No. 3 - November 15, 2000 Edited by Thierry Montmerle & Marc Türler 
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Editorial

The first INTEGRAL announcement of opportunity (AO-1) was released two weeks ago on November 1st, 2000. The INTEGRAL Science Operations Centre (ISOC) located at ESTEC, the Netherlands is responsible of the AO and you will find all the documentation and the tools needed for writing observation proposals on the ISOC WWW page.

In this issue, you will find some impressive results from the ISDC observation simulator in the ``ISDC News'' section, while the ``INTEGRAL News'' section contains two contributions on the status of the gamma-ray spectrometer SPI and the X-ray monitor Jem-X. The ``Science News'' section is a bit lacking of abstract contributions this time. Do not hesitate to inform the astronomical community about your scientific results by sending us (at any time with the Web interface) the abstract of your accepted papers.

Good luck in preparing your INTEGRAL proposals,
Marc Türler & Thierry Montmerle


This section includes the following article:
Dithering Pattern and Galactic Plane Scan Simulations
Roland Walter, Ada Paizis and Pascal Favre (ISDC Geneva)

Status of the Observation Simulator

The Observation Simulator (OSim) developed at the ISDC was described in the last Newsletter (see this article and the OSim WWW page). Today, the ISDC has released version 1.0 of this simulator to selected users which accepted to act as external testers. Depending on the success of this first release outside of the ISDC, the OSim might be distributed widely to the scientific community in two months (mid-January) before the end of the first Announcement of Opportunity (AO-1). Below are some new results obtained with the OSim.

Hexagonal Dithering Simulation

Click for full-sized image The image on the right is an animation illustrating the hexagonal dithering pattern in the field of view including the bright quasar 3C 273 and the blazar 3C 279.

Each frame is a deconvolved sky image corresponding to an observation of 1200 seconds as simulated for the Imager on Board the INTEGRAL Satellite (IBIS). The entire field of view of this instrument is of 30 x 30 degrees and the hexagonal dithering pattern corresponds to a shift by 2 degrees from one frame to the other.

Two of the point sources visible near the centre of the image are 3C 273 and 3C 279, the other point sources are ghosts (cf. the OSim WWW page).

Galactic Plane Scan Simulation

Click for full-sized image The image on the left is a mosaic image of a series of 13 simulated IBIS images along the galactic plane. The exposure time of each pointing is of 1050 seconds and each frame was rotated by 5 degrees with respect to the previous one.

The input catalog used by the simulator is the 4th UHURU catalog with some additional active galactic nuclei from the Veron catalog. The position and the name of these sources is shown in blue on the IBIS image. Although, the position of the sources is correct, their fluxes are probably overestimated by the arbitrary choice of the gamma-ray spectral index. Other sources are ghosts, which appear dimmer in the mosaic image than in individual images thanks to the rotation from one pointing to the other. In the first frame on the left, one can see strong structures in the deconvolved sky image. This so called ``coding noise'' is induced by the bright Crab source present in this field of view.

Click for full-sized image The image on the right is the corresponding mosaic image as simulated for the X-ray monitor Jem-X. The Jem-X images are circles and the field of view is clearly smaller than for IBIS (13 degrees in diameter instead of a square of 30 x 30 degrees). The Jem-X deconvolved images do not have an uniform background, but show a three times repeated symmetric structure similar to the coded mask pattern. This artifact is not yet well understood, but it might be due to some small error in the code of the deconvolution software.


This section includes the following articles: Please note that ESA communicates information about the INTEGRAL mission including status of spacecraft, instruments, and science operations through its own channels, including ESA's science WWW site and the INTEGRAL WWW site at ESTEC.
The aim of this ``INTEGRAL News'' section is to convey informal news about the activities of the INTEGRAL Instrument Teams. For further information, please visit the WWW pages of these teams, which can be reached through the above mentioned ESA sites or through the list of ISDC WWW links.
Status of the Spectrometer SPI
Gilbert Vedrenne (CESR Toulouse) and Volker Schönfelder (MPE Garching)

Click for full-sized image Much progress has been achieved during the last few months in assembling the spectrometer SPI. All sub-systems (except for the cryo-coolers) have been delivered during this summer by the collaborating partners to the CNES. The mechanical and electrical integration of all subsystems as well as performance tests are now in progress.

The image on the right shows the entire SPI detector assembly with its 19 germanium detectors - the heart of SPI - which has now been calibrated with radioactive gamma-ray sources. The energy resolution of the 60Co gamma-ray lines (1.17 Mev and 1.34 MeV) lies between 2.2 and 2.5 keV (FWHM), which is well within specification.

News from the JEM-X Instrument
Allan Hornstrup (DSRI Copenhagen)

In late 1999, it was discovered that the JEM-X sensor box was unexpectedly sensitive to the high-energy cosmic particles, and thus could suffer from severe discharges. The INTEGRAL project started to pursue options to replace the JEM-X detector with another instrument.

The JEM-X consortia initiated immediately a study to overcome the problem. A solution to this kind of problem was already in use at different synchroton facilities, and the idea was to add an extra amplification stage (the GEM foil) in the detector. The JEM-X team received and tested GEM foils from CERN, but was not able to achieve the results needed to protect the detector from discharges and at the same time keep the performance required. The usage of a GEM was thus abandoned.

Click for full-sized image In parallel, redesigns were implemented in the JEM-X detector microstrip plate layout. The new design with chromium instead of gold strips has smoother curves in the layout, and the detector gas (Xe) pressure was reduced from 5 bar to 1.5 bar. These changes are implemented in the qualification model (Q-model) which is now under completion after having passed functional tests with satisfying results. The reduction of the gas pressure causes minor reductions in the position resolution and in the quantum efficiency at higher energies, but the detector is still complementing IBIS nicely, ensuring a smooth sensitivity curve between the two instruments. This is shown by the figure on the right showing the JEM-X (3 - 60 keV) and the IBIS (20 keV - 10 MeV) 5-σ continuum sensitivity, where the blue and red lines are for an observation of 1 ksec and 100 ksec, respectively. The green dotted lines represent the spectrum of a 1, 10 and 100 mCrab source with a photon index Γ = 1.7.

The reduction of the gas pressure had the effect of reducing the risk of discharging to an acceptable level and to improve slightly the energy resolution. The results obtained supported the re-confirmation in October 2000 of the JEM-X instrument as the X-ray monitor for the INTEGRAL spacecraft.

Status of the JEM-X models

The qualification model

Click for full-sized image The Q-model has undergone functional and performance tests, and has shown satisfying results. This model is now in Finland, and is being finally welded, a major milestone. The figure on the left shows an example of a Q-model image. It was recorded by moving (along a "JEM-X" pattern) a collimated (Ø 1.5 mm) 55Fe source (5.9 keV) in front of the JEM-X Q-model detector.

Click for full-sized image The figure on the right shows the spectrum emitted by Americium 241 as obtained by illuminating the Q-model detector by a radioactive source of 241Am. The achieved energy resolution as a function of energy

ΔE (FWHM) / E = 0.40 · E1/2
is well within the detector specifications.
The Q-model will undergo environmental tests from mid-December to mid-January, including shock, vibration, thermal-vacuum and EMC tests.

The engineering model

The E-model is currently in Alenia for support of the SVT test. This model has the electrical and software configuration similar to the two flight models.

The two flight models

The current status of the two F-models is: For more information about the JEM-X instrument please look at the JEM-X page at ESTEC.

Abstracts of recently accepted papers

Other papers picked up for you

Below are links to a list of selected papers from the e-print archive accepted in refereed journals and related in a way or another to the science relevant to the INTEGRAL mission.
Gamma-ray line emission from OB associations and young open clusters
I. Evolutionary synthesis models
M.Cerviño1,2, J.Knödlseder2,4, D.Schaerer1, P.von Ballmoos2, and G.Meynet3
1. Observatoire Midi-Pyrenees, 14, avenue Edouard Belin, 31400 Toulouse, France
2. Centre d'Etude Spatiale des Rayonnements, CNRS/UPS, B.P.4346, 31028 Toulouse Cedex 4, France
3. Observatoire de Genève, CH-1290 Sauverny, Switzerland
Accepted for publication in A&A on October 13, 2000
Abstract. We have developed a new diagnostic tool for the study of gamma-ray emission lines from radioactive isotopes (such as 26Al and 60Fe) in conjunction with other multi-wavelength observables of Galactic clusters, associations, and alike objects. Our evolutionary synthesis models are based on the code of Cerviñno and Mas-Hesse (1994), which has been updated to include recent stellar evolution tracks, new stellar atmospheres for OB and WR stars, and nucleosynthetic yields from massive stars during hydrostatic burning phases and explosive SN II and SN Ib events.
The temporal evolution of 26Al and 60Fe production, the equivalent yield of 26Al per ionising O7 V star (Y26O7 V), and other observables are predicted for a coeval population. The main results are:
  • The emission of the 26Al 1.809 MeV line is characterised by four phases: stellar wind dominated phase (< 3 Myr), SN Ib dominated phase (~ 3-7 Myr), SN II dominated phase (~ 7-37 Myr), and exponential decay phase (> 37 Myr).
  • The equivalent yield Y26O7 V is an extremely sensitive age indicator for the stellar population which can be used to discriminate between Wolf-Rayet star and SN II 26Al nucleosynthesis in the association.
  • The ratio of the 60Fe/26Al emissivity is also an age indicator that constrains the contribution of explosive nucleosynthesis to the total 26Al production.
We also employed our model to estimate the steady state nucleosynthesis of a population of solar metallicity. In agreement with other works, we predict the following relative contributions to the 26Al production: ~9% from stars before the WR phase, ~33% from WR stars, ~14% from SN Ib, and ~44% from SN II. For 60Fe we estimate that ~39% are produced by SN Ib while ~61% come from SN II. Normalising on the total ionising flux of the Galaxy, we predict total production rates of 1.5 M0 Myr-1 and 0.8 M0 Myr-1 for 26Al and 60Fe, respectively. This corresponds to 1.5 M0 of 26Al and 1.7 M0 of 60Fe in the present interstellar medium.
To allow for a fully quantitative analysis of existing and future multi-wavelength observations, we propose a Bayesian approach that allows the inclusion of IMF richness effects and observational uncertainties in the analysis. In particular, a Monte Carlo technique is adopted to estimate probability distributions for all observables of interest. We outline the procedure of exploiting these distributions by applying our model to a fictive massive star association. Applications to existing observations of the Cygnus and Vela regions will be discussed in companion papers.
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