Effelsberg Monitoring of a Sample of RadioAstron Blazars: Analysis of Intra-Day Variability

Abstract

We present the first results of an ongoing intra-day variability (IDV) flux density monitoring program of 107 blazars, which were selected from a sample of RadioAstron space very long baseline interferometry (VLBI) targets. The~IDV observations were performed with the Effelsberg 100-m radio telescope at 4.8\,GHz, focusing on the statistical properties of IDV in a relatively large sample of compact active galactic nuclei (AGN). We investigated the dependence of rapid ($<$3 day) variability on various source properties through a likelihood approach. We found that the IDV amplitude depends on flux density and that fainter sources vary by about a factor of 3 more than their brighter counterparts. We also found a significant difference in the variability amplitude between inverted- and flat-spectrum radio sources, with the former exhibiting stronger variations. $\gamma$-ray loud sources were found to vary by up to a factor 4 more than $\gamma$-ray quiet ones, with 4$\sigma$ significance. However a galactic latitude dependence was barely observed, which suggests that it is predominantly the intrinsic properties (e.g., angular size, core-dominance) of the blazars that determine how they scintillate, rather than the directional dependence in the interstellar medium (ISM). We showed that the uncertainty in the VLBI brightness temperatures obtained from the space VLBI data of the RadioAstron satellite can be as high as $\sim$70\% due to the presence of the rapid flux density variations. Our statistical results support the view that IDV at centimeter wavelengths is predominantly caused by interstellar scintillation (ISS) of the emission from the most compact, core-dominant region in an AGN.

arXiv comment23 pages, 9 figures, published online by MDPI Galaxies

References in corpus (30)

• Blazars in the Fermi Era: The OVRO 40-m Telescope Monitoring Program
• Doppler factors, Lorentz factors and viewing angles for quasars, BL Lacertae objects and radio galaxies
• The Wisconsin H-Alpha Mapper Northern Sky Survey
• The Structure of the Local Interstellar Medium V: Electron Densities
• Relativistic beaming and gamma-ray brightness of blazars
• On the relation between AGN gamma-ray emission and parsec-scale radio jets
• High-Sensitivity 86GHz (3.5mm) VLBI Observations of M87: Deep Imaging of the Jet Base at a 10 Schwarzschild-Radius Resolution
• The discovery of a microarcsecond quasar: J1819+3845
• Rapid Variability and Annual Cycles in the Characteristic Time-scale of the Scintillating Source PKS 1257-326
• The Micro-Arcsecond Scintillation-Induced Variability (MASIV) Survey II: The First Four Epochs
• Interstellar scintillation as the origin of rapid radio variability in the quasar J1819+3845
• Radio/gamma-ray time delay in the parsec-scale cores of active galactic nuclei
• First Results from MASIV: The Micro-Arcsecond Scintillation-Induced Variability Survey
• A Connection Between Apparent VLBA Jet Speeds and Initial Active Galactic Nucleus Detections Made by the Fermi Gamma-ray Observatory
• Connecting radio variability to the characteristics of gamma-ray blazars
• RadioAstron Observations of the Quasar 3C273: a Challenge to the Brightness Temperature Limit
• Testing the inverse-Compton catastrophe scenario in the intra-day variable blazar S5 0716+71, III. Rapid and correlated flux density variability from radio to sub-mm bands
• Rapid interstellar scintillation of PKS B1257-326: two-station pattern time delays and constraints on scattering and microarcsecond source structure
• Milky Way scattering properties and intrinsic sizes of active galactic nuclei cores probed by very long baseline interferometry surveys of compact extragalactic radio sources
• Intra-Day Variability and the Interstellar Medium Towards 0917+624
• The connection between the radio jet and the gamma-ray emission in the radio galaxy 3C 120
• Interstellar Scintillation Observations of 146 Extragalactic Radio Sources
• Extreme Brightness Temperatures and Refractive Substructure in 3C273 with RadioAstron
• Extreme radio-wave scattering associated with hot stars
• Acceleration of Compact Radio Jets on Sub-parsec Scales
• The connection between the parsec-scale radio jet and gamma-ray flares in the blazar 1156+295
• Two-year monitoring of intra-day variability of quasar 1156+295 at 4.8 GHz
• Intra-day variability observations and the VLBI structure analysis of quasar S4 0917+624
• Interstellar scintillation as a probe of microarcsecond scale structure in quasars
• The Role of Millimeter VLBI Observations in AGN Research

Cited by in corpus (8)

• Detection statistics of the RadioAstron AGN survey
• The relationship between the radio core-dominance parameter and spectral index in different classes of extragalactic radio sources (III)
• Localizing the $\gamma$-ray emitting region in the blazar TXS 2013+370
• Probing the innermost regions of AGN jets and their magnetic fields with RadioAstron IV. The quasar 3C 345 at 18 cm: Magnetic field structure and brightness temperature
• Optical and Radio Variability of the Blazar S4 0954+658
• Lunar Orbital VLBI Experiment: motivation, scientific purposes and status
• Intra-Day Variability Observations of Two Dozens of Blazars at 4.8 GHz
• Interstellar Scintillation Monitoring of the RadioAstron Blazars