Lobster-eye Telescope Research Articles

Target Detection Framework for Lobster Eye X-Ray Telescopes with Machine-learning Algorithms

Lobster eye telescopes are ideal monitors to detect X-ray transients because they could observe celestial objects over a wide field of view in the X-ray band. However, images obtained by lobster eye telescopes are modified by their unique point-spread functions, making it hard to design a high-efficiency target detection algorithm. In this paper, we integrate several machine-learning algorithms to build a target detection framework for data obtained by lobster eye telescopes. Our framework would first generate two 2D images with different pixel scales according to positions of photons on the detector. Then, an algorithm based on morphological operations and two neural networks would be used to detect candidates of celestial objects with different flux from these 2D images. Finally, a random forest algorithm will be used to pick up final detection results from candidates obtained by previous steps. Tested with simulated data of the Wide-field X-ray Telescope on board the Einstein Probe, our detection framework could achieve over 94% purity and over 90% completeness for targets with flux more than 3 mcrab (9.6 × 10−11 erg cm−2 s−1) and more than 94% purity and moderate completeness for targets with lower flux at acceptable time cost. The framework proposed in this paper could be used as references for data processing methods developed for other lobster eye X-ray telescopes.

Detection system of the lobster eye telescope with large field of view.

The lobster eye telescope is promising for large-field x ray imaging in astronomy. The special structure of the lobster eye system makes the focal plane a sphere, resulting in detector defocus when the field is large. In this study, we established a model based on the principle of lobster eye imaging and simulated the imaging at different image distances. The results reveal the relationship between the defocus and position accuracy and angular resolution. To ensure the optical performance of the large field lobster eye telescope, we propose a detection system design method using multiple detectors stitched together to form a spherical-like surface and apply it to the development of the Einstein Probe/wide-field x ray telescope (EP/WXT) submodule. About 70% of the detection area is out of focus within 0.5 mm. The scanning image of the integrated WXT submodule shows good uniformity of the point spread function (PSF) for various incident angles, and the effect of defocus on imaging is acceptable.

Perspectives of the LOBSTER-EYE monitor in the soft X-ray observing the Galactic center region

We show the lobster-eye (LE) monitor's perspectives and observing plan based on a small LE telescope on a small (CubeSat-like) satellite platform. This instrument is important because it is able to provide wide-field X-ray imaging. We present the possibilities of monitoring the Galactic center region in the soft X-ray energy band. The reason is that many X-ray binaries, especially those with a low-mass lobe-filling secondary and mostly the neutron star accretor, concentrate in the bulge surrounding the center of our Galaxy. Several such binaries are expected to be present in our monitor's field of view (a square of about 5×5degrees). We show the long-term activity of the examples of X-ray binaries located in this region. We present the typical features of such objects' long-term X-ray activity (e.g., outbursts and state transitions) and discuss how the lobster-eye monitor can contribute. Observing in the soft X-ray band is the most promising because their X-ray intensity is the highest in this band.

Geant4 simulations of a wide-angle x-ray focusing telescope

The rapid development of X-ray astronomy has been made possible by widely deploying X-ray focusing telescopes on board many X-ray satellites. Geant4 is a very powerful toolkit for Monte Carlo simulations and has remarkable abilities to model complex geometrical configurations. However, the library of physical processes available in Geant4 lacks a description of the reflection of X-ray photons at a grazing incident angle which is the core physical process in the simulation of X-ray focusing telescopes. The scattering of low-energy charged particles from the mirror surfaces is another noteworthy process which is not yet incorporated into Geant4. Here we describe a Monte Carlo model of a simplified wide-angle X-ray focusing telescope adopting lobster-eye optics and a silicon detector using the Geant4 toolkit. With this model, we simulate the X-ray tracing, proton scattering and background detection. We find that: (1) the effective area obtained using Geant4 is in agreement with that obtained using Q software with an average difference of less than 3\%; (2) X-rays are the dominant background source below 10 keV; (3) the sensitivity of the telescope is better by at least one order of magnitude than that of a coded mask telescope with the same physical dimensions; (4) the number of protons passing through the optics and reaching the detector by Firsov scattering is about 2.5 times that of multiple scattering for the lobster-eye telescope.

Optics for Nano-Satellite X-Ray Monitor

Abstract The Schmidt lobster eye design for a grazing incidence X-ray optics provides a field of view of the order of many degrees, for this reason it can be a convenient approach for the construction of space X-ray monitors. It is possible to assemble Schmidt lobster eye telescopes with the dimensions and focal lengths acceptable for nano-class satellites. In this paper, a draft of nano-class space mission providing monitoring of specific sky areas is presented. A preliminary optical design study for such mission is performed. Two of possible optical designs are presented, for which the field of view, the effective input area and other basic optical parameters are calculated. Examples of the observed images are also presented.

Comparison of focal properties of square-channel and meridional lobster-eye lenses.

The lobster-eye telescope with square cross-section channels has been suggested as a possible candidate for a wide-field-of-view x-ray all-sky monitor. However, due to the difficult construction, especially with metals, variations of lobster-eye lenses have been proposed as possible alternatives. This work is a computational comparison of the focal properties of one variant, the meridional lens, with the square-channel lens. For both types of lens, the efficiency of focusing for imaged photons as well as the point-spread function in one dimension is studied for collimated sources.

Detailed simulation of a Lobster-eye telescope

The concept of an x-ray telescope based on the optics of the eye of certain types of crustacea has been in currency for nearly thirty years. However, it is only in the last decade that the technology to make the telescope and the opportunity to mount it on a suitable space platform have combined to allow the idea to become a reality. Accordingly, we have undertaken a detailed simulation study, updating previous simplified models, to properly characterise the performance of the instrument in orbit. The study reveals details of how the particular characteristics of the lobster-eye optics affect the sensitivity of the instrument and allow us to implement new ideas in data extraction methods.

Sidewall slopes and roughness of SU-8 HARMST

In recent years we have investigated the feasibility of deep X-ray lithography in SU-8 as a means of fabricating very high aspect ratio and densely packed arrays of square channels. We have demonstrated how to overcome the problems in adhesion and stiction accompanying the fabrication of such high aspect ratio structures. We have also examined how to calculate the development time of these structures and how this can be used to optimize the dimensional fidelity of the resulting structures. More recently we have considered the effect of the non-uniform dose deposition and beam hardening as a function of depth in the resist on factors such as the surface roughness and the sidewall taper. In this paper we describe our experimental program, review these results and discuss their implications for the operation of our target device—the lobster-eye telescope.

Variable X–ray sky with Lobster Eye Telescopes

The variable X-ray sky requires wide–field monitoring with high sensitivity. We refer on novel X–ray telescopes with high sensitivity as well as large field of view. The results are very promising, allowing the proposals for space projects with very wide–field Lobster–eye X–ray optics to be considered. The novel telescopes will monitor the sky with unprecedented sensitivity and angular resolution of order of 1 arcmin. They are expected to contribute essentially to study and to understand various astrophysical objects such as AGN, SNe, GRBs, X–ray flashes, galactic binary sources, stars, CVs, X-ray novae, various transient sources, etc.

LIGA for lobster: First observation of lobster-eye focusing from lithographically produced optics

The prospect of making a lobster-eye telescope is drawing closer with recent developments in the manufacture of microchannel-plate optics. This would lead to an x-ray all-sky monitor with vastly improved sensitivity and resolution over existing and other planned instruments. We consider a new approach, using deep etch x-ray lithography, to making a lobster-eye lens that offers certain advantages even over microchannel-plate technology.

Deconvolution of an extended object viewed by a lobster-eye telescope

X-ray telescopes based on the lobster-eye principle offer considerable promise for an all-sky monitor mission. The extended cruciform point-spread function of the lobster-eye optic has typically not been a major issue as sources in the classical X-ray band (0.5–3.5 keV) at the sensitivities that will be observed are generally point-like and well separated. However, lobster-eye optics may also be used as the basis for an imaging spectrometer for near-earth objects. Such a mission requires that the effect of the lobster-eye point spread function be considered. This paper finds that deconvolution of the point-spread function is feasible at contrast levels as low as 10% for a reasonable orbital configuration and mission duration.

Lobster-eye all-sky monitors: A comparison of one- and two-dimensional designs

X-ray all-sky monitors (ASMs) have played a vital role in the development of x-ray astronomy. In order for them to continue to do so ASMs with high sensitivity, broad energy band coverage, and large sky coverage will be required. The best way to achieve these goals is for the next generation of ASMs to have focusing capability. Lobster-eye optics offer a way to construct a focusing ASM and a design is presented for a lobster-eye ASM that offers an order of magnitude increase in sensitivity over previous nonfocusing instruments. Simpler versions of the lobster-eye telescope, based on arrays of flat reflectors in one dimension only, have also been suggested in the past. In this article we compare the one- and two-dimensional (lobster-eye) configurations and conclude that, for intense short-lived phenomena, where the background is negligible, the one-dimensional configuration is optimal, whereas for ultimate sensitivity of background-limited faint sources the two-dimensional configuration is preferred.

A novel wide-field hard x-ray telescope

We discuss a hard x-ray telescope for the range 25–70 keV based on a one-dimensional lobster-eye telescope and x-ray supermirror coatings. This approach enables wide field-of-view imaging. A telescope suitable for a large balloon payload, with a 50×100 cm frontal area, could have an effective area of 50–100 cm2 and a 100×100 field of view, and thereby detect AGN that are 0.5 milliCrab in the soft x-rays in a 104 second exposure. 29% of the sky could be surveyed to this limit in a 2-week balloon flight, reaching 6 times fainter than the HEAO A-4 all-sky survey.