PROPOSED FIELD OF WORK AT ESA
The combination of using the high-energy data from the European satellites INTEGRAL and
XMM-Newton, and of the NASA/RXTE (as long as it operates) allow one to study accurately
the spectral and timing properties of high energy emissions generated around stellar mass
accreting black holes, with possible extension to the study of neutron star binaries and Active
Galactic Nuclei. While ESA/XMM-Newton allows to study X-ray novae or binaries in
quiescence, ESA/INTEGRAL permits to analyze broad-band high energy (X-ray/gammarays) spectra in distinct spectral states (hard, intermediate, soft) and time variability
properties in a systematic way on X-ray novae and persistent sources. NASA/RXTE can be
used as a complementary observatory and for timing studies. With the help of regularly
submitting Chandra and Suzaku proposals (complementary energy bands satellites) and
combining multiwavelength observations (in radio, infrared, optical) for which our team have
currently running programs, this research programme will allow to:
- study the origin of the hard X-ray/soft gamma-ray emission. Indeed, the energy distribution,
location and cloud geometry of the electron population which could be either thermal
(Maxwellian distribution), non-thermal (power law distribution, Grove et al. 1998), in free fall
(Laurent & Titarchuk 1999) or a combination of the three are still basically unknown;
- study the connection between the disc and jets. Its nature is unclear (Fender et al. 2005;
Markoff et al. 2005): there is an ongoing discussion on how much the jet contributes to the
overall emission;
- study the spectral variability behaviour. The processes which lead to spectral transitions
and the possible role of non-thermal (synchrotron) radiation are still very uncertain. Spectral
evolutions cannot be simply explained by a large variation in the accretion rate: at least an
additional physical parameter, for example linked to the corona, to the jets or to the magnetic
field, must determine the spectral changes from hard to softer states at almost constant
luminosity (Homan et al. 2001, Belloni et al. 2006);
- study the role of non-thermal emission. The absence of high-energy cut-off (Zdziarski et al.
2001) or the need to include sometimes non-thermal components (Cadolle Bel et al. 2006a)
seem to favour emission from hybrid (both thermal and non-thermal) electron distributions
(Poutanen & Svensson 1996 and Coppi 1999) but this issue is still debated.
The nature (location, geometry, and origin) of the hot plasma that gives rise to the gammaray radiation and its relation with jets of relativistic particles and low energy time variability
are still unknown. I therefore propose a new approach to solve part of these problems by
extending in a systematic way the high frequency (0.1-1000 Hz) variability analysis,
performed up to now only at low energies (≤ 30 keV) to the high energy bands (30-300 keV)
while simultaneously analyzing links between the derived variability patterns and the spectral
evolutions. This can be achieved today by the combination of the data readily available from
the following space missions: ESA/XMM-Newton, ESA/INTEGRAL and NASA/RXTE (and
possibly Chandra and Suzaku afterwards). Timing analysis of the emission from stellar mass
black holes can be carried out, performed till now only with PCA, with INTEGRAL. This
analysis will show how the characteristic quantities of the timing variability (amplitudes, break
frequency and slope of the high frequency noise, frequency and amplitude of QPO features,
pattern of hardness ratios versus intensity) change in the high energy band. Then,
performing standard spectral analysis on all the INTEGRAL data allow to study the highest
energies. One interesting thing is to compare the parameters (temperature and optical depth
of the hot gas, amplitude of the reflection, maximum energy and amplitude of the nonthermal component, etc.) to the timing ones. This will then be possibly compared to the
spectral parameters obtained during the quiescence of the sources with XMMNewton/Chandra satellites. With the additional use of simultaneous radio/IR data obtained
from external collaborators as well as the ones at ESAC, this systematic work will allow to
determine the connections between accretion disc instabilities, corona changes and jet
genesis as it combines high energy spectra properties to timing characteristics.
ESAC, as the XMM-Newton and INTEGRAL data reception centre, is the best place to carry
out such a project. ESAC scientists have a deeper knowledge on the instruments and data
analysis. ESA has launched the space telescope INTEGRAL only few years ago while XMMNewton still operates: both provide important results on high energy physics. Another
important scientific aspect of this project is the close collaboration of two European countries
and institutes: SAp (CEA-Saclay, France) responsible for INTEGRAL instruments and for
data analysis and ESAC (Spain) with experts on INTEGRAL and XMM-Newton data
programmes/analysis. Also, through the proposed programme, the scientific return of the
current ESA missions will be increased with the full exploitation of these unique data,
increasing attractiveness and competitiveness of ESA while developing long-term synergies.
BIBLIOGRAPHY
Belloni et al. 2006, MNRAS, 367, 1113
Cadolle Bel et al. 2006a, A&A, 446, 659
Coppi 1999, ASP Conference Series, 161, 37599
Fender et al. 2005, ASS, astro-ph 0506469
Markoff et al. 2005, ApJ, 635, 1203
Grove et al. 1998, ApJ, 500, 899
Homan et al. 2001, ApJS, 132, 377
Laurent & Titarchuk 1999, ApJ, 511, 289
Poutanen & Svensson 1996, ApJ, 470, 249
Zdziarski et al. 2001, ApJ, 554, L45