The Tianlai Cylinder Pathfinder is a radio interferometer array designed to test techniques for 21 cm intensity mapping in the post-reionization Universe, with the ultimate aim of mapping the large scale structure and measuring cosmological parameters such as the dark energy equation of state. Each of its three parallel cylinder reflectors is oriented in the north-south direction, and the array has a large field of view. As the Earth rotates, the northern sky is observed by drift scanning. The array is located in Hongliuxia, a radio-quiet site in Xinjiang, and saw its first light in September 2016. In this first data analysis paper for the Tianlai cylinder array, we discuss the subsystem qualification tests, and present basic system performance obtained from preliminary analysis of the commissioning observations during 2016-2018. We show typical interferometric visibility data, from which we derive the actual beam profile in the east-west direction and the frequency band-pass response. We describe also the calibration process to determine the complex gains for the array elements, either using bright astronomical point sources, or an artificial on site calibrator source, and discuss the instrument response stability, crucial for transit interferometry. Based on this analysis, we find a system temperature of about 90 K, and we also estimate the sensitivity of the array.

Combining the latest Planck, Wilkinson Microwave Anisotropy Probe (WMAP), and baryon acoustic oscillation (BAO) data, we exploit the recent cosmic microwave background (CMB) B-mode power spectra data released by the BICEP2 collaboration to constrain the cosmological parameters of the ΛCDM model, esp. the primordial power spectra parameters of the scalar and the tensor modes, ns, αs, r, nt. We obtained constraints on the parameters for a lensed ΛCDM model using the Markov Chain Monte Carlo (MCMC) technique, the marginalized 68% bounds are r = 0.1043± 0.0307 0.0914 , ns = 0.9617± 0.0061 0.0061 , αs = −0.0175± 0.0105 0.0097 , nt = 0.5198 ± 0.4515 0.4579 . We found that a blue tilt for nt is favored slightly, but it is still well consistent with flat or even red tilt. Our r value is slightly smaller than the one obtained by the BICEP team, as we allow nt as a free parameter without imposing the single-field slow roll inflation consistency relation. If we impose this relation, r = 0.2130± 0.0446 0.0609 . For most other parameters, the best fit values and measurement errors are not altered much by the introduction of the BICEP2 data.