Mathematics – Logic
Scientific paper
Jul 2011
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2011yera.confe..40s&link_type=abstract
The 41st Young European Radio Astronomers Conference, held at University of Manchester/Jodrell Bank Observatory, 18-20 July 2011
Mathematics
Logic
Scientific paper
The F-GAMMA program (Fermi-GST AGN Multi-frequency Monitoring Alliance) is meant to investigate the physics of AGNs via a multi-frequency monitoring approach. Blazars are AGNs that show intense variability in flux and polarisation and super-luminal motions due to small viewing angles to the jet axis. Hence, there is very extreme physics at work and despite decades of study the exact physics are still unclear. A method to distinguish between different emission models are the multi-frequency variability studies. The Fermi-GST scans the entire sky every three hours. So, for the first time it provides densely sampled gamma-ray light curves which can be cross-correlated with radio, optical or other light curves. To fully exploit these features 65 Fermi-GST detectable blazars are being monitored monthly in radio wavelength since 2007. The core program involves observations with the 100-m Effelsberg telescope at 8 frequencies between 2.6 and 43 GHz, the 30-m IRAM telescope at 86, 145 and 240 GHz and the APEX 12-m telescope at 345 GHz. Spectra simultaneous within a week are produced for cross-band studies.
In this talk results of time series analysis studies will be presented in an attempt to search for characteristic timescales and study the brightness temperatures and variability Doppler factors of these objects. Furthermore, it will be shown that all the spectra can be grouped in only 9 phenomenological classes of spectral variability pattern. Seven of these classes are clearly dominated by spectral evolution and can be interpreted as a quiescent optically thin spectrum with a super-imposed flaring event. The different classes can be explained by different redshifts and intrinsic-source/flare parameters as simulations showed. The other 2 classes vary self-similarly with almost no apparent shift of the peak frequency implying that a totally different mechanism is at work.
From all this it is concluded that only two mechanisms have been observed to produce variability. Given that none of these sources was found to switch mode, the variability mechanism must be a finger-print of the source or it depends on conditions that do not change within the time covered by F-GAMMA program.
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