INTEGRAL The INTErnational Gamma-Ray Astrophysics Laboratory

1. INTEGRALThe INTErnational Gamma-Ray Astrophysics Laboratory INTEGRAL is an ESA managed mission, devoted to high-resolution Gamma-Ray imaging and spectroscopy. Launch will be in October, 2002 on a Proton rocket Here INTEGRAL is being prepared for thermal & structural testing at ESTEC Elements 2002 Workshop C.Shrader/INEGRAL

2. Although they are highly penetrating in the ambient dust and gas environment of interstellar space, they are very efficiently absorbed by the Earth’s atmosphere Gamma-Ray Detection The predecessor to INTEGRAL (as well as to GLAST and Swift) was the Compton Gamma-Ray Observatory Elements 2002 Workshop C.Shrader/INEGRAL

3. INTEGRAL is a follow up to the CGRO OSSE and COMPTEL experiments Forthcoming Gamma-Ray Observatories Elements 2002 Workshop C.Shrader/INEGRAL

4. Gamma-rays are the highest energy component of the electromagnetic spectrum Unlike radio, infrared, optical or UV light, they are detected by their particle-like rather than their wavelike manifestation They are produced through a variety of mechanisms, depicted here schematically. Cosmic Gamma Rays

5. Gamma rays interact in detectors via 3 basic mechanisms Compton scattering pair production photo-electric effect Each type of interaction occurs in INTEGRAL’s detectors How are Gamma-Ray Detected? Compton scattering involves a photon-electron collision Photo electric effect: photon impinges on an atom; electron is ejected Pair annihilation; becomes dominant above ~10 MeV Elements 2002 Workshop C.Shrader/INEGRAL

6. Gamma rays are not easily focused or reflected For a given radiative power, a celestial source emits far fewer gamma-rays than less energetic photons The background, due to internal radioactivity and impinging cosmic ray particles far exceeds typical signal Difficulties Elements 2002 Workshop C.Shrader/INEGRAL

7. Unlike lower energy photons, gamma-rays cannot be focused with mirrors or lenses The INTEGRAL instruments utilize the Coded-Mask Imaging technique Alternate transparent and absorbing elements are arranged into a pattern; a shadow “image is projected onto the detector plane Coded Mask Imaging Elements 2002 Workshop C.Shrader/INEGRAL

8. Instrumental and Cosmic Background • The biggest problem is separating the desired signal from the far more intense background noise • Above left: a sample background spectrum from pre-launch lab tests. Right: a simulated background spectrum, with a bright source (Cygnus X-1) superposed (red) Elements 2002 Workshop C.Shrader/INEGRAL

9. INTEGRAL has 2 primary instruments, IBIS, for imaging SPI for spectroscopy INTEGRAL Instruments “Imager onboard INTEGRAL” (IBIS) detector vessel Cut away view of “Spectrometer onboard INTEGRAL” (SPI) Elements 2002 Workshop C.Shrader/INEGRAL

10. Gamma-rays pass through a “coded mask” of absorbing/transmitting elements Interactions within solid state detectors lead to formation of electron-hole pairs, which migrate to anode/cathode An electrical pulse readout records an event,and its energy Unwanted events, e.g. from off-axis, can be “vetoed” by active shielding How do INTEGRAL’s Dectectors Work? Elements 2002 Workshop C.Shrader/INEGRAL

11. The spectrometer SPI will obtain spectra of -ray sources over an energy range of 20-8000 keV It has 19 hexagonal germanium (Ge) detectors. A cooling system maintains the spectrometer at 85 Kelvin (-188 deg C). SPI Facts • Cosmic protons and neutrons will slowly damage the Ge crystals resulting in a loss of resolution and efficiency. • To restore the crystals, they will be occasionally heated to 100 C for 24 hrs. Elements 2002 Workshop C.Shrader/INEGRAL

12. IBIS is optimized for fine imaging and positioning. The tungsten coded mask, is 3.2 meters above the detectors. Angular resolution is determined by the number of sensitive elements called pixels (picture elements). The detector will use 2 parallel pixel planes, sensitive to low- & high-energies. IBIS Facts • Optimum angular resolution of 12 arcmin (the full moon is about 30 arcminutes) Elements 2002 Workshop C.Shrader/INEGRAL

13. This illustrates relative spectral resolving power of SPI, and its CGRO predecessor, OSSE For narrow lines, there is s substantial increase of signal to background Advantage of High Spectral Resolution Elements 2002 Workshop C.Shrader/INEGRAL

14. Historically, improvements in spatial resolution have led to major advances in observational astronomy Gamma-rays, unlike soft-X-ray,UV, & optical photons, are impervious to dust and gas absorption Advantage of High Spatial Resolution Elements 2002 Workshop C.Shrader/INEGRAL

15. INTEGRAL will operate as a public observatory with broad participation among an international astrophysics community Numerous science topics are to be covered Here, I will focus on those related to the formation of the elements, and their abundances and distribution within our Galaxy Such studies are categorized as “Nuclear Astrophysics” What Will INTEGRAL Observe? Elements 2002 Workshop C.Shrader/INEGRAL

16. -rays offer the most direct view of nucleosynthesis Nucleosynthesis Elements 2002 Workshop C.Shrader/INEGRAL

17. Observable Nuclei Elements 2002 Workshop C.Shrader/INEGRAL

18. Anticipated Radioisotopes Candidate astrophysical radioisotopes Elements 2002 Workshop C.Shrader/INEGRAL

19. As noted in an earlier presentation, supernova, although rare in our Galaxy (or its vicinity), offer a rare glimpse of element formation Gamma-rays from supernova in turn offer the most direct account of many of these element forming processes Supernova Elements 2002 Workshop C.Shrader/INEGRAL

20. Supernova 1987A SN1987A was the closest supernova event to earth in three centuries A gamma-ray telescope, launched from Australia on a balloon made this measurement of the radioactive decay of Cobalt (56Co) Elements 2002 Workshop C.Shrader/INEGRAL

21. The early decay light curve was powered by the energy release of radioactive nuclei The current light output may be as well, although a pulsar (rotating, magnetized neutron star) is another possibility Supernova 1987A Elements 2002 Workshop C.Shrader/INEGRAL

22. About 5 years after the event, the longer- lived isotope 57Co was detected by CGRO Observations with INTEGRAL over the coming years, will search for the 44Ti ~100 year isotope Supernova 1987A Elements 2002 Workshop C.Shrader/INEGRAL

23. SN 1991T; bright SN Ia, 17 Mpc possible CGRO 56Co detection SN 1993J; CGRO, faint -ray continuum SN 1998 BU; long (~12 weeks total, spanning 5 months)observations upper limits Other Supernova Observations Elements 2002 Workshop C.Shrader/INEGRAL

24. Thermonuclear detonation on a white dwarf 22Na, 1.2 MeV line 3-yr 1/2 life Detectable to ~1 kpc for isotopic subclass (NeOMg Nova) Prompt 511 keV lines, 7Be -Rays from Nova Elements 2002 Workshop C.Shrader/INEGRAL

25. Galactic Supernova History 26Al is produced in SNe and deposited in the interstellar medium; it has a ~million year half-life • INTEGRAL can help to understand the dynamical and chemical evolution of the Galaxy, by studying the spuernova history on ~million and ~hundred year timescales 44Ti has a ~100 year halflife. Both isotopes have been detected in Vela Elements 2002 Workshop C.Shrader/INEGRAL

26. 26Al Radioactive Decay Elements 2002 Workshop C.Shrader/INEGRAL

27. 26Al Radioactive Decay Additional information is contained in the shape, or profile of the -ray line. A broader line, indicates a higher velocity source. Recent measurements indicate velocities greater than those expected from Galactic rotation. Elements 2002 Workshop C.Shrader/INEGRAL

28. One example of a “hidden” supernova may already have been found by CGRO However, this is remains uncertain. Additional examples are needed Hidden Supernovae Elements 2002 Workshop C.Shrader/INEGRAL

29. The central region of our Galaxy is an intense source of e-e+ annihilation radiation INTEGRAL can produce a refined map; SPI has10X better energy resolution and 5X better spatial resolution Galactic Center: e+e- Annihilation Elements 2002 Workshop C.Shrader/INEGRAL

30. Galactic SN are rare, desirable to sample external galaxies to ~10’s of Mpc General problem: sensitivity scales with square-root of collecting area Internal background scales ~linearly with instrument volume (mass) Thus, can’t simply make a bigger INTEGRAL Future Gamma-Ray Telescopes Elements 2002 Workshop C.Shrader/INEGRAL

31. Compton Telescopes increase effective area improved background rejection Type Ia SN to ~50 Mpc ? Basic feasibility already demonstrated; CGRO COMPTEL instrument Laue diffraction focus low-energy -rays, thus orders of magnitude reduction background possible problem: only over very narrow bandpass Future Gamma-Ray Telescopes Elements 2002 Workshop C.Shrader/INEGRAL

32. In A Compton Telescope, an incoming -ray scatters an electron The event geometry is governed by the Compton scattering formula In principle, the direction and energy of the incident photon can be determined Future Gamma-Ray Telescopes The CompTel Instrument on CGRO was the first orbiting Compton telescope. Elements 2002 Workshop C.Shrader/INEGRAL

33. Future Gamma-Ray Telescopes Laue diffraction telescope. Uses crystal lattice as diffraction grating. -ray wavelengths must be similar to crystal spacing. Diffraction angles obey the Bragg formula. Elements 2002 Workshop C.Shrader/INEGRAL

34. Fresnel lenses large collecting area,focus -rays to subarcsec problem: large focal length, separate spacecraft Ground based Telescopes (high-energy -rays) fabricate very large collecting areas potential already demonstrated not directly relevant to nucleosynthesis Future Gamma-Ray Telescopes Elements 2002 Workshop C.Shrader/INEGRAL

35. Very energetic (~1 trillion electron volts) -rays collide with atmospheric material, leading to “Cerenkov” radiation The relevance to nucleosynthesis studies is indirect site of cosmic ray acceleration star-formation history of the universe Future Gamma-Ray Telescopes Ground-based -ray telescopes use the Earth’s atmosphere as a detector Elements 2002 Workshop C.Shrader/INEGRAL