China’s Einstein Probe (EP) mission is designed for time-domain astrophysics with energy band of 0.5-4 keV. The payloads of EP include a wide-field X-ray telescope (WXT) and a follow-up X-ray telescope (FXT). The field of view (FOV) of WXT is about 3600 square degrees with sensitivity at least 10 times better than traditional X-ray all-sky monitors applying collimators or coded-masks. Back-side illuminated scientific CMOS (BSI sCMOS) is the best choice for WXT after several types of X-ray detectors are investigated. In this work, we study a BSI sCMOS sensor, GSENSE400BSI developed by Gpixel Inc., which is treated as a pathfinder for the focal plane detector of WXT. GSENSE400BSI has a pixel array of 2048×2048 with pixel size of 11 μm. We have characterized this BSI sCMOS as an X-ray detector. Based on the excellent performance of GSENSE400BSI, a new BSI sCMOS device with large sensitive area of 6×6 cm2 has been proposed as the focal plane detector for WXT.
The Einstein Probe (EP) is a small satellite dedicated to time-domain astronomy to monitor the sky in the soft X-ray band. It is a mission led by the Chinese Academy of Sciences and developed in its space science programme with international collaboration. Its wide-field imaging capability is achieved by using established technology of the micro-pore lobster-eye X-ray focusing optics. Complementary to this is deep X-ray follow-up capability enabled by a Wolter-I type X-ray telescope. EP is also capable of fast transient alerts triggering and downlink, aiming at multi-wavelength follow-up observations by the world-wide community. EP will enable systematic survey and characterisation of high-energy transients at unprecedented sensitivity, spatial resolution, grasp and monitoring cadence. Its scientific goals are mainly concerned with discovering new or rare types of transients, including tidal disruption events, supernova shock breakouts, high-redshift GRBs, and of particular interest, electromagnetic sources of gravitational wave events.
The X-ray imaging with Micro-Pore Optic (MPO) plates can provide huge field of view with light mass, which will be applied for the Wide-field X-ray telescope (WXT), one of the two payloads onboard China’s Einstein Probe (EP) mission. Since each MPO plate has millions of micro square pores with width of 20 μm which actually behave as honeycomb materials, the mechanical properties of the MPO plates will be much more complex than normal optical glass as homogeneous material. This work estimated the mechanical properties of MPO plates, provided an equivalent mechanical properties as homogeneous material to greatly simplify the Finite-Element Analysis (FEA). Three basic material properties of MPO plates - relative density, effective elastic stiffness (Young’s module) and the effective Poisson’s ratio are estimated and preliminary validated with FEA simulations.
The Einstein Probe mission that will be launched in 2022, is dedicated to time-domain high-energy astrophysics. Its primary goals are to discover high-energy transients and to monitor variable objects in 0.5-4 keV energy band. To realize these objectives, EP is equipped with a Wide-filed X-ray Telescope (WXT) which applies the micro-pore optics (MPO). Background is critical for a space X-ray instrument, since it is related to sensitivity and observation data quality. In this work, we study the background components of WXT induced by cosmic X rays, soft X rays from the Galaxy based on ray tracing program. We also investigate the background due to energetic cosmic rays, the count rate of which varies with the thickness of detector sensitive layer. Furthermore, we simulate the contribution of low-energy electrons to the background of WXT, which would degrade the sensitivity notably without electron diverters. The electron diverters for WXT are under development based on simulations.
eXTP is a science mission designed to study the state of matter under extreme conditions of density, gravity and magnetism. Primary goals are the determination of the equation of state of matter at supra-nuclear density, the measurement of QED effects in highly magnetized star, and the study of accretion in the strong-field regime of gravity. Primary targets include isolated and binary neutron stars, strong magnetic field systems like magnetars, and stellar-mass and supermassive black holes. The mission carries a unique and unprecedented suite of state-of-the-art scientific instruments enabling for the first time ever the simultaneous spectral-timing-polarimetry studies of cosmic sources in the energy range from 0.5-30 keV (and beyond). Key elements of the payload are: the Spectroscopic Focusing Array (SFA) - a set of 11 X-ray optics for a total effective area of ∼0.9 m2 and 0.6 m2 at 2 keV and 6 keV respectively, equipped with Silicon Drift Detectors offering <180 eV spectral resolution; the Large Area Detector (LAD) - a deployable set of 640 Silicon Drift Detectors, for a total effective area of ∼3.4 m2, between 6 and 10 keV, and spectral resolution better than 250 eV; the Polarimetry Focusing Array (PFA) – a set of 2 X-ray telescope, for a total effective area of 250 cm2 at 2 keV, equipped with imaging gas pixel photoelectric polarimeters; the Wide Field Monitor (WFM) - a set of 3 coded mask wide field units, equipped with position-sensitive Silicon Drift Detectors, each covering a 90 degrees x 90 degrees field of view. The eXTP international consortium includes major institutions of the Chinese Academy of Sciences and Universities in China, as well as major institutions in several European countries and the United States. The predecessor of eXTP, the XTP mission concept, has been selected and funded as one of the so-called background missions in the Strategic Priority Space Science Program of the Chinese Academy of Sciences since 2011. The strong European participation has significantly enhanced the scientific capabilities of eXTP. The planned launch date of the mission is earlier than 2025.
The Large Observatory For x-ray Timing (LOFT) is a mission concept which was proposed to ESA as M3 and M4 candidate in the framework of the Cosmic Vision 2015-2025 program. Thanks to the unprecedented combination of effective area and spectral resolution of its main instrument and the uniquely large field of view of its wide field monitor, LOFT will be able to study the behaviour of matter in extreme conditions such as the strong gravitational field in the innermost regions close to black holes and neutron stars and the supra-nuclear densities in the interiors of neutron stars. The science payload is based on a Large Area Detector (LAD, >8m2 effective area, 2-30 keV, 240 eV spectral resolution, 1 degree collimated field of view) and a Wide Field Monitor (WFM, 2-50 keV, 4 steradian field of view, 1 arcmin source location accuracy, 300 eV spectral resolution). The WFM is equipped with an on-board system for bright events (e.g., GRB) localization. The trigger time and position of these events are broadcast to the ground within 30 s from discovery. In this paper we present the current technical and programmatic status of the mission.
Einstein Probe (EP) is a proposed small scientific satellite dedicated to time-domain astrophysics working in the soft X-ray band. It will discover transients and monitor variable objects in 0.5-4 keV, for which it will employ a very large instantaneous field-of-view (60° × 60°), along with moderate spatial resolution (FWHM ∼ 5 arcmin). Its wide-field imaging capability will be achieved by using established technology in novel lobster-eye optics. In this paper, we present Monte-Carlo simulations for the focusing capabilities of EP’s Wide-field X-ray Telescope (WXT). The simulations are performed using Geant4 with an X-ray tracer which was developed by cosine (http://cosine.nl/) to trace X-rays. Our work is the first step toward building a comprehensive model with which the design of the X-ray optics and the ultimate sensitivity of the instrument can be optimized by simulating the X-ray tracing and radiation environment of the system, including the focal plane detector and the shielding at the same time.
Experimental demonstrations of the Super-High Angular Resolution Principle (SHARP) for coded aperture
imaging are presented. SHARP has been theoretically proven to be an extension of the coded aperture imaging
system by taking advantage of the significant diffraction-interference effects of pinholes on the mask, which
operates beyond the diffraction limit of a single pinhole. We first set up an optical experiment, the so-called
SHARP-O, in order to verify the theoretical predictions on SHARP. The images of point sources are successfully
reconstructed, with an angular resolution of about 26 arcsec and position accuracy of 2 arcsec, whereas the
diffraction limit of a single mask pinhole in the mask is 870 arcsec. We then set up a SHARP-X demonstration
experiment at an X-ray beam line facility; encouraging results are obtained, indicating that the SHARP concept
is feasible in the soft X-ray band. It is thus possible to achieve sub-arcsec X-ray imaging with a simple coded
mask system working beyond the diffraction limit of a single pinhole.