Interstellar Scintillation Monitoring of the RadioAstron Blazars

TL;DR

This paper discusses a monitoring program of RadioAstron AGN targets to understand how interstellar scintillation affects brightness temperature measurements in space VLBI observations.

Contribution

It introduces a dedicated ISS monitoring program for RadioAstron AGN targets and analyzes its impact on brightness temperature measurements.

Findings

ISS influences observed flux densities of AGN targets.

Monitoring helps distinguish intrinsic source variability from ISS effects.

Case study of B0529+483 illustrates ISS impact on measurements.

Abstract

The RadioAstron space radio telescope provides a unique opportunity to study the extreme brightness temperatures ($\mathrm{T_B }$) in AGNs with unprecedented long baselines of up to 28 Earth diameters. Since interstellar scintillation (ISS) may affect the visibilities observed with space VLBI (sVLBI), a complementary ground based flux density monitoring of the RadioAstron targets, which is performed near in time to the VLBI observation, could be beneficial. The combination/comparison with the sVLBI data can help to unravel the relative influence of source intrinsic and ISS induced effects, which in the end may alter the conclusions on the $\mathrm{T_B }$ measurements from sVLBI. Since 2013, a dedicated monitoring program has been ongoing to observe the ISS of RadioAstron AGN targets with a number of radio telescopes. Here we briefly introduce the program and present results from the statistical analysis of the Effelsberg monitoring data. We discuss the possible effects of ISS on $\mathrm{T_B }$ measurements for the RadioAstron target B0529+483 as a case study.