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Astronomy with Radioactivities IV
and Filling the Sensitivity Gap in MeV
Astronomy Kloster
Seeon Conference Center, Germany May
26-30,2003 Program,
Presentations, and Abstracts |
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Astronomy with Radioactivities IV
and Filling the Sensitivity Gap in MeV
Astronomy Kloster
Seeon Conference Center, Germany May
26-30,2003 Program,
Presentations, and Abstracts |
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10:30h-11:00h 11:00h-11:30h 11:30h-12:00h |
Welcome/Introduction Massive Stars and Modelling of their
Nucleosynthesis Gamma-Rays from Classical Novae: Expectations
from Present & Future Missions |
Diehl Rauscher Hernanz Fields |
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14:00h-15:30h 14:00h-14:30h 14:30h-14:50h 14:50h-15:10h 15:10h-15:30h |
Overviews/Reviews
on Astronomical Instrumentation Perspectives in MeV Astronomy Instrumentation
INTEGRAL’s Spectrometer SPI: Status, Science
Performance, and Prospects |
(Chair: Diehl) Kurfess Winkler Knödlseder Ott |
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16:00h-18:30 16:00h-16:30h 16:30h-17:00h 17:00h-17:30h 17:30h-18:00h 18:00h-18:30h |
Massive
Stars, Supernovae: Theory Aspects and Models Rotating Models of WR Stars: Impact on 26Al
Synthesis Core Collapse Supernova Mechanism Radioactive Decay Lines from Asymmetric Supernova
Explosions Nucleosynthesis in SNII coupled to multidimensional
hydrodynamics |
(Chair:
Prantzos) Meynet Fryer Hungerford Travaglio Isern |
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09:00h-10:15h 09:00h-09:25h 09:25h-09:50h 09:50h-10:15h |
Supernova Environments and SNR Unfolding
Cosmic Rays and Supernova Physics Birth Sites and the Distribution of Massive Stars Observational Consequences of Radioactive
Decay in SN Envelopes |
(Chair: Leising) Biermann Kroupa Danziger |
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10:45h-12:00h 10:45h-11:10h 11:10h-11:35h 11:35h-12:00h |
Continuum and 44Ti Line Emission from
Cas A |
(Chair:
Knödlseder) Vink Mochizuki Tatischeff |
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14:00h-15:40h 14:00h-14:25h 14:25h-14:50h 14:50h-15:15h 15:15h-15:40h |
Nucleosynthesis Events and the Interstellar
Medium
Elemental Composition and Distribution
in SNRs: X-Ray Spectroscopy 26Al in Galaxy Regions: Massive-Star Interactions
with the ISM |
(Chair:
Chupp) Decourchelle Diehl
Smith Milne
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16:15h-17:40 16:15h-16:40h 16:40h-17:05h 17:05h-17:30h |
Chemical
Evolution and Cosmic-Rays |
(Chair: Ott) Leising Kratz Pfeiffer |
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17:30h-18:00 17:30h-18:00h |
Nuclear
Physics in the Sun and in the Laboratory Production of Solar Flare Gamma-Ray Lines by Energetic
Ion Interactions |
Chupp
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18:00h-18:05h |
Poster
Advertisements; Part I |
Winkler;
all |
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Wednesday
May 28, 2003
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09:00h-10:15h 09:00h-09:30h 09:30h-09:55h 09:55h-10:15h |
The Solar Environment and Early Solar
Nebula
Short-lived Nuclides in the Early Solar System:
Ambiguities and Implications AGB Early Solar System Radioactivities Connection
Revisited Low energy particle production of short-lived
nuclides in the early solar system |
(Chair:
Korschinek) Goswami Gallino Marhas
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10:45h-12:00h 10:45h-11:15h 11:15h-11:35h 11:35h-12:00h |
Live Radioactivities in Terrestrial Matter
Samples
Evidence for Live 60Fe in Meteorites
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(Chair: Korschinek) Mostefaoui Knie Vockenhuber |
Thursday
May 29, 2003
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09:00h-10:30h
09:00h-09:20h |
Lessons and Perspectives for Experiments
Future Instrumentation for Isotopic Analysis
of Presolar Grains |
(Chair: Kanbach) Ott |
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09:20h-09:50h |
Schönfelder |
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09:50h-10:20h |
Ryan |
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10:50h-12:05h
10:50h-11:20h |
Principles for Building Gamma-Ray Telescopes
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(Chair: Schönfelder)
Skinner
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11:20h-11:45h |
Smith
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11:45h-12:05h |
Ryan
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14:00h-15:00h
14:00h-14:20h |
Design of Gamma-Ray Telescopes: Simulation
and Data Analysis Tools
The GEANT Package and its Use in the Design of
Compton Telescopes |
(Chair: Kurfess)
Kippen
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14:20h-14:40h |
MC Simulations of Gamma-Ray Backgrounds:
TGRS/WIND and INTEGRAL |
Weidenspointner
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14:40h-15:10h |
Zoglauer
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15:10h-15:30h |
Zych
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16:00h-18:15h
16:00h-16:20h |
Gamma-Ray Telescope Development Projects (I)
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(Chair:
Ryan) v. Ballmoos |
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16:20h-16:40h |
Reconstruction of Interaction Sequences in Compton
Telescopes |
Oberlack |
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16:40h-17:00h |
Kanbach
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17:00h-17:20h |
Takahashi
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17:20h-17:40h |
Kurfess
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17:40h-18:00h |
Bloser
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Poster
Presentations |
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Friday
May 30, 2003
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09:00h-10:35h
09:00h-9:20h |
Gamma-Ray Telescope Projects (II)
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(Chair:
Diehl) Hartmann |
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09:20h-9:45h |
Xenon Compton Telescope Development at
Columbia: the post LXeGRIT phase |
Aprile
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09:45h-10:10h |
Aprile |
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10:10h-10:35h |
Andritschke |
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11:00h-12:20h
11:00h-11:20h |
Gamma-Ray Telescope Projects (III)
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(Chair:
Aprile) Tanimori |
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11:20h-11:30h |
Smith |
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11:30h-11:40h |
Winker/Diehl |
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11:40h |
Closing
Remarks |
Kanbach |
Poster
Program
Monday
May 26 - Friday
May 30, 2003
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Astronomy with Radioactivities
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Winkler |
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Gamma-Ray Telescopes
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A Prototype Calorimeter with Silicon Drift
Detectors for Compton Telescopes |
Marisaldi |
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AGILE: Satellite Description, and Prospects for
the Mini-Calorimeter |
Celesti |
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A high resolution Schottky CdTe diode for gamma-ray
detectors |
Tanaka |
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High resolution CdTe imaging devices for a Compton
Telescope |
Mitani |
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(Abstract not received)
A review of the main features of the gamma-ray emission from classical novae will be presented. I will concentrate on the theoretical predictions, with all the most recent nuclear reaction rates discussed. Both the long lasting emission, produced by electron captures on 7Be and 22Na decay, and the prompt emission, produced by electron-positron annihilation (with positrons coming from 13N and 18F decays), will be described, as well as the contribution of novae to the galactic content of 26Al. The observability of novae by INTEGRAL (SPI and IBIS) and future missions, like EXIST and MAX, will be discussed.
(Abstract not received)
Although remarkable progress has been made in gamma ray astrophysics recently, and amazing discoveries have been realized (witness the history of our understanding of gamma ray bursts), many of the early scientific objectives remain unfulfilled. This is due primarily to the rather modest improvement in sensitivity (about 100x) from the pioneering balloon observations to the CGRO and INTEGRAL missions when compared with the improvements in other energy bands ( ~ 105 in X-ray astronomy). Important objectives related to supernovae and novae, and the search for line emissions from compact objects will benefit from another factor of 100 gain in sensitivity. Several approaches to achieving dramatic improvements will be discussed. These include advanced Compton telescopes using detectors with high spectral and spatial resolution, and concepts for Laue collectors and imaging gamma ray telescopes. The latter has potential for a remarkable increase in sensitivity, but will require major advances in mission implementation.
INTEGRAL, ESA's gamma-ray observatory mission was launched from Baikonur cosmodrome by a Proton rocket on 17 October 2002, and injected into its operational orbit with highest precision. Subsequent activation of spacecraft and instruments proceeded smoothly as planned. The commissioning phase including instrument performance and verification observations of the Cygnus region has been completed successfully. Early results indicate that the instruments are working well with scientific performances close to those predicted prior to launch. This talk will provide a summary of the observatory status, discuss a selection of first scientific results and present the future observing programme.
With the successful launch of ESA's INTEGRAL satellite in october 2002, a gamma-ray observatory has become available to the scientific community which for the first time combines excellent imaging and spectroscopic capacities in the 20 keV to 10 MeV energy range. I will present the status and the inflight science performances of the spectrometer SPI on INTEGRAL, as assessed during the initial performance verification and calibration phase. First scientific results will be presented, with special emphasis on gamma-ray line spectroscopy.
The NanoSIMS is a new generation ion microprobe which was installed at MPI for Chemistry in 2001. This instrument is characterized by a high spatial resolution (down to 50 nm) and high detection efficiency for secondary ions. The combination of these two features makes the NanoSIMS a unique tool for the study of extraterrestrial materials. Here, we present our first results from a number of research projects related to extinct radioactivities in presolar grains and solar system solids, and the search for presolar grains in meteoritic thin sections. Presolar SiC X grains, believed to have formed in SN explosions, were studied for Ca-Ti-V isotopic systematics. Large excesses in 44Ca and 49Ti are indicative for the presence of radioactive 44Ti (half-life 60 y) and 49V (half-life 330 d) at the time of grain formation. A positive correlation between 49Ti excesses and V/Ti ratios suggests grain formation on a time scale of several months after SN explosion. The study of the isotopic systematics of Al-Mg in plagioclase from ordinary chondrites, Mn-Cr in carbonates from Orgueil, and Fe-Ni in troilite from Semarkona has clearly revealed the presence of radiogenic 26Mg (from the decay of 26Al, half-life 0.7 My), radiogenic 53Cr (from the decay of 53Mn, half-life 3.7 My), and radiogenic 60Ni (from the decay of 60Fe, half life 1.5 My), respectively. These results indicate (i) widespread distribution of 26Al in the early solar system, (ii) early aqueous activity on the Orgueil parent body, and (iii) high 60Fe abundances in the early solar system, making 60Fe a potential heat source for planetary melting.
We examine the properties of Wolf--Rayet (WR) stars predicted by models of rotating stars taking account of new mass loss rates for O--type stars and WR stars and of the wind anisotropies induced by rotation. Models having a typical velocity for the O--type stars have WR lifetimes on the average two times longer than for non--rotating models. The increase of the WR lifetimes is mainly due to that of the H--rich eWNL phase, during which 26Al is ejected. The mass threshold for forming WR stars is lowered from 37 to 22 M¤ for typical rotation. The comparisons of the predicted number ratios WR/O, WN/WC and of the number of transition WN/WC stars show very good agreement with models with rotation, while this is not the case for models with the present--day mass loss rates and no rotation. These effects induced by rotation (namely the increase of the WNL lifetimes, and the decrease of the mass threshold for forming WR stars when the initial rotational velocity increases) tend to increase the contribution of the WR stars in 26Al.
The past year has brought considerable progress in the study of the mechanism behind core-collapse supernovae. From the first 3-dimensional collapse simulations to the use of increasingly sophisticated transport schemes in 2-dimensions, the latest generation of computers have allowed scientists to study supernovae in a new level of detail. I will review the current mechanism behind core collapse supernovae, highlighting the discoveries made in the past year. I will concentrate on the Los Alamos effort to study the collapse and explosion of massive stars in 3-dimensions, providing new insights into the asymmetries that develop in the explosion. These asymmetries can significantly alter the nuclear yields and observations of supernovae.
High energy emission from supernovae provide a direct window into the quantity and distribution of radioactive elements produced in these explosions. Combining supernova explosion calculations with 3D Monte Carlo gamma-ray transport, I have studied the effect mixing and asymmetries have on the hard X-ray and gamma-ray spectra. With sufficient spectral resolution, the emission line profiles from Nickel decay have enough information to distinguish between spherical and mildly asymmetric supernova explosions. The clumping of Nickel due to mixing has decided features in the line profile as well. Longer lived radioactive species also exhibit observable artifacts due to asymmetries in the explosion and I will conclude by presenting new results on these asymmetries.
We investigate explosive carbon, neon and oxygen burning in core collapse supernovae by coupling a tracer particle method to multi-dimensional Eulerian hydrodynamic calculations. Adopting the most recently available experimental and theoretical nuclear data, we compute the nucleosynthetic yields by post-processing the temperature and density history of advected tracer particles. To verify the method for its future application to multidimensional calculations, we compare our results to 1D calculations recently published in the literature.
Since the dynamics of the explosion is reflected in the distribution of the mass of the single isotopes in velocity space, this is of crucial importance for an understanding of the evolution of the supernova beyond the first second. Using our marker particles approach, we therefore performed a study of velocity distributions of different isotopes (12C, 16O, 28Si, 44Ti, 56Ni) within 3 sec after the core bounce (time when the explosive nucleosynthesis is frozen).
(Abstract not received)
Standard shock acceleration in the Interstellar Medium leads to energies far below the feature in the cosmic ray spectrum usually referred to as the knee, at $3 \, 10^{15}$ eV, where the spectrum bends down by about 1/3. There is one proposal published that links this feature to the explosion of very massive stars, red supergiants and Wolf Rayet stars. In this proposal the knee is predicted to be at near $Z \; 10^{15}$ eV approximately, and the ankle, where the spectrum is in transition to the extragalactic component, at $Z \; 3 \; 10^{17}$ eV, where $Z$ is the charge of the nucleus. The spectrum is predicted to be $E^{-2.67}$ below the knee, and $E^{-3.07}$ above the knee, with some expected error range. The observed features, at knee and ankle are so well defined that the critical $E/Z$ ratio must be very well defined in Nature, and be common to all sites contributing to our cosmic ray population. This then leads back to the argument by Bisnovatyi-Kogan (1970), based on an earlier suggestion by Kardashev (1964), that supernovae are powered by potential energy, and that the energy is transmitted from rotation via magnetic fields to the outside; this argument can be made quantitative. Considering then the abundances of cosmic rays this proposal requires that very massive stars explode with $10^{52}$ ergs, rather more than usually assumed. These explosions may provide a new standard candle in cosmology, if we found a way to correct for non-sphericity. This is easily explained in Bisnovatyi-Kogan's (1970) picture. Tests will be mainly the gamma ray spectrum of the Galaxy, and its spatial variation, the abundances of the various chemical elements in cosmic rays, the fraction of anti-protons, and the precise cosmic ray spectrum at knee and ankle. For the energies above $3 \, 10^{18}$ eV we very briefly discuss the various options, mainly differentiated by the effect of cosmic magnetic fields; radio galaxies are a major competitor for the origin of these events.
Massive stars which are taken here to mean those that explode as supernovae and have masses larger than 8Msun, appear to be born exclusively in populous clusters. Their IMF is found to be a Salpeter power-law for a wide range of cluster densities and metallicities, showing a rather remarkable universality. There is theoretical and observational evidence suggesting that massive stars form within the centers of their clusters, and that most massive stars have one or more companions. Such cores of multiple massive systems can be unstable dynamically, depending on the number of stars in the core. Unstable cores decay within a few core crossing times (of the order of 104 yrs) thereby ejecting massive stars. Some of these may leave the cluster with large velocities (up to a few 100 km/s). The massive stars disrupt the nebula embedding the cluster owing to their energetic feedback (radiation and winds). Nebula disruption seems to occur within less than a few cluster dynamical times (105 yrs or less) leading to cluster expansion. This is accompanied by the loss of the majority of stars from the embedded cluster thus rapidly adding low-mass stars to the Galactic-field population, as well as leaving a low-density open cluster as a remnant of a splendour gone by.
A description will be given of the ways in which the energy released by radioactive decay in Type II supernova envelopes manifests itself. These manifestations are observable and quantifiable in the optical wavelength range. Both light curves and Balmer line emission areexamples. New results for Type IIP supernovae will be presented including a summary of what is known about 56Ni production in a sample of 12 objects.
I will review the our current understanding of Cas A in order to
put its Ti-44 emission in context. I will address the mass of the
progenitor, its mass loss history, explosive nucleosynthesis and dynamics.
Especially, the observation that iron moves faster than silicon deserves
attention as the kinematics of Ti-44 is likely to have similar properties.
The key isotope 44Ti decays purely by orbital-electron capture. Very roughly speaking, the electron-capture-beta-decay rate for the H-like atom is half the rate for the neutral atom. We can therefore easily expect that its radioactivity depends strongly on its ionization history in an evolving young supernova remnant. The crucial point here is whether 44Ti atoms can attain a high degree of ionization and how long they can keep it. In this talk, I will first discuss the ionization effect of 44Ti on its initial abundance in Cas A, taking an updated hydrodynamical SNR model and recent information on the X-ray observation of the elemental distribution and also on atomic recombination properties into consideration. We aim to see if the ionization effect, i.e., the retardation of the electron-capture decay, can remove the apparent discrepancy between 44Ti production in the Cas A explosion as inferred from the compilation of COMPTEL gamma-line measurements and the theoretical expectations from current supernova nucleosynthesis models. Then I will briefly discuss the detection possibility of 44Ti nuclear lines from SN 1987A from our analysis of the bolometric luminosities observed recently.
Observations with INTEGRAL of nuclear interaction gamma-ray lines from the interstellar medium would provide a unique tool to study Galactic cosmic-ray ions at energies below 100 MeV/nucleon. If the lines produced in the gas phase are expected to be significantly Doppler-broadened, some lines produced in interstellar dust grains can be very narrow, because some of the excited nuclei can stop in solid materials before emitting gamma-rays. The latter are prime candidates for detection with the INTEGRAL spectrometer. The most promising of such lines are at 0.847 from 56Fe, 1.369 MeV from 24Mg, 1.779 MeV from 28Si and 6.129 MeV from 16O. We performed detailed calculations of their profiles and intensities, using in particular available laboratory measurements combined with nuclear physics theory to evaluate the energy distributions of the recoil nuclei. We also used recent results concerning the composition and size distribution of interstellar grains. Predicted line fluxes from the inner Galaxy will be discussed.
I will present recent results from the XMM-Newton and Chandra X-ray satellites on young Supernova Remnants. I will show that X-ray spectro-imagery is a key approach to investigate their elemental composition, the spatial distribution of these synthesized elements, as well as particle acceleration at their shocks.
The major part of Galactic 26Al is presumably ejected from the winds and supernovae of massive stars. The parental stellar associations have evolved over their lifetimes of tens of Myrs, and thus have shaped the interstellar morphology in the region of the association. On the other hand, 26Al radioactivity is seen only from the latest massive-star activity within the 1 Myr decay time of 26Al. We discuss how this may affect the search for tracers of 26Al, using the Orion region as example.
The Reuven Ramaty High Energy Solar Spectroscopic
Imager (RHESSI), although designed for solar observations, sees the whole
sky at gamma-ray energies (minus Earth occultation) due to the very light
spacecraft structure and lack of shields around its Ge detectors. A year of data has been processed to search for lines
from radioactivity in the inner Galaxy. The
1809 keV line from 26Al is detected with over 11 sigma significance,
and is found to be considerably narrower than the GRIS result (Naya et al.
1996). We are still working on reducing the
systematic errors in the background subtraction (currently 1--2%) for the
lines of 60Fe, so I will present only an upper limit at this
time.
Nine years of observations with the CGRO/OSSE instrument have allowed the first maps of positron annihilation radiation to be created. The maps have revealed that galactic annihilation occurs in both the bulge and the disk of the Galaxy. Attempts to derive maximal information from the OSSE data-set have been hindered by difficulties extracting the line and continuum components of annihilation radiation from the individual OSSE spectra. In this talk I will discuss what I consider to be the most important puzzles that remain unsolved after three decades of observing galactic positron annihilation radiation.
(Abstract not received)
Supernova shocks provide the energy for the acceleration of Galactic cosmic rays, but the source material is an openquestion. The similarity between ultra-heavy cosmic rays (UHCR) and the interstellar medium (ISM) suggested that they may be accelerated out of the well-mixed ISM. But, since most of the heavy elements are ejected into the ISM by supernovae (SN) (which are clustered in space and time), the relative abundance ratios will not differ between these ejecta and the well-mixed ISM. However, the UHCR abundances of the actinide elements, Th, U, Pu and Cm, can provide critical constraints on the major sites of their acceleration and metallicity, as well as on the time scales involved.
The expected range of actinide abundances in the cosmic rays is derived from the r-process yields in core-collapse SN calculated within the "waiting-point approximation". From these yields the mean actinide abundances over time following the SN are predicted.
Future measurements of the abundance ratios will help to solve these questions. First results of experiments performed on the MIR space station (ECCO) and with balloon flights (TIGER) are promising.
We compare r-process model predictions with recent astronomical observations from the solar system, ultra-metal-poor (UMP) halo stars and meteoritic r-process signatures, i.e. containing elemental as well as isotopic abundances. We deduce (1) astrophysical conditions (n_n-ranges for weak and main r-process components) under which such r-patterns can be obtained, and (2) criteria to determine Th/U chronometric ages.
Solar-system abundance provides precise data to identify the origin of the p-process, which contributes to the understanding of the chemical evolution of the Galaxy. Although many possible astrophysical sites have ever been proposed, the origin of the p-process elements has been unidentified clearly for about half a century after the first indication of the p-process in BBFH. This is presumably because there was no clear observational or experimental evidence showing the physical condition of the p-process exclusively. We woudl like to present two scaling laws between p- and s-process elements based on the observed Solar abundance, which is the first observational evidence constraining the origin of the p-process precisely. These scalings suggest that the environmental condition of the p-process is universal in the Galaxy and that the scalings provide the frequency of explosive p-process events uniquely. We deomonstrate the power of these two scaling laws in our theoretical calculations of SN explosion models. We also propose a new nuclear cosmochronometer of the p-process, 176Lu-176Hf-174Hf, by applying the scalings, whose half-life is long enough for the age estimate of the Galaxy. This chronometer is useful for the determination of the timescale of a single p-process event before the Solar-system formation as well as a mean timescale of the p-process events.
The acceleration of energetic ions during solar flares can produce narrow and broad nuclear gamma-ray deexcitation lines, by nuclear interactions with the ambient solar atmosphere. The line intensities depend directly on the ambient and accelerated particle abundances. In addition production of neutrons in several reactions leads to emission of the neutron-proton capture gamma-ray line, in the photosphere, at an energy of 2.223 MeV . The rate of decay in intensity of this line depends direcly on the photospheric 3He/H abundance ratio. Observations of solar flare gamma-ray spectra have been made since 1972, by satellite-borne gamma-ray spectrometers on OSO 7, HEAO 3, SMM, HINOTORI, GRANAT, YOHKOH and CGRO. We will review the basic physics involved in determining abundance ratios. Also, we review the current analysis results which give a photospheric He3/H abundance ratio of 2.3 ± 1.4. In addition, a study of narrow gamma-ray line fluxes from several flares suggests that the ratio of (Mg+Si+Fe) to (C+N+O) abundances changes with time during the flare. Since this ratio measures the abundance ratio of low first ionization potential (FIP) elements to high FIP elements, the gamma-ray production site "may" start in the lower chromosphere and move into the corona, where the low/high FIP abundance ratio increases, as the flare progresses. Furthemore, a study of the broad gamma-ray line fluxes can, in principle, determine the abundances of the flare accelerated heavy ions. We will also compare abundances determined from gamma-ray lines to other determinations of solar abundances.
Evidence for the presence of ten short-lived now-extinct nuclides with half-life ranging from 100,000 years to ~100 Ma have been found in meteorites. An understanding of the source and origin of these nuclides provides insight into possible stellar relationship during the birth of the solar system. The nuclides with half-life less than a couple of million years (Ca-41, Al-26, Be-10, Fe-60) must have been produced either shortly before or during the very early stages of the formation of the solar system. This is also substantiated by the limits on gamma ray fluxes from Al-26 and Fe-60 decay which indicate that galactic abundances of these nuclides are at least an order of magnitude below the inferred initial values for the early solar system. The nuclides with intermediate half-life (Mn-53 and Pd-107) could have been produced either along with these short-lived nuclides or may be products of continuous galactic nucleosynthesis. Two possibilities are considered as source of these nuclides; a single stellar source (e.g., SN, TP-AGB, WR) or energetic particle production in solar, presolar or stellar environments. While the presence of Be-10 argues for an energetic particle production mechanism, this cannot concurrently produce the other nuclides (Ca-41, Al-26 and Mn-53) in the required amounts. Further, production of Fe-60 by energetic particle interactions is extremely difficult due to lack of abundant targets. A Single stellar source can potentially produce most of the nuclides (other than Be-10). However, there remain ambiguities about which could be the most probable source. A TP-AGB star appeared to be a distinct possibility but the recent data for initial solar system abundance of Fe-60 puts a question mark on this. The new data favors a SN source for which Al-26 remains a problematic issue. The presence of freshly synthesized products from an evolved star also led to the hypothesis of a triggered origin of the solar system. Simulation studies of triggered collapse of molecular clouds support such a hypothesis and there are indirect, although rare, observational hints for triggered star formation.
We review possible stellar origins of
short-lived nuclei that were shown to be alive in the early solar system.
A revival of a close-by AGB polluting the protosolar nebula depends on the
very debated problem of 60Fe. Aims and difficulties of a Supernova
scenario are outlined.
Presence of short-lived nuclides in the early solar system is either due to their injection into the protosolar cloud from a nearby stellar source or due to interactions of energetic particles in a nebular or presolar environment. The later scenario gained importance after the discovery of Be-10 in CAIs, as Be-10 is not a product of stellar nucleosynthesis. Various scenarios for production of short-lived nuclides by energetic particles have been discussed, e.g., galactic cosmic rays, r-process jets, x-wind, low energy particle irradiation in the solar nebula or in protosolar cloud. We present results obtained for production of short lived nuclides (Al-26, Ca-41, Mn-53, Be-10) due to interaction of solar energetic particles (SEP) from early active sun with nebular dust at 1 A.U. These results indicate that the power spectra of solar energetic particles play an important role in production of particular short-lived nuclide. A flatter power spectra can lead to production of Be-10 that can match the amounts seen in refractory phases of meteorites considered to be some of the earliest solar system solids, whereas production of other short-lived nuclides (e.g. Al-26, Ca-41) are much below their canonical early solar system values. Such an irradiation scenario is consistent with recent experimental data that revealed absence of Al-26 and presence of Be-10 in some hibonite grains from carbonaceous chondrites. The experimental results and production calculations indicate that the sources of the short lived nuclide Be-10 and others (Al-26, Ca-41) are decoupled. While Be-10 is a product of energetic particle irradiation, origin of the other short-lived nuclides present in the early solar system may be traced to a stellar source. The injection of these freshly synthesized nuclides might have also triggered the collapse of proto solar molecular cloud leading to the formation of the solar system. The short-lived nuclide Mn-53 may have contribution from both energetic particle production as well as stellar nucleosynthesis.
There are several indications for one or even more supernova(e) rather close to the solar system during the last million of years. A unique indication for such an event is the (background free) detection of long lived radioisotopes ejected by the SN and deposited on Earth. At the beginning of this search we concentrated on 60Fe (T1/2=1.5Myr), because of a negligible solar system background and a high production yield in core collaps SNe. After a first detection of 60Fe in a deep ocean ferromanganese crust we now have measured a very detailed 60Fe profile in a different crust, resulting in at least one clear signal of a nearby SN during the last 14 Myr. Besides of the 60Fe measurements, profiles of other possibly SN produced radionuclides (10Be, 26Al, 53Mn, 244Pu) have been measured in the this crust.
1Vienna Environmental Research Accelerator
(VERA), Institut für Isotopenforschung und Kernphysik, Universität
Wien, Währinger Strasse 17, A-1090 Vienna, Austria 2Racah Institute of Physics, Hebrew University of
Jerusalem, 91904 Jerusalem, Israel 3Atominstitut der Österreichischen Universitäten,
Stadionallee 2, A-1020 Wien, Austria
The presence of live 182Hf (T1/2 ~ 9 Myrs) in the Early-Solar System is well established, with most recent values for the 182Hf/180Hf initial abundance determined as 1.0x10-4. The understanding of this abundance compared to other r-process nuclides in terms of astrophysical models is still challenging but there is little doubt that live 182Hf should be present in the Interstellar Medium (ISM) as a result of recent nucleosynthesis activity. We are attempting a search for live 182Hf possibly deposited on Earth either by isolated supernovae events (similarly to recently observed 60Fe) or from steady-state accretion of ISM grains. The search focuses on deep-ocean sediments, and a method for chemical extraction of the Zr-Hf fraction from sediments has been developed. The detection of 182Hf is performed at the Vienna Environmental Research Accelerator (VERA), a dedicated facility for accelerator mass spectrometry (AMS) recently upgraded for heavy nuclide measurements. Measurements of Hf and W isotopic abundances for the Zr-Hf fraction extracted from deep-sea sediment samples were performed. The samples originate from two sections (3 and 12 cm sediment depth) of a deep-sea piston core (TRIPOD expedition, 17o30' N, 113o00' W) at 3763 m water depth. Present limits for the 182Hf abundance derived from the measured isotopic abundances will be discussed.
In this report we present the in situ finding of 60Ni isotopic anomalies produced by the decay of short lived 60Fe (half-life 1.5 Ma) in troilite (FeS) and pyroxene in the Chervony Kut "CK" eucrite and in the Semarkona "SMK" (LL3.0) ordinary chondrite using the new state-of-the-art NanoSIMS technique at MPI in Mainz. In SMK, troilites in 4 different locations show 60Ni excesses of up to 105 +- 57 permil (2sigma). A clear correlation is seen between 60Ni excesses and 56Fe/58Ni ratios, providing evidence for live 60Fe in the early solar system (SS). The inferred 60Fe/56Fe ratio of (1.08 +- 0.18)x10-6 is much higher than previously estimated for the initial SS value and approaches 1.6x10-6 inferred from a CAI (known to be one of the first objects formed in the SS). In terms of a chronological interpretation, assuming a homogeneous distribution of 60Fe in the SS, this difference between the two values corresponds to less than one half life of 60Fe. In CK, two pyrrhotite {Fe(1-x)S} types (abundant Pyr-1 crystals and rare Pyr-2 veins) and pyroxene {(Mg,Fe)SiO3} grains also show 60Ni excesses. They vary from 22 +- 16 permil in Pyr-1 to an extremely high value of 1770 +- 250 permil in Pyr-2. No clear correlation is seen between the 60Ni excess and Fe/Ni ratio, which does not allow a plausible explanation for the extreme excess encountered in Pyr-2. Additional measurements are in progress to clarify this ambiguity. At any rate, the new much higher SS 60Fe abundance would invariably lead to early melting of relatively small planetesimals.
We review recent and upcoming developments in laboratory isotopic analysis of small samples such as presolar grains in meteorites and IDPs, with special emphasis on the NanoSIMS. Other topics include TOF-SIMS, resonance ionization (RIMS) and improvements in noble gas mass spectrometry.
The history of Compton Telescope developments is reviewed, and general guidelines for the next generation of Compton Telescopes are derived from the experience with COMPTEL.
Meeting the challenges of gamma-ray astronomy in a single
instrument will be difficult. The variety of
sources and the nature of their emissions over a wide range of energy and
intensities will undoubtedly require an integrated observatory, or its equivalent,
in the fashion of Compton. One
of the remarkable accomplishments of Compton was its success
in observing and measuring sources with multiple instruments, thereby providing
information that would not be available to a single instrument. The instruments of Compton primarily
differed in their energy ranges and it obtained measurements over as much
as four orders of magnitude in the energy domain. Future
goals not only include conducting observations over a similar wide energy
range, but also performing the best possible measurements of narrow and
broad lines, point sources and extended objects, and steady state and transient
sources with a large dynamic range. We review
the demands on medium energy gamma-ray telescopes in the context of a solitary
mission and an integrated observatory.
Coded mask imaging systems
provided the first hard X-ray images of cosmic sources 25 years ago. But
they are an indirect and inefficient way of obtaining
an image – reconstruction of the intensity at a particular point in the
detector involves harvesting photons from all over a detector. The detector
has to be large - larger than the effective area required for the telescope
because no concentration takes place. Thus there a large number of background
events background (the weeds) are harvested
at the same time. The mean level of the background is subtracted, but the
associated random noise remains, and noise from every background event contaminates
every image pixel. Why, then, are they in such wide use today (4 such instruments
on INTEGRAL)? And why are they currently planned
for missions which will not be launched for perhaps another 10-15 years
or more (e.g. Exist)? The logic behind the adoption of the coded mask principle
will be presented, the operation of such instruments and the analysis of
data from them will be considered, and developments and possible future code
mask instruments will be discussed.
The Rotating Modulation
Collimator (RMC) technique converts spatial information into temporal modulation
of the signal from a source, allowing image reconstruction from Fourier components
in a manner mathematically analogous to what is done in radio astronomy. I will quickly review the principle and some of the
image reconstruction techniques (cleaned back projection, maximum entropy,
pixons), and show data from RHESSI, including the first RMC image of a gamma-ray
line: the neutron capture line from the solar flare of June 23, 2002 (Hurford
et al. 2003). Finally, I will discuss the potential
of the technique for future hard x-ray and gamma-ray missions.
Electromagnetic radiation
is defined by four properties. Each photon can
be completely characterized by its time of arrival, its energy, its direction
of arrival, and its polarization state. To date, our understanding of high-energy
emissions has come largely from measurements of the first three of these
quantities. Several mechanisms can lead to linearly
polarized emissions at hard X-ray and soft gamma-ray energies, including
magnetobremsstrahlung radiations (cyclotron, synchrotron and curvature radiation),
electron-proton bremsstrahlung, Compton scattering and magnetic photon splitting.
Efforts to study the fourth quantity (polarization) have so far met with
only very limited success, in part, because there has been little effort
towards developing instruments that are optimized for polarization measurements. We review the current status of experimental efforts
to measure high energy polarization, the latest results from both solar
flares and gamma-ray bursts, and the prospects for future measurements.
The Compton gamma-ray imaging technique is inherently based on the assumption of scattering with free electrons. In reality, electron binding momentum blurs this ideal scattering response in a process known as Doppler broadening. As advanced Compton telescopes make use of component detectors with increasingly better energy and spatial resolution, the imaging performance becomes limited by the physics of Doppler broadening, rather than the component detector performance. The design and understanding of modern telescopes thus depends critically on the ability to account for Doppler broadening effects. For this purpose, a Monte Carlo package that simulates detailed Doppler broadening has been developed for use with the powerful, general-purpose GEANT and GEANT4 codes. I will describe the design of this package, and show results of comparison with selected experimental data. I will also present examples of how the code can be used to model complex Compton telescopes.
Intense and complex instrumental backgrounds, against which the much smaller signals from celestial sources have to be discerned, are a notorious problem for low and intermediate energy gamma-ray astronomy (~50 keV -- 10 MeV). Therefore a detailed qualitative and quantitative understanding of instrumental line and continuum backgrounds is crucial for most stages of gamma-ray astronomy missions, ranging from the design and development of new instrumentation through performance prediction and mission planning to data reduction. We have developed MGGPOD, a suite of Monte Carlo codes built around the widely used GEANT (Version 3.21) package, to simulate ab initio the physical processes relevant for the production of instrumental backgrounds. These include the build-up and delayed decay of radioactive isotopes as well as the prompt de-excitation of excited nuclei, both of which give rise to a plethora of instrumental gamma-ray background lines in addition to continuum backgrounds. We demonstrate the capabilities of the MGGPOD suite by modeling high resolution gamma-ray spectra recorded by the Transient Gamma-Ray Spectrometer (TGRS) on board Wind during 1995, and by the SPI spectrometer on board the recently launched INTEGRAL observatory in late 2002.
The data analysis for combined Compton and Pair telescopes like the Medium Energy Gamma-ray Astronomy telescope (MEGA) separates into 3 basic stages: calibration and low-level data-analysis, event reconstruction and all high level data analysis like image reconstruction, spectrum and polarization. The basic layout of the data-analysis will be presented in this talk. The most critical part in the analysis, the event reconstruction, has to identify all event types (Pair-creation, Compton events, charged particles, etc) while effectively suppressing different kinds of background (photons from below, chance coincidences, activation, etc). The current state of our algorithms is capable of identifying and analyzing tracked, not-tracked and multiple Compton events as well as pair-creation events and separate them from background events. For the last stage of the data analysis, an unbinned image reconstruction technique, called List-Mode Maximum-Likelihood Expectation-Maximization, is used. The current implementation is able to incorporate all event types with their different parameter sets into one image in an appropriate coordinate system (far-field spherical, near-field Cartesian 2D/3D), while preserving all measured information and managing high background situations.The current performance of the data analysis will be demonstrated by the latest calibration measurements of the MEGA prototype.
Various concepts of advanced Compton telescopes have turned toward a compact design, aimed at overcoming the intrinsically low efficiency of the classical concept of two distant detector planes. While this greatly increases detection efficiency, it also makes the successful time-of-flight ordering of the interaction sequence a la COMPTEL impractical. It has long been realized that imaging efficiency now depends crucially on successful sequence ordering by other means. Using redundant kinematic information, proper sequencing and additional background suppression may be achieved. We review previous approaches, and then focus on the development of a new algorithm that assigns sequence probabilities, given instrumental uncertainties, in both an accurate and practical way. We further discuss the dependency of reconstruction and background suppression efficiency on detector properties.
On June 14 2001, the balloon-borne gamma-ray lens telescope CLAIRE was launched by the French Space Agency CNES from its base at Gap-Tallard in the French Alps and was recovered near Bordeaux after roughly 5 hours at float altitude. CLAIRE's objective was to validate the concept of a Laue diffraction lens for nuclear astrophysics. While a diffraction lens is ideally suited to the observation of gamma-ray lines, proving the principle with a balloon prototype ironically required observing a continuum spectrum - the Crab nebula.
CLAIRE's lens consists of 556 crystals mounted on the eight rings of a 45 cm diameter Titanium frame. Every crystal has been tuned individually to concentrate 170 keV photons onto a small 3x3 array of high-purity Germanium detectors. The detector matrix is actively shielded by a CsI(Tl) veto shield and an active BGO collimator. Two almost independent systems stabilise the telescope and point the lens at a target close to the sun - on June 14 the Crab is at 1° only. The 3m long telescope structure consists of carbon fiber spars and honeycomb platforms; the entire instrument weighs only 500 kg.
We present the telescope and its performance, the balloon measurements and data analysis, before focussing on CLAIREs' first light : the first astrophysical observation with a gamma-ray lens.
A prototype balloon-borne telescope is being constructed for gamma-ray observations in the low MeV energy range. The Tracking and Imaging Gamma Ray Instrument (TIGRE) uses multi-layers of thin silicon detectors to track and measure the energy losses of Compton recoil electrons. When combined with the direction and energy of the Compton scattered gamma ray a unique incident direction for each photon event is determined. This facilitates improved background rejection, image reconstruction and sensitivity. The converter/tracker also serves as an electron-positron pair detector for gamma rays up to 100 MeV. It consists of 16 layers of 300 mm thick double-sided silicon strip detectors. Each detector is 10 cm x 10 cm with 128 orthogonal strips per side at 765 mm pitch. Each layer consists of 4 detectors for a sensitive area of 400 cm2. Five 256-element CsI(Tl)-Photodiode arrays and a plastic scintillator charge particle shield complete the telescope configuration. The initial continental U.S. flight will be used to determine the sub-orbital atmospheric backgrounds and search for polarized gamma emission for the Crab pulsar. Longer southern hemisphere flights with an enhanced instrument will map out the Al26 emissions from the galactic center region. Details of the critical performance features and payload design will be presented.
A Medium Energy Gamma-Ray Astronomy (MEGA) project, is being developed as a successor to COMPTEL and EGRET on CGRO. The MEGA energy band 0.4 - 50 MeV is of great astrophysical importance for the study of cosmic particle accelerators and radioactive nucleosynthesis sites; however this energy band, with no scheduled missions, is characterized by a severe 'sensitivity gap' for the forseeable future. MEGA aims to improve the sensitivity by at least an order of magnitude and could bridge the gap between operating/scheduled missions in the hard X-ray/low MeV range (INTEGRAL, SWIFT) and high-energy gamma-ray missions (GLAST, AGILE). MEGA will be a large field-of-view imaging telescope and is especially suited for large-scale surveys, detection and monitoring of transient (GRBs, XRBs) and highly variable sources (AGN), and the study of the cosmic background radiation. MEGA records and images gamma-rays by detection and tracking of Compton and pair creation events in a stack of double sided Si-strip track detectors in coincidence with a surrounding pixelated CsI calorimeter. In the course of devoloping MEGA, a scaled down prototype detector with 25% of the geometrical area and 33% of the depth of a potential satellite detector has been built. We describe here some properties of this prototype, the plans for a balloon payload, and a concept for a future satellite telescope.
A multi-Compton gamma-ray telescope based on high resolution semiconductor materials (Semiconductor Multi-Compton Telescope (SMCT) or Advanced Compton Telescope (ACT)) is a promising approach to achieve high sensitivity for gamma-rays with energies from several hundred keV up to several MeV. A SMCT utilizing several tens of layers of thin CdTe (Cadmium Telluride) detector is an attractive concept to obtain higher detection efficiency in comparison with Si-based SMCT. Recently we have developed high energy-resolution CdTe diode detectors. A large-area detector with dimensions of 2.15x 2.15 cm: with a thickness of 0.5 mm shows an energy resolution of better than 3 keV (FWHM) at 60 keV. In order to extend the application of CdTe diodes to the detection of MeV gamma-rays, we have constructed a stacked detector consisting of 40 layers of large CdTe diodes. Here we report the recent progress on the high-resolution CdTe diode and describe the conceptual design of new Multi-Compton Gamma-ray telescopes based on Monte Carlo simulation. An idea of active pair production telescope is briefly described.
The development of high-resolution
position-sensitive solid-state detectors enables gamma ray instruments with
improved sensitivity and imaging capabilities. For gamma ray astronomy,
an improvement in sensitivity of 20-50 over previous missions is anticipated
with the Advanced Compton Telescope mission. The gamma ray astrophysics
group at NRL has been developing germanium strip detectors for several years.
We have shown that three-dimensional locations for gamma ray interactions
can be determined with mm accuracy, and have also demonstrated imaging capability
within a single germanium strip detector. Based on the realization that
three Compton interactions would enable the energy and direction cone of
the incident gamma ray to be determined, even when the total incident gamma
ray energy is not deposited in the detector, we
have also initiated work on thick, silicon strip detectors. We are investigating
the use of both thick Si(Li) and thick intrinsic silicon detectors. Progress
on this work, including initial tests of the multiple-Compton imaging technique
will be presented.
We present a concept for
an Advanced Compton Telescope (ACT) based on the use of pixelized gas micro-well
detectors to form a three-dimensional electron track imager. A micro-well detector consists of an array of individual
micro-patterned proportional counters opposite a planar drift electrode. When combined with thin film transistor (TFT) array
readouts, large gas volumes may be imaged with very good spatial and energy
resolution at reasonable cost. The third dimension
is determined by timing the drift of the ionization electrons. The primary
advantage of this approach is the excellent tracking of the Compton recoil
electron that is possible in a gas volume: using xenon gas as 3 atm read
out by micro-wells with a pitch of 150 mm, ~100 samples of the electron direction may be taken
within a number of radiation lengths equivalent to just one layer of a typical
silicon detector. Initial GEANT4 simulations indicate that the initial direction
of a 1 MeV electron may be determined with an RMS error of ~7°. Such good electron tracking allows us to reduce the
point spread function of a single incident photon dramatically, greatly
improving the imaging capability and sensitivity. The
polarization sensitivity, which relies on events with large Compton scattering
angles, is particularly enhanced. We describe
a possible ACT implementation of this technique, in which the gas tracking
volume is surrounded by a CsI calorimeter, and present our plans to build
and test a small prototype over the next three years.
We present the basic features of a Black Hole Finder probe to be proposed to NASA. EXIST will provide a broad census of black holes in the Universe. Stellar mass black holes in the Galaxy, and supermassive black holes in active galactic nuclei have been observationally established, and at the center of our Milky Way a few million solar masses reside in such a small volume that only a black hole appears to be the natural explanation for this density cusp. Most black holes, however, remain undetected due to obscuring gas in accretion flows surrounding these objects. EXIST will find and probe these hidden sources with a sensitive survey in the 10-600 keV band. EXIST will trace the cosmic accretion luminosity, find gamma ray bursts to large redshifts, and study black holes in galactic binary systems. EXIST will also address "secondary" objectives, such as nova and supernova observations, and a survey for recent undetected supernovae via line emission from radioactive 44Ti.
In the years from now to an Advanced Compton Telescope (ACT) mission in the middle of next decade, it is highly desirable to advance the field of MeV astrophysics with intermediate missions capable of new scientific discoveries, beyond the reach of INTEGRAL. Confident in the liquid Xenon TPC technology and with the extensive balloon flight experience gained with the LXeGRIT payload, we are planning the next generation Xenon Compton telescope as an EXPLORER class mission, with a LDB or ULDB as launch vehicle. Our goal is a sensitivity of a few 10-6 /cm2/s for MeV lines, with a 10 days mission launched from mid-latitude. Among the detector concepts under consideration for a Compton telescope, the liquid TPC is the most mature and remains the most promising to meet the essential requirements of large area and low background, at a reasonable level of complexity and cost.
A new phase of R&D of the liquid TPC technology will exploit more fully the unique combination of excellent ionization and scintillation properties of LXe to improve trigger efficiency, resolution and background rejection beyond LXeGRIT performance. Advancements in PMT technology, from compact metal channel to MCP, capable of high sensitivity at the VUV wavelength of Xe light and which work reliably at LXe temperature, offer new possibilities for a large scale telescope , including TOF capability. I will discuss these R&D activities and their impact on the design and performance of the next generation Xenon Compton telescope.
The Liquid Xenon Gamma-Ray Imaging Telescope (LXeGRIT) is the first balloon-borne instrument developed to validate the concept of a single 3-D imaging time projection chamber (TPC) as Compton telescope for MeV astrophysics. Gamma-ray imaging is achieved through the measurement of energy and position of multiple-site Compton scattering events occurring in the TPC homogeneous volume of high purity LXe. Compton kinematics and event visualization in 3-D are effectively exploited to identify the most likely scattering sequence and to reject background. The LXeGRIT TPC operates in the ionization mode, self-triggered with the fast scintillation light. The geometrical area is 400 cm2, an order of magnitude smaller than that of COMPTEL and the thickness of sensitive LXe is 7cm, of equivalent stopping power as COMPTEL D2 detector.
The energy and imaging response of LXeGRIT has been fully characterized in calibration experiments on the ground and in balloon flight experiments, under different trigger conditions and external shielding. During the most successful flight campaign of 27 hr from Ft Sumner, in Fall 2000, the LXeTPC was operated without gamma-ray or charged particle shields. The gamma-ray background, measured at float altitude in the 0.1 – 10 MeV energy band, is well explained by the atmospheric gama-ray flux and its zenith dependence. Multiple-site gamma-ray events detected during 6 hours with the Crab in the FOV of ~60 degree, have been analyzed for Compton imaging of the source, using the COMPASS Maximum Likelihood imaging algorithm developed for COMPTEL. Results on LXeGRIT in flight performance, effective area, angular resolution, minimum flux sensitivity and background level are presented.
This talk will describe the calibration measurements of the MEGA prototype, a tracking Compton and pair creation telescope. The measurements were performed at the High Intensity Gamma Source (HIGS) facility at Duke University (Durham, N.C.) between 22.04. and 06.05.2003 . The main goal of this calibration was directed at higher energies than available from radioactive lab sources and at polarisation.
HIGS is an inverse Compton beam. Gamma-rays are generated by a storage ring free electron laser, where laser photons scatter at an (additional) electron bunch in the storage ring. After collimating to 1.27 or 2.54cm diameter HIGS delivers monochromatic (1-2% FWHM), nearly 100% polarised photons. The measurements take advantage of the broad energy bandwidth, ranging from 700keV up to 50MeV. Since the beam illuminates only a small fraction of the sensitive area of the MEGA prototype, the instrument was mounted on a XY-table to be moveable in vertical and horizontal directions. Every measurement point consists of 11 positions. To get different incident angles of the beam the table is additionally turnable around the vertical axis. Data is taken at angles between 0 and 180 degrees mine the detector response in the field of view as well as from the back side directions (to test background suppression). For measuring the incoming beam flux a beam monitor consisting of a NaI(Tl) (25cm diameter, 12.5cm thick) and a 1cm thick plastic detector is used. An overview over the performed measurements will be given. Also some very preliminary instrument characteristics will be presented.
We have proposed the new wide-view imaging gamma-ray detector for MeV gamma rays. By measuring the direction and energy of not only a scattered gamma ray but also a scattered electron, the direction of an incident gamma ray would be reconstructed event by event. Furthermore, one of two measured (zenith and azimuthal) angles of a scattered electron gives us an additional redundancy which enable us to reject almost all the background events by kinematic fitting. In order to obtain 3-D information of the track of a scattered electron, the micro Time Projection Chamber(TPC) has been developed (10cm-cubic), which measures the position of the track of charged particles in a few hundred micron meter pitch successively. This TPC consists of the new type of a gas proportional chamber: Micro Pixel Gas Chamber (MPGC) which is a one of wireless gas chamber and expected to be robust and reliable. Using this micro TPC and the NaI Anguar camera for the detection of a recoil gamma ray, we successfully obtained the first gamma-ray image by the full reconstruction of the direction of gamma rays event by event. In addtion, we present the status of the improvement of the MPGC, and the simulation results of the performance as a space gamma-ray detector.
(Abstract not received)
An alternate approach to those discussed here for studying newly created nuclei in supernovae and the interstellar medium is to measure the X-ray lines emitted following electron-capture decays of proton-rich unstable nuclei. Relative to gamma-ray line astronomy, advantages include better line sensitivity, better angular resolution, lower instrumental backgrounds, and better prospects for new missions. Disadvantages are fewer promising nuclei, higher interaction cross-sections, smaller fields of view, lower branching ratios (fluorescent yields) and more potentially confusing photons.
Here we outline our first searches for these X-ray lines in current imaging spectrometers, using archival data from Chandra ACIS and XMM-Newton EPIC. These include lines from 55Fe (t1/2= 2.7y) in SN 1987A, 59Fe (t1/2= 75ky) in Tycho’s SNR, and 44Ti in Cas A. This work is supported by NASA NAG 5-10764.
2Physics Division, Argonne National Laboratory,
Argonne, IL 60439, USA
3Environmental Research Division, Argonne National
Laboratory, Argonne, IL 60439, USA
4Racah Institute of Physics, Hebrew University of
Jerusalem, 91904 Jerusalem, Israel
In 1960 Kuroda suggested that 244Pu (T1/2 = 81 million years) was present in the early-solar system producing isotopic anomalies of xenon. The final proof for this hypothesis came from a comparison between measured xenon isotopic abundances in meteorites with those resulting from spontaneous fission of 244Pu in the laboratory. Although the detection of live 244Pu in nature has been reported in the same year, this finding is not unequivocally accepted. In particular, the question of possible contamination with man-made plutonium was raised. Due to the recent interest in detecting live 244Pu from the Interstellar Medium (ISM), the question of the presence of anthropogenic 244Pu in the environment became of interest again. So far, two different 244Pu/239Pu isotope ratios have been reported from locations at low northern latitudes in the Central Pacific. A ratio of 10-4 was measured in a deep-sea-floor sediment from 5800 m water depth at 9˚30’ N, 174˚18’W, and a ratio of 10-3 was found in manganese nodules from 5000 m water depth at 9˚18’N, 146˚03’W.
In order to better assess the 244Pu fallout on earth, we have started a program at VERA to measure 244Pu in sediments from Lake Michigan, routinely sampled for 239,240Pu measurements. First results on the methodology of 244Pu detection were reported at the AMS-9 conference in Nagoya, September 2002. In the present contribution we report on ongoing measurements of 244Pu in Lake Michigan samples, with the goal to establish the 244Pu fallout at a location where considerable information on fallout of plutonium and other radionuclides exists.
We present the project of a new calorimeter
module for Compton telescopes based on an array of silicon drift detectrors
(SDD) coupled to thallium activated cesium iodide (CsI(Tl)) scintillating
crystals. Because of their low output capacitance and the possibility to
have the first amplifying stage directly integrated on chip, SDDs show better
noise performances than traditional p-i-n photodiodes. For this reason, SDDs
coupled to scintillators show a higher energy resolution than similar systems
based on p-i-n photodiodes. In this project, 10 square millimeters SDDs with
integrated JFET have been optically coupled to CsI(Tl) crystals to realize
stand alone gamma-ray detector pixels. The operation conditions have been
carefully adjusted to maximize detectors performances. The pixels were integrated
in an array with read-out based on custom made ASIC's built to match with
the SDDs electrical properties. Shaped signals are digitally converted by
a Digital Front-End Electronic Board which also takes care of ASICs handshaking.
The system architecture is based on the PICsIT instrument (developed by the
CNR-IASF Bologna team) on board the INTEGRAL satellite, at present fully
operative. The calorimeter prototype was designed to fly as a technological
demonstrator on the MEGABALL balloon mission, planned to be launched from
Sicily in summer 2003. In this paper an overview of the instrument will be
given and the status of the project will be reported.
AGILE is an ASI space mission for high
energy astrophysics in the gamma ray energy range 30MeV-50GeV, and in the
X-ray band (10keV-40keV). AGILE is composed of three detecting systems:
a Tungsten-Silicon Tracker, a CsI Mini-Calorimeter and a Silicon based X-ray
detector (Super-Agile), plus an anticoincidence system for background rejection.
The satellite will have good imaging performances (with angular resolution
of a few arc-minutes in the gamma ray band), good timing resolution and
a large field of view (about 1/5 of the sky). AGILE detection principle
is based on the pair production process that arises from the interaction
of high energy photons with the Tungsten layers of the Silicon Tracker. The
Silicon Tracker determines the direction of the incoming radiation, while
the Mini-Calorimeter evaluates the energy of the interacting photons. The
Mini-Calorimeter can also work as a stand-alone gamma ray detector in the
energy range 250keV-250MeV, with no imaging capabilities, for the detection
of transients and gamma ray burst events (in cooperation with Super-Agile)
and for the evaluation of gamma ray background fluctuations.
Cadmium teluride (CdTe) is one of the
most attractive semiconductor materials for the next generation of gamma-ray
detector. We have been working on a high resolution CdTe diode detector
which features low leakage current realized by the Schottkey diode configuration.
-- In order to further reduce the leakage current of the CdTe diode, we
have adopted a guard-ring on the cathode face (Pt). By this, we have succeeded
in reducing the leakege current by an order of magnitude. This can be explained
by the fact that most of the leakage current of CdTe diode flows along the
edge surface. Using the CdTe diode with a guard-ring
, we have achieved an energy resolution of 980eV at 60keV operated at room temperature. This detector shows high stability
at least for 24 hours even at room temperature. We also developed a detector
with dimentions of 21.5mm by 21.5mm. This large detector is an important
step for CdTe-based gamma-ray detectors in the future. We will also report
on the stacked CdTe diode detector which provides both high energy resolution
and a good efficiency for gamma-rays.
A new generation of Compton Telescope
is believed to bring a breakthrough in the observation of the gamma-ray
universe. To realize such a Compton Telescope, we have been working on the
development of the Semiconductor Multi-Compton Telescope(SMCT). In the SMCT
the energy, positional and timing resolution must be high. The imaging device
based on the high resolution CdTe diode is a very promising candidate for
the component of the SMCT. Based on the
recent achievements of the high resolution CdTe diode, we have developed
various kinds of imaging devices ranging from a pixel size of 200 um to
2 mm. Here we report results obtained
from a 18 mm x 18 mm CdTe detector pixellated with 2 mm square pixels. Signals
from 64(8x8) pixels are fed into a newly-developed low noise analog ASIC,
"VA32TA". We obtained 64 uniform spectra and achieved an energy resolution
of 1.7 keV(FWHM) at 60 keV. Results from a gamma camera with dimensions
of 5 cm x 5 cm will also be presented. The camera consists of 1024 individual
CdTe elements with a thickness of 5 cm. With this thickness, the detector
is effective as the absorber part of the SMCT.
"ASTRONOMY WITH RADIOACTIVITIES IV" and "FILLING THE SENSITIVITY
GAP IN MEV ASTRONOMY" ,
INTERNATIONAL WORKSHOP AT THE KLOSTER SEEON CONFERENCE CENTER, SEEON,
BAVARIA, GERMANY MAY 26-30, 2003
Website: http://www.mpe.mpg.de/gamma/science/lines/workshops/seeon03.htm
Organized by Roland Diehl and Gottfried Kanbach
(MPE Garching, also the contact persons / coordinators), Gunther Korschinek
(TU München), Dieter Hartmann (Clemson
University), Jürgen Knödlseder (CESR Toulouse), Uli Ott (MPIfCh
Mainz), Nikos Prantzos (IAP Paris), and Volker Schönfelder (MPE Garching).