Gamma Ray Coded Mask Telescope on board Spanish MINISAT-01. In operation since launch on April 1997 until February 2002. LEGRI was the fist space mission in which CdZnTe detectors were used for Astrophysical purposes.

LEGRI (Low Energy Gamma Ray Imager) was selected in 1994 as a payload for the first mission of the Spanish MINISAT-01 platform and launched in April 1997. The objective of LEGRI is to demonstrate the viability of HgI2 and CdZnTe detectors for Space Astronomy, providing imaging and spectroscopical capabilities in the 10-100 keV range. LEGRI consists of a Coded Mask Aperture System and an array of 10x10 cristals etector plane (80 HgI2 and 20 CdZnTe). LEGRI was being built by a consortium including the University of Valencia, the University of Southampton, the University of Birmingham, Rutherford Appleton Laboratory, Centro de Investigaciones Energéticas, Medioambientales y Tecnológicas (Ciemat) and INTA.

Scientific Objectives.

• Location of known gamma-ray sources with better accuracy. Identification of couterparts in optical frequences.
• Spectra study of strong gamma-ray sources in the zone dominated by synchrotron radiation.
• Map diffuse Galactic emission and extended sources.
• Gamma-Ray extragalactic astronomy.
• Cover the energy range between 10-200 keV. This region has a particular importance: unique astrophysical information regarding nuclear excitation process, radioactivity, cyclotron emission and line formation is contained into this region.

Technologic Objectives.

• Explore the possibilities for gamma-ray astronomy of HgI2 detectors.
• Possibility and efficiency of gamma-ray imagers in the low energy range (10-100 keV) based in HgI2 detectors.
• Survival capability under space conditions of HgI2 detectors.
• Continue and deepen the studies about HgI2 detectors technology, began since some years by CIEMAT.

LEGRI assembly

The LEGRI system is constituted by the following units:
 

•   Detector Unit: a position-sensitive gamma-ray detector consisting on an array of 100 HgI2 detection elements, each 0.5 mm thick, arranged on a 12x12 mm**2 space square grid; the associated Front End Electronics (FEE), based on a 16 channel low-noise preamplifier and shaping-amplifier chip, developed using gate array type technology and a commercial ADC; a mechanical collimator made of tungsten; and a main mechanical assembly and passive shield. (See LEGRI Detector Unit)

• Mask Unit: located at 540 mm from the detector plane and parallel to it, consisting on a static coded aperture mask made by tungsten elements on a honeycomb plate and a support structure. It will provide a wide field of view and fine angular resolution, allowing to monitor simultaneously the source and detector background. (See Mask Pattern)

• Power Supply and Digital Processing Units: which will act as direct interfaces to the PLM for power and data transmision.High Voltage Unit: which will supply the high voltage needed to operate the detectors.

• Star Sensor: which will be used to determine precisely and continuously the satellite attitude, allowing for the reconstruction on ground of the gamma-ray images without spatial blurring caused by platform drift or jitter.

• Ground Support Equipment: needed to test and calibrate the instrument before launch and then for analysis of the data when the instrument becomes operational. The Science Operation Center (SOC) shall be located in Valencia.

The SOC

The LEGRI Science Operation Center (SOC) is located at GACE facilities at the University of Valencia.
 
SOC duties are:

1. Download of LEGRI raw data
2. Preprocessing of raw data (decompression of data packets, extract separatedly HK data and raw image, follow up of HK data...)
3. Storage of the data, update of archive databases and generation of reports and alerts.

LEGRI Working Team