Detection of Six Rapidly Scintillating AGNs and the Diminished Variability of J1819+3845

Abstract

The extreme, intra-hour and > 10% rms flux density scintillation observed in AGNs such as PKS 0405-385, J1819+3845 and PKS 1257-326 at cm wavelengths has been attributed to scattering in highly turbulent, nearby regions in the interstellar medium. Such behavior has been found to be rare. We searched for rapid scintillators among 128 flat spectrum AGNs and analyzed their properties to determine the origin of such rapid and large amplitude radio scintillation. The sources were observed at the VLA at 4.9 and 8.4 GHz simultaneously at two hour intervals over 11 days. We detected six rapid scintillators with characteristic time-scales of < 2 hours, none of which have rms variations > 10%. We found strong lines of evidence linking rapid scintillation to the presence of nearby scattering regions, estimated to be < 12 pc away for ~ 200 muas sources and < 250 pc away for ~ 10 muas sources. We attribute the scarcity of rapid and large amplitude scintillators to the requirement of additional constraints, including large source compact fractions. J1819+3845 was found to display ~ 2% rms variations at ~ 6 hour time-scales superposed on longer > 11 day variations, suggesting that the highly turbulent cloud responsible for its extreme scintillation has moved away, with its scintillation now caused by a more distant screen ~ 50 to 150 pc away.

5 pages, 3 figures, accepted for publication in Astronomy and Astrophysics

References in corpus (7)

• 100 Microarcsecond Resolution VLBI Imaging of Anisotropic Interstellar Scattering towards Pulsar B0834+06
• The Micro-Arcsecond Scintillation-Induced Variability (MASIV) Survey II: The First Four Epochs
• Rapid interstellar scintillation of PKS B1257-326: two-station pattern time delays and constraints on scattering and microarcsecond source structure
• The Origin of Radio Scintillation In the Local Interstellar Medium
• Emergence and disappearance of micro-arcsecond structure in the scintillating quasar J1819+3845
• Dual-Frequency Observations of 140 Compact, Flat-Spectrum Active Galactic Nuclei for Scintillation-Induced Variability
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• The intra-hour variable quasar J1819$+$3845: 13-year evolution, jet polarization structure and interstellar scattering screen properties
• Nowhere to Hide: Radio-faint AGN in the GOODS-N field. II. Multi-wavelength AGN selection techniques and host galaxy properties
• Radio and optical intra-day variability observations of five blazars
• The MASIV Survey IV: relationship between intra-day scintillation and intrinsic variability of radio AGNs
• The presence of interstellar scintillation in the 15 GHz interday variability of 1158 OVRO-monitored blazars
• Interstellar Scintillation of an Extreme Scintillator: PKS B1144-379
• Intra-Day Variability Observations of Two Dozens of Blazars at 4.8 GHz