Astronomy and Astrophysics – Astronomy
Scientific paper
Jan 2010
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2010aas...21560204s&link_type=abstract
American Astronomical Society, AAS Meeting #215, #602.04; Bulletin of the American Astronomical Society, Vol. 36, p.1121
Astronomy and Astrophysics
Astronomy
Scientific paper
A significant fraction of flat spectrum AGN exhibit rapid variability both in total intensity as well as polarization at cm wavelengths, on time scales ranging from a few hours to a few days, a phenomenon termed intra day variability (IDV). The physical process responsible for this behavior is not well understood, though various models ranging from source-intrinsic (e.g., shock-in-jet) to source-extrinsic (e.g., scintillation due to electron density fluctuations in the interstellar medium) have been proposed. The absence of multi-epoch data (especially in the 2cm range) exacerbates the situation. We present the results of analysis of archival VLBA data for a flux density limited sample of bright, flat spectrum AGN located predominantly in the northern sky, collected under the aegis of the MOJAVE program.
We find a clear detection of IDV on timescales ≤ 10hrs. in 25% of the 360 sources analyzed. We find significant differences in the IDV properties of quasars and true BL Lacs. Intermediate objects near the BL Lac/quasar divide have IDV characteristics akin to those of quasars. As expected, the presumable weakly beamed CSS & GPS sources show no IDV. We find IDV properties to be correlated with source intrinsic properties such as Doppler factor, and apparent speed. Episodes of IDV activity are associated with radio flaring and/or component ejection, suggesting an intrinsic mechanism at work. However, we also find IDV to be strongly correlated with the galactic latitude of the source, indicative of a scintillation mechanism. We propose a qualitative model to explain these results.
The MOJAVE program is supported under the National Science Foundation grant 080786-AST and NASA Fermi grant NNX08AV67G.
Lister Matthew
Mojave Collaboration
Sarma Kuchibhotla Huthavahana
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