Artistic impression of GECAM satellites

* Mission Overview

The Gravitational Wave High-energy Electromagnetic Counterpart All-sky Monitor (GECAM) is a matched pair of satellites developed by the Chinese Academy of Science (CAS). The two satellites work in tandem to detect gamma-ray counterparts to gravitational wave sources (such as neutron star binary system mergers): each half of the pair is able to monitor an entire hemisphere of sky from low-earth orbit, and they are located on opposite sides of the Earth in order to get a simultaneous view of the entire sky.

The two satellites were co-launched on December 10, 2020 from the Xichang Satellite Launch Center aboard a Long March 11 rocket. They were placed in 600 km altitude low earth 29° inclination orbits located on opposite sides of the Earth. Each satellite weighs about 160 kg and has an identical payload of gamma-ray detectors and charge particle detectors. The two are dubbed GECAM A (KX 08A; Xiaji) and GECAM B (KX 08B; Xiamu). The primary mission goal is to find and monitor gamma radiation from gravitational wave event sources, but the mission will also yield insights on ultra-long gamma ray bursts (GRBs), X-ray flash sources, and a variety of other transient high-energy events.

* Instrumentation

Each of the two GECAM payload includes:

  • A dome-shaped array of 25 Gamma Ray Detectors (GRDs) configured to collectively see 50% of the sky. Each GRD consists of a cylindrical LaBr3:Ce scintillator crystal which is 76.2 mm in diameter and 15 mm thick, packed in an aluminium housing to protect the crystal from moisture and stray light. The entrance window is a 0.22 mm thick Be sheet with an ESR reflector. A quartz window under the crystal provides the view for the 50.44 x 50.44 mm2 SiPM 8×8 pixel array. The electronics can record in both high and low gain modes. The low gain mode provides detection in the range 5–500 keV; the high gain mode provides 30 keV–3 MeV. In the high gain mode, energy resolution was measured with laboratory sources to be 65.5% (∼3.86 keV(?)) at 5.9 keV in low gain mode, and 5.3% (∼35 keV(?)) at 662 keV. The GRD should be able to detect signals of 2.0×108 ergs/cm2/s with a localization accuracy of roughly 1° for a medium-bright GRB source.
  • A set of eight charge particle detectors
  • Supporting space flight electronics and power supply systems, including solar panels
Many elements of these systems have been flight-proven on other instruments: the LaBr3:Ce scintillator crystal design is also found in CALET’s CGBM instrument; the auto-gain and SiPM array systems are part of HXMT-Insight.

The satellites do not have high voltage systems and should not need to be cycled off during South Atlantic Anomaly transits.

* Science

The GECAM science objectives include:

  • Localize gravitational wave counterparts detected at high energies;
  • Detect and localize a variety of other transient high-energy sources: ultra-long GRBs, X-ray Flashs, Fast Radio Burst sources, and magnetars;
  • Provide near-real time results to ground and other observations for rapid follow-up observations.

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Last modified: Thursday, 22-Apr-2021 11:47:47 EDT