Ben-Gurion University of the NegevAstrophysics and Cosmology GroupAstrophysics, Relativity, Cosmology, and Space Physics |
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Speaker: Edoardo Striani (University Tor Vergata, Rome) July 11 The surprising Crab Nebula
The
Crab Nebula, with its powerful pulsar, is the remnant of a supernova
explosion observed in 1054. The Nebula emission for energies ranging
from radio to gamma rays (up to 100 MeV) is dominated by synchrotron
radiation of electrons accelerated by the pulsar, and shows a cutoff
around 100-200 MeV (the so called synchrotron burn-off). Because of its
very stable emission, the Crab Nebula was considered a calibrator for
High Energy Astrophysics telescopes. A big surprise was the discovery
by the AGILE satellite of a gamma-ray flare from the Crab Nebula in
September 2010, with a sub-day timescale, and a peak emission beyond
the synchrotron burn-off limit. The discovery of fast and efficient
gamma-ray transient emission from the Crab Nebula leads to
substantially revised current models of particle acceleration. I will
discuss the four major flaring gamma-ray episodes detected by AGILE and
Fermi from mid-2007 until now and the recent evidence of two types of
enhanced gamma-ray emission.
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Last updated
by Uri Keshet, November
2011 |