A comparative study of amplitude calibrations for East-Asia VLBI Network: a-priori and template spectrum methods

TL;DR

This study compares two amplitude calibration methods for the East-Asia VLBI Network at 22 and 43 GHz, demonstrating their consistency and potential for network sensitivity enhancement.

Contribution

It evaluates the a-priori and template spectrum calibration methods, showing their agreement and enabling inclusion of additional telescopes in EAVN.

Findings

Gain values from both methods are consistent within 10% at elevations above 10 degrees.

Total flux densities from different calibrations agree within 10%.

Template spectrum method allows more telescopes to participate, increasing sensitivity.

Abstract

We present the results of comparative study of amplitude calibrations for East-Asia VLBI Network (EAVN) at 22 and 43 GHz using two different methods of an "a-priori" and a "template spectrum", particularly on lower declination sources. Using observational data sets of early EAVN observations, we investigated the elevation-dependence of the gain values at seven stations of the KaVA (KVN and VERA Array) and three additional telescopes in Japan (Takahagi 32m, Yamaguchi 32m and Nobeyama 45m). By comparing the independently obtained gain values based on these two methods, we found that the gain values from each method were consistent within 10% at elevations higher than 10 degree. We also found that the total flux densities of two images produced from the different amplitude calibrations were in agreement within 10% at both 22 and 43 GHz. By using the template spectrum method, furthermore, the additional radio telescopes can participate in the KaVA (i.e. EAVN) so that it can give a notable sensitivity increase. Therefore, our results will constrain the detailed conditions to reliably measure the VLBI amplitude using EAVN and give a potential to extend possible telescopes comprising EAVN.