| No. 14 - 18 December 2003 | Edited by Thierry Montmerle & Marc Türler |
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The figure shows the INTEGRAL
exposure map (IBIS fully coded field-of-view) of the whole sky in galactic
coordinates for the 140 first revolutions (up to 9 Dec. 2003). The integration
time is color coded according to the scale on the right. The main targets are
labeled.
In parallel with these events, the ISDC staff and the Instrument Teams worked hard to improve the Off-line Scientific Analysis (OSA) for version 3.0. This new version has been released on December 9. The main changes compared to OSA 2.0 are described below.
The operations are proceeding well at the ISDC and you are welcome to visit us to analyse your data or to follow in real time the evolution of your observation. You will find here some guidelines for your visit.
The IBAS Team is relieved by the detection of GRB 031203 after 6 months without a new INTEGRAL Gamma-Ray Burst. The team plans to distribute next year also triggers from Soft Gamma-ray Reapeters (see below).
This Newsletter includes also an article on a very bright outburst of Vela X-1 and a sadder news about a problem with one of the SPI detectors.
The INTEGRAL mission was extended by ESA up to 2008, but first, let's hope that 2004 will be as fruitful for INTEGRAL and all of us as was 2003.
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| Release of the Off-line Scientific Analysis 3.0 | ||
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P. Kretschmar, N. Produit & M. Türler (ISDC Geneva) |
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Version 3.0 of the Off-line Scientific Analysis (OSA) software has been released on December 9. It includes instrument specific analysis software for the four INTEGRAL instruments (IBIS, SPI, JEM-X and OMC), and some generic tools. It can be downloaded from the ISDC Software page. A new option is the possible software installation without the ROOT third party software. A short description of the main changes for the scientific analysis of the four instruments is given below. A more complete list of changes and scientific validation reports are available from the software page.
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Concerning PICsIT, there is now an automatic source localization being performed.
Many more changes are expected for the next OSA release. The SPI scientific analysis is currently being reworked. The new analysis script will be presented in a next issue of the Newsletter.
Background model data from actual observations have now been included in the calibration files and background model information relevant to the individual Science Windows is now routinely extracted. The first results with these models show though, that further fine tuning is needed and by default the background model data is not used in subsequent steps yet.
For source spectra and lightcurves a new, refined algorithm is now used by default which treats vignetting in greater detail. This reduces the previously noted systematic scatter, but not down to the level of statistical uncertainties yet. Work on a better modeling of the instrument is still ongoing. The scaling of source fluxes has been normalized to an idealized illuminated area of 100 cm2 in order to simplify comparison between different analysis results.
Besides the abovementioned points, various less visible changes have been included to increase the stability of the software, the consistency of results across operating systems and to simplify the life of the user. One example is the ability to limit source searches to a given angle, avoiding spurious detections.
New, improved calibration files for flatfielding and flux to magnitude
correction have been included, which correct for contaminations during
the calibration measures. With these data, photometric accuracy is
about 2-3% in the central 4x4 degrees of the OMC FOV, while previously
it could have systematic variations of up to 15% in some cases.
| Guidelines for ISDC visitors | ||
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M. Chernyakova (ISDC Geneva) |
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Scientists are welcome to visit the ISDC to follow the evolution of their observation in real time and to analyse their data with some support from ISDC scientists. If you want to visit the ISDC please follow the rules given below, so that we will be able to make your stay as smooth as possible.
First write an e-mail to the INTEGRAL Helpdesk at least two weeks in advance, providing us with an information on the dates of your visit and specifying whether you need a temporary computer account at ISDC. If you need help with accommodation do not hesitate to ask us. Some information on hotels and how to access the ISDC is also available here.
During your stay, one of the ISDC scientists will be responsible to provide you with the needed help. The information on your areas of interest will help us to select a person with close scientific interests.
If you plan to analyse your private data at the ISDC, please give us detailed information about them. Private data in the Archive is not accessible, so we need some time to copy them to a place from where you can work.
If the data were already distributed, then the PI of the observation should send a request to the INTEGRAL Helpdesk to authorize us to give you access to these data. If the data were not distributed yet, then such a request should be sent from all the PIs of the observation of interest.
The data will be available for you for one month after you left the ISDC in order to let you finish your work from your home institute. Your ISDC account will however remain available for 2 additional months.
Within several days after your first e-mail to the INTEGRAL Helpdesk you will receive a confirmation that the ISDC is ready to welcome you including the name of the responsible scientist and other details.
We are looking forward to welcome you at the ISDC and we hope your stay will be
pleasant and fruitful.
| IBAS Announcement on Soft Gamma-ray Repeaters | ||
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S. Mereghetti (IASF Milano) |
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After getting used to the surprisingly regular rate of one GRB per month we had at the beginning of the mission, the long time interval between the May 1st and the December 3rd burst was beginning to cause some concerns among the users of the INTEGRAL Burst Alert System (IBAS). Although simple calculations show that these are just the effects of small number statistics, it was somewhat disappointing to see that our efforts to improve the IBAS system had to wait such a long time to be rewarded by the good localization of this exciting GRB (see below).
Actually, during these months we could verify the good health of IBAS thanks to the detection in near real time of different variable sources of various kinds, including Type I bursts from low mass X-ray binaries, galactic transients and the soft gamma-ray repeater SGR 1806-20. Since these triggers were clearly recognized as not due to GRBs, the corresponding alert packets were not distributed. This is automatically done by IBAS which, as a last step, compares the coordinates derived for the ``GRB candidate'' with those of several sources contained in the so called ``black list''.
Considering the scientific interest of rapid follow-up at other wavelengths of events from the Soft Gamma-Ray Repeaters, starting next January IBAS will distribute in real time the triggers from SGR 1900+14, SGR 1806-20, SGR 0525-66, SGR 1627-41 and SGR 1801-23, which are currently in the black list.
The corresponding Alert Packets will have the same format and content of those used for GRBs (i.e. the only scientifically relevant information will be the position and time of the trigger). The IBAS users interested only in GRBs should verify themselves that the coordinates in the Alert Packets do not correspond to one of these sources.
The PIs of General Program observations who do not want that this new
policy be applied during their observations should notify this to the IBAS
Team at the ISDC.
| SPI detector number 2 problem | ||
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M. Türler & P. Dubath (ISDC Geneva) |
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On Saturday 6 December 2003, one of the 19 Germanium detectors of SPI stopped
to function. This failure occurred abruptly and completely unexpectedly during
normal operations. The origin of this problem is currently under investigation
by the SPI Team and several recovery strategies are considered. If this problem
persists, updated response matrices will be needed for the scientific analysis
of SPI data.
Theimage
shows the number of events collected by the 19 Germanium crystals during one
Science Window of revolution 143. The hole is due to the missing counts of
the detector number 2.
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| XMM-Newton Observation of a Dust Echo from GRB 031203 | ||
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S. Mereghetti (IASF Milano) |
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A new record in GRB localization has been set by the INTEGRAL Burst Alert System (IBAS) on December 3rd. The coordinates of GRB 031203 were distributed at 22:01:45 UT, i.e. 20 seconds after the first photons from the burst reached the satellite. Despite the very short delay, the error circle automatically determined using the IBIS/ISGRI data had a radius of only 2.7 arcmin.
A few hours later fading X-ray and radio sources were detected close to
the center of the IBAS error circle with XMM-Newton and the VLA. A galaxy
at redshift 0.1 coincides with the radio source, while an optical
afterglow has not been reported to date.
The first XMM-Newton results are very exciting and were published by S. Vaughan et al. in GCN 2489. Thanks to the good IBAS localization and the efficient reaction of the XMM-Newton staff, the X-ray observation could start only 6 hours after the burst (another record!). The images obtained with the EPIC instrument show, for the first time, an X-ray afterglow (central source) surrounded by an expanding ring (see the animation). The ring is due to scattering of the GRB X-ray emission by dust grains in our Galaxy. The apparent expansion is due to the different light travel times of the photons scattered at various angles. This GRB ``echo'' is very important since it allows us to estimate the intensity of the prompt X-ray emission at the time of the gamma-ray burst.
Dust scattering halos around GRB had been predicted, but they were never
observed up to now, due to the lack of sensitive and rapid X-ray
follow-ups of bursts at low galactic latitude (i.e. where there is more
dust in the line of sight). Considering the extensive INTEGRAL coverage
of the Galactic plane, the future prospects for this combined exploitation
of the two ESA satellites are very promising.
| Historic outburst from Vela X-1 | ||
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P. Kretschmar (ISDC Geneva) |
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Vela X-1 is the archetypical wind accreting X-ray pulsar and known
to be quite variable in flux. But the flare observed on Nov 28, 2003
by INTEGRAL was the brightest ever recorded for this source with a
peak flux of about twice that of the Crab in the 20-60 keV band,
instead of the usual few tenths of the Crab flux. Detailed analysis is
ongoing, but first results indicate significant spectral variations
during the flare. The flare did not show up as remarkable in the RXTE ASM,
demonstrating that for highly absorbed sources the hard X-ray / low gamma-ray
band can yield informations which are literally hidden from instruments in the
classical X-ray band.
Figure: Quick-Look Analysis lightcurve of Vela X-1 obtained with IBIS/ISGRI. Each point corresponds to one pointing of INTEGRAL. The ISGRI Crab flux in this band is ~280 cps.
| An XMM observation of IGR J16320-4751=AX J1631.9-4752 | |
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J. Rodriguez1, J.A. Tomsick2, L. Foschini3, et
al. 1. CEA Saclay, DSM/DAPNIA/SAp (CNRS FRE 2591),F-91191 Gif sur Yvette Cedex, France and Integral Science Data Center, Chemin d'Ecogia, 16, CH-1290 Versoix, Switzerland 2. Center for Astrophysics and Space Sciences, Code 0424, University of California at San Diego, La Jolla, CA 92093, USA 3. IASF/CNR, sezione di Bologna, via Gobetti 101, 40129 Bologna, Italy | |
| Accepted for publication in A&A Letters on July 3, 2003 | |
| Abstract. The hard X-ray sensitivity and arcminute position accuracy of the recently launched International Gamma-Ray Laboratory (INTEGRAL) has led to the (re-)discovery of a class of heavily absorbed hard X-ray sources lying in the Galactic plane. We report on the analysis of an XMM observation of such a source IGR J16320-4751 = AX J1631.9-4752. Our analysis allowed us to obtain the most accurate X-ray position to date (Rodriguez et al. 2003), and to identify a likely infrared counterpart (Tomsick et al. 2003). We present the detailed analysis of the IGR J1632-4751 XMM spectrum. The PN spectrum can be well represented by a single powerlaw or a comptonized spectrum with a high equivalent absorption column density of ~2 x 1023 cm-2. The current analysis and the comparison with the properties of other sources favor the possibility that the source is a Galactic X-Ray Binary (XRB). The identification of two candidate IR counterparts is in good agreement with this identification. The hard spectrum previously seen with ASCA, and the brightness of the candidate counterparts indicate that IGR J1632-4751 is most probably a highly absorbed High Mass X-ray Binary, hosting a neutron star. | |
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E-mail contact | Preprint access |
| Simultaneous multi-wavelength observations of GRS 1915+105 | |
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Y. Fuchs1, J. Rodriguez1,2, I.F. Mirabel1,3, S.
Chaty1, M. Ribo1, et al. 1. CEA Saclay, DSM/DAPNIA/SAp, Orme des Merisiers, Bat 709, F-91191, Gif Sur Yvette Cedex France 2. INTEGRAL Science Data Centre, ch. d' Ecogia 16, CH-1290 Versoix, Switzerland 3. IAFE/CONICET, cc67, suc 28, 1428 Buenos Aires, Argentina | |
| Accepted for publication in A&A on September 03, 2003 | |
| Abstract. We present the result of multi-wavelength observations of the microquasar GRS 1915+105 in a plateau state with a luminosity of ~7.5x1038 erg/s (~40% LEdd), conducted simultaneously with the INTEGRAL and RXTE satellites, the ESO/NTT, the Ryle Telescope, the NRAO VLA and VLBA, in 2003 April 2-3. For the first time were observed concurrently in GRS 1915+105 all of the following properties: a strong steady optically thick radio emission corresponding to a powerful compact jet resolved with the VLBA, bright near-IR emission, a strong QPO at 2.5 Hz in the X-rays and a power law dominated spectrum without any cutoff in the 3-400 keV range. | |
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E-mail contact | Preprint access |
| XMM-Newton Observations of the Ultraluminous Nuclear X-ray Source in M33 | |
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L. Foschini, J. Rodriguez, Y. Fuchs, L. C. Ho, M. Dadina, G. Di Cocco, T. J.-L.
Courvoisier & G. Malaguti IASF-CNR, Sezione di Bologna (Italy) | |
| Accepted for publication in A&A on December 3, 2003 | |
| Abstract. We present observations with XMM-Newton of M33 X-8, the ultraluminous X-ray source (L0.5-10 keV ~ 2x1039 erg/s) closest to the centre of the galaxy. The best-fit model is similar to the typical model of Galactic black holes in very high state. Comparison with previous observations indicates that the source is still in a very high state after about 20 years of observations. No state transition has been observed even during the present set of XMM-Newton observations. We estimate the lower limit of the mass of the black hole greater than 6 M⊙, but with proper parameters taking into account different effects, the best estimate becomes 12 M⊙. Our analysis favours the hypothesis that M33 X-8 is a stellar mass black hole candidate, in agreement with the findings of other authors. In addition, we propose a different model where the high luminosity of the source is likely to be due to orientation effects of the accretion disc and anisotropies in the Comptonized emission. | |
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E-mail contact | Preprint access |
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