The Fermi symposium 2011: AGNs, pulsars and gamma ray bursts

The results presented at the III Fermi symposium in Rome reflected, in particular, what a magnificent instrument the Fermi LAT is for observing active galactic nuclei and pulsars. The 2 source catalogue 2FGL was presented and will soon be released with 1888 sources. Much attention was given to the blazar 3C454.3 which has been monitored since the launch and has undergone a series of very bright outbursts. The multiwavelength analysis by Stefan Larsson revealed a far more complex behaviour than expected in the simple picture we had of AGN jets before the launch of Fermi. The discovery of spectral breaks at GeV energies was nicely interpreted by the former Stockholm astronomer Juri Poutanen and collaborators as a result of gamma-ray absorption via photon-photon pair production on He II Lyman recombination continuum and lines within the broad-line region.

The Aula Magna at La Sapienza, Rome

It was also made clear that all models we have for description of the high energy emission around pulsars are, more or less, wrong. Fermi has told us for certain that the emission is from high altitudes in the outer magnetosphere; Fermi has killed the polar cap model and the classical TPC, while the other models are in need of modifications. The soon to be launched PoGOLite experiment will give us important new information on the high energy emission from the Crab pulsar by observing the complementary polarisation of the X and gamma-rays.

Similarily, the observations of gamma-ray bursts made by Fermi does not fit into any of the frameworks of existing models and we have to re-address the questions that we thought to have been solved. In particular, it is clear that multiple spectral components are present in the spectra and high energy cutoff also exist. Tanja Nymark presented a paper on the behaviour of the photospheric emission component in GRBs, observed by the gamma-ray bursts monitor on Fermi, and argued for the existence of subphotospheric dissipation.

The most important announcement at the conference was probably the VERITAS detection of a pulsed signal from the Crab pulsar at energies larger than 120 GeV at a 6 sigma level. This is the first detection of a pulsar in energies above 100 GeV and shows interestingly that there is now spectral cut off in the high energy spectrum of the Crab nebula. Moreover these observations again show us that the emission must come from a height of at least 10 stellar radii and that the emission at these energies cannot be from curvature radiation.

Finally, Fermi is also noticing that the Sun is waking up!

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