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M87 Workshop: Towards the 100th Anniversary of the Discovery of Cosmic Jets
May 23(Mon)-27(Fri), 2016
Taipei, Taiwan

Oral Presentation

EHT observations during enhanced very-high-energy gamma-ray state in 2012

Author(s): Kazunori Akiyama

Presenter: Kazunori Akiyama (MIT Haystack)

The radio galaxy M87 is an excellent laboratory for investigating the formation process of the relativistic jet and the production mechanism of high energy photons in the vicinity of super-massive black holes. The ultra-high-resolution of the Event Horizon Telescope (EHT) is ideally suited to address these topics. In this talk, I report on EHT observations performed in the middle of an enhancement in very-high-energy (VHE) γ-ray flux in 2012, presumably originating in the vicinity of the central black hole. We have acquired 230 GHz VLBI interferometric phase information on M87 through measurement of closure phase on the triangle of long baselines for the first time, which is broadly consistent with physically-motivated models for 230 GHz structure. We found no significant variation in the size of the event-horizon-scale structure during the VHE enhancement. Our measurements, combined with results of multi-wavelength observations, favor a scenario in which the VHE region has an extended size of ∼20-60 Rs. Finally, I briefly introduce the current status of the sparse imaging techniques for future EHT observations.

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