| No. 4 - January 17, 2001 | Edited by Thierry Montmerle & Marc Türler |
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This issue of the ISDC-Astrophysics Newsletter should prove particularly interesting for AO-1 proposers, since it announces the public release of the Observation Simulator developed at the ISDC. It also continues to be an active forum for scientific results and useful news for the community.
By the way, don't forget that the Chandra AO-3 has been released with a deadline fixed to March 15, which is why we are postponing the next issue of the Newsletter by a few days.
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| The ISDC at the start of the millennium |
| Thierry J.-L. Courvoisier (PI of the ISDC) |
The ISDC has come to the end of 2000 reaching some significant steps in its development.
We have been able to use our system on-line during a set of tests that involved the INTEGRAL satellite with the OMC and JEM-X instruments and the ground segment. This showed that we are able to receive the telemetry, decode it, perform the technical analysis we need to make and safely store the data. The second important step reached is a first demonstration of the scientific analysis software that could be given at the ISDC meeting of December. The meaning here is that a significant fraction of the building blocks of the analysis are available in a first version and that they can be made to work together in a coherent data analysis chain.
None of the tests made as of yet indicates, however, that we have finished our development. A large effort of formal testing of the system will be made in the coming months and several tests will have to be performed once the SPI and IBIS instruments are installed on board. The scientific analysis on the other hand will be further enhanced and developed in an iterative way in the coming months so that we can gain confidence in the results generated.
You will see below that we decided to make the INTEGRAL Observation Simulator available to the astronomical community. We do this in a spirit of openness, well aware of the limitations of the tool, which are detailed in the article below. We hope with this delivery not only to make what we have available to the community at large, but also to gain experience in the delivery of software well in advance of delivering real analysis software. Your reactions, requests for help and contributions to enhancements will be most useful in the scaling of the work ahead of us. We hope with this decision to enter in a fruitful collaboration with you.
| The release of the INTEGRAL Observation Simulator |
| Ada Paizis & Roland Walter (ISDC Geneva) |
The observation simulator (OSim) is a software package that simulates INTEGRAL observations. OSim was developed with the main purpose of generating accurate simulated data to test the scientific analysis software.
Please note that OSim data are only an approximation of the reality. These simulated data can, nevertheless, be used - using preliminary analysis software - to evaluate the results of an observation and to get preliminary experience with the INTEGRAL data.
Note, also, that the Observation Time Estimator (OTE), made available by the INTEGRAL Science Operations Centre (ISOC), has to be used to determine the exposure time of an observation proposal in all cases. The OSim shall not be used for this purpose.
As the standard analysis chains are not yet available only part of the standard products can be generated. The current version (1.2) of OSim can be used to produce sky images for the imager IBIS (both for the ISGRI and the PICsIT detectors) and for the X-ray monitors JEM-X. It is also possible to produce source spectra, but only for the ISGRI detector of IBIS.
The OSim was developed at the ISDC in close collaboration with some Instrument Teams, which provided part of the software. A presentation of the OSim is given on a dedicated OSim WWW page and additional information can be found in the second (September 2000) and the third (November 2000) issues of this Newsletter.
Since November 2000, the OSim was tested by several selected users outside of the ISDC. It is now made available to the community, even if it suffers from several limitations:
To download, install and run the OSim, please refer to the ISDC Software Release page.
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| The X-ray sources at the center of the supernova remnant RXJ0852.0-4622 | |
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Sandro Mereghetti IFC - CNR, Milano | |
| Accepted for publication in ApJLetters on December 8, 2000 | |
| Abstract. We present a BeppoSAX observation of the X-ray source AX J0851.9-4617.4 that has been proposed as the neutron star associated to the shell like-supernova remnant RX J0852.0-4622. The image at E>5 keV shows the presence of a new source, SAX J0852.0-4615, not resolved from AX J0851.9-4617.4 in previous observations. The improved positional accuracy obtained for AX J0851.9-4617.4 confirms its possible identification with an early type star, also consistent with its soft thermal spectrum (kT~1.3 keV). SAX J0852.0-4615, with a harder X-ray spectrum and a higher X-ray to optical flux ratio, is a more likely candidate for the neutron star associated to the supernova remnant. | |
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E-mail contact | |
| The nature of dwarf nova outbursts | |
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V. Buat-Ménard1, J.-M. Hameury1 & J.-P.
Lasota2 1. Observatoire de Strasbourg, 11 rue de l'univertité, F-67000 Strasbourg, France 2. Institut d'Astrophysique de Paris, 98bis boulevard Arago, 75014 Paris, France | |
| Accepted for publication in A&A on November 14,2000 | |
| Abstract. We show that if the dwarf-nova disc instability model includes the effects of heating by stream impact and tidal torque dissipation in the outer disc, the calculated properties of dwarf-nova outbursts change considerably, and several notorious deficiencies of this model are repaired. In particular: (1) outside-in outbursts occur for mass transfer rates lower than in the standard model as required by observations; (2) the presence of long (wide) and short (narrow) outbursts with similar peak luminosities is a natural property of the model. Mass-transfer fluctuations by factors ~ 2 can explain the occurrence of both long and short outbursts above the cataclysmic variable period gap, whereas below 2 hr only short normal outbursts are expected (in addition to superoutbursts which are not dealt with in this article). With additional heating by the stream and tidal torques, such fluctuations can also explain the occurrence of both outside-in and inside-out outbursts in SS Cyg and similar systems. The occurrence of outside-in outbursts in short orbital-period, low mass-transfer-rate systems requires the disc to be much smaller than the tidal-truncation radius. In this case the recurrence time of both inside-out and outside-in outbursts have a similar dependence on the mass-transfer rate dM/dt. | |
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E-mail contact | Preprint access |
| Disk-Jet connection in the Microquasar GRS 1915+105 and IR and radio emission | |
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J. S. Yadav Tata Institute of Fundamental Research, Homi Bhabha Road, Mumbai 400005, India | |
| Accepted for publication in ApJ on October 17, 2000 | |
| Abstract. We present evidence of a direct accretion disk-jet connection in the Galactic microquasar GRS 1915+105 based on our analysis of RXTE/PCA data with a ``spike'' in X-ray light curves. We find that the radio emission increases as the hardness ratio increases during the low hard state. We suggest that the ``spike'' which separates the dips with hard and soft spectra marks the beginning of the burst phase when the luminosity of the soft X-rays (5-15 keV) increases by a large factor (~10). This produces a major ejection episode of the synchrotron - emitting plasma termed as ``baby jets'' which are associated with infrared (IR) and radio flares of about half an hour period widely reported in the literature. Subsequent short but frequent soft dips produce overlapping faint flares which result in an enhanced level of quasi-steady emission. We discuss the differences between ``baby jets'' and relativistic radio jets and especially investigate their signatures in X-rays. | |
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E-mail contact | Preprint access |
| A Gamma-Ray Burst Monitor for GLAST | |
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A. von Kienlin1, M. S. Briggs3, R. Diehl1, G. J.
Fishman2 et al. 1. Max-Planck-Institut fuer extraterrestrische Physik, D-85741 Garching, Germany 2. NASA/Marshall Space Flight Center, Mail Code SD50, Huntsville, AL 35812, USA 3. University of Alabama, Huntsville, AL 35899, USA | |
| Accepted for publication in ESA - SP Series on December 5, 2000 | |
| Abstract. The Gamma-Ray Large-Area Space Telescope GLAST is the next NASA mission in the high-energy γ-ray regime (10 MeV to about 500 GeV), with launch anticipated in 2006. Recently a design using silicon strips for the electron-positron pair tracking was selected for the main instrument. One of the key scientific objectives of the GLAST mission is to determine the high-energy behaviour of γ-ray bursts and transients. The importance of studying bursts with GLAST has been emphasized by choosing a burst monitor as the secondary instrument on GLAST. A proposal to the NASA AO for such a burst monitor was submitted jointly by a collaboration between the Marshall Space-Flight Center/University of Alabama (both in Huntsville / Alabama) and the Max-Planck-Institut für extraterrestrische Physik in Garching. This GLAST Burst Monitor will complement the main instrument information about bursts in the energy range between 5 keV and 30 MeV. It will provide real-time burst locations over a wide FOV with sufficient accuracy to repoint the GLAST spacecraft. Time resolved spectra of many bursts recorded with GLAST and the burst monitor will cover unprecedented 6 decades of energy. This will help to advance our understanding of the mechanisms by which γ-rays are generated in γ-ray bursts. Mid of March 2000 this proposal for GLAST's burst monitor has been selected. | |
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E-mail contact | Preprint access |
| Monte-Carlo Simulations of Thermal-Nonthermal Radiation from a Neutron Star Magnetospheric Accretion Shell | |
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M. Böttcher1,2, E. P. Liang1 1. Physics and Astronomy Department, Rice University, MS 108, Houston, TX 77005-1892, USA 2. Chandra Fellow | |
| Accepted for publication in ApJ on January 2001 | |
| Abstract. We discuss the space-and-time-dependent Monte Carlo code we have developed to simulate the relativistic radiation output from compact astrophysical objects, coupled to a Fokker-Planck code to determine the self-consistent lepton populations. We have applied this code to model the emission from a magnetized neutron star accretion shell near the Alfvén radius, reprocessing the radiation from the neutron star surface. We explore the parameter space defined by the accretion rate, stellar surface field and the level of wave turbulence in the shell. Our results are relevant to the emission from atoll sources, soft-X-ray transient X-ray binaries containing weakly magnetized neutron stars, and to recently suggested models of accretion-powered emission from anomalous X-ray pulsars. | |
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E-mail contact | Preprint access |
| How Do GRBs Associated with Supernovae Avoid Baryon Contamination? | |
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K.S.Cheng1 & Z.G.Dai2 1. Department of Physics, University of Hong Kong, China 2. Department of Astronomy, Nanjing University, China | |
| Accepted for publication in Astroparticle Physics on November 30, 2000 | |
| Abstract. Current hypernova models for γ-ray bursts (GRBs) associated with supernovae suffer from the baryon contamination problem, which prevents formation of relativistic shocks and emission of γ-rays. Here we present a possible solution to this difficulty. Our model can be divided into two steps. In the first step, the core collapse of a star with mass ≥ 19 M⊙ leads to a massive neutron star and a supernova, and subsequently, one jet produced via neutrino annihilation during hypercritical accretion of the neutron star will push out of its front matter, resulting in a small cone relatively free of baryons. In the second step, once the mass of the neutron star reaches the maximum value, it will promptly implode to a rapidly rotating black hole surrounded by a torus. The gravitational binding energy of the torus will convert to the expansion energy of the supernova ejecta, thus yielding a hypernova, while the rotational energy of the black hole will be extracted via the Blandford-Znajek process to generate another jet responsible for a GRB. We show that the mass of baryons loading with the second jet is smaller than 10-3 M⊙ and the Lorentz factor of this jet is larger than 100. Thus our model can avoid the baryon contamination problem suffered from in the hypernova models. | |
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E-mail contact | |
| Prospects of the observation with SPI in the light of the 44Ti γ-rays | |
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R. Georgii, R. Diehl, A. Iyudin, G.G. Lichti, V.Schönfelder & A. Strong Max-Planck-Institut für extraterrestrische Physik, Giessenbachstr., D-85748 Garching, Germany | |
| Accepted for publication in ESA-SP on January 5, 2001 | |
| Abstract. The recent detection of a supernova remnant in the light of the 1157 keV γ-ray decay line of 44Ti with COMPTEL underlines the usefulness of this method in detecting young supernova remnants. The prospects for the observation of near-by supernova remnants in the γ-rays from the 44Ti decay will be presented using the latest information about the spectral resolution and the expected background of the spectrometer on-board INTEGRAL (SPI). Observation times for various candidate objects are estimated, taking into account the uncertainties in distances, expansion velocities, source strengths and instrumental parameters. We compare different estimations based on the published sensitivity of the instrument SPI. | |
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E-mail contact | Preprint access |
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