Astronomy and Astrophysics – Astrophysics
Scientific paper
Mar 1994
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1994a%26a...283...51t&link_type=abstract
Astronomy and Astrophysics (ISSN 0004-6361), vol. 283, no. 1, p. 51-58
Astronomy and Astrophysics
Astrophysics
43
Active Galactic Nuclei, Bl Lacertae Objects, Brightness Temperature, Quasars, Radio Galaxies, Viewing, Radio Emission, Red Shift, Relativistic Effects, Very Long Base Interferometry
Scientific paper
We use 22 and 37 GHz continuum flux data from the Metsahovi monitoring program to derive variability timescales and associated brightness temperatures for a flux-limited sample of 41 quasars, BL Lacs and radio galaxies. Even with H0 = 100 km/s/Mpc, about half of the sources have had at least one outburst exceeding the synchrotron limit Tb approximately equal to 1012K, indicating the need for relativistic boosting. The Tb distributions for various classes of active galactic nuclei (AGN) are different, with highly polarized (blazar-type) quasars generally having the highest brightness temperatures, followed by low polarization (ordinary) quasars and finally radio galaxies. We argue that this results from different average viewing angles, in accordance with orientation-dependent unification schemes for active galactic nuclei. We have further calculated the viewing angle theta for the sources with measured apparent very large base interferometry (VLBI) expansion speeds. We find that a radio galaxy appears as a quasar if the viewing angle is approximately less than 35 deg and as a highly polarized quasar (blazar) if theta approximately less than 18 deg. For this radio galaxy/ QSO population the intrinsic Lorentz factor gamma ranges between 10 and 40. BL Lacs come from a different parent population with 4 approximately less than gamma approximately less than 12 and theta approximately less than 40 deg. The small superluminal expansion speeds of BL Lacs are due to smaller Lorentz factors, not especially small viewing angles.
Terasranta Harri
Valtaoja Esko
No associations
LandOfFree
Brightness temperatures and viewing angles for extragalactic radio sources: A test of unification schemes for active galactic nuclei does not yet have a rating. At this time, there are no reviews or comments for this scientific paper.
If you have personal experience with Brightness temperatures and viewing angles for extragalactic radio sources: A test of unification schemes for active galactic nuclei, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Brightness temperatures and viewing angles for extragalactic radio sources: A test of unification schemes for active galactic nuclei will most certainly appreciate the feedback.
Profile ID: LFWR-SCP-O-1869894