JEM-X Coded Masks
The X-Ray Monitor on INTEGRAL (JEM-X) will perform observations with arc minute angular resolution in the 3–60 keV band. The instrument is based on the same measurement principle as the two gamma-ray instruments on INTEGRAL (SPI and IBIS): sky imaging using a Coded Aperture Mask.
JEM-X Masks description
The JEM-X Mask code pattern is based on a Hexagonal Uniformly Redundant Array (HURA) of 22501 elements, with approximately 25% of them open. This transparency achieves better sensitivity than a 50% open code, particularly in complex fields with many sources, and reduces the number of events to be processed.
The design driver was to provide a system able to survive the launch and operational thermal and mechanical conditions, maintaining the best scientific performances of the Mask. The main requirements are the following:
The Interface with INTEGRAL PLM is defined by a Ti forged ring. This interface is provided by 12 equi-spaced holes. 44 Cu-Be elements pre-stress the machined Coded Plate to increase its stiffness and strength. The use of Cu-Be elements is quite innovative and reduces dramatically the need of any additional support structure.
Two strongbacks are located on both sides of the Code to reinforce the plate stiffness. These elements have been designed to minimise the occlusion of open pixels. Less than 2% of the open pixels are covered by the exoskeleton structure.
Two Optical Cubes are located on the Mask Ring in order to define an Optical reference of the Code for alignment of the Masks with the JEM-X detectors and INTEGRAL Line of Sight.
The Mask design has successfully passed the different thermoelastic and mechanical tests at Subsystem and Satellite level, providing a first axial eigenfrequency close to 200Hz, more than 3 times higher than required.
JEM-X Masks FM1 & FM2 were assembled in Nov 1999 at GACE 1,000 class Clean Room by SENER and GACE engineers and passed successfully their Acceptance Test Campaign at INTA from November 1999 to January 2000.
Main results of the test on the FM Mask refers to the scientific performances of the Mask. The Mask optical capabilities as a Spatial Multiplexing System are defiend by the pixel size and positioning accuracy over the code. Several Dimensional Controls were performed on the FM Masks, with successful results: the values for pixels size and positioning uncertainty:
Average deviation in angular units is 2.2. arc sec for a focal length of 3.4m.
See the image gallery for more pictures.