Astronomy and Astrophysics – Astronomy
Scientific paper
Dec 2003
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2003aas...203.8804m&link_type=abstract
American Astronomical Society Meeting 203, #88.04; Bulletin of the American Astronomical Society, Vol. 35, p.1348
Astronomy and Astrophysics
Astronomy
Scientific paper
We investigate the recent remarkable claim of Stirling et al. (MNRAS, 341, 450 ,2003) that the inner radio core of BL Lac has a 2.3 year periodic oscillating nozzle structure. We have analyzed 43 GHz VLBA maps made at nine epochs overlapping the time span analyzed by Stirling et al. using a similar Gaussian model fitting scheme for the inner core. Our results are not inconsistent with a periodic oscillation with a 2.3 yr period, but they are equally consistent with the null hypothesis that there is no precession. The most important difference in our analysis and that of Stirling et al. is in the uncertainty estimation of the position angle of the inner core subcomponents, on which evidence for precession critically depends. We use simulated data to investigate the uncertainties expected from radiometer noise and systematic effects, and suggest a more definitive test of the precession hypothesis.
Denn Grant Russell
Mutel Robert L.
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