Publications (37)1.45 Total impact
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Article: DUAL Gamma-Ray Mission
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ABSTRACT: Gamma-ray astronomy presents an extraordinary scientific potential for the study of the most powerful sources and the most violent events in the Universe. In order to take full advantage of this potential, the next generation of instrumentation for this domain will have to achieve an improvement in sensitivity over present technologies of at least an order of magnitude. The DUAL mission concept takes up this challenge in two complementary ways: a very long observation of the entire sky, combined with a large collection area for simultaneous observations of Type Ia SNe. While the Wide-Field Compton Telescope (WCT) accumulates data from the full gamma-ray sky (0.1-10 MeV) over the entire mission lifetime, the Laue-Lens Telescope (LLT) focuses on 56Co emission from SNe Ia (0.8-0.9 MeV), collecting gamma-rays from its large area crystal lens onto the WCT. Two separated spacecraft flying in formation will maintain the DUAL payloads at the lens' focal distance. Comment: White paper for US National Academy of Sciences Decadal Survey "Astro2010"06/2010; -
Article: The Swift-BAT 58 Month Survey
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ABSTRACT: We present the catalog derived from the first 58 months of data from the Swift-BAT all sky hard X-ray (15-195 keV) survey. The 58 month catalog is the first to use a newly improved data processing technique that incorporates an individual CZT detector gain correction as well as improved noise handling and source detection. We report on the number of AGN and galactic sources detected in the survey. We also find clear evidence of large scale structure in the BAT AGN sample and detect nearby structure such as the Great Attractor and supergalactic plane. We will discuss the spatial distribution of AGN in the survey and their correlation with large scale structure in the nearby galaxy population (z < 0.05).01/2010; 42:675. -
Article: Swift BAT Upper Limits on Non-thermal Hard X-ray Emission from Clusters of Galaxies
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ABSTRACT: Swift BAT is a coded aperture instrument covering 1/8 of the whole sky in each pointing. While it is waiting for gamma-ray bursts at various pointing directions, the BAT accumulates all events from the sky, essentially performing an all sky survey. In the 22-month BAT all sky survey, we have detected 10 clusters of galaxies at >5sigma Perseus, Coma, Ophiuchus, Cygnus A, A2319, A754, A3266, A2142, A3571, Triangulum Australis. The BAT spectra of Perseus, Cygnus A, and A2142 in the 14-100 keV band are dominated by the AGN component in or around the clusters. The other 7 clusters are all hot (kT 10 keV) and their BAT spectrum is consistent with an extension of the thermal emission modeled with ASCA archival data in the 2-10 keV band, and does not require any additional component. In other words, there is no evidence of a non-thermal diffuse component in these clusters. A combined spectrum of the merging clusters shows a small indication of the existence of non-thermal emission compared with the relaxed clusters. However it can be also explained by a thermal model (kT 6.7 keV) with slightly higher temperature than weighted average (=5.8 keV). We estimated the upper limit of the non-thermal emission by adding a power-law model to the spectral fit for the 10 detected clusters. The upper limit is 6x10-12 ergs/cm2/s in average and the lower limit of the magnetic field B ranges 0.2-1 uG assuming inverse Compton scattering of Cosmic Microwave Background photons by relativistic electrons in the cluster. This magnetic field is slightly higher than the value reported by BeppoSAX, but is consistent with variation of B over the cluster obtained by Faraday rotation, since the BAT spectrum is dominated by flux from the 30 arcmin around the cluster center, while BeppoSAX collected most of the cluster flux.12/2008; 41:337. -
Article: Results from SWIFT/BAT Searches for Prompt Gamma-ray Emission from RS Ophiuchi and other Novae
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ABSTRACT: Nova explosions are expected to be observable in the hard X-ray/γ-ray domain due to electron-positron annihilation comptonized down to a few tens of keV. Positrons come from the radioactive decay of short-lived isotopes. The period during which such emission is strong is predicted to be very short -- only a few hours -- and to precede the visual discovery of the nova. We present results from retrospective searches in the SWIFT/BAT data for γ-ray emission from the direction of 18 novae during the period 20 days before and after their discovery. In the case of the recurrent nova RS Oph we obtained a 9.9 sigma detection in the 14-25 energy band, but this emission is probably due to shocks in the ejecta. For the other novae upper limits have so far been obtained.11/2008; 401:323. -
Article: The Use of the BAT Instrument on Swift for the Detection of Prompt Gamma-Ray Emission from Novae
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ABSTRACT: Gamma-rays are expected to be emitted during and immediately following a nova explosion due to the annihilation of positrons emitted by freshly produced short-lived radioactive isotopes. The expected gamma-ray emission is relatively short-lived and as nova explosions are unpredictable, the best chance of detecting the gamma-rays is with a wide field instrument. At the time when the flux is expected to reach its peak, most of the gamma-ray production is at depths such that the photons suffer several Compton scatterings before escaping, degrading their energy down to the hard X-ray band (10s of keV). SWIFT/BAT is a very wide field coded mask instrument working in the energy band 14-190 keV and so is very well suited to the search for such gamma-rays. A retrospective search is being made in the BAT data for evidence for gamma-ray emission from the direction of novae at around the time of their explosion. So far the only positive detection is of RS Ophiuchi and in this case the emission is probably due to shock heating.11/2008; 401:318. -
Article: R&D progress on second-generation crystals for Laue lens applications
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ABSTRACT: The concept of a gamma-ray telescope based on a Laue lens offers the possibility to increase the sensitivity by more than an order of magnitude with respect to existing instruments. Laue lenses have been developed by our collaboration for several years : the main achievement of this R&D program was the CLAIRE lens prototype. Since then, the endeavour has been oriented towards the development of efficient diffracting elements (crystal slabs), the aim being to step from a technological Laue lens to a scientifically exploitable lens. The latest mission concept featuring a gamma-ray lens is the European Gamma-Ray Imager (GRI) which intends to make use of the Laue lens to cover energies from 200 keV to 1300 keV. Investigations of two promising materials, low mosaicity copper and gradient concentration silicon-germanium are presented in this paper. The measurements have been performed during three runs on beamline ID15A of the European Synchrotron Radiation Facility, and on the GAMS 4 instrument of the Institute Laue-Langevin (both in Grenoble, France) using highly monochromatic beam of energy close to 500 keV. Despite it was not perfectly homogeneous, the presented copper crystal exhibits peak reflectivity of 25% in accordance with theoretical predictions, and a mosaicity around 26 arcsec, the ideal range for the realization of a Laue lens such as GRI. Silicon-germanium featuring a constant gradient have been measured for the very first time at 500 keV. Two samples showed a quite homogeneous reflectivity reaching 26%, which is far from the 48% already observed in experimental crystals but a very encouraging beginning. This results have been used to estimate the performance of the GRI Laue lens design.09/2008; -
Article: Swift/BAT teams announces website with catalog of AGN from the first 9
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ABSTRACT: The Swift/BAT team announces a new website featuring 153 AGN found in the first 9 months of the BAT all sky survey. Several of the detections in the 9-month survey are the first high energy detections of these galaxies, including objects not known to be AGN before detection in this survey. The website can be found at http://swift.gsfc.nasa.gov/docs/swift/results/bs9mon/ . The website presents the data from the BAT instrument for the catalog sources including the hard X-ray flux in 4 bands and the 9-month lightcurves.The Astronomer's Telegram. 02/2008; 1429:1. -
Conference Proceeding: New Clues to the Origin of Galactic Positrons
SF2A-2006: Semaine de l'Astrophysique Francaise; 06/2006 -
Article: The ECLAIRs micro-satellite for multi-wavelength studies of gamma-ray burst prompt emission
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ABSTRACT: The cosmological revolution of 1997 has established that (at least long duration) gamma-ray bursts (GRB) are among the most energetic events in the Universe and occur at cosmological distances. The ECLAIRs micro-satellite, to be launched in 2009, will provide multi-wavelength observations for astrophysical studies of GRB and for their possible use as cosmological probes. It is expected to be the only space borne GRB trigger available for ground based robotic telescopes operational at that time. This paper presents the ECLAIRs project and its status. An X/gamma-ray camera onboard ECLAIRs with a wide field of view of ~2 sr, will detect ~100 GRB/yr in the 4-50 keV energy range, localize the GRB with a precision of ~10 arcmin on the sky, and transmit this information to the ground in near real-time, as a GRB trigger for ground based optical telescopes. Inspired by the INTEGRAL imager IBIS, it is based on a CdTe detection plane of ~1000 cm<sup>2</sup>, placed 35 cm below a coded mask. An optical camera, sensitive to magnitude-15 stars, covering up to 1/4th of the X/gamma-ray camera's field of view, will observe the prompt emission and a possible precursor of ~10 GRB/yr in the visible-band. It will continuously acquire images at a rate of ~5 per second, dumped into an on-board memory. A GRB event, detected by the X/gamma-ray camera, triggers a seek-back in memory for the GRB optical precursor. The full X/gamma-ray and visible-band data of a GRB are sent to ground when a high data-rate telemetry ground receiver is reachableIEEE Transactions on Nuclear Science 01/2006; · 1.45 Impact Factor -
Chapter: MAX, a Laue diffraction lens for nuclear astrophysics
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ABSTRACT: The next generation of instrumentation for nuclear astrophysics will have to achieve a factor of 10–100 improvement in sensitivity over present technologies. With the focusing gamma-ray telescope MAX we take up this challenge: combining unprecedented sensitivity with high spectral and angular resolution, and the capability of measuring the polarization of the incident photons. The feasibility of such a crystal diffraction gamma-ray lens has recently been demonstrated with the prototype lens CLAIRE. MAX is a proposed mission which will make use of satellite formation flight to achieve 86m focal length, with the Laue lens being carried by one satellite and the detector by the other. In the current design, the Laue diffraction lens of MAX will consist of 13740 copper and germanium (Ge1−x Six, x ∼ 0.02) crystal tiles arranged on 36 concentric rings. It simultaneously focuses in two energy bands, each centred on one of the main scientific objectives of the mission: the 800–900 keV band is dedicated to the study of nuclear gamma-ray lines from type Ia supernovae (e.g. 56Co decay line at 847 keV) while the 450–530 keV band focuses on electron-positron annihilation (511 keV emission) from the Galactic centre region with the aim of resolving potential point sources. MAX promises a breakthrough in the study of point sources at gamma-ray energies by combining high narrow-line sensitivity (better than 10−6 cm−2 s−1) and high energy resolution (E/dE ∼ 500). The mission has successfully undergone a pre-phase A study with the French Space Agency CNES, and continues to evolve: new diffracting materials such as bent or composite crystals seem very promising.12/2005: pages 269-278; -
Article: The all-sky distribution of 511 keV electron-positron annihilation emission
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ABSTRACT: We present a map of 511 keV electron-positron annihilation emission, based on data accumulated with the SPI spectrometer aboard ESA's INTEGRAL gamma-ray observatory, that covers approximately 95% of the celestial sphere. 511 keV line emission is significantly detected towards the galactic bulge region and, at a very low level, from the galactic disk. The bulge emission is highly symmetric and is centred on the galactic centre with an extension of 8 deg. The emission is equally well described by models that represent the stellar bulge or halo populations. The disk morphology is only weakly constrained by the present data, being compatible with both the distribution of young and old stellar populations. The 511 keV line flux from the bulge and disk components is 1.05e-3 ph cm-2 s-1 and 0.7e-3 ph cm-2 s-1, respectively, corresponding to a bulge-to-disk flux ratio in the range 1-3. Assuming a positronium fraction of 0.93 this translates into annihilation rates of 1.5e43 s-1 and 3e42 s-1, respectively. The ratio of the bulge luminosity to that of the disk is in the range 3-9. We find no evidence for a point-like source in addition to the diffuse emission, down to a typical flux limit of 1e-4 ph cm-2 s-1. We also find no evidence for the positive latitude enhancement that has been reported from OSSE measurements; our 3 sigma upper flux limit for this feature is 1.5e-4 ph cm-2 s-1. The disk emission can be attributed to the beta+ decay of the radioactive species 26Al and 44Ti. The bulge emission arises from a different source which has only a weak or no disk component. We suggest that Type Ia supernovae and/or low-mass X-ray binaries are the prime candidates for the source of the galactic bulge positrons. Light dark matter annihilation could also explain the observed 511 keV bulge emission characteristics.07/2005; -
Article: INTEGRAL/SPI Observations of Electron-Positron Annihilation Radiation from our Galaxy
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ABSTRACT: The spectrometer on INTEGRAL (SPI) is a coded-aperture gamma-ray telescope with moderate angular resolution (3 deg) and superior energy resolution (2 keV at 511 kev). One of it's principal science goals is the detailed study of 511 keV electron-positron annihilation from our Galaxy. The origin of this radiation remains a mystery, however current morphological studies suggest an older stellar population. There has also been recent speculation on the possibility of the existence of light (< 100 MeV) dark matter particles whose annihilation or decay could produce the observed 511 keV emission. In this paper we summarize the current results from SPI, compare them with previous results and discuss their implication on possible models for the production of the annihilation radiation.02/2005; -
Article: Long Distance Test of the CLAIRE Gamma-Ray Lens
09/2004; 552:757. -
Article: The MAX Mission: Focusing on High-Sensitivity Gamma-Ray Spectroscopy
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ABSTRACT: The mission concept MAX is a space borne crystal diffraction telescope for nuclear astrophysics. With its Laue lens consisting of Cu and Ge crystals, MAX is capable of concentrating gamma-rays onto a small, low background detector. The Lens and detector are situated on two formation flying spacecraft. MAX observes simultaneously in two energy bands of high astrophysical relevance (450-540 keV and 800-900 keV); its effective lens area in each band is roughly 600 cm 2 . A small position sensitive detector (strip Ge detector, Si/CdTe matrix, or single segmented Ge detector) performs high resolution spectroscopy and provides the capability for measuring the polarization of the incident photons. The primary scientific objective of MAX is the study of type Ia supernovae by measuring intensities, shifts and shapes of their nuclear gamma-ray lines in the 800-900 keV energy band. When finally understood and calibrated, these strongly radioactive events will be crucial in measuring the geometry and evolution of the entire Universe. Observing the radioactivities from a substantial sample of supernovae and novae will significantly improve our understanding of explosive nucleosynthesis. Moreover, sensitive gamma-ray line spectroscopy performed with MAX is expected to clarify the nature of sources of e - e + annihilation radiation which would appear in the 450-540 keV band, including jets in Galactic microquasars, neutrons stars and pulsars, X-ray Binaries, AGN, solar flares, and gamma-ray afterglows from gamma-burst counterparts. Keywords: instruments for nuclear astrophysics, gamma-ray optics, formation flying09/2004; 552:747. -
Article: The SPI/INTEGRAL Survey of the Galactic Plane After One Year
09/2004; 552:147. -
Article: The INTEGRAL View of the Galactic Nucleus
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ABSTRACT: We present the preliminary results of the observational campaign performed in 2003 to study the Galactic Nucleus with INTEGRAL. The mosaicked images obtained with the IBIS/ISGRI coded aperture instrument in the energy range above 20 keV, give a yet unseen view of the high-energy sources of this region in hard X and gamma-rays, with an angular resolution of 12'. We report on the discovery of a source, IGR J17456-2901, compatible with the instrument's point spread function and coincident with the Galactic Nucleus Sgr A* to within 0.9'. The source is visible up to 60-80 keV with a 20-100 keV luminosity at 8 kpc of 3 x 10E35 erg/s. Although we cannot unequivocally associate the new INTEGRAL source to the Galactic Nucleus, this is the first report of significant hard X-ray emission from within the inner 10' of the Galaxy and a contribution from the galactic center supermassive black hole itself cannot be excluded. Here we discuss the results obtained and the perspectives for future observations of the Galactic Nucleus with INTEGRAL and other observatories08/2004; -
Article: Calibration of the Spectrometer aboard the INTEGRAL satellite
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ABSTRACT: SPI, the Spectrometer on board the ESA INTEGRAL satellite, to be launched in October 2002, will study the gamma-ray sky in the 20 keV to 8 MeV energy band with a spectral resolution of 2 keV for photons of 1 MeV, thanks to its 19 germanium detectors spanning an active area of 500 cm2. A coded mask imaging technique provides a 2 deg angular resolution. The 16 deg field of view is defined by an active BGO veto shield, furthermore used for background rejection. In April 2001 the flight model of SPI underwent a one-month calibration campaign at CEA in Bruy\`eres le Ch\^atel using low intensity radioactive sources and the CEA accelerator for homogeneity measurements and high intensity radioactive sources for imaging performance measurements. After integration of all scientific payloads (the spectrometer SPI, the imager IBIS and the monitors JEM-X and OMC) on the INTEGRAL satellite, a cross-calibration campaign has been performed at the ESA center in Noordwijk. A set of sources has been placed in the field of view of the different instruments in order to compare their performances and determine their mutual influence. Some of those sources had already been used in Bruy\`eres during the SPI standalone test. For the lowest energy band calibration an X-ray generator has been used. We report on the scientific goals of this calibration activity, and present the measurements performed as well as some preliminary results.11/2003; -
Article: SPI/INTEGRAL in-flight performance
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ABSTRACT: The SPI instrument has been launched on-board the INTEGRAL observatory on October 17, 2002. SPI is a spectrometer devoted to the sky observation in the 20 keV-8 MeV energy range using 19 germanium detectors. The performance of the cryogenic system is nominal and allows to cool the 19 kg of germanium down to 85 K with a comfortable margin. The energy resolution of the whole camera is 2.5 keV at 1.1 MeV. This resolution degrades with time due to particle irradiation in space. We show that the annealing process allows the recovery of the initial performance. The anticoincidence shield works as expected, with a low threshold at 75 keV, reducing the GeD background by a factor of 20. The digital front-end electronics system allows the perfect alignement in time of all the signals as well as the optimisation of the dead time (12%). We demonstrate that SPI is able to map regions as complex as the galactic plane. The obtained spectrum of the Crab nebula validates the present version of our response matrix. The 3 $\sigma$ sensitivity of the instrument at 1 MeV is 8 10$^{-7}$ph$\cdot$cm$^{-2}\cdot$s$^{-1}\cdot$keV$^{-1}$ for the continuum and 3 10$^{-5}$ph$\cdot$cm$^{-2}\cdot$s$^{-1}$ for narrow lines. Comment: 10 pages, 18 figures, accepted for publication in A&A (special INTEGRAL volume)10/2003; -
Article: SPI/INTEGRAL observation of the Cygnus region
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ABSTRACT: We present the analysis of the first observations of the Cygnus region by the SPI spectrometer onboard the Integral Gamma Ray Observatory, encompassing ${\sim}$ 600 ks of data. Three sources namely Cyg X-1, Cyg X-3 and EXO 2030+375 were clearly detected. Our data illustrate the temporal variability of Cyg X-1 in the energy range from 20 keV to 300 keV. The spectral analysis shows a remarkable stability of the Cyg X-1 spectra when averaged over one day timescale. The other goal of these observations is SPI inflight calibration and performance verification. The latest objective has been achieved as demonstrated by the results presented in this paper. Comment: 6 pages, 10 figures, accepted for publication in A&A (special INTEGRAL volume)10/2003; -
Article: INTEGRAL/SPI ground calibration
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ABSTRACT: Three calibration campaigns of the spectrometer SPI have been performed before launch in order to determine the instrument characteristics, such as the effective detection area, the spectral resolution and the angular resolution. Absolute determination of the effective area has been obtained from simulations and measurements. At 1 MeV, the effective area is 65 cm^2 for a point source on the optical axis, the spectral resolution ~2.3 keV. The angular resolution is better than 2.5 deg and the source separation capability about 1 deg. Some temperature dependant parameters will require permanent in-flight calibration. Comment: 9 pages, 12 figures, 2 tables. Accepted for publication in A&AL (INTEGRAL Special issue)08/2003;
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2004
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French National Centre for Scientific Research
Lyon, Rhone-Alpes, France
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