Among active galaxies, 3C 454.3 must be a monster. Indeed, it is now the brightest source in the gamma-ray sky, after a series of flares that began on 15 September. It is located billions of light-years away and triggered a large interest from astronomers and physicists around the globe, thanks to very recent observations of the Fermi Gamma Ray Space Telescope. Most of the time, the brightest persistent source in the gamma-ray sky is the Vela pulsar, which at a distance of about 1,000 light-years lies practically next door. «3C 454.3 is millions of times farther away, yet the current flare makes it twice as bright as Vela,» said Lise Escande from CNRS/IN2P3 in France. «That represents an incredible energy release, and one the source can’t sustain for very long.» Blazars, like many active galaxies, emit oppositely directed jets of particles traveling near the speed of light when matter falls toward their central supermassive black holes. What makes a blazar so bright in gamma rays is its orientation: One of the jets happens to be aimed straight at us. But scientists are not able yet to explain the changes ocurring within that jet, regarding such a flare. Fermi and the multiwavelength sky
3C 454.3 also is flaring at radio and visible wavelengths, if less dramatically. «In red light, the blazar brightened by more than two and a half times to magnitude 13.7, and it is also very bright at high radio frequencies» said Massimo Villata at Italy’s Torino Observatory. Unprecedented flares from the blazar 3C 454.3 in the constellation Pegasus now make it the brightest persistent gamma-ray source in the sky. That title usually goes to the Vela pulsar in our galaxy, which is millions of times closer (Credit: NASA/DOE/Fermi LAT Collaboration). More than ever, multiwavelength astronomy becomes a major issue to understand what really happens within such very violent events. Indeed, the changes of brightness are so fast that correlated observations with a variety of telescopes and detectors are needed in order to make sure that the final full picture describes the same occurrence, at any wavelength. It is why the Fermi team sends alerts to astronomers to monitor >>
| Composite image of galaxy M82. Credit: X-ray: NASA/CXC/JHU/D.Strickland; Optical: NASA/ESA/STScI/AURA/The Hubble Heritage Team; IR: NASA/JPL-Caltech/Univ. of AZ/C. Engelbracht.
such events over as broad a range of wavelengths as possible. This multiwavelength approach includes gamma ray telescopes on the ground such as MAGIC in the Canary Islands and H.E.S.S in Namibia, which can observe the same sources at even higher energies.
During its first year of operation, the Fermi Gamma Ray Space Telescope mapped the extreme sky with unprecedented resolution and sensitivity. It captured already more than 1,000 discrete sources of gamma rays, unveiling a new picture of the extreme Universe.
The Fermi telescope was developed in collaboration with important contributions from France, Germany, Italy, Japan, Sweden and the United States.
Left: the Fermi Telescope has made the first unambiguous detection of high-energy gamma-rays from the microquasar Cygnus X-3.
Right: Fermi’s Large Area Telescope (LAT) has shown that an intense star-forming region in the Large Magellanic Cloud is also a source of diffuse gamma rays.
Brighter colours indicate larger numbers of detected gamma rays (Credit: Fermi collaboration).
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The Fermi collaboration just announced it detected the brightest-ever blazar flare. Almost every month, the Fermi satellite has revealed new impressive results, unveiling a completely new picture of the extreme Universe.
