Interstellar Scintillation of an Extreme Scintillator: PKS B1144-379

Abstract

The University of Tasmania Ceduna radio telescope has been used to investigate rapid variability in the radio flux density of the BL Lac object PKS B1144-379 at 6.7 GHz. High-cadence monitoring of this extreme scintillator was carried out over a period of approximately nine years, between 2003 and 2011. We have used structure functions created from the intensity time series to determine the characteristic timescale of the variability. The characteristic timescale is consistently observed to increase during certain periods of each year, demonstrating the annual cycle expected for scintillation through an interstellar scattering screen. The best-fitting annual cycle model for each year suggests that the scintillation pattern has an anisotropic structure and that the upper limit of its scattering screen is at a distance of ~0.84 kpc. Higher anisotropy in some of the annual cycle fits suggests that changes in the intrinsic source structure might be influencing the variability timescale. We found a prominent annual cycle is only present in the variability timescale for certain years where other evidence suggests that the core is compact. From our measurements, we calculated that the core angular size varied between 5.65-15.90 $\mu$as (0.05-0.13 pc). The core component was found to be at its most compact during two flares in the total flux density, which were observed in 2005 and 2008. We conclude that the long-term variability in the radio flux density of PKS B1144-379 is due to intrinsic changes in the source and that these affect our ability to measure an annual cycle in its variability time scale.

24 pages, 22 figures

References in corpus (12)

• Bright AGN Source List from the First Three Months of the Fermi Large Area Telescope All-Sky Survey
• MOJAVE: Monitoring of Jets in AGN with VLBA Experiments. V. Multi-epoch VLBA Images
• 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 first estimate of radio jet proper motion at z>5
• Folded Fields as the Source of Extreme Radio-Wave Scattering in the Galactic Center
• The IDV source J1128+5925, a new candidate for annual modulation?
• Emergence and disappearance of micro-arcsecond structure in the scintillating quasar J1819+3845
• Intra-day variability observations of S5 0716+714 over 4.5 years at 4.8 GHz
• A Compact Extreme Scattering Event Cloud Towards AO 0235+164
• Spica and the annual cycle of PKS B1322-110 scintillations
• J1128+592: a highly variable IDV source

Cited by in corpus (2)

• A VLBI Proper Motion Analysis of the Recoiling Supermassive Black Hole Candidate Mrk 1018
• The Annual Cycle in Scintillation Timescale of PMN J1726+0639