Angular Broadening of Intraday Variable AGNs. II. Interstellar and Intergalactic Scattering
| dc.contributor.author | Lazio, T. Joseph W. | |
| dc.contributor.author | Ojha, Roopesh | |
| dc.contributor.author | Fey, Alan L. | |
| dc.contributor.author | Kedziora-Chudczer, Lucyna | |
| dc.contributor.author | Cordes, James M. | |
| dc.contributor.author | Jauncey, David L. | |
| dc.contributor.author | Lovell, James E. J. | |
| dc.date.accessioned | 2020-03-27T14:23:36Z | |
| dc.date.available | 2020-03-27T14:23:36Z | |
| dc.date.issued | 2008-01-01 | |
| dc.description.abstract | We analyze a sample of 58 multiwavelength, Very Long Baseline Array observations of active galactic nuclei (AGNs) to determine their scattering properties. Approximately 75% of the sample consists of AGNs that exhibit centimeter-wavelength intraday variability (interstellar scintillation), while the other 25% do not show intraday variability. We find that interstellar scattering is measurable for most of these AGNs, and the typical broadening diameter is 2 mas at 1 GHz. We find that the scintillating AGNs are typically at lower Galactic latitudes than the nonscintillating AGNs, consistent with the scenario that intraday variability is a propagation effect from the Galactic interstellar medium. The magnitude of the inferred interstellar broadening measured toward the scintillating AGNs, when scaled to higher frequencies, is comparable to the diameters inferred from analyses of the light curves for the more well-known intraday variable sources. However, we find no difference in the amount of scattering measured toward the scintillating versus nonscintillating AGNs. A consistent picture is one in which the scintillation results from localized regions (‘‘clumps’’) distributed throughout the Galactic disk, but that individually make little contribution to the angular broadening. Of the 58 AGNs observed, 37 (64%) have measured redshifts. At best, a marginal trend is found for scintillating (nonscintillating) AGNs to have smaller (larger) angular diameters at higher redshifts. We also use our observations to try to constrain the possibility of intergalactic scattering. While broadly consistent with the scenario of a highly turbulent intergalactic medium, our observations do not place significant constraints on its properties. | en_US |
| dc.description.sponsorship | We thank the referee for suggestions that improved the presentation of these results. The National Radio Astronomy Observatory is a facility of the National Science Foundation, operated under cooperative agreement by Associated Universities, Inc. This research has made use of the United States Naval Observatory (USNO) Radio Reference Frame Image Database (RRFID); the National Aeronautics and Space Administration’s (NASA) Astrophysics Data System bibliographic services; the SIMBAD database, operated at CDS, Strasbourg, France; and the NASA/IPAC Extragalactic Database (NED), which is operated by the Jet Propulsion Laboratory, California Institute of Technology, under contract with NASA. Basic research in radio astronomy at the Naval Research Laboratory (NRL) is supported by the NRL base funding. | en_US |
| dc.description.uri | https://iopscience.iop.org/article/10.1086/520572 | en_US |
| dc.format.extent | 7 pages | en_US |
| dc.genre | journal articles | en_US |
| dc.identifier | doi:10.13016/m2azf2-a8rs | |
| dc.identifier.citation | T. Joseph W. Lazio, Roopesh Ojha, Alan L. Fey, Lucyna Kedziora-Chudczer, James M. Cordes, David L. Jauncey, and James E. J. Lovell,T. Joseph W. Lazio1, Roopesh Ojha2, Alan L. Fey3, Lucyna Kedziora-Chudczer4, James M. Cordes5, David L. Jauncey6, and James E. J. Lovell,T. Joseph W. Lazio1, Roopesh Ojha2, Alan L. Fey3, Lucyna Kedziora-Chudczer4, James M. Cordes5, David L. Jauncey6, and James E. J. Lovell, Vol#672, 2008,https://iopscience.iop.org/article/10.1086/520572 | en_US |
| dc.identifier.uri | http://hdl.handle.net/11603/17707 | |
| dc.identifier.uri | http://simbad.u-strasbg.fr/simbad/sim-ref?querymethod=bib&simbo=on&submit=submit+bibcode&bibcode=2008ApJ...672..115L | |
| dc.identifier.uri | https://ned.ipac.caltech.edu/cgi-bin/objsearch?search_type=Search&refcode=2008ApJ...672..115L | |
| 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 | Public Domain Mark 1.0 | * |
| dc.rights | This work was written as part of one of the author's official duties as an Employee of the United States Government and is therefore a work of the United States Government. In accordance with 17 U.S.C. 105, no copyright protection is available for such works under U.S. Law | |
| dc.rights.uri | http://creativecommons.org/publicdomain/mark/1.0/ | * |
| dc.title | Angular Broadening of Intraday Variable AGNs. II. Interstellar and Intergalactic Scattering | en_US |
| dc.type | Text | en_US |