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These results were obtained from radio and very high energy observations of Messier 87 in 2008. Scientists from the MAGIC (Major Atmospheric Gamma-Ray Imaging Cherenkov) Telescope, VERITAS (Very Energetic Radiation Imaging Telescope Array System) and H.E.S.S. (High-energy Stereoscopic System) collaborations, together with a group of astronomers using the high-resolution Very-Long Baseline Array (VLBA) radio telescope system teamed up for an unprecedented, coordinated 120-hour observational campaign. Gamma rays constitute the highest energy electromagnetic radiation observable. They are generated by the most violent cosmic objects such as supernovae, active galactic nuclei, and gamma-ray bursts, and allow us to study a realm of extreme physical conditions, far beyond what can be studied in laboratories here on Earth. However, the exact location of the origin of the gamma-ray emission in Messier 87 remained unknown so far due to the rather poor angular resolution of the observing instruments. Messier 87 is a giant elliptical radio galaxy in our immediate cosmic vicinity, just 55 million light years away. In its center, it hosts a super-massive black hole, about six billion times more massive than our own Sun. In a “jet”, a giant outflow from the central engine of this galaxy, charged particles (electrons and protons) may be accelerated to velocities close to the speed of light. Necessary by-products of these acceleration processes are very-high-energy gamma rays, photons a thousand billion times more energetic than optical light. They are produced when the accelerated particles interact with their environment. First indications for very-high energy gamma radiation from Messier 87 were found as early as 1998 with the HEGRA telescopes, which were the predecessor experiment of MAGIC and H.E.S.S. This detection could be confirmed with the H.E.S.S. telescopes in 2006 in an observation also revealing a fast variability of the gamma-ray flux within few days, as seen again in the 2008 campaign. This implies that the extension of the gamma-ray source must be exceptionally compact. From January to May 2008, the three world-leading instruments sensitive to gamma rays in this energy domain, MAGIC, VERITAS and H.E.S.S. were jointly used to observe Messier 87, collecting 120 hours’ worth of data. During this campaign, Messier 87 underwent two major outbursts of gamma-ray emission. Simultaneous high resolution radio observations of the activity of this radio galaxy using the VLBA, a system of radio telescopes spanning the United States, indicate a persistent increase of the radio flux from the innermost “core” of Messier 87, which is associated with the immediate vicinity of the central black hole. Only the close collaboration of observatories sensitive to the lowest and highest parts of the electromagnetic spectrum made it possible to pin down the location of activity during the gamma-ray outbursts and thus the site of the particle accelerator in Messier 87. The MAGIC telescope on the Canary island of La Palma, as well as the H.E.S.S (Namibia) and VERITAS (Arizona, US) instruments are latest-generation air-shower Cherenkov telescopes. With their telescopes of 17 m (MAGIC) and 4 x 13 m (H.E.S.S. and VERITAS each) diameter and ultrafast electronics, they record the flashes of dim blue light (Cherenkov light) from the cascades of subatomic particles that arise when very-high-energy gamma-ray photons interact high in the atmosphere. Altogether, about 400 scientists are involved in these projects, and constitute a large part of the world-wide gamma-ray astrophysics community. Background Information on the MAGIC Telescope MAGIC was built and is operated by about 150 researchers from Germany, Italy, Spain, Switzerland, Poland, Finland, Croatia, Bulgaria and the United States. Operational since 2004, MAGIC has, among other important results, so far discovered the most distant source of very-high-energy gamma rays more than five billion light years away from us, as well as gamma rays from a fast rotating neutron star, the Crab pulsar. Recently, a second MAGIC telescope has become operational. Stereoscopic observations will boost the sensitivity of the two largest Cherenkov telescopes further, enabling even fainter gamma-ray sources to be detected and still more precise measurements to be conducted. For the future, the MAGIC and H.E.S.S. teams are continuing their successful collaboration in the European project Cherenkov Telescope Array (CTA). This next-generation gamma-ray observatory will consist of roughly a hundred telescopes, leading to a significant improvement in sensitivity, by a factor 10 compared to the current generation of instruments.

Original Publication: V. A. Acciari et al. (The VERITAS, H.E.S.S., MAGIC Collaborations and the VLBA 43 GHz M87 Monitoring Team), "Radio Imaging of the Very-High-Energy Gamma-Ray Emission Region in the Central Engine of a Radio Galaxy", Science 325 (2009) 444-448 The giant radio galaxy Messier 87 (upper left corner) is located in our immediate “cosmic vicinity”, only about 55 million light years away. In the bright outflow of matter from the center of Messier 87, particles are accelerated to near the speed of light. Scientists were now able to show, combining observations from the lowest and highest end of the electromagnetic spectrum, that particle acceleration to the highest energies takes place very close the center of Messier 87. Lower right corner: The 17-meter MAGIC gamma-ray telescope on the Canary island of La Palma during sunset. Using it (and the H.E.S.S. and VERITAS telescope systems), the scientists were able to follow up the evolution of the gamma-ray flux from Messier 87 during the campaign in early 2008. Picture credit: NASA and the Hubble Heritage Team (STScI/AURA); Robert Wagner, MPI für Physik.

The Core Scientific Results

This time series of radio difference images (with respect to the temporal average image) of the innermost part of M87 shows a substantial brightening of the innermost core region in spring 2008, which coincides with the period of increased very high energy gamma-ray emission. Picture copyright: VERITAS/MAGIC/HESS/M87-VLBA teams

Upper panel: Very-high-energy gamma-ray emission from M87 during 2007-2008 (H.E.S.S, MAGIC & VERITAS). The regular gaps in the light curve correspond to phases of full moon during which no observations are possible. The vertical grey box indicates the time period of the strong flaring activity. Lower panel: Radio flux as measured with the VLBA from a region very close to the supermassive black hole in M87. Picture copyright: VERITAS/MAGIC/HESS/M87-VLBA teams

The Instruments Involved

Contact persons

Dr. Daniel Mazin
Institut de Física d'Altes Energies
Tel.: +34 93 581-4988
E-mail: mazin@ifae.es

Dr. Robert Wagner
Max Planck Institute for Physics, München
Tel.: +49 89 32354-546, +49 179 113 4687
E-mail: robert.wagner@mpp.mpg.de

Prof. Dr. Masahiro Teshima (Spokesperson of the MAGIC Collaboration)
Max Planck Institute for Physics, München
Tel.: +49 89 32354-301
E-mail: masahiro.teshima@mpp.mpg.de

Echoes in the press and media

• Spektrum direkt: Vier Hundertschaften gegen M87
• Astronomy now online: Gamma rays burst from M87's black hole
• Universe today: Messier 87 Shows Off for Hundreds of Earth-bound Astronomers
• Astronews.com: Neue Einblicke ins Innere der Riesengalaxie

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Information by our collaborators:

• Max Planck Society: A galaxy as particle accelerator
• VERITAS: Pinpointing origin of gamma rays from a supermassive black hole
• NRAO: VLBA Locates Origin of Superenergetic Bursts Near Giant Black Hole
• H.E.S.S: A Close Scientific Collaboration Identifies an Extragalactic Particle Accelerator

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