  The Lobster Eye Imager for Astronomy (LEIA), a pathfinder of the Wide-field
X-ray Telescope of the Einstein Probe (EP) mission, was successfully launched
onboard the SATech-01 satellite of the Chinese Academy of Sciences on 27 July
2022. In this paper, we introduce the design and on-ground test results of the
LEIA instrument. Using state-of-the-art Micro-Pore Optics (MPO), a wide
field-of-view (FoV) of 346 square degrees (18.6 degrees * 18.6 degrees) of the
X-ray imager is realized. An optical assembly composed of 36 MPO chips is used
to focus incident X-ray photons, and four large-format complementary
metal-oxide semiconductor (CMOS) sensors, each of 6 cm * 6 cm, are used as the
focal plane detectors. The instrument has an angular resolution of 4 - 8 arcmin
(in FWHM) for the central focal spot of the point spread function, and an
effective area of 2 - 3 cm2 at 1 keV in essentially all the directions within
the field of view. The detection passband is 0.5 - 4 keV in the soft X-rays and
the sensitivity is 2 - 3 * 10-11 erg s-1 cm-2 (about 1 mini-Crab) at 1,000
second observation. The total weight of LEIA is 56 kg and the power is 85 W.
The satellite, with a design lifetime of 2 years, operates in a Sun-synchronous
orbit of 500 km with an orbital period of 95 minutes. LEIA is paving the way
for future missions by verifying in flight the technologies of both novel
focusing imaging optics and CMOS sensors for X-ray observation, and by
optimizing the working setups of the instrumental parameters. In addition, LEIA
is able to carry out scientific observations to find new transients and to
monitor known sources in the soft X-ray band, albeit limited useful observing
time available.
