1634742000-1634745600@www.atnf.csiro.au
SUMMARY:S&A Colloquium: Nithyanandan Thyagarajan (CSIRO)
DESCRIPTION:Towards a General Theory of Closure Invariants in Radio Interferometry\n\nAbstract\n\nRecent “planet-scale” very long baseline interferometry (VLBI) efforts at millimetre wavelengths have resulted in the first detailed images near the event horizon of the supermassive black hole (SMBH) at the centre of M87 by the Event Horizon Telescope (EHT) collaboration. Calibration of the radio signals received by such widely separated VLBI stations is one of the key challenges in the accurate reconstruction of images. Closure phases and amplitudes in co-polar interferometry\, have long provided calibration-independent observables immune to multiplicative\, station-dependent corruptions. Very recently\, “closure traces” for full polarimetric interferometry have been introduced and used in the recent study of the magnetic field structures around the M87 central black hole. So far\, a systematic method for explicitly exhibiting a full set of invariants has still remained unclear. Using the mathematical framework of the gauge theories of particle physics and Lorentz transformations\, I will describe a general formalism\, applicable to interferometer arrays of arbitrary size\, that uses only triangular combinations of correlations as basic building blocks to precisely isolate a complete and independent set of invariants\, and unifies the treatment for all closure invariants\, from which the closure phases and closure amplitudes familiar in co-polar interferometry naturally emerge. These results can find significant applications in ongoing and future (including space-based) observations of SMBHs using the current and the next-generation EHT (ngEHT)\, and more generally\, polarimetric radio interferometry. \nWatch recording\nSlides\n\nNT_ClosureInvariants_CSIRO_SandA_colloquium_20-Oct-2021Download\n\nEvent details\nDownload iCal\nCategory\nColloquia
URL:https://www.atnf.csiro.au/event/sa-colloquium-nithyanandan-thyagarajan-csiro/
LOCATION:NSW
CATEGORIES:Colloquia
ATTACH;FMTTYPE=image/jpeg:https://www.atnf.csiro.au/wp-content/uploads/2024/12/Colloq-20102021.jpg
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DTSTART;TZID=Australia/Sydney:20211027T150000
DTEND;TZID=Australia/Sydney:20211027T160000
DTSTAMP:20260515T180112
CREATED:20250819T101910Z
LAST-MODIFIED:20250819T101911Z
UID:14988-1635346800-1635350400@www.atnf.csiro.au
SUMMARY:S&A Colloquium: Michael Janssen (MPIfR / Radboud University)
DESCRIPTION:The latest results from the Event Horizon Telescope: Zooming into the heart of Centaurus A\n\nAbstract\n\nCentaurus A is the closest radio galaxy to Earth and has been studied extensively as a laboratory for AGN feedback and potential UHECR source after its discovery as one of the first extragalactic radio sources in 1949. I will present the results from our EHT observations of this southern source. Compared to previous VLBI studies\, we have imaged the AGN jet of Cen A at a 16x sharper resolution and 10x higher observing frequency. This allows us to probe the launching region of an extragalactic radio jet on sub-lightday scales. We can directly compare our image to VLBI observations of M87 at a lower frequency\, as both probe the same size scales in terms of gravitational radii. Based on the similarity of these jets\, we show that our observations provide further support for the fundamental plane of black hole activity in an intermediate mass regime. From the location of the resolved radio core in Cen A\, we predict the source’s black hole shadow to be visible at THz frequencies\, which marks Cen A for future high-frequency space VLBI missions. I will conclude with an outlook of our next observational and modeling steps. \nWatch recording\nEvent details\nDownload iCal\nCategory\nColloquia
URL:https://www.atnf.csiro.au/event/sa-colloquium-michael-janssen-mpifr-radboud-university/
LOCATION:NSW
CATEGORIES:Colloquia
ATTACH;FMTTYPE=image/jpeg:https://www.atnf.csiro.au/wp-content/uploads/2024/12/EHT-20072021-1.jpg
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