VLBA > Amplitude Calibration

# Amplitude Calibration

Traditional calibration of VLBI fringe amplitudes for continuum sources requires knowing the on-source system noise in Jy (SEFD; Moran & Dhawan 1995).  System temperatures in Kelvin ($T_{\rm sys}$) are measured continuously during observations at VLBA stations, with mean values tabulated at least once per source/frequency combination or once every user-specified interval (default 2 minutes), whichever is shorter.  These $T_{\rm sys}$ values are used in fringe amplitude calibration by AIPS task APCAL, which converts $T_{\rm sys}$ to SEFD by dividing by the VLBA antenna gains in $\rm K\: Jy^{-1}$, expressed as a peak gain multiplied by a normalized "gain curve".  The latter data are based on regular monitoring of all receiver and feed combinations.  $T_{\rm sys}$ and gain values for VLBA antennas are delivered in TY and GC tables, respectively.  Single-station spectra can be used for amplitude calibration of spectral line observations.