The Fundamental Performance of FAST with 19-beam Receiver at L Band
  The Five-hundred-meter Aperture Spherical radio Telescope (FAST) passed
national acceptance and is taking pilot cycle of 'Shared-Risk' observations.
The 19-beam receiver covering 1.05-1.45 GHz was used for most of these
observations. The electronics gain fluctuation of the system is better than 1\%
over 3.5 hours, enabling enough stability for observations. Pointing accuracy,
aperture efficiency and system temperature are three key parameters of FAST.
The measured standard deviation of pointing accuracy is 7.9$''$, which
satisfies the initial design of FAST. When zenith angle is less than
26.4$^\circ$, the aperture efficiency and system temperature around 1.4 GHz are
$\sim$ 0.63 and less than 24 K for central beam, respectively. The measured
value of these two parameters are better than designed value of 0.6 and 25 K,
respectively. The sensitivity and stability of the 19-beam backend are
confirmed to satisfy expectation by spectral HI observations toward N672 and
polarization observations toward 3C286. The performance allows FAST to take
sensitive observations in various scientific goals, from studies of pulsar to
galaxy evolution.
