230 GHz VLBI Observations of M87: Event-horizon-scale Structure during an Enhanced Very-high-energy γ-Ray State in 2012

Citation:

Kazunori Akiyama, Ru-Sen Lu, Vincent L. Fish, Sheperd S. Doeleman, Avery E. Broderick, Jason Dexter, Kazuhiro Hada, Motoki Kino, Hiroshi Nagai, Mareki Honma, Michael D. Johnson, Juan C. Algaba, Keiichi Asada, Christiaan Brinkerink, Ray Blundell, Geoffrey C. Bower, Roger Cappallo, Geoffrey B. Crew, Matt Dexter, Sergio A. Dzib, Robert Freund, Per Friberg, Mark Gurwell, Paul T. P. Ho, Makoto Inoue, Thomas P. Krichbaum, Laurent Loinard, David MacMahon, Daniel P. Marrone, James M. Moran, Masanori Nakamura, Neil M. Nagar, Gisela Ortiz-Leon, Richard Plambeck, Nicolas Pradel, Rurik A. Primiani, Alan E. E. Rogers, Alan L. Roy, Jason SooHoo, Jonathan-León Tavares, Remo P. J. Tilanus, Michael Titus, Jan Wagner, Jonathan Weintroub, Paul Yamaguchi, Ken H. Young, Anton Zensus, and Lucy M. Ziurys. 2015. “230 GHz VLBI Observations of M87: Event-horizon-scale Structure during an Enhanced Very-high-energy γ-Ray State in 2012.” The Astrophysical Journal, 807.

Abstract:

We report on 230 GHz (1.3 mm) very long baseline interferometry (VLBI)observations of M87 with the Event Horizon Telescope using antennas onMauna Kea in Hawaii, Mt. Graham in Arizona, and Cedar Flat inCalifornia. For the first time, we have acquired 230 GHz VLBIinterferometric phase information on M87 through measurement of theclosure phase on the triangle of long baselines. Most of the measuredclosure phases are consistent with 0° as expected by physicallymotivated models for 230 GHz structure such as jet models and accretiondisk models. The brightness temperature of the event-horizon-scalestructure is ∼ 1× {10}10 K derived from the compactflux density of ∼1 Jy and the angular size of ∼40 μ {as}∼ 5.5 {R}{{s}}, which is broadly consistent with the peakbrightness of the radio cores at 1–86 GHz located within ∼{10}2 {R}{{s}}. Our observations occurred in themiddle of an enhancement in very-high-energy (VHE) γ -ray flux,presumably originating in the vicinity of the central black hole. Ourmeasurements, combined with results of multi-wavelength observations,favor a scenario in which the VHE region has an extended size of∼20–60 {R}{{s}}.