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We report on the detailed radio status of the M87 jet during the Very-High-Energy (VHE) gamma-ray flaring event in April 2010, obtained from high-resolution, multi-frequency, phase-referencing VLBA observations. We especially focus on the properties for the jet base (the radio core) and the peculiar knot HST-1, which are currently favored as the gamma-ray emitting sites. During the VHE flaring event, the HST-1 region remains stable in terms of its structure and flux density in the optically thin regime above 2GHz, being consistent with no signs of enhanced activities reported at X-ray for this feature. The radio core shows an inverted spectrum at least up to 43GHz during this event. Astrometry of the core position, which is specified as ~20Rs from the central engine in our previous study, shows that the core position is stable on a level of 4Rs. The core at 43 and 22GHz tends to show slightly (~10%) higher flux level near the date of the VHE flux peak compared with the epochs before/after the event. The size of the 43-GHz core is estimated to be ~17Rs, which is close to the size of the emitting region suggested from the observed time scale of rapid variability at VHE. These results tend to favor the scenario that the VHE gamma-ray flare in 2010 April is associated with the radio core.
We report our intensive radio monitoring observations of the jet in M87 with the VLBI Exploration of Radio Astrometry (VERA) and the European VLBI Network (EVN) from February 2011 to October 2012, together with contemporaneous high-energy gamma-ray l
The intermediate-frequency peaked BL Lacertae (IBL) object 3C 66A is detected during 2007 - 2008 in VHE (very high energy: E > 100 GeV) gamma-rays with the VERITAS stereoscopic array of imaging atmospheric Cherenkov telescopes. An excess of 1791 even
We report on 230 GHz (1.3 mm) VLBI observations of M87 with the Event Horizon Telescope using antennas on Mauna Kea in Hawaii, Mt. Graham in Arizona and Cedar Flat in California. For the first time, we have acquired 230 GHz VLBI interferometric phase
The nearby radio galaxy M87 offers a unique opportunity for exploring the connection between gamma-ray production and jet formation at an unprecedented linear resolution. However, the origin and location of the gamma-rays in this source is still elus
Abridged: The giant radio galaxy M 87 with its proximity, famous jet, and very massive black hole provides a unique opportunity to investigate the origin of very high energy (VHE; E>100 GeV) gamma-ray emission generated in relativistic outflows and t