Amplitude Correction Factors of Korean Vlbi Network Observations

Abstract

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 find 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.

INTERFEROMETRIC MONITORING OF GAMMA-RAY BRIGHT AGNs. I. THE RESULTS OF SINGLE-EPOCH MULTIFREQUENCY OBSERVATIONS

“…Thanks to the good quality of the system temperatures, antenna gains, and atmospheric opacity for KVN stations, we expect the uncertainty of the amplitude calibration to be within 10%-30% at the 22-129 GHz bands. Renormalization of the fringe amplitudes was made to correct for the amplitude distortion due to quantization, and the quantization and re-quantization losses were corrected (Lee et al 2015a). …”

Spatially Resolved HCN Absorption Features in the Circumnuclear Region of NGC 1052

“…The correlation was processed at the Korea-Japan Correlation Center (Yeom et al 2009;Lee et al 2015a). We corrected the visibility amplitude decrement due to the digital quantization loss and the characteristics of the KJCC, using the method of Lee et al (2015b).…”

The intrinsic structure of Sagittarius A* at 1.3 cm and 7 mm

“…The data were calibrated using NRAO Astronomical Imaging Processing System (AIPS; Greisen 2003). The cross-power spectra were first normalized using the autocorrelation power spectra (ACCOR in AIPS), and a multiplicative correction factor of 1.3 was applied to all data to correct the quantization loss in the Daejeon hardware correlator (Lee et al 2015). For the amplitude calibration, we used the system temperature and antenna gain curve information (a-priori calibration method; APCAL in AIPS) for 1.3 cm data.…”