New gamma-eye for the H.E.S.S family: The telescope has a antenna with a diameter of 28 meters and weighs over 6000 tons. Image: H.E.S.S. Collaboration, Clementina Medina/Irfu-CEA |
On
26 July 2012, the H.E.S.S. II telescope started operation in Namibia.
Dedicated to observing the most violent and extreme phenomena of the
Universe in very high energy gamma-rays, H.E.S.S. II is the largest
Cherenkov telescope ever built, with its 28-meter-sized mirror. Together
with the four smaller (12-m) telescopes already in operation since
2004, the H.E.S.S. (“High Energy Stereoscopic System”) observatory will
continue to define the forefront of ground-based gamma ray astronomy and
will allow deeper understanding of known high-energy cosmic sources
such as supermassive black holes, pulsars and supernovae, and the search
for new classes of high-energy cosmic sources.
With
a mass of almost 600 tons and its 28-m mirror—the area of two tennis
courts—the new arrival is just huge. This very large telescope named
H.E.S.S. II saw its first light at 0:43 a.m. (German time zone) on 26
July 2012, detecting its very first images of atmospheric particle
cascades generated by cosmic gamma rays and by cosmic rays, marking the
next big step in exploring the Southern sky at gamma-ray energies.
“The
new telescope not only provides the largest mirror area among
instruments of this type worldwide, but also resolves the cascade images
at unprecedented detail, with four times more pixels per sky area
compared to the smaller telescopes,” states Pascal Vincent from the
French team responsible for the photo sensor package at the focus of the
mirror.
Gamma
rays are believed to be produced by natural cosmic particle
accelerators such as supermassive black holes, supernovae, pulsars,
binary stars, and maybe even relics of the Big Bang. The universe is
filled with these natural cosmic accelerators, impelling charged
particles such as electrons and ions to energies far beyond what the
particle accelerators built by mankind can reach. As high-energy gamma
rays are secondary products of these cosmic acceleration processes,
gamma ray telescopes allow us to study these high-energy sources.
Today,
well over one hundred cosmic sources of very high-energy gamma rays are
known. With H.E.S.S. II, processes in these objects can be investigated
in superior detail, also anticipating many new sources, as well as new
classes of sources. In particular, H.E.S.S. II will explore the gamma
ray sky at energies in the range of tens of Giga-electronvolts—the
poorly-explored transition regime between space-based instruments and
current ground-based telescopes, with a huge discovery potential.
The
most extreme gamma ray emitters—Active Galactic Nuclei—shine in gamma
rays with an apparent energy output which is one hundred times the
luminosity of the entire Milky Way, yet the radiation seems to emerge
from a volume much smaller than that of our Solar System, and turns on
and off in a matter of minutes, a strong signature of supermassive black
holes. For some of the objects seen with the four H.E.S.S. telescopes
in the last years, no counterpart at other wavelengths is known; they
may represent a new type of celestial object that H.E.S.S. II will help
to characterize.
Images of particle cascades viewed simultaneously by the H.E.S.S. II telescope and by the H.E.S.S. I telescopes. Color encodes light intensity. The image illustrates the dramatically improved intensity and resolution with which H.E.S.S. II views the particle cascades. The H.E.S.S. I cameras are shown in reduced size. Image: H.E.S.S. Collaboration |
When
gamma rays interact high up in the atmosphere, they generate a cascade
of secondary particles that can be imaged by the telescopes on the
ground and recorded in their ultra-fast photo sensor ‘cameras’, thanks
to the emission known as Cherenkov radiation—a faint flash of blue
light. The high-tech camera of H.E.S.S. II is able to record this very
faint flash with an “exposure time” of a few billionths of a second,
almost a million times faster than a normal camera. The H.E.S.S. II
camera—with an area of the size of a garage door and a weight of almost 3
tons—is “flying” 36 m above the primary mirror in the focal plane—at
the height of a 20-story building when pointing up. Despite its size,
the new telescope will be able to slew twice as fast as the smaller
telescopes to immediately respond to fast and transient phenomena such
as gamma ray bursts anywhere in the sky.
The
telescope structure and its drive system were designed by engineers in
Germany and South Africa, and produced in Namibia and Germany. The 875
hexagonal mirror facets which make up the huge reflector were
manufactured in Armenia, and individually characterized in Germany. The
mirror alignment system results from a cooperation of German and Polish
institutes. The camera, with its integrated electronics, was designed
and built in France. The construction of the new H.E.S.S. II telescope
was driven and financed largely by German and French institutions, with
significant contributions from Austria, Poland, South Africa and Sweden.
“The
successful commissioning of the new H.E.S.S. II telescope represents a
big step forward for the scientists of H.E.S.S., for the astronomical
community as a whole, and for Southern Africa as a prime location for
this field of astronomy”—so Werner Hofmann, spokesperson of the
project—“H.E.S.S. II also paves the way to the realization of CTA—the
Cherenkov Telescope Array—the next generation instrument ranked top
priority by astroparticle physicists and funding agencies in Europe”.
The
H.E.S.S. observatory has been operated for almost a decade by the
collaboration of more than 170 scientists, from 32 scientific
institutions and 12 different countries: Namibia and South Africa,
Germany, France, the UK, Ireland, Austria, Poland, the Czech Republic,
Sweden, Armenia, and Australia. To date, the H.E.S.S. Collaboration has
published over 100 articles in high-impact scientific journals,
including the Nature and Science journals.
H.E.S.S.
was awarded in 2006 the Descartes Prize of the European Commission—the
highest recognition for collaborative research—and in 2010 the
prestigious Rossi Prize of the American Astronomical Society. In a
survey in 2006, H.E.S.S. was ranked the 10th most influential
observatory worldwide, joining the ranks with the Hubble Space Telescope
or the telescopes of the European Southern Observatory ESO in Chile.
