2002ApJ...568...99H


Query : 2002ApJ...568...99H

2002ApJ...568...99H - Astrophys. J., 568, 99-119 (2002/March-3)

Parsec-scale blazar monitoring: flux and polarization variability.

HOMAN D.C., OJHA R., WARDLE J.F.C., ROBERTS D.H., ALLER M.F., ALLER H.D. and HUGHES P.A.

Abstract (from CDS):

We present analysis of the flux density and polarization variability of parsec-scale radio jets from a dual-frequency, six-epoch, VLBA polarization experiment monitoring 12 blazars. The observations were made at 15 and 22 GHz at bimonthly intervals over 1996. Here we analyze the flux density, fractional polarization, and polarization position angle behavior of core regions and jet features, considering both the linear trends of these quantities with time and more rapid fluctuations about the linear trends. The dual frequency nature of the observations allows us to examine spectral evolution, to separate Faraday effects from changes in magnetic field order, and also to deduce empirical estimates for the uncertainties in measuring properties of VLBI jet features (see the Appendix). Our main results include the following: On timescales ≳1 yr, we find that jet features generally decayed in flux, with older features decaying more slowly than younger features. Using the decay rates of jet features from six sources, we find I∝R–1.3±0.1. Short-term fluctuations in flux tended to be fractionally larger in core regions than in jet features, with the more compact core regions having the larger fluctuations. We find significant spectral index changes in the core regions of four sources. Taken together these are consistent with an outburst-ejection cycle for new jet components. Jet features from one source showed a significant spectral flattening over time. Jet features either increased in fractional polarization with time or showed no significant change, with the smallest observed changes in the features at the largest projected radii. Increasing magnetic field order explains most of the increasing fractional polarization we observed. Only in the case of 3C 273 is there evidence of a feature emerging from behind a Faraday depolarizing screen. We find a number of significant polarization angle rotations, including two very large (≳180°) rotations in the core regions of OJ 287 and J1512-09. In general, polarization angle changes were of the same magnitude at both observing bands and cannot be explained by Faraday rotation. The observed polarization angle changes most likely reflect underlying changes in magnetic field structure. In jet features, four of the five observed rotations were in the direction of aligning the magnetic field with the jet axis, and coupled with the tendency of jet features to show a fractional polarization increase, this suggests increasing longitudinal field order.

Abstract Copyright:

Journal keyword(s): Galaxies: BL Lacertae Objects: General - Galaxies: Active - Galaxies: Jets - Galaxies: Kinematics and Dynamics - Galaxies: Seyfert - Galaxies: Quasars: General

Simbad objects: 13

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Number of rows : 13
N Identifier Otype ICRS (J2000)
RA
ICRS (J2000)
DEC
Mag U Mag B Mag V Mag R Mag I Sp type #ref
1850 - 2022
#notes
1 Mrk 1506 Sy1 04 33 11.0958197353 +05 21 15.617543663   15.72 15.05 10.08   ~ 1892 2
2 QSO J0530+13 Bla 05 30 56.41672 +13 31 55.1495     20.0 19.35   ~ 904 1
3 QSO J0738+1742 BLL 07 38 07.39374766 +17 42 18.9982302   16.76 16.22 15.78   ~ 914 1
4 QSO J0854+2006 BLL 08 54 48.8749311881 +20 06 30.642936668   15.91 15.43 15.56   ~ 2117 1
5 4C 21.35 QSO 12 24 54.4583467193 +21 22 46.385219365   17.56 17.50 18.2   ~ 597 2
6 3C 273 BLL 12 29 06.6996828061 +02 03 08.598846466   13.05 14.830 14.11   ~ 5493 1
7 3C 279 Bla 12 56 11.1664521013 -05 47 21.531840471   18.01 17.75 15.87   ~ 2824 2
8 7C 1308+3236 BLL 13 10 28.66387 +32 20 43.7831   15.61 15.24 17.91   ~ 778 1
9 QSO J1512-0906 Bla 15 12 50.53292491 -09 05 59.8295878   16.74 16.54     ~ 1204 1
10 3C 345 QSO 16 42 58.8100340220 +39 48 36.999540578   16.81 16.59 16.84   ~ 1597 2
11 4C 09.57 BLL 17 51 32.81857318 +09 39 00.7284829   17.46 16.78 15.57   ~ 856 1
12 4C 73.18 BLL 19 27 48.4944745594 +73 58 01.571908984     15.5 15.11   ~ 502 2
13 8C 2007+777 BLL 20 05 30.9981060951 +77 52 43.245329882     16.5 17.36   ~ 416 1

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