Controlling for the Ionospheric and Baseline-Offset Uncertainties in the CHIME/FRB Outriggers VLBI Network for Milliarcsecond Precision

Abstract

Fast radio bursts (FRBs) are a novel form of radio transients discovered in 2007. These bright, extragalactic radio signals have an inferred all-sky rate of hundreds of detections per day. The properties of FRBs hold valuable clues about the extreme physical processes driving them while also holding information about the astrophysical plasmas they traverse on their journey to Earth. The Canadian Hydrogen Intensity Mapping Experiment (CHIME)/FRB project has led the field with the hundreds of FRB detections the collaboration has published to date. However, these detections typically have localization regions so large that we cannot identify a single host galaxy, never mind its local environment. To improve upon this, CHIME/FRB has been transformed into a very long baseline interferometry (VLBI) array, drastically increasing the angular resolution of CHIME/FRB from arcminute to sub-arcsecond precision.

In this work, I present my contributions to commissioning the CHIME/FRB VLBI Outrigger station located at the Green Bank Observatory (GBO) in West Virginia. This includes measuring and validating GBO's exact position to enable the localization of FRBs to sub-arcsecond precision.

For VLBI networks spanning thousands of kilometers, the difference in the local ionospheric environments is significant and leads to errors in the CHIME/FRB Outrigger localizations. I present a thin shell model of the ionosphere to parameterize the local ionospheric environment for each VLBI station. This model may be used to interpolate the error induced by the ionosphere in FRB observations.