INTEGRAL LOGO Integral Scientific Objectives (continued)

Gamma-Ray Astronomy

Gamma-ray astronomy explores the most energetic phenomena that occur in nature and addresses some of the most fundamental problems in physics and astrophysics. It embraces a great variety of gamma-ray continuum and gamma-ray line processes: nuclear excitation, radioactivity, positron annihilation and Compton scattering; and an even greater diversity of astrophysical objects and phenomena: nucleosynthesis, nova and supernova explosions, the interstellar medium, cosmic-ray interactions and sources, neutron stars, black holes, gamma-ray bursts, active galactic nuclei and the cosmic gamma-ray background. Not only do gamma-rays allow us to see deeper into these objects, but the bulk of the power radiated by them is often at gamma-ray energies.

Further reading:
Gamma-ray production and absorption processes (PDF file, 0.9 Mb)
R. Diehl, Nov. 2000, Introduction to the book "The Universe in Gamma-Rays", edited by V. Schoenfelder, Springer Verlag 2001

Integral in the context of the history of gamma-ray astronomy  (PDF file, 1.7 Mb)
V. Schoenfelder, invited paper, 4th INTEGRAL workshop, ESASP-459, p.3, 2001

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Diffuse Emission

Our Galaxy contains diffuse sources of gamma-ray line and continuum radiation. The 511 keV positron annihilation line and the 1.809 MeV line from radioactive Al26 are tracers of sites of nucleosynthesis in the past million years and diagnostics of the conditions in the interstellar medium. In the MeV range, the gamma-ray continuum may be used to study the low-energy cosmic-ray electrons. These fluxes are now being studied by the instruments on the CGRO, but Integral's complementary combination of high spectral and angular resolution is necessary to exploit them fully.

The gamma-ray emission from the Galactic plane will be mapped on a wide range of angular scales from arc-minutes to degrees in both discrete nucleosynthesis lines, e.g. 1.809 MeV from Al26 and 511 keV, and the wideband continuum. At the same time, source positioning at the arc-minute level within a wide field of view, of both continuum and discrete line emissions, is required to allow an extensive range of astrophysical investigations to be performed on a wide variety of sources, both targeted and serendipitious, with a good chance of identification at other wavelengths.

Further reading:
Diffuse continuum gamma-rays from the Galaxy (PDF file, 5.7 Mb)
A. Strong et al., ApJ, 537, 763 (2000)

Positron Annihilation Radiation from the Inner Galaxy (PS file, 0.3 Mb)
R. L. Kinzer et al. Ap.J.  559, 282, (2001)

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Galactic Centre

The Centre of our Galaxy is known from observations in the radio and infrared windows to be the site of violent activity. Observations made so far indicate that at gamma-ray energies the behaviour of the this region is no less extreme. It houses some of the most energetic gamma-ray objects in the Galaxy and is host to sources of transient emission, including variable line emission from the annihilation of positrons. Integral will provide the tools for using gamma-rays as a sensitive probe of the astrophysical processes going on within a few hundred parsec of the nucleus of our galaxy.

Further reading:
The centre of our Galaxy: activity and high-energy emission of the closest massive black-hole  (PDF file, 0.7 Mb)
A. Goldwurm, Proc. 4th INTEGRAL workshop, Alicante 2000, ESA SP-459, p. 455, 2001

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Compact Objects

One of the most important scientific objectives of Integral is to study compact objects, e.g. neutron stars and black holes. Virtually all types of compact objects are significant sources of high-energy emission. Integral will image these objects in unprecedented detail at high energies, and the spectroscopic capabilities of the mission will provide the first detailed physical diagnostics of these systems at gamma-ray energies.
Among the prime sources of interest will be the massive black hole candidate GRS1915+105.

Click herefor the animation (0.5 MB) of an accretion disk around a black hole.

Further reading:
Sources of relativistic jets in the Galaxy  (PDF file, 1.0 Mb)
I.F. Mirabel & L.F. Rodriguez, Annu.Rev. Astron.Astrophys. 37, 409 (1999)

Gamma-Ray Pulsars (PDF file, 0.5 Mb)
G. Kanbach, Proceedings of the 270. WE-Heraeus Seminar on Neutron Stars, Pulsars and Supernova Remnants, Jan.
21-25, 2002, Physikzentrum Bad Honnef, eds W. Becker, H. Lesch & J. Truemper. Proceedings are available as MPE-Report 278

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Explosive Nucleosynthesis

Observations of gamma-ray lines from nuclear transitions in the decay of radio nuclei and the annihilation of positrons produced in various explosive nucleosynthetic processes (supernovae and novae, including historic events) provide the most direct method of studying current sites, rates and models of nucleosynthesis. Measurements with Integral of the shapes of the gamma-ray line profiles from supernovae will provide information about the expansion velocity and density distribution inside the envelope, whilst the relative intensities of the lines provide direct insight into the physical environment at the time of the production.

Further reading:
Nucleosynthesis (PDF file, 2.2 Mb)
R. Diehl, Nov. 2000, Contribution to the book "The Universe in Gamma-Rays", edited by V. Schoenfelder, Springer Verlag 2001

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High-Energy Transients

Transient sources in the gamma-ray region display unprecedented variability in both temporal and spectral domains. Integral will monitor the Galactic plane regularly in order to detect transient sources, determine their duty cycle and their luminosity function. Gamma-ray bursts will be studied using the very broad energy range provided by the two main instruments and the two X-ray and optical monitors.

Further reading:
X-ray transients in the galactic center region (PDF file, 0.7 Mb)
J. in't Zand, Proc. 4th INTEGRAL workshop, Alicante 2000, ESA SP-459, p. 463, 2001

Gamma-ray burst afterglows (PDF file, 4.7 Mb)
J. v. Paradijs et al., Annu.Rev.Astron.Astrophys., 38, 379 (2000)

Observing GRB's with INTEGRAL (PDF file, 0.4 Mb)
C. Winkler, Proc. 5th Huntsville GRB Symposium, AIP , 1999

The INTEGRAL burst alert system (PDF file, 0.2 Mb)
S. Mereghetti et al., Proc. 4th INTEGRAL workshop, Alicante 2000, ESA SP-459, p. 513, 2001

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Active Galaxies

The study of active galaxies in both fine and broadband spectroscopy will yield unprecedented knowledge of the particle interactions which take place in the region where the central engine's energy meets the galaxy's matter. The concurrent monitoring by the X-Ray Monitor and the Optical Monitoring Camera onboard Integral provide important simultaneous data in the X-ray and optical range, respectively. Because of the greatly improved sensitivity of Integral, sub-degree resolution imaging is absolutely essential to avoid source confusion from the large population of AGN (Active Galactic Nuclei) and to associate gamma-ray sources unambiguously with their optical, infrared and radio counterparts.

Further reading:
AGN: the high-energy status before INTEGRAL (PDF file, 0.7 Mb)
W. Collmar, Proc. 4th INTEGRAL workshop, Alicante 2000, ESA SP-459, p. 241, 2001

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