A VLBI receiving system for the South Pole Telescope

Abstract

We have developed a 230 and 345 GHz very-longbaseline interferometry (VLBI) receiver for the South Pole Telescope (SPT). With the receiver installed, the SPT has joined the global Event Horizon Telescope (EHT) array. The receiver optics select the 230 or 345 GHz mixers by rotating the tertiary mirror around the optical axis, directing the chief ray from the secondary mirror to the feed horn of the selected frequency band. The tertiary is installed on top of the receiver cryostat, which contains both mixer assemblies. The feed horns are placed symmetrically across the centerline of the telescope optics and tilted inward by 5.7 degrees from the vertical plane so that their beams intersect at the chief ray intersection on the tertiary mirror. We have performed vector beam measurements of the SPT VLBI receiver in both frequency bands. The measurements preserved the relative location of the beams, to establish the relative locations of the phase centers of the two horns. Measurements in two parallel reference planes above the cryostat were used to suppress reflected light. To model the beam, we derive a general expression of the electric field vector on the measurement plane for a tilted beam and infer the feed horn position parameters for both frequency bands by fitting models to data with a Markov chain Monte Carlo (MCMC) method. The inferred parameters such as the tilt angle of the feed horn are in good agreement with the design. We present the measurement setup, amplitude and phase pattern of the beam, and the fitting result here.We now have the normalized electric field distribution for the tilted beam on the scanning plane

First M87 Event Horizon Telescope Results. I. The Shadow of the Supermassive Black Hole

“…Development and deployment of broadband VLBI systems (Whitney et al 2013;Vertatschitsch et al 2015) led to data recording rates that now exceed those of typical cm-VLBI arrays by more than an order of magnitude. Parallel efforts to support infrastructure upgrades at additional VLBI sites, including the Atacama Large Millimeter/submillimeter Array (ALMA; Matthews et al 2018;Goddi et al 2019) and the Atacama Pathfinder Experiment telescope (APEX) in Chile (Wagner et al 2015), the Large Millimeter Telescope Alfonso Serrano (LMT) in Mexico (Ortiz-León et al 2016), the IRAM 30 m telescope on Pico Veleta (PV) in Spain (Greve et al 1995), the Submillimeter Telescope Observatory in Arizona (SMT; Baars et al 1999), the James Clerk Maxwell Telescope (JCMT) and the Submillimeter Array (SMA) in Hawai'i (Doeleman et al 2008;Primiani et al 2016;Young et al 2016), and the South Pole Telescope (SPT) in Antarctica (Kim et al 2018a), extended the range of EHT baselines and coverage, and the overall collecting area of the array. These developments increased the sensitivity of the EHT by a factor of ∼30 over early experiments that confirmed horizon-scale structures in M87 * and Sgr A * (Doeleman et al 2008(Doeleman et al , 2012Akiyama et al 2015;Johnson et al 2015;Fish et al 2016;Lu et al 2018).…”

First M87 Event Horizon Telescope Results. II. Array and Instrumentation

“…For the most part, the EHT consists of pre-existing telescopes that perform single-dish or connected-element astronomy observations during most of the year, but which required modifications or upgrades (in some cases significant ones) to carry out VLBI. The GLT, for example, was commissioned primarily to image M87 (Inoue et al 2014), and a heterodyne receiver for the SPT was built specifically for EHT observations (Kim et al 2018a). Details of how each site was modified for EHT work are given in the Appendix.…”

“…VLBI setup and testing is performed by a twoperson SPT winter-over team, with remote supervision from Arizona. EHT observing at the SPT employs a dual-frequency 230/345 GHz VLBI receiver (Kim et al 2018a), which was constructed at the University of Arizona. The receiver was first installed in late 2014 and first operated in 2015 January (Kim et al 2018b).…”

Event Horizon Telescope observations of the jet launching and collimation in Centaurus A

“…3). The observations were carried out by the Atacama Large Millimeter/submillimeter Array (ALMA), Atacama Pathfinder Experiment (APEX), James Clerk Maxwell Telescope (JCMT), Large Millimeter Telescope Alfonso Serrano (LMT), South Pole Telescope (SPT) 31 , Submillimeter Array (SMA) and Submillimeter Telescope (SMT) 32 . For ALMA, 37 of the 12 m dishes were phased-up 33 .…”