In-orbit Background and Sky Survey Simulation Study of POLAR-2/LPD

Abstract The Low-Energy X-ray Polarization Detector (LPD) is one of the payloads in the POLAR-2 experiment, designed as an external payload for the China Space Station deployment in early 2026. LPD is specifically designed to observe the polarization of gamma-ray burst (GRB) prompt emission in the e...

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Bibliographic Details
Published in:The Astrophysical journal 2024-01, Vol.960 (1), p.87
Main Authors: Feng, Zu-Ke, Liu, Hong-Bang, Xie, Fei, Feng, Huan-Bo, Mai, Qian-Nan, Tuo, Jiang-Chuan, Zhong, Qian, Sun, Jian-Chao, He, Jiang, Wang, Yuan-Hao, Liu, Qian, Yi, Di-Fan, Ma, Rui-Ting, Wang, Bin-Long, Tang, Zhen-Yu, Zhang, Shuang-Nan, Liang, En-Wei
Format: Article
Language:English
Subjects:
Algorithms
Astronomical instrumentation
Astrophysics
Charged particles
Cosmic x rays
Diffuse x-ray background
Energy bands
Gamma ray bursts
Gamma rays
Payloads
Photoelectricity
Polarimeters
Polarization
Preliminary designs
Sensors
Simulation
Sky surveys (astronomy)
Soft x rays
Space stations
Spacecraft components
X ray sources
X-ray astronomy
X-ray surveys
X-rays
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Summary:Abstract The Low-Energy X-ray Polarization Detector (LPD) is one of the payloads in the POLAR-2 experiment, designed as an external payload for the China Space Station deployment in early 2026. LPD is specifically designed to observe the polarization of gamma-ray burst (GRB) prompt emission in the energy range of 2–10 keV, with a wide field of view (FoV) of 90° in preliminary design. This observation is achieved using an array of X-ray photoelectric polarimeters based on gas pixel detectors. Due to the wide FoV configuration, the in-orbit background count rate in the soft X-ray range is high, while GRBs themselves also exhibit high flux in this energy band. In order to assess the contribution of various background components to the total count rate, we conducted detailed simulations using the GEANT4 C++ package. Our simulations encompassed the main interactions within the instrument materials and provided insights into various background components within the wide-FoV scheme. The simulation results reveal that among the background components, the primary contributors are the cosmic X-ray background (CXB) and bright X-ray sources. The total background count rate of LPD, after applying the charged particle background rejection algorithm, is approximately 0.55 counts cm –2 s –1 on average, and it varies with the detector’s orbit and pointing direction. Furthermore, we performed comprehensive simulations and comparative analyses of the CXB and X-ray bright sources under different FoVs and detector pointings. These analyses provide valuable insights into the background characteristics for soft X-ray polarimeter with wide FoV.
ISSN:0004-637X
1538-4357
DOI:10.3847/1538-4357/acfc43