Search

The next large NASA mission in the field of γ-ray astronomy is the Gamma-Ray Large Area Space Telescope (GLAST), which is scheduled for a launch end of 2007. This satellite consists of the main instrument LAT (Large-Area Telescope) which is sensitive in the energy range between 10 MeV and 300$>>300 GeV, and a secondary instrument, the Gamma-Ray Burst Monitor (GBM), sensitive from 10 keV to 30 MeV. This omnidirectional monitor is an important instrument for γ-ray burst (GRB) science with GLAST, as it provides the link between the majority of the γ-ray busts emitting at lower energies and the high-energy events of γ-ray bursts and other transients. It will also serve as a trigger to increase the detection rate of γ-ray burst with the LAT. The GBM will provide real-time burst locations over a wide field-of-view (FoV) with sufficient accuracy to repoint the whole GLAST spacecraft. Time-resolved spectra of bursts recorded with LAT and the burst monitor will allow the investigation of the relation between the keV and the MeV–GeV emission from GRBs over seven decades in energy and will provide new insights into the physics of GRBs in general. In addition, the excellent localization of GRBs by the LAT will stimulate follow-up observations at other wavelengths which may yield clues about the nature of the burst sources.

We performed a spectroscopic study of the 1809 keV gamma-ray line from 26Al decay in the Galaxy using the SPI imaging spectrometer with its high-resolution Ge detector camera on the INTEGRAL observatory. We analyzed observations of the first two mission years, fitting spectra from all 7130 telescope pointings in narrow energy bins to models of instrumental background and the 26Al sky. Instrumental background is estimated from independent tracers of cosmic-ray activation. The shape of the 26Al signal is compared to the instrumental response to extract the width of the celestial line. We detect the 26Al line at \~16sigma significance. The line is broadened only slightly, if at all; we constrain the width to be below 2.8 keV (FWHM, 2 sigma). The average Doppler velocities of 26Al at the time of its decay in the interstellar medium (decay time~1.04 My) therefore are probably around 100 km/s, in agreement with expectations from Galactic rotation and interstellar turbulence. The flux and spatial distribution of the emission are found consistent with previous observations. The derived amount of 26Al in the Galaxy is 2.8 (+/-0.8) M_solar.

We present results of the analysis of 1.275 MeV γ-ray line global distribution derived from the all-sky data accumulated by COMPTEL on board the Compton Gamma Ray Observatory (CGRO) from 1991 to 1997. Previously the 1.275 MeV γ-ray line was believed to be largely produced in the decay of radioactive isotope 22 Na that is synthesised in the classical nova (CN) thermonuclear runaway (TNR). Another way to produce the 1.275 MeV line emission is via the excitation of 22 Ne-nuclei, e.g. through the low-energy cosmic ray interactions with the nuclei of the interstellar matter that lead to the production of 22 Ne*, or of 22 Na. This scenario, as we now believe, can be dominant in contributing to the total 1.275 MeV γ-ray line emission from the galactic bulge. Unfortunately, systematic uncertainties in the analysis of the COMPTEL data hinder a clear distinction between two alternative scenarios.

We present the sample of gamma-ray bursts detected with the anti-coincidence shield ACS of the spectrometer SPI on-board INTEGRAL for the first 26.5 months of mission operation (up to Jan 2005). SPI-ACS works as a nearly omnidirectional gamma-ray burst detector above ~80 keV but lacks spatial and spectral information. In this catalogue, the properties derived from the 50 ms light curves (e.g., T90, Cmax, Cint, variability, V/Vmax) are given for each candidate burst in the sample. A strong excess of very short events with durations, 10 pages, 9 figures, A&A accepted

The closest Wolf-Rayet star, WR 11 in the binary system γ 2 Velorum, is the only star for which the spectral signature of the 26Al produced in its core is expected to be detectable with current gamma-ray instruments, through the 1.8 MeV gamma-ray line produced by the radioactive decay of the 26Al nuclei. We present here the current status of both model predictions, from calculations of massive star evolution including rotation of stellar interior, and from data on γ 2 Velorum obtained by the ESA's gamma-ray satellite INTEGRAL over the first year of its mission.

A giant flare from the Soft Gamma-ray Repeater SGR 1806-20 has been detected by several satellites on 2004 December 27. This tremendous outburst, the first one observed from this source, was a hundred times more powerful than the two previous giant flares from SGR 0525-66 and SGR 1900+14. We report the results obtained for this event with the Anticoincidence Shield of the SPI spectrometer on board the INTEGRAL satellite, which provides a high-statistics light curve at E>~80 keV. The flare started with a very strong pulse, which saturated the detector for ~0.7 s, and whose backscattered radiation from the Moon was detected 2.8 s later. This was followed by a ~400 s long tail modulated at the neutron star rotation period of 7.56 s. The tail fluence corresponds to an energy in photons above 3 keV of 1.6x10^44 (d/15 kpc)^2 erg. This is of the same order of the energy emitted in the pulsating tails of the two giant flares seen from other soft repeaters, despite the hundredfold larger overall emitted energy of the SGR 1806-20 giant flare. Long lasting (~1 hour) hard X-ray emission, decaying in time as t^-0.85, and likely associated to the SGR 1806-20 giant flare afterglow has also been detected.

It is believed that core-collapse supernovae (CCSN), occurring at a rate about once per century, have seeded the interstellar medium with long-lived radioisotopes such as 60Fe (half-life 1.5 Myr), which can be detected by the gamma rays emitted when they beta-decay. Here we report the detection of the 60Fe decay lines at 1173 keV and 1333 keV with fluxes 3.7 +/- 1.1 x 10(-5) ph cm(-2) s(-1) per line, in spectra taken by the SPI spectrometer on board INTEGRAL during its first year. The same analysis applied to the 1809 keV line of 26Al yielded a line flux ratio 60Fe/26Al = 0.11 +/- 0.03. This supports the hypothesis that there is an extra source of 26Al in addition to CCSN.

The precision measurement of the 1809 keV gamma-ray line from Galactic $^{26}$Al is one of the goals of the SPI spectrometer on INTEGRAL with its Ge detector camera. We aim for determination of the detailed shape of this gamma-ray line, and its variation for different source regions along the plane of the Galaxy. Data from the first part of the core program observations of the first mission year have been inspected. A clear detection of the \Al line at about 5--7 $\sigma$ significance demonstrates that SPI will deepen \Al studies. The line intensity is consistent with expectations from previous experiments, and the line appears narrower than the 5.4 keV FWHM reported by GRIS, more consistent with RHESSI's recent value. Only preliminary statements can be made at this time, however, due to the multi-component background underlying the signal at \about 40 times higher intensity than the signal from Galactic $^{26}$Al.

In its space environment the INTEGRAL observatory is subject to an intense irradiation by energetic cosmic-ray particles that leads, via nuclear interactions with the telescope and spacecraft materials, to an important background of false events. In this paper we present the characteristics of the instrumental background that is observed in the spectrometer SPI (SPectrometer of INTEGRAL). We explain the tuning that has been performed on the parameters of the anticoincidence system in order to optimise the telescope sensitivity over the full energy range. Temporal variations of the instrumental background are discussed and methods are proposed that allow for their modelling in first order.

We study a set of 28 GRB light-curves detected between 15 December 2002 and 9 June 2003 by the anti-coincidence shield of the spectrometer (SPI) of INTEGRAL. During this period it has detected 50 b ...

Supernova 1998bu in the galaxy M96 was observed by COMPTEL for a total of 88 days starting 17 days after the explosion. We searched for a signal in the 847 keV and 1238 keV lines of radioactive 56Co from this type Ia supernova. Using several different analysis methods, we did not detect SN1998bu. Our measurements should have been sensitive enough to detect 60Co gamma-rays as predicted from supernova models. Our 2-sigma flux limit is 2.3 10^{-5} photons cm^{-2} s^{-1}; this would correspond to 0.35 solar mass of ejected 56Ni, if SN1998bu were at a distance of 11.3 Mpc and transparent to MeV gamma rays for the period of our measurements. We discuss our measurements in the context of common supernova models, and conclude disfavoring a supernova event with large mixing and major parts of the freshly-generated radioactivity in outer layers.

The spectrometer SPI aboard the ESA INTEGRAL satellite, which will be launched in 2002, will study the gamma ray sky in the 20-keV to 8-MeV energy band. It achieves the excellent spectral resolution of about 2 keV for photons of 1 MeV thanks to its 19 germanium detectors. A coded mask imaging technique provides an angular resolution of 2/spl deg/. An active BGO veto shield is used for the definition of the field of view and for background rejection. After integration and testing at CNES in Toulouse, the flight model of SPI recently underwent a one-month prelaunch calibration at the CEA center of Bruyeres le Chatel, using an accelerator for homogeneity measurements and high-activity radioactive sources for imaging performance measurements. This paper presents the scientific goals and the different detector components of SPI and reports on the testing and calibration campaigns. The methods used to achieve good timing alignment using the digital front end electronics are described and the first detector performance and imaging capabilities are presented.

The European Space Agency's International Gamma-Ray Astrophysics Laboratory (INTEGRAL) will be launched in 2002. One of its two main instruments is the spectrometer SPI. It uses 19 HPGe detectors to observe the sky in the energy range of 20 keV to 8 MeV with a resolution of /spl Delta/E/E/spl ap/0.2%. Directional information is obtained using a coded mask. The expected angular resolution is about 20, The SPI imaging test setup (SPITS) was built at the Max-Planck-Institut fur Extraterrestische Physik, Germany, to allow experimental verification of the imaging properties of SPI. SPITS consists of a coded hexagonal uniformly redundant array (HURA) mask and two germanium detectors. The mask is built from 63 opaque tungsten-alloy elements. The two hexagonal Ge-detectors are housed in a common aluminum end cap. They are mounted on an XY-table and can be moved to cover the 19 SPI Ge-detector positions. Mask and germanium detectors are made of SPI materials, with the exception of some Be parts, which have been replaced by thinner Al parts to allow experimental verification of the imaging properties of SPI, SPITS consists of a coded HURA mask and two germanium detectors. The mask is built from 63 opaque tungsten-alloy elements. The two hexagonal Ge-detectors are housed in a common aluminum end cap. They are mounted on an XY-table and can be moved to cover the 19 SPI Ge-detector positions. Mask and germanium detectors are made of SPI materials, with the exception of some Be parts, which have been replaced by thinner Al parts. The imaging properties of SPITS are being measured with several radioactive sources at a distance of 9 m from the detector plane. We obtain an angular resolution of about 20 at 1.8 MeV and a point-source location capability of SPITS of 15 arcmin at 1.17 MeV.

The imaging Compton telescope COMPTEL aboard NASA's Compton Gamma-Ray Observatory has opened the MeV gamma-ray band as a new window to astronomy. COMPTEL provided the first complete all-sky survey in the energy range 0.75 to 30 MeV. The catalogue, presented here, is largely restricted to published results. It contains firm as well as marginal detections of continuum and line emitting sources and presents upper limits for various types of objects. The numbers of the most significant detections are 32 for steady sources and 31 for gamma-ray bursters. Among the continuum sources, detected so far, are spin-down pulsars, stellar black-hole candidates, supernova remnants, interstellar clouds, nuclei of active galaxies, gamma-ray bursters, and the Sun during solar flares. Line detections have been made in the light of the 1.809 MeV 26Al line, the 1.157 MeV 44Ti line, the 847 and 1238 keV 56Co lines, and the neutron capture line at 2.223 MeV. For the identification of galactic sources, a modelling of the diffuse galactic emission is essential. Such a modelling at this time does not yet exist at the required degree of accuracy. Therefore, a second COMPTEL source catalogue will be produced after a detailed and accurate modelling of the diffuse interstellar emission has become possible., Comment: 50 pages including 4 figures; accepted for publication in A&A Supplements

COMPTEL observations of the Orion/Monoceros region have shown distinct evidence for excessive 3-7 MeV emission that was attributed to nuclear de-excitation lines from accelerated 12C and 16O nuclei. Unfortunately, we must conclude now that this appears to be a spurious result. This conclusion follows from a better understanding of the instrumental background, from a better exposure of the region, and from an improved analysis method. We show here how the impact of each of these gradually reduces the signal to a less than 3 σ result. The prime underlying cause seems to be 24Na activation in and around the upper COMPTEL detectors. Combining all available data, we now set a 2 σ flux upper limit on the 3-7 MeV emission of Orion of 3 × 10-5 γ cm-2 s-1, to be compared with the previously derived flux of ~10-4 γ cm-2 s-1.

Context. SN2011fe was detected by the Palomar Transient Factory in M101 on August 24, 2011, a few hours after the explosion. From the early optical spectra it was immediately realized that it was a Type Ia supernova, thus making this event the brightest one discovered in the past twenty years. Aims. The distance of the event offered the rare opportunity of performing a detailed observation with the instruments onboard INTEGRAL to detect the γ-ray emission expected from the decay chains of 56Ni. The observations were performed in two runs, one before and around the optical maximum, aimed to detect the early emission from the decay of 56Ni, and another after this maximum aimed to detect the emission of 56Co. Methods. The observations performed with the instruments onboard INTEGRAL (SPI, IBIS/ISGRI, JEMX, and OMC) were analyzed and compared with the existing models of γ-ray emission from this kind of supernova. In this paper, the analysis of the γ-ray emission has been restricted to the first epoch. Results. SPI and IBIS/ISGRI only provide upper limits to the expected emission due to the decay of 56Ni. These upper limits on the gamma-ray flux are 7.1 × 10−5 ph/s/cm2 for the 158 keV line and 2.3 × 10−4 ph/s/cm2 for the 812 keV line. These bounds allow rejecting at the 2σ level explosions involving a massive white dwarf, ∼1 M in the sub-Chandrasekhar scenario and specifically all models that would have substantial amounts of radioactive 56Ni in the outer layers of the exploding star responsible for the SN2011fe event. The optical light curve obtained with the OMC camera also suggests that SN2011fe was the outcome of the explosion of a CO white dwarf, possibly through the delayed detonation mode, although other ones are possible, of a CO that synthesized ∼0.55 M of 56Ni. For this specific model, INTEGRAL would have only been able to detect this early γ-ray emission if the supernova had occurred at a distance

SN2011fe was detected by the Palomar Transient Factory on August 24th 2011 in M101 a few hours after the explosion. From the early optical spectra it was immediately realized that it was a Type Ia supernova thus making this event the brightest one discovered in the last twenty years. The distance of the event offered the rare opportunity to perform a detailed observation with the instruments on board of INTEGRAL to detect the gamma-ray emission expected from the decay chains of $^{56}$Ni. The observations were performed in two runs, one before and around the optical maximum, aimed to detect the early emission from the decay of $^{56}$Ni and another after this maximum aimed to detect the emission of $^{56}$Co. The observations performed with the instruments on board of INTEGRAL (SPI, IBIS/ISGRI, JEMX and OMC) have been analyzed and compared with the existing models of gamma-ray emission from such kind of supernovae. In this paper, the analysis of the gamma-ray emission has been restricted to the first epoch. Both, SPI and IBIS/ISGRI, only provide upper-limits to the expected emission due to the decay of $^{56}$Ni. These upper-limits on the gamma-ray flux are of 7.1 $\times$ 10$^{-5}$ ph/s/cm$^2$ for the 158 keV line and of 2.3 $\times$ 10$^{-4}$ ph/s/cm$^2$ for the 812 keV line. These bounds allow to reject at the $2\sigma$ level explosions involving a massive white dwarf, $\sim 1$ M$\odot$ in the sub--Chandrasekhar scenario and specifically all models that would have substantial amounts of radioactive $^{56}$Ni in the outer layers of the exploding star responsible of the SN2011fe event. The optical light curve obtained with the OMC camera also suggests that SN2011fe was the outcome of the explosion, possibly a delayed detonation although other models are possible, of a CO white dwarf that synthesized $\sim 0.55$ M$_\odot$ of $^{56}$Ni. For this specific model., Comment: Accepted for publication in A&A. 10 pages, 10 figures

The Compton Gamma Ray Observatory (CGRO) completed a full sky survey in November 1993 during which the number of known gamma-ray pulsars more than doubled. During this survey the Compton Telescope (COMPTEL) observed the classical isolated pulsars Crab and Vela and detected PSR 1509-58. Attempts to detect the newly discovered pulsars, Geminga, PSR 1706-44 and PSR 1055-52, in the COMPTEL energy range provide only upper limits. The results of these analyses are presented together with the outcome of a search for further candidate radio pulsars whose ephemerides are given in the Princeton Pulsar Catalogue.

The sky region containing the active radio-galaxy Centaurus A has repeatedly been observed with the (COMPTEL) instrument onboard the Compton Gamma Ray Observatory (CGRO). The nine observation periods during the CGRO phases I and II in which Cen A was in the field of view of COMPTEL are spread over 18 months in the years 1991 to 1993. The energy range 0.75 to 30 MeV is covered. Clear evidence for a source with emission up to several MeV is seen from a region coinciding with the position of Cen A. The spectra change significantly over approximately 6 months between the two observation phases. A possible source confusion with the nearby gamma-ray source MS1312.1-4221 is discussed.

The Compton Gamma-Ray Observatory (C-GRO) has completed a full-sky survey during which the number of known γ-ray pulsars has more than doubled. COMPTEL has observed the classical pulsars Crab and Vela on several occasions and has derived detailed pulse patterns and spectral parameters in the 0.7-30 MeV energy interval. The new C-GROγ-ray pulsars have different properties in terms of energy spectra and light-curve shapes, and, in fact, only the Crab is seen by all four C-GRO instruments. This raises intriguing questions about the particle acceleration processes and beaming taking place in the neutron magnetosphere. We have examined the COMPTEL data to add information on these objects in the 0.7-30 MeV energy interval and present evidence for the detection of one of them, PSR B1509-58. We have also undertaken a search for candidate radio pulsars whose ephemerides are well defined. The results of these analyses are presented.Subject headings: gamma rays: observations — pulsars: general

During the first part of the COMPTON Gamma Ray Observatory sky survey, COMPTEL has detected the quasars 3C273 and 3C279 and the radio galaxy Centaurus A. This paper summarizes the preliminary findings and gives an upper limit on the MeV flux of the Seyfert galaxy NGC4151.

Summary.Pulsar measurements performed by the experiment COMPTEL, aboard the Compton Gamma Ray Observatory, are described. The main results refer to the Crab and Vela pulsars whose pulse shape characteristics are given in some detail and light curves are compared with those above 50 MeV, as observed by the COS-B satellite. No other gamma-ray pulsars have been detected to date by COMPTEL, the upper limit on the pulsed signal from Geminga being compatible with indications by other experiments.

The COMPTEL experiment on the Compton Gamma-Ray Observatory is designed to image celestial gamma radiation in the energy range from 0.75–30 MeV within a field of view of 1 steradian. It can locate stronger point sources with an accuracy better than 0.5° and is capable of mapping diffuse emission as well. The Galactic-center region was observed by COMPTEL for several 2-week periods in 1991/1992. These observations show evidence for 1.8 MeV line emission along the Galactic disk (attributed to radioactive 26 Al), extending over at least 40 degrees in longitude.

The Fermi Gamma‐ray Space Telescope launched on June 11, 2008 carries two experiments onboard—the Large Area Telescope (LAT) and the Gamma‐ray Burst Monitor (GBM). The primary mission of the GBM instrument is to support the LAT in observing γ‐ray bursts (GRBs) by providing low‐energy measurements with high temporal and spectral resolution as well as rapid burst locations over a large field‐of‐view (⩾8 sr). The GBM will complement the LAT measurements by observing GRBs in the energy range 8 keV to 40 MeV, the region of the spectral turnover in most GRBs. The GBM detector signals are processed by the onboard digital processing unit (DPU). We describe some of the hardware features of the DPU and its expected limitations during intense triggers.

The primary scientific goal of the GRIPS mission is to revolutionize our understanding of the early universe using gamma-ray bursts. We propose a new generation gamma-ray observatory capable of unprecedented spectroscopy over a wide range of gamma-ray energies (200 keV-50 MeV) and of polarimetry (200-1000 keV). The gamma-ray sensitivity to nuclear absorption features enables the measurement of column densities as high as 10(28)cm (-aEuro parts per thousand 2). Secondary goals achievable by this mission include direct measurements of all types of supernova interiors through gamma-rays from radioactive decays, nuclear astrophysics with massive stars and novae, and studies of particle acceleration near compact stars, interstellar shocks, and clusters of galaxies.

The onboard Data Processing Unit (DPU), designed and built by Southwest Research Institute, performs the high‐speed data acquisition for GBM. The analog signals from each of the 14 detectors are digitized by high‐speed multichannel analog data acquisition architecture. The streaming digital values resulting from a periodic (period of 104.2 ns) sampling of the analog signal by the individual ADCs are fed to a Field‐Programmable Gate Array (FPGA). Real‐time Digital Signal Processing (DSP) algorithms within the FPGA implement functions like filtering, thresholding, time delay and pulse height measurement. The spectral data with a 12‐bit resolution are formatted according to the commandable look‐up‐table (LUT) and then sent to the High‐Speed Science‐Date Bus (HSSDB, speed=1.5 MB/s) to be telemetered to ground. The DSP offers a novel feature of a commandable & constant event deadtime. The ADC non‐linearities have been calibrated so that the spectral data can be corrected during analysis. The best temporal resolution is 2 μs for the pre‐burst & post‐trigger time‐tagged events (TTE) data. The time resolution of the binned data types is commandable from 64 msec to 1.024 s for the CTIME data (8 channel spectral resolution) and 1.024 to 32.768 s for the CSPEC data (128 channel spectral resolution). The pulse pile‐up effects have been studied by Monte Carlo simulations. For a typical GRB, the possible shift in the Epeak value at high‐count rates (∼100 kHz) is ∼1% while the change in the single power‐law index could be up to 5%.

We report on how the the GLAST Burst Monitor (GBM) Flight Software will detect gamma‐ray rate increases, a process known as “triggering”, and on how the Flight Software will locate and classify the causes of the triggers.

The GLAST Burst Monitor (GBM) is designed to provide wide field of view observations of gamma‐ray bursts and other fast transient sources in the energy range 10 keV to 30 MeV. The GBM is composed of several unshielded and uncollimated scintillation detectors (twelve NaI and two BGO) that are widely dispersed about the GLAST spacecraft. As a result, reconstructing source locations, energy spectra, and temporal properties from GBM data requires detailed knowledge of the detectors’ response to both direct radiation as well as that scattered from the spacecraft and Earth’s atmosphere. This full GBM instrument response will be captured in the form of a response function database that is derived from computer modeling and simulation. The simulation system is based on the GEANT4 Monte Carlo radiation transport simulation toolset, and is being extensively validated against calibrated experimental GBM data. We discuss the architecture of the GBM simulation and modeling system and describe how its products will be used for analysis of observed GBM data. Companion papers describe the status of validating the system.

The Gamma Ray Large Area Space Telescope (GLAST), scheduled for launch in 2006, comprises a Large Area Telescope (LAT) and a GLAST Burst Monitor (GBM). The LAT is a pair telescope with unprecedented sensitivity in the 20 MeV to 300 GeV energy range. The GLAST Burst Monitor consists of an array of NaI and BGO scintillation detectors operating in the 10 keV to 25 MeV range and covering a wide field of view. The GBM will enhance LAT observations of GRBs by extending the spectral coverage into the range of current GRB databases, and will provide a trigger for repointing the spacecraft to observe delayed emission from bursts outside the LAT field of view.

A ToO observation of the TeV-emitting blazar Mrk 421 with INTEGRAL was triggered in June 2006 by an increase of the RXTE count rate to more than 30 mCrab. The source was then observed with all INTEGRAL instruments with the exception of the spectrometer SPI for a total exposure of 829 ks. During this time several outbursts were observed by IBIS and JEM-X. Multiwavelength observations were immediately triggered and the source was observed at radio, optical and X-ray wavelengths up to TeV energies. The data obtained during these observations are analysed with respect to spectral evolution and correlated variability. Preliminary results of the analysis are presented in this poster., Comment: 2 pages, 3 figures; to appear in the Proc. of the First Int. GLAST Symp. (Stanford, Feb. 5-8, 2007), eds. S.Ritz, P.F.Michelson, and C.Meegan, AIP Conf. Proc

The GLAST Burst Monitor (GBM) comprises 12 NaI and 2 BGO detectors dispersed about the GLAST spacecraft. The GBM instrument simulation software must generate an accurate response function database for all detectors in their flight configuration to optimize the mission science return. Before science analysis codes use the response database, we must confirm that our simulation codes and models can reproduce laboratory observations. To validate the simulation effort, Monte Carlo results are compared to calibrated laboratory measurements collected with a variety of radiation sources.

The GLAST Burst Monitor (GBM) consists of 12 NaI detectors and 2 BGO detectors mounted on two sides of the spacecraft. This provides detection capability for energies between 10 keV and 30 MeV, and sensitivity to all directions in the sky. Extensive measurements using radioactive sources have been performed on the isolated detectors. Simulations of these measurements using the GEANT4 Monte Carlo radiation transport simulations toolset have also been preformed. For gamma‐ray burst the spacecraft itself will have a significant impact on the detector response, therefore the final stage of validations involves measuring the detector response to radioactive sources after the spacecraft is fully assembled, and validating the results using simulation. Details of these simulations will be given in this paper.

The GLAST Burst Monitor (GBM) is the secondary instrument on NASA's next Gamma-ray mission GLAST. It will enhance the capabilities of GLAST by locating and detecting cosmic gamma-ray bursts at lower energies by the use of 12 NaI detectors (energy range 10 keV to 1 MeV) and 2 BGO-detectors (energy range 150 keV to 30 MeV). GBM was built in a close collaboration between the MPE and the Marshall Space Flight Center (MSFC). The angular and energy response of each GBM detector has been calibrated using various radioactive sources at different incidence angles relative to the detector in a laboratory environment at the MPE in 2005. To facilitate the understanding of the reconstruction of the detector response, a detailed simulation of the whole laboratory environment and the setup of the calibration source were performed. A modified version of the CERN GEANT 4 simulation software (provided by collaborators at the Los Alamos National Laboratory) was used.

One of the scientific goals of the Large‐Area Telescope (LAT) on GLAST is the study of gamma‐ray bursts (GRBs) in the energy range from ∼20 MeV to ∼300 GeV. In order to extend the energy measurement towards lower energies a secondary instrument, the GLAST Burst Monitor (GBM), will measure GRBs from ∼10 keV to ∼30 MeV and will therefore allow the investigation of the relation between the keV and the MeV‐GeV emission from GRBs over more than six energy decades. These unprecedented measurements will furthermore permit the exploration of the unknown aspects of the high‐energy burst emission. The status of the GBM project approximately one year before launch is reported here.

Nearly 400 years have passed since a supernova was last observed directly in the Milky Way (by Kepler, in 1604). Numerous Galactic supernovae are expected to have occurred since then1, but only one (Cassiopeia A) may have been seen2. The historical record of supernovae is therefore incomplete, as demonstrated by the spatial distribution of young supernova remnants3. The discovery4,5 of γ-ray emission from the decay of 44Ti nuclei associated with Cassiopeia A, the youngest known remnant, has revealed a new way to search for the remnants of other relatively recent supernovae (less than ∼1,000 years old). Here we report the discovery of 44Ti line emission from a previously unknown young supernova remnant, in the direction of the Vela remnant. We estimate a distance of ∼200 parsecs and an age of ∼680 years for the remnant, making it the closest young remnant to the Earth. Why it was not recorded historically remains unknown.

The anticoincidence shield (ACS) of the INTEGRAL-spectrometer SPI consists of 512 kg of BGO crystals. This massive scintillator allows the measurement of gamma-ray bursts (GRBs) with a very high sensitivity. Estimations have shown that with the ACS some hundred gamma-ray bursts per year on the 5 sigma level can be detected, having an equivalent sensitivity to BATSE. The GRB detection will be part of the real-time INTEGRAL burst-alert system (IBAS). The ACS branch of IBAS will produce burst alerts and light curves with 50 ms resolution. It is planned to use ACS burst alerts in the 4th interplanetary network (IPN).

The selection of the GLAST burst monitor (GBM) by NASA will allow the investigation of the relation between the keV and the MeV-GeV emission from gamma-ray bursts. The GBM consists of 12 NaI and 2 BGO crystals allowing a continuous measurement of the energy spectra of gamma-ray bursts from ~5 keV to \~30 MeV. One feature of the GBM is its high time resolution for time-resolved gamma-ray spectroscopy. Moreover the arrangement of the NaI crystals allows a rapid on-board location (, 4 pages with 2 figures

Gamma-rays from radioactive 26Al (half life ~7.2 10^5 yr) provide a 'snapshot' view of ongoing nucleosynthesis in the Galaxy. The Galaxy is relatively transparent to such gamma-rays, and emission has been found concentrated along the plane of the Galaxy. This led to the conclusion1 that massive stars throughout the Galaxy dominate the production of 26Al. On the other hand, meteoritic data show locally-produced 26Al, perhaps from spallation reactions in the protosolar disk. Furthermore, prominent gamma-ray emission from the Cygnus region suggests that a substantial fraction of Galactic 26Al could originate in localized star-forming regions. Here we report high spectral resolution measurements of 26Al emission at 1808.65 keV, which demonstrate that the 26Al source regions corotate with the Galaxy, supporting its Galaxy-wide origin. We determine a present-day equilibrium mass of 2.8 (+/-0.8) M_sol of 26Al. We use this to estimate that the frequency of core collapse (i.e. type Ib/c and type II) supernovae to be 1.9(+/- 1.1) events per century., Comment: accepted for publication in Nature, 24 pages including Online Supplements, 11 figures, 1 table

Soft-gamma-ray repeaters (SGRs) are galactic X-ray stars that emit numerous short-duration (about 0.1 s) bursts of hard X-rays during sporadic active periods. They are thought to be magnetars: strongly magnetized neutron stars with emissions powered by the dissipation of magnetic energy. Here we report the detection of a long (380 s) giant flare from SGR 1806-20, which was much more luminous than any previous transient event observed in our Galaxy. (In the first 0.2 s, the flare released as much energy as the Sun radiates in a quarter of a million years.) Its power can be explained by a catastrophic instability involving global crust failure and magnetic reconnection on a magnetar, with possible large-scale untwisting of magnetic field lines outside the star. From a great distance this event would appear to be a short-duration, hard-spectrum cosmic gamma-ray burst. At least a significant fraction of the mysterious short-duration gamma-ray bursts therefore may come from extragalactic magnetars., Comment: 21 pages, 5 figures. Published in Nature

The next large NASA mission in the field of gamma-ray astronomy, GLAST, is scheduled for launch in 2007. Aside from the main instrument LAT (Large-Area Telescope), a gamma-ray telescope for the energy range between 20 MeV and > 100 GeV, a secondary instrument, the GLAST burst monitor (GBM), is foreseen. With this monitor one of the key scientific objectives of the mission, the determination of the high-energy behaviour of gamma-ray bursts and transients can be ensured. Its task is to increase the detection rate of gamma-ray bursts for the LAT and to extend the energy range to lower energies (from ~10 keV to \~30 MeV). It will provide real-time burst locations over a wide FoV with sufficient accuracy to allow repointing the GLAST spacecraft. Time-resolved spectra of many bursts recorded with LAT and the burst monitor will allow the investigation of the relation between the keV and the MeV-GeV emission from GRBs over unprecedented seven decades of energy. This will help to advance our understanding of the mechanisms by which gamma-rays are generated in gamma-ray bursts., 8 pages, 7 figures, to appear in SPIE conference proceedings vol 5488, "UV-Gamma Ray Space Telescope Systems," Glasgow UK, 21-24 June 2004

One of the scientific objectives of the GLAST mission is the study of gamma-ray bursts (GRBs) which will be measured by the Large-Area Telescope, the main instrument of GLAST, in the energy range from ~20 MeV to ~300 GeV. In order to extend the energy measurement towards lower energies a secondary instrument, the GLAST Burst Monitor (GBM) will measure GRBs from ~10 keV to ~25 MeV and will thus allow the investigation of the relation between the keV and the MeV-GeV emission from GRBs. The GBM consists of 12 circular NaI crystal discs and 2 cylindrical BGO crystals. The NaI crystals are optimized for gamma radiation from ~10 keV to ~1 MeV and the BGO crystals from ~150 keV to ~25 MeV. The NaI crystals are oriented in such a way that the measured relative counting rates allow a rapid determination of the position of a gamma-ray burst within a wide FoV of ~8.6 sr. This position will be communicated within seconds to the LAT which may then be reoriented to observe the long-lasting high-energy gamma-ray emission from GRBs. This will allow the exploration of the unknown aspects of the high-energy burst emission and their connection with the well-known low-energy emission. Another important feature of the GBM is its high time resolution of ~10 microseconds for time-resolved gamma-ray spectroscopy.

SPI is a high spectral resolution gamma-ray telescope on board the ESA mission INTEGRAL (International Gamma Ray Astrophysics Laboratory). It consists of an array of 19 closely packed germanium detectors surrounded by an active anticoincidence shield of BGO. The imaging capabilities of the instrument are obtained with a tungsten coded aperture mask located 1.7 m from the Ge array. The fully coded field-of-view is 16º, the partially coded field of view amounts to 31º, and the angular resolution is 2.5º. The energy range extends from 20 keV to 8 MeV with a typical energy resolution of 2.5 keV at 1.3 MeV. Here we present the general concept of the instrument followed by a brief description of each of the main subsystems. INTEGRAL was successfully launched in October 2002 and SPI is functioning extremely well. Sanchez Martinez, Filomeno, filomeno.sanchez@ific.uv.es

The spectrometer SPI, one of the two main instruments of the INTEGRAL spacecraft, has strong capabilities in the Field of Gamma-Ray Burst (GRB) detections. In its 16 degree Field of view (FoV) SPI is able to trigger and to localize GRBs. With its large anticoincidence shield (ACS) of 512 kg of BGO crystals SPI is able to detect GRBs quasi omnidirectionally with a very high sensitivity. The ACS GRB alerts will provide GRB arrival times with high accuracy but with no or very rough positional information. The expected GRB detection rate in SPI's FoV will be one per month and for the ACS around 300 per year. At MPE two SPI software contributions to the real-time INTEGRAL burst-alert system (IBAS) at the INTEGRAL science data centre ISDC have been developed. The SPI-ACS branch of IBAS will produce burst alerts and light-curves with 50 ms resolution. It is planned to use ACS burst alerts in the 3rd interplanetary network. The SPI-FoV branch of IBAS is currently under development at MPE. The system is using the energy and timing information of single and multiple events detected by the Germanium-camera of SPI. Using the imaging algorithm developed at the University of Birmingham the system is expected to locate strong bursts with an accuracy of better than 1 degree., Comment: 11 pages, 5 figures

Classical novae are considered to be the major source of the ISM enrichment with the isotopes of 13C, 15N, and 22 Na. The latter, radioactive 22 Na, that decays producing penetrating 1.275 MeV γ‐ray photon, could be very useful as a probe of the galactic global distribution of novae. It is expected that the accumulation of 22 Na from the frequent novae in the bulge will lead to an observable extended emission. Additionally, a 22 Na detection from the single nova can be used to verify predictions of the modern thermonuclear runaway theory (TNR) applied to classical novae. To gain a better insight into this problem we have used a two‐way approach. Namely: (1) ‐ we have studied the global galactic distribution of the 1.275 MeV γ‐ray line emission assuming that it is mostly originates from decay of the novae‐produced 22 Na; and (2) ‐ we pursued the 22 Na line emission detection from recent individual novae. The combination of both approaches makes possible to tap rather uncertain galactic novae rate by comparing observations of the individual Galactic novae with the integrated 22 Na line emission from the disk and/or bulge population. The COMPTEL telescope on board the Compton Gamma‐Ray Observatory (CGRO), due to its combination of imaging and spectroscopic capabilities, is suitable to address the above ideas.

The SPI Imaging Test Setup (SPITS) was built at MPE to allow experimental verification of the imaging properties of the SPectrometer onboard INTEGRAL (SPI). Of special importance is the possibility to validate simulations—which are needed for SPI image reconstruction—with laboratory measurements. SPITS consists of a coded mask and two Germanium detectors. The coded mask has the same tungsten-alloy HURA mask coding as SPI and is made of SPI flight model materials. The two hexagonal Ge-detectors are from the SPI flight detector manufacturing line. Housed in a common Al vacuum cap and mounted on an XY-table, they can be moved to cover the 19 Ge detector positions of the SPI camera. We have measured the response of SPITS to radioactive sources (60 keV to 1.8 MeV) at a distance of 9 m from the detector plane. We use both image deconvolution algorithms foreseen for SPI data analysis (spiros and spiskymax) for our analysis. We present our findings for the angular resolution and the point-source-location capability of SPITS for several photon energies and for several source geometries relative to the mask coding.

The COMPTEL telescope on board the Compton Gamma-Ray Observatory (CGRO) is capable of imaging γ-ray line sources, like classical novae, in the MeV regime at a level of sensitivity up to a few 10−5 photons cm−2s−1. At this level of sensitivity quite high expectations can be placed on the detection of the predicted 22Na γ-ray line at 1.275 MeV from nearby novae. Unfortunately, no positive detection of the nova-produced 22Na was reported until recently. We have used COMPTEL data collected up to the 2nd CGRO reboost to assess (1)—sodium production by individual novae, and (2)—the Galactic distribution of the nova-produced 22Na.

Limitations in COMPTEL 44Ti line searches arise from uncertainties in different background modelling techniques, and in different event selection criteria to suppress a large part of the background. Therefore, the significance of the reported detections of Cas A and RX J0852-4622/GRO J0852-4642 have been reassessed in great detail.