XRAY DETECTORS FOR

1
X-RAY DETECTORS FOR THE INTEGRAL SATELLITE
O. Vilhu1, J. Huovelin1, S. Maisala1, P. Muhli1,
J. Schultz1, L. Alha1, D. Hannikainen1, P.
Hakala1, I. Soranta1, P. Nikula1, H. Sipilä2, T.
Andersson2, S. Nenonen2, T. Koivula2 1Observatory
, P.O.B. 14, FIN-00014 University of Helsinki,
Finland 2Metorex International Oy, Espoo,
Finland Email osmi.vilhu_at_helsinki.fi,
juhani.huovelin_at_helsinki.fi
The consortium has built two imaging X-ray
detectors for the coded mask double-telescope
JEM-X of the INTEGRAL satellite 1, to be
launched by ESA in October 2002. Jem-X 3 is a
Danish-coordinated collaboration. The detectors
(below) are position sensitive microstrip
proportional counters (3 20 keV) filled with
xenon gas and recently integrated with the
satellite. Metorex International has
manufactured the sensors with TEKES funding,
while the University of Helsinki Observatory
coordinates the project management and its
scientific return with Academy of Finland
funding.   While JEM-X covers the softer
energy range, two major telescopes onboard,
IBIS and SPI, cover the hard X/Gamma-region up to
10 MeV, to study e.g. the ee- annihilation line
at 511 keV and the radioactive Al-line at 1.8
MeV. The payload includes also an optical
monitor OMC. The Integral Science Data Centre
(ISDC) is located in Switzerland (Versoix/Geneve).
The consortium plans to study hot X-ray emitting
gas and non-thermal phenomena in strong
gravitational and magnetic fields existing
close to neutron star surfaces and black hole
horizons, via several core and open time
programmes 2. The thermometer above shows that
very hot gas radiates X-rays such gas exists in
extremely strong fields.   Acknowledgement This
research is a part of the consortium High Energy
Astrophysics and Space Astronomy (HESA), financed
by the Academy of Finland and the Finnish
Technology agency TEKES within the framework of
the Finnish space research programme
ANTARES. References 1 Exploring the Gamma-Ray
Universe, 2001, Fourth Integral workshop, ESA
SP-459. 2 Science with Jem-X, N.J.
Westergaard, C. Budtz-Jorgensen, H.W. Schnopper,
R. Svensson, O. Vilhu, A.C. Fabian, A.
Castro-Tirado, 1997, in the Transparent
Universe, ESA SP-382, 605. 3 JEM-X, Lund N.
et al., in 3rd INTEGRAL Workshop The Extreme
Universe, ESA SP
With the SPI ?-spectrometer one can study
radioactive and annihilation radiation close to
the center of the Milky Way galaxy. The
radioactive 26Al, with half-life 1.1 million
years, radiates at 1.8 MeV (upper map above, from
the Compton GRO observatory). With the 511 keV
annihilation line one can probe the positron
distribution around the Center (lower map above,
from CGRO). These observations may solve the old
question about the existence of a massive black
hole there, having swallowed millions of stars
(below).
INTEGRAL satellite will be launched in October
2002 into an eccentric 3 day orbit. More
Information www.astro.helsinki.fi/projects/jemx/ i
ntegral.html