The GECAM and its payload

感谢张双南、卢方军、徐玉朋、王焕玉、刘聪展、何会林、董永伟、刘志东、田宗军、吴金杰、陈晓敏、朱光武、沈理达、邱明波、张飞、孟斌、文星、李陆、王于仨、侯懂杰、张承模、杨家卫、张爱梅、李正伟、张翼飞, 及GECAM卫星工程两总和各级领导: 王赤、吴季、孟新、荆涛、耿浩、林柯妡、余金培、张科科、黄佳、陈友梅、韩兴博、杨勇、王建平等同志在本项目立项和研制过程中给予的支持和帮助. 感谢北京玻璃研究院在GRD探测器溴化镧晶体封装件生产和供货方面给予的支持. 感谢西北稀有金属材料研究院在铍片供应方面给予的支持. 感谢山东航天电子技术研究所在探测器工程化、集成测试、试验等方面给予的支持.

References

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Figure 1
(a) Schematic diagram of the field of view of two satellites in orbit; (b) layout of the whole satellite.
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Figure 2
GECAM payload structure design (a) and physical photos of initial sample identification parts (b).
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Figure 3
GECAM payload system block diagram.
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Figure 4
Schematic diagram of GRD single structure design scheme.
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Figure 5
Ancillary Response File (ARF) of all-around peak in two kinds of crystal of one GRD with different thicknesses and incident angles. The incident angle of ARF of each color is from 0° (vertical incidence) to 80° respectively from top to bottom, and increases at 5° intervals.
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Figure 6
Redistribution Matrix File (RMF) at 30° incident for a single probe.
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Figure 7
The positioning accuracy distribution obtained by using three typical energy spectra of soft, medium and hard GRB as input is shown in eq. (1) and Table 1. (a)–(c) respectively correspond to the soft, medium and hard spectral indexes in Table 1. In each group of figures, the upper and lower figures correspond to two half day areas, respectively.
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Figure 8
The background energy spectrum of collimator schemes with different field sizes, in which different curves correspond to the half opening angles of the field of view (unit: degree), N corresponds to 90°, i.e. no collimator.
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Figure 9
Comparison between the location capabilities of GECAM (blue) and GBM (black). For both instruments, the dots are the locations, and the three circles from inside to outside are the 1σ, 2σ, 3σ confidence intervals, respectively. The red pentagram is the optical counterpart location of GW 170817 [24].
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Figure 10
The 5.9 keV pulse height histogram distribution of GRD measured at 25°C (a) and −25°C (b).
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Figure 11
(a) Curve of GRD pulse amplitude with temperature from −40°C to 30°C under the condition of fixed bias; (b) the change of ²⁴¹Am peak value measured under different bias at 20°C under normal temperature. Smooth lines are polynomial fitting results.
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Figure 12
The relationship between energy and energy channel of GRD detector, (b) and (c) are the fine measurement results at the absorption edge. The red lines are the results of linear fitting. (a) 8–160 keV;(b) 8.3–24 keV; (c) 33.8–51.4 keV.
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Figure 13
Energy resolution of GRD at 8.1 keV–1.33 MeV. The red line is the fitting result.
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Figure 14
Schematic diagram of CPD single structure design scheme.
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Figure 15
Background spectrum of CPD embedded with calibration source. The Gaussian peak comes from the contribution of α particle of²⁴¹Am source.
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Figure 16
Electron deposition energy spectra of plastic scintillators with different thicknesses. Different color curves correspond to different electron incident energies. (a) 6 mm; (b) 10 mm; (c) 20 mm.
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Figure 17
Detection efficiency of CPD for gamma rays and charged particles.
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Figure 18
Energy spectrum of ²⁰⁷Bi electron source and ¹³⁷Cs gamma source measured by CPD. (a) ²⁰⁷Bi; (b) ¹³⁷Cs.
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Figure 19
GECAM payload electrical connection diagram.
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Figure 20
The sky map orientation of each GRD and CPD, different colors correspond to different data acquisition boards.
Table 1 Definition of soft, medium and hard Band spectrum

Band谱
低能谱指数
高能谱指数
峰值能量 (keV)
软
−1.9
−3.7
70
中
−1.0
−2.3
230
硬
0.0
−1.5
1000

Table 2 signal to noise ratio of different collimator fields of view corresponding to typical GRB (θ=30°, φ=100°; nor=0.004841, index=−1.454; exp_t=22 s)

准直器半张角 (°)	弥散X射线本底	总本底	ARF	信噪比	备注
50	0.28	0.3137	0.3981	15.18	−
60	0.38	0.4116	0.5159	16.03	−
70	0.51	0.5327	0.6450	16.64	−
80	0.68	0.6963	0.7782	17.17	−
90	1.00	1.0000	1.0000	17.23	无准直器

Table 3 GRD performance parameters

内容	指标要求	设计/实测指标
探测器	LaBr₃晶体+SiPM	LaBr₃晶体+SiPM
数量	≥20	25
探测面积(单体)	≥40 cm²	45.36 cm²
探测能区	8 keV–2 MeV	5 keV–5 MeV
能量分辨率FWHM	<18%@59.5 keV	≤13%@59.5 keV
伽马射线探测效率	>50%@8 keV	≥70%@8 keV
死时间(正常事例)	≤5 µs	4 µs

Table 4 Identify the burst mode of gamma ray bursts and space charged particles (GRD: 3σ), and the duration of the bursts is 2 s

事件	能谱	GRD计数及误差 (8–5000 keV)	CPD计数及误差 (0.3–5 MeV)	CPD/GRD计数之比及其误差
伽马暴	Band软谱	120.0±41.5	0.008±5.7	0.0001±0.05
	Band中谱	120.0±41.5	0.06 ±5.7	0.0005±0.05
	Band硬谱	120.0±41.5	1.1±5.8	0.0090±0.05
空间荷电粒子事件 (电子)	Band软谱	120.0±41.5	32.5±8.0	0.27±0.12
	Band中谱	120.0±41.5	35.5±8.2	0.30±0.12
	Band硬谱	120.0±41.5	43.3±8.7	0.36±0.14
	幂率谱指数−1	120.0±41.5	48.6±9.0	0.40±0.16
	幂率谱指数−2	120.0±41.5	37.5±8.3	0.31±0.13

Table 5 Performance indexes of CPD

内容	指标要求	设计/实测指标
探测器	塑料闪烁体+SiPM	塑料闪烁体+SiPM
数量	≥5	8
塑闪单体尺寸	≥15 cm²	16 cm²
探测能区	300 keV–5 MeV	270 keV–5 MeV
伽马射线探测效率	<20%@8–2000 keV	<7%@全能区
死时间	≤5 µs	3 µs

Table 6 Grouping of GRD and CPD corresponding to each data acquisition board

数采板编号
GRD分组
CPD分组
1
1
9
11
14
16
AC03
AC05
2
2
6
13
20
25
AC01
AC04
3
3
7
12
18
23
AC02
AC06
4
4
15
17
19
22
AC07
–
5
5
8
10
21
24
AC08
–

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07.87.+v	Spaceborne and space research instruments, apparatus, and components (satellites, space vehicles, etc.) (for instrumentation for space plasma physics, ionosphere, and magnetosphere, see 94.80.+g; see also 95.55.-n and 95.40.+s in astronomy)
29.40.Gx	Tracking and position-sensitive detectors
07.05.Hd	Data acquisition: hardware and software

The GECAM and its payload

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Band谱	低能谱指数	高能谱指数	峰值能量 (keV)
软	−1.9	−3.7	70
中	−1.0	−2.3	230
硬	0.0	−1.5	1000

数采板编号	GRD分组					CPD分组
1	1	9	11	14	16	AC03	AC05
2	2	6	13	20	25	AC01	AC04
3	3	7	12	18	23	AC02	AC06
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