Abstrakti
We report that active galactic nucleus (AGN) jets are causally connected
on parsec scales, based on 15 GHz Very Long Baseline Array (VLBA) data
from a sample of 133 AGN jets. This result is achieved through a new
method for measuring the product of the jet Lorentz factor and the
intrinsic opening angle Γθj from measured
apparent opening angles in flux density limited samples of AGN jets. The
Γθj parameter is important for jet physics
because it is related to the jet-frame sidewise expansion speed and
causal connection between the jet edges and its symmetry axis. Most
importantly, the standard model of jet production requires that the jet
be causally connected with its symmetry axis, implying that
Γθj ≲ 1. When we apply our method to the
MOJAVE flux density limited sample of radio loud objects, we find
Γθj ≈ 0.2, implying that AGN jets are
causally connected. We also find evidence that AGN jets viewed very
close to the line of sight effectively have smaller intrinsic opening
angles compared with jets viewed more off-axis, which is consistent with
Doppler beaming and a fast inner spine/slow outer sheath velocity field.
Notably, gamma-ray burst (GRB) jets have a typical
Γθj that is two orders of magnitude higher,
suggesting that different physical mechanisms are at work in GRB jets
compared to AGN jets. A useful application of our result is that a jet's
beaming parameters can be derived. Assuming Γθj
is approximately constant in the AGN jet population, an individual jet's
Doppler factor and Lorentz factor (and therefore also its viewing angle)
can be determined using two observable quantities: apparent jet opening
angle and the apparent speed of jet components.
Alkuperäiskieli | Englanti |
---|---|
Artikkeli | A144 |
Sivumäärä | 9 |
Julkaisu | Astronomy & Astrophysics |
Vuosikerta | 558 |
DOI - pysyväislinkit | |
Tila | Julkaistu - 2013 |
OKM-julkaisutyyppi | A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä |