Документ взят из кэша поисковой машины. Адрес оригинального документа : http://hea.iki.rssi.ru/SXG/PROJECT/Yam_SRG_f.doc Дата изменения: Mon Jan 19 16:00:40 2004 Дата индексирования: Mon Oct 1 22:43:47 2012 Кодировка: Поисковые слова: x-ray

Russian Academy of Sciences

Space Research Institute

















Spectrum-X-Gamma Project


based on Yamal platform






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2003

contents

CONTENTS 1

INtroduction 1

1. high apogee orbit 1

1.1 Active Galactic Nuclei (AGNs) 1
1.2 A supermassive black hole in the center of the Galaxy 1
2. the near-earth orbit 1

2.1 Sensitivity to resolve objects with a low surface brightness 1
2.2 Scientific objectives for the JET-X telescope 1
2.2.1 Cosmic X-ray background 1
2.2.2 Observations of the outer regions of clusters of galaxies 1
2.2.3 Shock waves in the interstellar medium 1
2.2.4 Diffuse emission in the Galactic center region 1
3. Launch facilities and the ballistic scenario for s/C delivery to the
operationAL orbit 1

3.1 Results of the ballistic analysis for the Spectrum-X-Gamma S/C
operation orbits and launch vehicles 1
4. instruments 1

References 1



INtroduction

Recent limitation of funding in Russia has forced the Spectrum-X-Gamma
collaboration to change from the very expensive heavy PROTON to a less
expensive middle class launcher with a booster. This decision makes
possible to decrease the launch cost several times thus bringing the
Spectrum-XG (SXG) launch feasible within the next few years. Otherwise the
launch date is shelved for a considerably period.
However this decision strongly governs the SXG design. The middle class
launcher with a booster (e.g. SOYUZ LV + FREGAT booster) is able to put one
ton at most in the SXG orbit. The present spacecraft dimension doesn't fit
the installation requirements for the SOYUZ's fairing. As a result IKI is
considering the option of SXG without the SODART telescope and the YAMAL
bus provided by the ENERGY Rocket & Space Corporation (Fig. 1). This bus is
noted for its several successful launches with the communications payload
and its performance and adapters well fit the SXG modified design. In
addition this decision also allows to save money for the modern Spectrum
satellite development.

Fig. 1. Overview of the SXG spacecraft

According to the requirements to get an approval of the SXG modified
design IKI with RSC Energy should present a report on scientific and
technical advantages of the new SXG concept to Space Council of the Russian
Academy of Sciences and Rosaviacosmos at the end of this year.
IKI and the Energy Corporation are studying two possible launch options
(high and low apogee orbits) for modified SXG.

high apogee orbit

In the proposed configuration the observatory will be focused on the two
scientific objectives:
- Extended (up to several months) quasi-continuous observation of a
thoroughly selected set of 5-10 sources - AGNs and the supermassive
black hole in the center of our Galaxy within a wide energy range
from the UV to the hard X-rays. Optionally: agreed multi-wavelength
observations in radio and optical ranges from the Earth.
- Extensive (up to 30-40% of the observation period) TOO program
(gamma-ray bursts afterglow, X-ray transients, supernovae in nearby
galaxies, etc.) in a broad energy range from UV to hard X-rays.
The operating observatories (like Chandra or XMM-Newton) possess
significantly higher sensitivity in the X-ray band. However a very
versatile research program (this is unavoidable and typical for «large»
observatories) hinders from long-term observation of a particular object
due to frequent changes in the instrument orientation due to the
observation schedule agreed. Typical exposure time does not exceed 30-100
ks for these observatories, while TOO share does not exceed 5% of the
observation time. Moreover these observatories offer limited multi-
wavelength capabilities.

1 Active Galactic Nuclei (AGNs)

During the recent 5-7 years a considerable progress has been achieved in
understanding the physics of accretion onto a compact object in the X-ray
binaries through the studies of the X-ray flux fast variability, in
particular using the RXTE data. The RXTE instrument is distinct for a very
good sensitivity and an excellent time resolution of about 1 microsecond.
In this case the time resolution plays the principal role since the
characteristic time scales are of an order of 1-10 milliseconds in the
vicinity of black holes with a mass (10 mass of our Sun. The spectra of
many X-ray binaries are similar to the spectra of many AGNs. This makes it
possible to assume that similar physical mechanisms operate for the both
classes of sources. However the characteristic time scales strongly differ
near a black hole with a mass comparable to the stellar mass and a
supermassive black hole. E.g. typical rotation period for a particle in the
close vicinity of the 108 solar masses black hole is of an order of 105
seconds - i.e. about one day. The data accumulated for the X-ray binaries
makes it possible to assume that the strongest variability is associated
with the time scales being 10-100 longer than the rotation period for the
innermost stable orbits. For AGNs this means the variability on scales of
10-100 days possesses the most interest. Unfortunately duration of a
typical AGN observation is limited to