Amplitude Correction Factors of KVN Observations

TL;DR

This study investigates amplitude calibration for KVN VLBI observations by comparing them with VLBA data, revealing correction factors needed due to quantization and correlator differences.

Contribution

It provides the first estimation of amplitude correction factors for KVN observations correlated with Daejeon and DiFX correlators, improving calibration accuracy.

Findings

KVN amplitudes need correction factors of 1.10 and 1.35 for DiFX and Daejeon correlators.

Corrections are due to 2-bit quantization and correlator characteristics.

Results enhance calibration precision for KVN VLBI data.

Abstract

We report results of investigation of amplitude calibration for very long baseline interferometry (VLBI) observations with Korean VLBI Network (KVN). Amplitude correction factors are estimated based on comparison of KVN observations at 22~GHz correlated by Daejeon hardware correlator and DiFX software correlator in Korea Astronomy and Space Science Institute (KASI) with Very Long Baseline Array (VLBA) observations at 22~GHz by DiFX software correlator in National Radio Astronomy Observatory (NRAO). We used the observations for compact radio sources, 3C 454.3, NRAO 512, OJ 287, BL Lac, 3C 279, 1633+382, and 1510-089, which are almost unresolved for baselines in a range of 350-477 km. Visibility data of the sources obtained with similar baselines at KVN and VLBA are selected, fringe-fitted, calibrated, and compared for their amplitudes. We found that visibility amplitudes of KVN observations should be corrected by factors of 1.10 and 1.35 when correlated by DiFX and Daejeon correlators, respectively. These correction factors are attributed to the combination of two steps of 2-bit quantization in KVN observing systems and characteristics of Daejeon correlator.