The Lobster Eye Imager for Astronomy (LEIA), a pathfinder of the Wide-field X-ray Telescope of the Einstein Probe mission, was successfully launched onboard the SATech-01 satellite of the Chinese Academy of Sciences on 2022 July 27. 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 of 346 square degrees (18.°6 × 18.°6) 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 size 6 cm × 6 cm, are used as the focal plane detectors. The instrument has an angular resolution of 4′–8′ (in terms of 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 soft X-rays and the sensitivity is 2–3 × 10⁻¹¹ erg s⁻¹ cm⁻² (about 1 milliCrab) with a 1000 s observation. The total weight of LEIA is 56 kg and the power is 85 W. The satellite, with a design lifetime of 2 yr, 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 with limited useful observing time available.

We report on results of the on-ground X-ray calibration of the Wide-field X-ray Telescope (WXT), built from novel lobster-eye micro-pore optics, on board the Einstein Probe (EP) satellite. To fully characterize the performance and properties of the WXT instrument, a series of tests and calibrations were conducted at different levels of devices, assemblies and the complete module before the launch of EP. In this paper, we present the calibration results of three flight model modules (FM1, FM5 and FM11) obtained during their end-to-end module calibration experiments carried out at the 100-m X-ray Test Facility (100XF) of the Institute of High Energy Physics (IHEP), Chinese Academy of Sciences (CAS). Measurements of the Point Spread Function (PSF), effective area, and energy response were performed for multiple incident directions and several characteristic X-ray emission line energies. Specifically, the distributions of the PSF and effective areas are found to be roughly uniform across the FoV, in large agreement with the prediction of lobster-eye optics. Their energy-dependent behavior aligns well with theoretical predictions and Monte Carlo simulations. At \(\sim 1.25\) keV, the full width at half maximum (FWHM) of the focal spot ranges from \(3-7\) arcmin (with a median of \(\sim 4.2\) arcmin) and the effective area is in range of \(\sim 2-3~\mathrm{cm^2}\). Noticeably, the flight model instruments demonstrate a \(\sim 1.5\) arcmin improvement in spatial resolution over the previously launched Lobster Eye Imager for Astronomy. The properties of the complementary metal-oxide semiconductor (CMOS) sensors were also calibrated. The gain coefficients are in range of \(6.4-6.9~\mathrm{eV/DN}\). The energy resolutions are in range of \(\sim 120\) to 140 eV at 1.25 keV, meeting design requirements. These calibration results have been ingested into the first version of calibration database (CALDB) and applied to the analysis of the scientific data acquired by WXT after the launch of EP.

In recent years, scientific CMOS (sCMOS) sensors have been widely used for imaging and spectroscopy in the optical and soft X-ray bands. A sCMOS camera has been developed, along with its auxiliary algorithms, for soft X-ray imaging spectroscopy, which is equipped with a Gsense400BSI chip operating at a frame rate up to 48 Hz. In this paper, we report the finding of a new crosstalk phenomenon in X-ray imaging data taken with the sCMOS sensor exposed to an Fe55 X-ray source. A simple correlogram method for the diagnostics of the crosstalk is introduced. Experiments are carried out for various set-ups and operating conditions of the sCMOS sensor. It is found that the crosstalk occurs in about 2.0% of the X-ray events registered, and there is no dependence of the crosstalk on the voltage configurations, temperature or entrance window of the chip. The cause of the crosstalk has been identified to be an imperfect isolation of the readout nodes inherent in the design. It is demoustrated that the true X-ray spectrum can be restored after careful correction for this effect, which should be taken into account for applications of accurate X-ray spectroscopy using the Gsense400BSI sCMOS sensor.