A New Method for Identifying Contaminating Sources and Locating Target Sources through the Cross-Arm Features of Micro Pore Optics

Abstract

The Pathfinder of the Type-A satellites in the Chasing All Transients Constellation Hunters (CATCH) space mission is equipped with Micro-Pore Optics (MPOs) and four single-pixel Silicon Drift Detectors (SDDs). Due to the lack of position resolution in an individual SDD, we propose a new method based on the cross-arms in the point spread function (PSF) of MPOs to enhance the satellite's capability in identifying contaminating sources and locating target sources. By placing one detector on each of the horizontal and vertical cross-arms on the focal plane, we can use the changes in the relative counts on the cross-arms detectors to deduce the location of the source. Simulated observations demonstrate that, for a target source with a flux of 1 Crab and an exposure time of 200 s, the cross-arms detectors can identify contaminating source with the same flux level at an off-axis angle larger than 8', and improve positioning accuracy to 6'. Furthermore, we extend the simulation study to CATCH Type-A, which plans to use an SDD array. In situations where sources exhibit the same flux of 1 Crab and the exposure time is merely 1 s, a 16x16 SDD array is capable of identifying contaminating source with an off-axis angle greater than 2.4' and can achieve a positioning precision of 1.8'.

Figures (23)

• Figure 1: Panel (a): Configuration of the Pathfinder of CATCH Type-A. Panel (b): Partial enlarged view of the MPOs. Panel (c): Enlarged view of the detector system.
• Figure 2: Simulated PSF of the MPOs used in the Pathfinder of CATCH Type-A. It comprises a focused spot, horizontal and vertical cross-arms, and some diffuse patches. These arise from different photon reflection numbers: two reflections form the focal spot, an odd number creates the arms, and zero or an even number yields the diffuse patches. The color bar on the right represents the normalized counts. The gaps at $\pm$45 mm are caused by the shadow of the supporting frame.
• Figure 3: Distribution of angular distances to the $N$-th nearest neighbors ($N=1$--$5$). Different colors indicate different neighbor orders, and the red dashed line denotes the FOV.
• Figure 4: Projection of the source PSF onto the detector system plane in the initial layout.
• Figure 5: Schematic diagram of the relative position relationship between the observed source and the MPOs. In this diagram, the MPOs is approximated as a plane. The plane where the MPOs is located represents the X-Y plane, and the direction perpendicular to the MPOs is the Z-direction.