Parsec-Scale Blazar Monitoring: Flux and Polarization Variability
| dc.contributor.author | Homan, Daniel C. | |
| dc.contributor.author | Ojha, Roopesh | |
| dc.contributor.author | Wardle, John F. C. | |
| dc.contributor.author | Roberts, David H. | |
| dc.contributor.author | Aller, Margo F. | |
| dc.contributor.author | Aller, Hugh D. | |
| dc.contributor.author | Hughes, Philip A. | |
| dc.date.accessioned | 2020-04-24T13:00:59Z | |
| dc.date.available | 2020-04-24T13:00:59Z | |
| dc.date.issued | 2002-03-20 | |
| dc.description.abstract | 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. | en_US |
| dc.description.sponsorship | This work has been supported by NASA rants NGT51658 and NGT 5-50136 and NSF grants AST 91-22282, AST 92-24848, AST 94-21979, AST 95-29228, AST 98-02708, and AST 99-00723. We thank C. C. Cheung and G. Sivakoff for their assistance in the initial organization of the model fit data, and Alan Bridle for helpful discussion regarding jet flux profiles. This research has made use of the NASA=IPAC Extragalactic Database (NED), which is operated by the Jet Propulsion Laboratory, California Institute of Technology, under contract with the National Aeronautics and Space Administration. This research has also made use of NASA’s Astrophysics Data System Abstract Service. | en_US |
| dc.description.uri | https://iopscience.iop.org/article/10.1086/338701 | en_US |
| dc.format.extent | 21 pages | en_US |
| dc.genre | journal articles | en_US |
| dc.identifier | doi:10.13016/m2yh8r-jww8 | |
| dc.identifier.citation | Daniel C. Homan, Roopesh Ojha, John F. C. Wardle, David H. Roberts, Margo F. Aller, Hugh D. Aller and Philip A. Hughes, Parsec-Scale Blazar Monitoring: Flux and Polarization Variability, The Astrophysical Journal, Volume 568, Number 1,https://doi.org/10.1086%2F338701 | en_US |
| dc.identifier.uri | https://doi.org/10.1086%2F338701 | |
| dc.identifier.uri | http://hdl.handle.net/11603/18234 | |
| dc.identifier.uri | http://simbad.u-strasbg.fr/simbad/sim-ref?querymethod=bib&simbo=on&submit=submit+bibcode&bibcode=2002ApJ...568...99H | |
| dc.identifier.uri | https://ned.ipac.caltech.edu/cgi-bin/objsearch?search_type=Search&refcode=2002ApJ...568...99H | |
| dc.language.iso | en_US | en_US |
| dc.publisher | IOP | en_US |
| dc.relation.isAvailableAt | The University of Maryland, Baltimore County (UMBC) | |
| dc.relation.ispartof | UMBC Physics Department Collection | |
| dc.relation.ispartof | UMBC Center for Space Sciences and Technology (CSST) / Center for Research and Exploration in Space Sciences & Technology II (CRSST II) | |
| dc.rights | This item is likely protected under Title 17 of the U.S. Copyright Law. Unless on a Creative Commons license, for uses protected by Copyright Law, contact the copyright holder or the author. | |
| dc.rights | © 2002. The American Astronomical Society. All rights reserved. | |
| dc.title | Parsec-Scale Blazar Monitoring: Flux and Polarization Variability | en_US |
| dc.type | Text | en_US |