Radio interferometry data of microquasar GRS1915+105

We performed phase-referencing calibrations using the Astronomical Image Processing System (AIPS; E. W. Greisen 2003). A priori amplitude calibration was performed using antenna gain curves and system temperatures, with a scaling factor of 1.3 applied to account for amplitude losses in the Daejeon correlator (S.-S. Lee et al. 2015). However, the system temperature was not measured for the YM station.

Hence, we corrected its amplitude by adopting an a priori system equivalent flux density of 286 Jy at 6.7 GHz,12 using the task CLCOR.13 Bandpass calibration was derived from scans of bright fringe-finder sources.For phase calibration, we first read a “recalculation table” into the data, which contains an up-to-date geodynamical model, Earth orientation parameters, station coordinates, ionospheric delay, and tropospheric delay (e.g., T. Nagayama et al. 2020; N. Sakai et al. 2023).14 In particular, we note that the ionospheric delay cannot be well calibrated using the recalculation tables at the 6.7 GHz band.

We then applied corrections for the parallactic angle and instrumental delays. Following this, we carried out global fringe fitting exclusively on the calibrator J1925+1227 to derive residual delay, rate, and phase solutions. These solutions were interpolated to the scans of GRS 1915+105.

Finally, we obtained the phasereferenced images for GRS 1915+105 in DIFMAP (M. C. Shepherd 1997).