The MART-LIME high-energy coded aperture telescope

IAS, a CNR institute for space research in astrophysics at Frascati (Italy), in collaboration with IKI (Russian Academy of Sciences) on their invitation, has developed, and is now building, an X-ray imaging and spectroscopic telescope as the high energy instrument on board the observatory Spectrum-X-Gamma. The name of this instrument is MART-LIME. It is a follow-up in a series of X-ray detectors that have been developed, built at IAS and flown on board stratospheric balloons.


The base-line photon detection system of MART-LIME is a high pressure (5 bar) Xenon-filled MWPC behind a coded mask aperture. The MWPC will be sensitive to energies 5-150 keV with an efficiency higher than 10%. The background rate will be substanstially reduced through a fluorescence gated coincidence mode wherein events for which two coincident pulses are produced are accepted only when a K-alpha or K-beta etc. fluorescence photon (30 keV) is detected within the sensitive volume. The location of photons will be performed through the delay line concept, to an accuracy of the order of 1 mm. Collimation, together with the active veto system of the detector, reduces the background further.

The aperture pattern and imaging

The mask is a URA twin prime with a basic pattern of 71X73 pixels. It will repeated partly with 18 pixels on each side. A collimator, with cells sizes equal to that of a mask pixel, ensures an optimum imaging environment of this coded aperture camera.

A picture of the MART-LIME pattern (courtesy Dr. Natalucci, IAS)

Scientific objective

The scientific objective of MART-LIME is emphasized on the study of Within the instrument package of Spectrum-X-Gamma, MART-LIME covers the study of the high energy part of the EM spectrum.

Characteristics of MART-LIME

Detector type Multi-Wire Proportional Counter Detector gas Xe Detector gas pressure at 5 atm Active detector area 1744 cm**2 Distance Aperture-Detector 2300 mm Field of View 4.6 X 4.9 (FCFOV), ~6 X 6 (PCFOV) Mask size 73 X 71 elements (basic, 105 X 105 total) Mask element size 5.8 X 5.8 mm**2 Mask open fraction 0.5 Angular Resolution (FWHM), on-axis 8.7 arcmin (40 arcsec SLA for a 5sigma) Active photon energy range 5-150 keV Photon energy resolution <= 5% Sensitivity typical ~mCrab in one day

The above info is an excerpt from "MART-LIME: A high energy imaging and spectroscopic experiment on board Spectrum-X-Gamma" by Bazzano, Amoretti, La Padula, Natalucci, Soggiu, Ubertini and Waldron, in Advances in Multilayer and Grazing Incidence X-Ray/EUV/FUV Optics, Hoover and Walker (eds), SPIE Proc. 2279, page 446 (1994). Also, Dr. Natalucci from IAS at Frascati was kind to provide some additional data.