Astronomy and Astrophysics – Astronomy
Scientific paper
Feb 2005
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2005aipc..745..505a&link_type=abstract
HIGH ENERGY GAMMA-RAY ASTRONOMY: 2nd International Symposium on High Energy Gamma-Ray Astronomy. AIP Conference Proceedings, Vo
Astronomy and Astrophysics
Astronomy
Active And Peculiar Galaxies And Related Systems, Gamma-Ray Sources, Gamma-Ray Bursts
Scientific paper
Centaurus A (NGC5128), at a distance of 3.4 Mpc is the nearest Active Galaxy, classified as a low luminosity Fanaroff-Riley class I object. Although the central source is completely obscured at optical wavelengths, VLBI studies at radio frequencies show an unresolved core and an asymmetric jet at sub-parsec scales. Kinematical studies of the jet components show subluminal expansion velocities, which together with the jet-counterjet intensity ratio implies that the jet direction forms a large angle with the line of sight (50° to 80°). The nuclear emission is highly variable at all wavelengths, from radio to γ-rays. Single dish radio observations showed that the stronger, long duration outbursts (months to years) present a correlation at radio and X-rays, although it is not clear whether the emission mechanism is synchrotron radiation at both frequencies or if the inverse Compton process dominates at high energies. Moreover, no information is available about the correlation between the emission at these two frequencies at shorter timescales (days and hours), due to the lack of short term monitoring at radio frequencies. In this work we report 43 GHz monitoring of Cantaurus A at the Itapetinga Radio Observatory during the last year, with daily resolution during a three-month period. We found very large variations (factor of two) within a few days, which puts Centaurus A in the blazar category. These variations were superimposed to a continuous rise in flux density that lasted until the end of 2003, when it started a fast decline. No apparent correlation with the All Sky Monitor (ASM/RXTE) data was found at these short timescales.
Abraham Zulema
Barres de Almeida Ulisses
Caproni Anderson
Dominici Tânia P.
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