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.
Detector
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
- X-ray binaries, in particular the search for cyclotron
lines as a direct probe of the magnetic field strength
- the location of hard X-ray emission in complex regions
- the shape of AGN spectra
- the energy resolved spectra of Cluster of Galxies and search for
non-thermal emission
- the X-ray cosmic background in the hard X-ray range
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.