C-BASS

Abstract:

In a companion Letter, Jones et al. report the discovery of a cosmic microwave background decrement, indicative of a distant cluster with mass ∼1015 M⊙, toward the quasar pair PC 1643+4631A, B (z = 3.79, 3.83, separation 1980). To search for the cluster responsible, we have obtained R-, J-, and K-band images of the field and have also carried out optical spectroscopy of selected objects in it. No such cluster is evident in these images. Assuming that the cluster causing the decrement is similar to massive clusters already known, our magnitude limits imply that it must lie at about or beyond z = 1. This provides independent support for the X-ray-based distance argument of Jones et al. The cluster must gravitationally lens objects behind it; for a cluster z around 1-2, the Einstein ring radius for sources at z ≈ 3.8 is ∼100″. Simple modeling, producing simultaneously the Sunyaev-Zeldovich effect and the lensing, shows that the source positions of quasars A and B lie within 1100 of each other and may indeed be coincident. The two quasar spectra are found to be remarkably similar apart from their 1% redshift difference. Assuming that A and B are images of a single quasar, we present a possible explanation of this difference.

Abstract:

RF system-on-chip (RFSoC) devices provide the potential for implementing a complete radio astronomy receiver on a single board, but performance of the integrated analogue-to-digital converters is critical. We have evaluated the performance of the data converters in the Xilinx ZU28DR RFSoC, which are 12-bit, 8-fold interleaved converters with a maximum sample speed of 4.096 Giga-sample per second (GSPS). We measured the spurious-free dynamic range (SFDR), signal-to-noise and distortion (SINAD), effective number of bits (ENOB), intermodulation distortion (IMD) and cross-talk between adjacent channels over the bandwidth of 2.048 GHz. We both captured data for off-line analysis with floating-point arithmetic, and implemented a real-time integer arithmetic spectrometer on the RFSoC. The performance of the ADCs is sufficient for radio astronomy applications and close to the vendor specifications in most of the scenarios. We have carried out spectral integrations of up to 100 s and stability tests over tens of hours and find thermal noise-limited performance over these timescales.