VLBI properties of compact interplanetary scintillators detected by the Murchison Widefield Array

Abstract

Interplanetary scintillation (IPS) provides an approach for identifying the presence of sub-arcsec structures in radio sources, and very long baseline interferometry (VLBI) technique can help verify whether the IPS sources have fine structures on milli-arcsec (mas) scales. We searched the available VLBI archive for the 244 IPS sources detected by the Murchison Widefield Array at 162~MHz and found 63 cross-matches. We analysed the VLBI data of the 63 sources and characterised the compactness index in terms of the ratio $R$ of the VLBI-measured flux density at 4.3~GHz to the flux density estimated using the Very Large Array Sky Survey (VLASS) at 3~GHz and NRAO VLA Sky Survey (NVSS) at 1.4~GHz ($S_{\mathrm{VLBI}}/S_{\mathrm{SA}}$). Eleven sources are identified as blazars according to their flat spectra and strong variability. They show high compactness indices with $R>0.4$, compact core-jet structure, and a broad distribution of normalised scintillation index (NSI). Other sources show diverse morphologies (compact core, core and one-sided jet, core and two-sided jets), but there is a correlation between $R$ and NSI with a correlation coefficient $r=0.47$. A similar $R$--NSI correlation is found in sources showing single steep power-law or convex spectra. After excluding blazars (which are already known to be compact sources) from the VLBI-detected IPS sources, a strong correlation is found between the compactness and scintillation index of the remaining samples, indicating that stronger scintillating sources are more compact. This pilot study shows that IPS offers a convenient method to identify compact radio sources without the need to invoke high-resolution imaging observations, which often require significant observational time.

28 pages, 7 figures, 4 tables, Accepted for publication in MNRAS

References in corpus (11)

• Roma-BZCAT: A multifrequency catalogue of Blazars
• Fast outflows in compact radio sources: evidence for AGN-induced feedback in the early stages of radio source evolution
• The Dynamic Evolution of Young Extragalactic Radio Sources
• Extragalactic Peaked-Spectrum Radio Sources at Low Frequencies
• The Sixth VLBA Calibrator Survey: VCS6
• The Fifth VLBA Calibrator Survey: VCS5
• The Micro-Arcsecond Scintillation-Induced Variability (MASIV) Survey II: The First Four Epochs
• Interplanetary Scintillation studies with the Murchison Wide-field Array II: Properties of sub-arcsecond compact sources at low radio frequencies
• Interplanetary Scintillation with the Murchison Widefield Array I: A sub-arcsecond Survey over 900 square degrees at 79 and 158 MHz
• Spectral Variability of Radio Sources at Low Frequencies
• The MASIV Survey IV: relationship between intra-day scintillation and intrinsic variability of radio AGNs

Cited by in corpus (1)

• Wide-Band Spectral Variability of Peaked Spectrum Sources