| No. 16 - 15 December 2004 | Edited by Marc Türler & Pierre-Olivier Petrucci |
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December 10: Change of All ISDC Phone Numbers:
+41 22 950 9 ### +41 22 379 2 ### (ISDC Tel: +41 22 379 2 100 ; Fax: +41 22 379 2 133) |
Two years after INTEGRAL's launch, it's time to review what has been achieved and to sketch the possible evolution of the ISDC. The ISDC is currently in a phase of consolidation, as can be seen from the changes to the data analysis software for ISGRI, PICsIT and JEM-X and to the Reference Catalog included in the new release of the Offline Scientific Analysis (OSA 4.2). The comparison of different analysis methods, in particular for ISGRI spectra, is also part of this consolidation.
Apart from the software, there has also been much effort put into making INTEGRAL results publicly available. In particular through the construction of the Bright Source Catalog and the inclusion of scientific results (images and light-curves) in the INTEGRAL Archive. Other changes include the distribution of IBAS triggers for non-GRB sources and the set up of a ``Script Forum'' allowing you to share your personal data analysis scripts.
Thanks to your contributions, the Science News section gives a broad overview of the progress of INTEGRAL science. The highlight is maybe the recent discovery of an exciting new source, IGR J00291+5934 which was first detected by INTEGRAL and found to be the fastest known accreting X-ray millisecond pulsar with the addition of follow-up observations in the X-rays, the optical, the infrared and the radio.
The unexpected is part of INTEGRAL science and we hope to have several other such exciting surprises in the years to come...
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| The Evolution of the ISDC | ||
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Thierry Courvoisier (ISDC Geneva) |
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With the launch of INTEGRAL 2 years back, it is high time to think about the evolution of the ISDC. The lines along which this evolution is to take place are in no way firmly established, discussions are, however, taking place and it is worth mentioning here some of main points we have in mind.
First and foremost, the INTEGRAL launch was indeed two years back, only two years. There is still a considerable amount of work to do to ensure an optimum exploitation of the data. This means that for the time being a large effort goes into improving the analysis tools, understanding the systematics and correcting them in the end products. This is the highest priority task of the ISDC now and in the years ahead. It is only when spectra, light curves etc. can routinely be obtained from the many thousands of pointings on many hundred objects in any energy band that this task will wind down. However as much as we would like this to be finished, we still see a considerable amount of work ahead of us.
A further task that is now shaping up is the way in which we want to work with the final archive and the scientific results that it will contain. We expect that many users will then not necessarily want to do the analysis themselves, but that they would rather either find the results they need in the archive or have it extracted for them "on the fly". As a first step in this direction we will develop an interface to the results on the web. Future steps will involve not only thinking about the archive, the products and "on the fly" analysis, but also thinking about how astronomers will want to access and analyse their data, when the power and memory of their laptops will be sufficient to consider solving tasks that involve large fractions of the data of a (any?) mission on their computers.
Operations and user support are tasks that are now running, and will continue and, certainly for the user support, continue to be enhanced, as more data become publicly available. The scientific exploitation of the INTEGRAL data is also an important activity that is only in its first steps.
In addition to the many INTEGRAL tasks we have, it is now also time to turn towards the future beyond INTEGRAL. The ISDC has developed a system to fulfill all the tasks of the science data analysis for all the INTEGRAL instruments. This system has been proven successful since launch and we think that the expertise thus acquired could and should be used in other contexts. The ISDC has also developed a way to work with many funding agencies and with the scientific community, be it the teams that built the instruments, the institutes of the consortium or the high energy astrophysics community. While we know that aspects of our way of working may need improvements in the future, we are nonetheless convinced that this forms a solid basis to envisage new challenges. We thus consider that both technically and in our organization we provide a solid basis on which the science analysis of future missions could be built.
Major projects of the ISDC in the future must be built on a, possibly small but certainly solid, local scientific expertise and a wider international basis (in the case of INTEGRAL this is given by the ISDC consortium). Only thus can we ensure that the needs of the community are well understood and taken into account. This means that high energy projects are certainly those in which it is most natural for us to consider making a high level contribution and taking a leading role in Europe. High energy astrophysics projects are, however, few and far apart, it is therefore important to take part, albeit possibly in a less important position, in some other projects along the route. This is needed to allow the team to keep abreast of developments and to give the engineers concrete projects on which to further development our system and tools. This we already did by taking the responsibility of the first level of data processing in the LFI consortium of the Planck mission. This activity conforted us in the opinion that indeed our system can be adapted to further missions and instruments with limited efforts.
We thus see ourselves now with an evolution for the next years that has three
main elements, the first is to progress on many fronts in the INTEGRAL data
exploitation, the second is to contribute in a major way in the next important
high energy astrophysics mission in Europe and the third is to take part in the
science analysis of different missions and, why not, Earth bound instruments
where we can bring our expertise in the service of a community with which we
have close scientific ties.
| Science Results in the INTEGRAL Archive | ||
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Roland Walter (ISDC, Geneva) |
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Following improvements of the scientific analysis software the INTEGRAL archive is now populated with standard scientific results. Those results are based on the second revision of the archive and were obtained with a analysis software nearly identical to OSA 4.2. OMC, ISGRI, JEM-X (and in the close future PICsIT) imaging scientific analysis are performed for every pointing. ISGRI, SPI and PICsIT analysis will be soon performed as well for longer datasets (observations). The analysis are performed in 5 energy bands for JEM-X, 12 bands for ISGRI, 8 bands for PICsIT and 5 bands for SPI. The resulting fluxes can therefore be used to obtain broad band spectra.
The Archive Browse interface gives access instantaneously to the results of those analyses for all public data. The following results are already available:
During the coming weeks the following scientific products will be made available as well:
Finally within a few months IBIS and JEM-X all sky images and source average spectra will be made available.
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The image on the left shows a portion of
the ISGRI 30-40 keV lightcurve of GRS 1915+105 obtained with the Archive Browse
plot applet.
The image on the right shows a preview of
an ISGRI sky image for a single pointing.
As usual in Browse, preview of images can be obtained through selecting observation data products and selecting the "Preview" button. Source lightcurves can be obtained by browsing the ISGRI, JEM-X or/and OMC source results catalogues, selecting (all) flux measurements and requesting a plot or downloading the results in ASCII format.
The science products are of course as good as the available analysis software and calibration (currently those of OSA 4.2). The main limiting aspects are the vignetting correction for JEM-X that still affect very much the reconstructed count rates and the off-axis correction for IBIS that mostly affect the count rates obtained below 30 keV.
We plan to regenerate the science products with the improved software and
calibration that will be made available in OSA 5, foreseen to be released in Spring 2005.
| OSA 4.2 Improvements for ISGRI | ||
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Nicolas Produit (ISDC, Geneva) |
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There is a significant improvement in OSA 4.2 for the IBIS/ISGRI analysis. The most important programs (ii_skyimage, ii_shadow_build and ibis_scripts) were changed and their new version is much better. Note, however, that there were many changes that are not backward compatible so you should not mix up any results or partial processing of your data with previous versions of OSA. In particular, the efficiency correction is no more done at the IMG step with ii_skyimage, but earlier in ii_shadow_ubc.
For spectral analysis, there is a new RMF response matrix, which reduces the systematic uncertainties to within 2%. For more details and a comparison of different spectral analysis methods with ISGRI, please read the article below.
A lot of effort was put in having correct timing information. Timing should now be absolutely correct except in Science Windows (ScW) where the TIMECORR keyword is set to 3 or 4 in the *-EVTS-ALL structures of the revision 2 archive. These values indicate that it is possible that some times in these ScWs are off by exactly 2 seconds, but we have no way to be sure.
Finally, the ibis_science_analysis script was made more user-friendly and
allows now to specify more than 10 energy bands for imaging. Before using OSA
4.2, please remind to read carefully the known issues
and the documentation. For the time being,
there is unfortunately no available ISGRI scientific evaluation report. We will
provide it as soon as we receive it from the Instrument Team.
| OSA 4.2 Improvements for PICsIT | ||
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Luigi Foschini (IASF/CNR, Bologna, Italy) |
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The OSA 4.2 for PICsIT contains some interesting improvements. The main
novelty is represented by the first release of the photon redistribution
(RMF) and ancillary (ARF) matrices, provided by P. Laurent (CEA, Saclay).
Therefore, now it is possible to extract the spectra of single point
sources.
As an example, the figure on the
rightshows the spectrum of the Crab from 20 to 1000 keV obtained by
combining the data from ISGRI (20-300 keV) and PICsIT (250-1000 keV).
Another important novelty is represented by an improvement in the mosaic specific for PICsIT, that now include the possibility to perform long integrations (successfully tested up to ~400 ScW) and with different projections. The projections now available are: gnomonic (TAN), that is also the default, zenithal equidistant (ARC), for polar regions, and stereographic (STG). (See Calabretta & Greisen, 2002, A&A 395, 1077 for more details on the sky projections).
Last, but not least, there are the first detections of the Crab with multiple
events, i.e. those events that are so energetic to interact with more than one
single pixel of PICsIT (see Fig. on the
left).
It is worth mentioning that these detections are preliminary and further
studies are on going to better assess these results.
| What is new in the JEM-X analysis software for OSA 4.2 ? | ||
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Carol Anne Oxborrow (DNSC, Copenhagen), Stefan Larsson (Stockholm Observatory) & Niels Jørgen Westergaard (DNSC, Copenhagen) |
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The JEM-X Science Analysis Software has been improved in many ways that remain hidden to the general user. However there are several areas where the accuracy and scope of the science results have been improved and extended over previous versions of OSA. Many of the changes reported here herald major improvements and additions to the software that will be available for OSA 5.0.
The concept of regularized shadowgram has been introduced for OSA 4.2.
Previously, the shadowgrams have been in skew format, for simplified handling
of the hexagonal mask hole pattern. More technical details about the production
of the shadowgram can be found in the JEM-X User Manual part of the OSA 4.2
documentation.
This extension of functionality paves the way for more advanced image deconvolution in OSA 5.0, which will produce less noisy images, more sensitive source detection and includes detailed modelling of the mask support, collimator geometry and microstrip irregularities.
The image on the right shows a JEM-X 1 detector shadowgram with the Crab Nebula on-axis and using pixel regularization as described above. This shadowgram was taken during revolution 239 (ScW 023900040010).
Detector pixels that cannot be "seen" from a particular source will act as background. Each detector pixel gets assigned a "Pixel Illumination Fraction" (PIF) which is a number between 0 and 1; 0 if there is absolutely no chance that a photon from the source will result in a count in that pixel, 1 if there is no obstruction between the pixel and the source. An ideal detector would see a sharp shadow pattern, i.e. PIF values of either 0 or 1. Due to the finite detector resolution some events in the source illuminated regions will "leak" into the non-illuminated (background) pixels. This leakage varies with energy and with source direction in the field of view. For each source the expected event distribution (PIF map) is computed at 10 different energies. A PIF_cut level is defined at each energy, such that the pixels with PIF > PIF_cut should contain 75% of the source flux onto the detector. The difference in event rate for pixels with PIFs above and below the cut level is used to solve for source fluxes independently for each time energy bin.
The spectrum and light curve extraction method in OSA 4.2 is the same as in OSA 4.0, except that an inconsistency in the handling of "dead anodes" in different steps of the analysis has been corrected.
The team has heard far fewer complaints about the behaviour and results of the 4.x software than for the 3.x releases. If science results produced by the software look strange, users is urged to contact one of the authors, the ISDC help desk, or the JEM-X instrument team.
| Methods of extracting ISGRI spectra | ||
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P. Lubinski (CAMK, Warsaw & ISDC), M. Chernyakova (ISDC), P. Kretschmar (MPI, Garching & ISDC), Nicolas Produit (ISDC), J. Rodriguez (CEA, Saclay & ISDC), S. Soldi (ISDC) & R. Walter (ISDC) |
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Systematic differences between various ISGRI spectral extraction methods
were studied on the Crab data. The standard spectral extraction produces
usually the largest fluxes. Average fluxes computed with method based on
mean flux from sky images and method using mosaic results are lower than
those from the standard method by about 3%. For method extracting directly
fluxes from mosaic images this discrepancy is larger, about 8%. These
differences are not larger than the current uncertainty of ISGRI absolute
calibration.
Figure: Count rate ratios obtained between various ISGRI spectral methods and the standard one (OSA `method' = 1). Results are shown for observations of the Crab in revolutions 043, 102 and 239. The methods are: Flux averages from sky images (blue dots), Fluxes from mosaic images (red circles), Fluxes from mosaic results (green triangles), OSA `method' = 2 (magenta triangles)
There is no correlation between the offset angle and the observed deviation of alternative methods fluxes from 'standard' fluxes, for offset angles not exceeding ~10 degrees and for energies below 250 keV. All methods based on image results lead to a very similar spectral shape when compared to the standard method.
When the source is observed at larger offset angles, results of all methods seem to be affected by the detector and background non-uniformity. Depending on the dithering pattern, these effects may be reduced or amplified, leading to different spectral shapes obtained with different methods. The influence of dithering strategy on the spectral results will be studied in future in connection with the non-uniformity investigations. Also the count rate discrepancies appearing for methods based on images need further studies.
Results obtained for Crab are confirmed by the tests performed for weaker objects. For on-axis observation all methods give the same spectra even for sources as weak as 10 mCrab. Analysis of data collected with large offset angles , e.g. GPS, should be performed with a special care. In this case the standard spectral extraction usually produces false, too hard spectra, for objects not bright enough to be well separated from the background. Therefore, for objects observed at larger offset angles, particularly for weaker sources, an alternative method based on averaging fluxes obtained in individual science window sky images is recommended. Moreover, if it is possible, data set should be limited to offset angles smaller than 10 degrees (FCFOV) and the influence of detector/background non-uniformity on the results should be reduced via averaging of spectra obtained for different pointings.
For additional information, read the document describing these various methods
available as a PDF file [ 11 pages, 224 kB ].
| The INTEGRAL General Reference Catalog | ||
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Arash Bodaghee (ISDC, Geneva) |
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The General Reference Catalog is the master list of all known high-energy sources of relevance to INTEGRAL. Version 17 of the catalog contains 1,404 objects that have been brighter than about 1 mCrab between 1 keV and 10 MeV. It is updated regularly when there are enough changes to warrant a new release. Various formats of the catalog can be downloaded from the catalog page. Formats in HTML, TeX, and ASCII are available to complement the FITS file. Identifiers are SIMBAD-compliant and all positions are referenced. In the HTML version, the source name links directly to the corresponding page in SIMBAD, and the position links to the reference in ADS.
A new feature, the instrument-specific flag, informs the user of sources that have been detected by an INTEGRAL instrument. For example, one can build a subset of the catalog by extracting all sources that have been seen by ISGRI. Flags for ISGRI, JEM-X, SPI and PICsIT have the value 0 if not detected, and 1 if detected.
Here are two ways to use this new feature:
The references used to set flags include lists of JEM-X sources provided by P.
Kretschmar, the SPI Bright Source Catalog of V. Beckmann, survey results,
publications, public data from IQLA, and scientists working on private data.
Eventually, the catalog will be populated exclusively with archived INTEGRAL
results.
| Distribution of IBAS Alerts for non-GRB Sources | ||
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Sandro Mereghetti (IASF/CNR, Milano, Italy) |
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The INTEGRAL Burst Alert System (IBAS) can detect different kinds of transient
events due to variable sources in the IBIS field of view.
As an example, a type I burst from a galactic Low Mass X-ray Binary detected in
real time by the IBAS programs is shown in the figure.
Other sources producing IBAS triggers are the Soft Gamma-ray Repeaters. Like in the case of GRBs, the Alerts for these events can have a delay as short as 30 seconds and might thus be of interest for rapid follow-up with robot telescopes.
In order to distribute the IBAS Alert messages for non-GRB sources only to the interested users, a new version of the IBAS Alert distribution system has been developed at the INTEGRAL Science Data Center and is now operational. This allows to select the classes of sources of interest.
Note that to receive the Alerts for non-GRB sources (i.e. type I bursts
and SGRs) it is necessary to subscribe directly to the IBAS service at the
ISDC (http://isdc.unige.ch/?Soft+ibas).
For further details see the IBAS News
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| INTEGRAL discovers IGR J00291+5934, the fastest accreting X-ray millisecond pulsar | ||
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J. Rodriguez (CEA, Saclay & ISDC), S.E. Shaw (Southampton Univ. & ISDC) , N. Mowlavi (ISDC), D. Eckert (ISDC), P. Ubertini (IASF Roma), K. Ebisawa (GSFC & ISDC), R. Walter (ISDC), N. Produit (ISDC) & T. J.-L. Courvoisier (ISDC) |
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On 2 December 2004, INTEGRAL discovered a new source labeled IGR J00291+5934
(Eckert et al. 2004, ATel 352).
The discovery image of IGR J00291+5934 was taken by IBIS/ISGRI on 2 Dec. 2004 (ScW 0261 0002 001 0) in the 20-60 keV energy band. The source is very close to the cataclysmic variable V* V709 Cas (20 arcmin away) and has a flux of 55±5 mCrab.
Very active and prompt follow up observations at various wavelengths have shown it to be the fastest (yet) known millisecond X-ray pulsar (f = 598.88 Hz (i.e. P = 1.6 ms), Markwardt et al. 2004a, ATel 353), whose X-ray spectrum is characteristic of an absorbed power law. The optical counterpart reveals a moderately bright new object in the R band (R~17.4, Fox and Kulkarni 2004), with possible emission features near the HeII line and Hα line (Roelofs et al. 2004, ATel 356). In the radio bands, early observations reveal a faint counterpart at 15 GHz with the Ryle telescope (Pooley 2004, ATel 355) that seems to have faded some days later (below 0.6 mJy at 3σ) while it was detected at 5 GHz with a level of 0.250 mJy (Fender et al. 2004, ATel 361). Archival search in the RXTE/ASM data reveal a possible outburst recurrence time of ~3 years (Remillard 2004, ATel 357). This source seems to be an X-ray binary with an orbital period of 147.412 min (Markwardt et al. 2004b, ATel 360).
A letter to A&A announcing the discovery of this source by INTEGRAL has been submitted recently by Shaw et al. (see abstract below). For further information please contact Simon Shaw.
Note: References are Astronomer's Telegrams (ATels), which can be accessed through the ISDC list of scientific circulars.
| Searching for the origin of the e+ e- annihilation line observed by INTEGRAL/SPI in the Galactic bulge region | ||
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Stéphane Schanne, on behalf of the CEA-Saclay INTEGRAL/SPI data analysis team |
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One of the major results from the first two years of
operation of the Spectrometer onboard INTEGRAL (SPI) is the detection of
gamma-ray emission at 511 keV in the Galactic center region [1,2,3,4,5].
The image shows the morphology of the 511 keV line emission, as detected by INTEGRAL/SPI. The emission is best fit (as published in [4]) by a Gaussian distribution with a full-width at half maximum of 8o (+3o/-2o, 2σ error-bar), representing the Galactic bulge.
The emission region coincides in shape with the Galactic bulge (see the image) and the flux of the 511 keV line implies an annihilation of 1.3 1043 positrons (e+) each second [6]. Consequently the question about the nature of the source capable of injection such a huge amount of e+ into the Galactic bulge is raised. Positrons can be produced by a variety of candidate sources. High energy processes like proton-proton interactions, neutralino decays or massive gravitons are excluded, since conjointly emitted high energy photons have not been observed. Accreting black holes, in particular micro-quasars, could inject e+, however they are not numerous enough and furthermore not permanently active. What remains are positron emitting (β+) radioactive nuclei produced by stellar nucleosynthesis, among which the most prominent one is 56Co, which decays to 56Fe and emits a e+ in 19% of the cases. 56Co is itself the decay product of 56Ni, synthesized massively in supernovae explosions (SN). SN of type II produce about 0.1 solar masses (M⊙) of 56Ni, but all e+ remain trapped inside the thick SN hydrogen envelope. SN of type Ia have a thinner envelope and produce 0.6 M⊙ of 56Ni, such that 3.3% of the e+ escape, corresponding to 8 1052 e+ per SN Ia. An explosion rate of 0.6 SN Ia per century in the Galactic bulge would be required, if SN Ia were the dominant e+ sources. However this rate has been evaluated to be 0.05 per century [7], considering the Galactic bulge as a elliptical galaxy embedded in our galaxy and using the SN Ia rate obtained by statistical studies of elliptical galaxies. Therefore SN Ia, considered up to now as the major e+ source, are insufficient to explain the observations.
In [7,8] a new kind of e+ source, namely hypernovae, have been proposed, for which the typical example is GRB 030329, one of the closest and most luminous Gamma-Ray Bursts ever observed, associated to an underlying SN of type Ic (SN 2003dh), resulting from the explosion of a rotating Wolf-Rayet star with an asymmetric ejection of matter into two opposite cones aligned with the rotation axis. Due to the ejection asymmetry the energy/mass ratio of the ejecta is much higher than in the SN Ia case and a simple model permits to compute an escape fraction of 42% of the e+ produced by the 0.5 M⊙ of 56Ni synthesized during the explosion. In case of 56Ni mixing with the ejecta, the escape fraction could be even higher, such that a SN 2003dh-like hypernova could release up to 25 times more e+ than a SN Ia. If hypernovae are the e+ sources, a rate of 0.02 per century is needed, which seems in excess of very first rate estimates. However a starburst, which occurred a few million years ago in the Galactic nucleus, could have produced a sufficient number of hypernovae, and their released e+ could still be annihilating today.
In the absence of a dominant astrophysical candidate, the road is open for an explanation advocating new physical processes. In the current cosmological model, the Universe is composed of 4% of baryonic matter and 23% of cold dark matter, and its geometry is rendered Euclidean by 73% of dark energy. The presence of dark matter is confirmed by studies of galactic rotation dynamics. Its nature remains a mystery for contemporary physics, and it could be made of a new kind of light particle [9,10]. Those particles could annihilate via a new intermediate boson U into a e+ e- pair and produce the observed e+. Without a direct coupling to the Z boson, those particles could have escaped detection at LEP. Dark matter annihilation is most likely to occur in regions of high dark matter density like the central region of the Galaxy [11,12]. Furthermore dark matter rich dwarf galaxies [13] also become prominent candidate sources for 511 keV emission.
| The radio - X-ray connection in GRS 1915+105 | ||
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J. Rodriguez (CEA Saclay & ISDC), D.C. Hannikainen, G. Pooley, S.E. Shaw, on behalf of a much larger collaboration |
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The monitoring campaign of GRS 1915+105 performed during INTEGRAL AO-1 has already given excellent results (e.g. Hannikainen et al. 2003, 2004, see the article in the last newsletter), and was naturally resubmitted for AO-2. Besides monitoring GRS 1915+105 with INTEGRAL, we have simultaneous coverage of the source with RXTE, which allows us to perform a thorough timing analysis in the soft X-rays (Rodriguez et al. 2004), and we observed in other wavebands as far as we are able. This kind of simultaneous multiwavelength campaign is very difficult to organize, but is the only way to probe the connection between accretion processes (manifesting in the X-rays) and ejections (in radio, and infrared).
Our first INTEGRAL AO 2 observation of GRS 1915+105 was performed on 2004
October 18-19, during INTEGRAL revolution #246. According to the zoology of
classes of variability defined by Belloni et al. (2000) GRS 1915 was in class
ν at the beginning of the observation then spent about 0.25 days in class
ρ and came back to class ν for the rest of our observation.
Class ν is particularly interesting. It manifests itself through soft X-ray
variations on short time scales, separated by ~20-40 minute dips during which
the source spectrum is harder. The return to the variability (and softer) state
is always accompanied by a huge spike as can be seen in the figure.
We had the chance to follow two such cycles simultaneously with the Ryle
Telescope at 15 GHz, and as already shown in the past (e.g. Klein-Wolt et al.
2002 for this particular class), each X-ray spike is followed by a radio spike
indicating the ejection of radio-emitting material. This confirms the strong
link between accretion and ejection: not all the material is accreted into the
black hole, but a significant part is ejected. The use of INTEGRAL here will
allow us to test the hypothesis that the ejected matter not uniquely comes
from the accretion disc, but that it is in fact the medium responsible for hard
X-ray production (the corona) that is primarily ejected as proposed for other
systems (XTE J1550-564, Rodriguez et al. 2003). Our simultaneous RXTE coverage
will, in addition, allow us to test the relation between the time variability
of the source (e.g. QPOs) and the accretion-ejection mechanisms.
| PSR B1259-63: H.E.S.S. triggers an INTEGRAL observation of a faint Be XRB system | ||
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S.E. Shaw (ISDC & Southampton Univ.) & J. Rodriguez (CEA Saclay & ISDC) |
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In March 2004 the H.E.S.S. Cherenkov telescope made the first ever detection at energies > 200 GeV of the PSR B1259-63 system, at a level corresponding to about 10% of the Crab nebula flux (Beilicke, 2004, IAUC 8300).
PSR B1259-63 is a 47.6 msec radio pulsar orbiting the Be star SS2883. Be stars are well known to have a strong stellar wind, and an equatorial disc of matter that may be thrown from the surface of the star as it rotates. The equatorial disc of this system is thought to be almost perpendicular to the orbital plane, such that the pulsar intersects the disc twice in the orbital period of ~3.4 years.
The H.E.S.S. detection coincided with the first passage of the pulsar through the disk, about 2 weeks before periastron of the system. Prompted by this detection, a special INTEGRAL ToO observation was requested for the period of March 21 - 24, to coincide with the second disc crossing.
The analysis of the INTEGRAL data was at that time at the very limit of the
capabilities of OSA 4.0. We found the source to be very faint - about 2mCrab
at 30 keV, but it was possible to construct a broad band spectrum with ISGRI.
Public RXTE observations also showed that the emission from PSR B1259-63 was
largely constant during the 200 ksec INTEGRAL observation.
The figure shows the high energy spectrum for PSR B1259-63 around periastron compared to a 1 mCrab spectrum (dashed line). The ISGRI and RXTE spectra are in good agreement and also agree with ASCA and OSSE measurements made during previous perigee passages. It should be noted that the only previous hard x-ray measurements, by OSSE, required approximately 3 weeks of integration time - approximately an order of magnitude more than the ISGRI exposure. This shows that time resolved spectra, which are important for models of the interaction of the pulsar and the solar wind during periastron passage, would easily be possible with ISGRI for a similar length observation.
One especially interesting aspect of the ISGRI data is that, for the first time, it was possible to investigate possible contamination of the hard x-ray emission by the nearby source 1RXP J130159.6-635806. This source has previously been detected at the ISDC during quick look analysis of NRT data, and seen to vary on short timescales to fluxes up to ~10 mCrab. The excellent imaging capabilities of ISGRI allowed us to show that the emission from the region was dominated by PSR B1259-63, which gave us confidence in the contemporaneous RXTE data.
If you are interested in reading more on the INTEGRAL results, they have recently been published in Shaw et al, 2004, A&A, 426, 33. The RXTE data suggests a sudden increase in the flux, sadly just after INTEGRAL observation. It will be very interesting to see if this also observed in the extended H.E.S.S. observation (currently in preparation by Aharonian and Schlenker).
The next perigee passage of PSR B1259-63 will be in August 2007. If, as we all
hope, INTEGRAL is still providing excellent x-ray data then repeated
observations will allow us to better understand this enigmatic source.
| INTEGRAL observation of Cygnus X-1 during an intermediate state | ||
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Julien Malzac (CESR, Toulouse) |
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The black hole Cygnus X-1 was observed with INTEGRAL on June 7-11 2003. Both spectral and variability properties of the source indicate that Cygnus X-1 was in an intermediate state between the canonical hard and soft states. However the long term RXTE/ASM light curve shows that the source does not reach the soft state after our observation but return to the hard state: this is a so-called failed state transition.
During the 4 day long observation the broad band (3-500 keV) luminosity varied by a factor of 4 and the source showed an important spectral and flaring variability. A principal component analysis demonstrates that most of this variability occurs through 2 independent modes: 1) changes in the overall luminosity with almost constant spectra (responsible for 65 % of the variance) and 2) pivoting of the spectrum around ~ 10 keV (20 % of the variance).
Cygnus X-1 is known to harbor a compact radio jet when in the hard state. It is
also known from other sources that the transition from hard to soft state is
associated with a quenching of the radio emission: the jet seems to be
suppressed in the soft state (Corbel et al. 2000; Gallo, Fender, Pooley 2003).
Therefore simultaneous radio observations during state transition (intermediate
states) can shed light on the coupling mechanism between the jet (radio) and
the hard X-ray emitting accretion flow. During our INTEGRAL observation the
source was monitored at 15 GHz with the Ryle telescope.
Figure: INTEGRAL hardness ratio versus radio flux. Each symbol represents an average over a science window. The INTEGRAL hardness is the IBIS (100-200 keV) to JEM-X (3-6 keV) count rates. The solid line represents the best power law model HR=K Fradb.
The radio jet emission does not appear to be correlated with the hard X-ray luminosity. On the other hand, we find a clear correlation between the radio flux and the pivoting pattern. As shown in the figure, radio fluxes are stronger when the INTEGRAL spectrum is harder. As the transition to the soft state also corresponds to a strong softening of the spectrum, this is consistent with the correlation between hardness and radio flux: when, during the observation, the source gets closer to the soft state the spectrum softens and simultaneously the radio flux decreases.
We note that a recent analysis of Ryle and RXTE data of Cyg X-1 (Gleissner et al., A&A, 2004) interestingly shows the same correlation tendencies during failed state transitions (Ryle/PCA: moderate anti-correlation, Ryle/HEXTE: correlation) as reported here, albeit on time-scales from weeks to years, our result suggests that the jet can respond to instabilities in the accretion flow on shorter time scales (< 1 day).
| Spectral Properties of Low Quasi-Periodic Oscillations in GRS 1915+105 | |
|
J. Rodriguez1, S. Corbel2, D.C. Hannikainen3, et al. 1. CEA Saclay, France & ISDC Versoix, Switzerland 2. Universite Paris 7 & CEA Saclay France 3. Observatory, University of Helsinki Finland | |
| Accepted for publication in ApJ on July 2 2004 | |
| Abstract. We report on the timing analysis of RXTE observations of the Galactic micro-quasar GRS 1915+105 performed in 2003. Out of a total of six times ~20 ks, we focus here only on the three observations during which GRS 1915+105 is found in a steady C-state (referred to as class χ) resulting in a total of ~50 ks. During these observations, we detect low frequency quasi-periodic oscillations with high (~14 %) rms amplitude in the 2-40 keV energy range. Contrary to what is usually observed in GRS 1915+105, in most of our observations the QPO frequency presents no correlation with the RXTE/PCA count rate, nor with the RXTE/ASM count rate. We present, for the first time, high resolution (22 spectral channels) 2-40 keV spectral fits of the energy dependence of the QPO amplitude (``QPO spectra''). The QPO spectra are well modeled with a cut-off power law except on one occasion where a single power law gives a satisfactory fit (with no cut-off at least up to ~40 keV). The cut-off energy evolves significantly from one observation to the other, from a value of ~21.8 keV to ~30 keV in the other observations where it is detected. We discuss the possible origin of this behavior and suggest that the compact jet detected in the radio contributes to the hard X-ray (> 20 keV) mostly through synchrotron emission, whereas the X-ray emitted below 20 keV would originate through inverse Compton scattering. The dependence of the QPO amplitude on the energy can be understood if the modulation of the X-ray flux is contained in the Comptonized photons and not in the synchrotron ones. | |
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| Discovery of a new INTEGRAL source: IGR J19140+0951 | |
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D.C. Hannikainen1, J. Rodriguez2, C. Cabanac3, et al. 1. Observatory, University of Helsinki Finland 2. CEA Saclay, France & ISDC Versoix, Switzerland 3. LAOG Observatoire de Grenoble, France | |
| Accepted for publication in A&A on June 30, 2004 | |
| Abstract. IGR J19140+0951 (formerly known as IGR J19140+098) was discovered with the INTEGRAL satellite in March 2003. We report the details of the discovery, using an improved position for the analysis. We have performed a simultaneous study of the 5-100 keV JEM-X and ISGRI spectra from which we can distinguish two different states. From the results of our analysis we propose that IGR J19140+0951 is a persistent Galactic X-ray binary, probably hosting a neutron star although a black hole cannot be completely ruled out. | |
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| The first XMM-Newton study of two Narrow-Line Seyfert 1 galaxies discovered in the Sloan Digital Sky Survey | |
|
L. Foschini1, V. Braito2, G.G.C. Palumbo3, G. Ponti1,3, M. Dadina1, R. Della Ceca2, G. Di Cocco1, P. Grandi1, G. Malaguti1 1. IASF-CNR/INAF, Sezione di Bologna (Italy) 2. INAF-Osservatorio Astronomico di Brera, Milano (Italy) 3. Dipartimento di Astronomia, Università di Bologna (Italy) | |
| Accepted for publication in A&A on August 1, 2004 | |
| Abstract. The Early Data Release of the Sloan Digital Sky Survey (SDSS) contains 150 Narrow-Line Seyfert 1 (NLS1) galaxies, most of them previously unknown. We present here the study of the X-ray emission from two of these active galaxies (SDSS J030639.57+000343.2 and SDSS J141519.50-003021.6), based upon XMM-Newton observations. The spectral and timing characteristics of the two sources are presented and compared against the typical properties of known NLS1 galaxies. We found that these two NLS1 are within the dispersion range of the typical values of this class of AGN, although with some interesting features that deserve further studies. | |
|
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| INTEGRAL observations of the field of the BL Lacertae object S5 0716+714 | |
|
E. Pian1,2, L. Foschini2, V. Beckmann3, et al. 1. INAF - Osservatorio Astronomico di Trieste (Italy) 2. IASF-CNR/INAF, Sezione di Bologna (Italy) 3. NASA-GSFC, Greenbelt (MD, USA) | |
| Accepted for publication in A&A on August 26, 2004 | |
| Abstract. We have performed observations of the blazar S5 0716+714 with INTEGRAL on 2-6 April 2004. In the first months of 2004, the source had increased steadily in optical brightness and had undergone two outbursts. During the latter, occurred in March, it reached the extreme level of R = 12.1 mag, which triggered our INTEGRAL program. The target has been detected with IBIS/ISGRI up to 60 keV, with a flux of ~3 x 10e-11 erg/s/cm2 in the 30-60 keV interval, a factor of ~2 higher than observed by the BeppoSAX PDS in October 2000. In the field of S5 0716+714 we have also detected the Flat Spectrum Radio Quasar S5 0836+710 and the two Seyfert galaxies Mkn 3 and Mkn 6. Their IBIS/ISGRI spectra are rather flat, albeit consistent with those measured by BeppoSAX. In the spectrum of Mkn 3 we find some evidence of a break between ~60 and ~100 keV, reminiscent of the high energy cut-offs observed in other Seyfert galaxies. This is the first report of INTEGRAL spectra of weak Active Galactic Nuclei. | |
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| High-energy observations of the state transition of the X-ray nova and black hole candidate XTE J1720-318 | |
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M. Cadolle Bel1, J. Rodriguez1,2, P. Sizun1, et al. CEA Saclay, DSM/DAPNIA/SAp, Bat 709, Orme des Merisiers, F-91191 Gif Sur Yvette, France | |
| Accepted for publication in A&A (426, p659) on July, 7, 2004 | |
| Abstract. We report the results of extensive high-energy observations of the X-ray transient and black hole candidate XTE J1720-318 performed with INTEGRAL, XMM-Newton and RXTE. The source, which underwent an X-ray outburst in 2003 January, was observed in February in a spectral state dominated by a soft component with a weak high-energy tail. The XMM-Newton data provided a high column density Nh of 1.2*1022 cm-2 which suggests that the source lies at the Galactic Centre distance. The simultaneous RXTE and INTEGRAL Target of Opportunity observations allowed us to measure the weak and steep tail, typical of a black-hole binary in the so-called High/Soft State. We then followed the evolution of the source outburst over several months using the INTEGRAL Galactic Centre survey observations. The source became active again at the end of March: it showed a clear transition towards a much harder state, and then decayed to a quiescent state after April. In the hard state, the source was detected up to 200 keV with a power law index of 1.9 and a peak luminosity of 7*1036 erg s-1 in the 20-200 keV band, for an assumed distance of 8 kpc. We conclude that XTE J1720-318 is indeed a new member of the black hole X-ray novae class which populate our galactic bulge and we discuss its properties in the frame of the spectral models used for transient black hole binaries. | |
| Preprint access | |
| Hard X-ray Emission Clumps in the γ-Cygni Supernova Remnant: an INTEGRAL-ISGRI View | |
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A.M. Bykov1, A.M. Krassilchtchikov1, Yu.A. Uvarov1, H. Bloemen2, R.A. Chevalier3, et al. 1. A.F.Ioffe Institute for Physics and Technology, 26 Politechnicheskaia, 194021 St.Petersburg, Russia 2. SRON National Institute for Space Research, Sorbonnelaan 2, 3584 CA Utrecht, The Netherlands 3. Department of Astronomy, University of Virginia, P.O. Box 3818, Charlottesville, VA 22903, USA | |
| Accepted for publication in A&A Letters on October 9, 2004 | |
| Abstract. Spatially resolved images of the galactic supernova remnant G78.2+2.1 (γ-Cygni) in hard X-ray energy bands from 25 keV to 120 keV are obtained with the IBIS-ISGRI imager aboard the International Gamma-Ray Astrophysics Laboratory INTEGRAL. The images are dominated by localized clumps of about ten arcmin in size. The flux of the most prominent North-Western (NW) clump is (1.7±0.4)·10-11 erg cm-2 s-1 in the 25-40 keV band. The observed X-ray fluxes are in agreement with extrapolations of soft X-ray imaging observations of γ-Cygni by ASCA GIS and spatially unresolved RXTE PCA data. The positions of the hard X-ray clumps correlate with bright patches of optical line emission, possibly indicating the presence of radiative shock waves in a shocked cloud. The observed spatial structure and spectra are consistent with model predictions of hard X-ray emission from nonthermal electrons accelerated by a radiative shock in a supernova interacting with an interstellar cloud, but the powerful stellar wind of the O9V star HD 193322 is a plausible candidate for the NW source as well. | |
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| Unveiling the nature of three INTEGRAL sources through optical spectroscopy | |
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N. Masetti, E. Palazzi, L. Bassani, A. Malizia & J.B. Stephen IASF/CNR, Sezione di Bologna, Italy | |
| Accepted for publication in A&A, 426, L41 on September 10, 2004 | |
| Abstract. The results of an optical spectroscopy campaign performed at the Astronomical Observatory of Bologna in Loiano (Italy) on three hard X-ray sources detected by INTEGRAL (IGR J17303-0601, IGR J18027-1455 and IGR J21247+5058) are presented. These data have allowed a determination of the nature for two of them, with IGR J17303-0601 being a low mass X-ray binary in the Galaxy and IGR J18027-1455 a background Type 1 Seyfert galaxy at redshift z = 0.035. IGR J21247+5058, instead, has a quite puzzling spectroscopic appearance, with a broad, redshifted Hα complex superimposed onto a `normal' F/G-type Galactic star continuum: these features, together with the spatially coincident extended radio emission, might suggest a chance alignment between a relatively nearby star and a background radio galaxy. These results underline the still non-negligible importance of smaller telescopes in modern astrophysics. | |
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| TeV Emission from the Galactic Center Black-Hole Plerion | |
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A. Atoyan1, C.D. Dermer 2, 1. CRM, Universite de Montreal, C.P. 6128, Montreal, Canada H3C 3J7 2. EO.Hulburt Center for Space Research, Code 7653, Naval Research Laboratory, Washington, DC 20375 USA | |
| Accepted for publication in ApJ Letters on November 11, 2004 | |
| Abstract. The HESS collaboration recently reported highly significant detection of TeV γ-rays coincident with Sgr A*. In the context of other Galactic Center (GC) observations, this points to the following scenario: In the extreme advection-dominated accretion flow (ADAF) regime of the GC black hole (BH), synchrotron radio/sub-mm emission of ~100 MeV electrons emanates from an inefficiently radiating turbulent magnetized corona within 20 RS (Schwarzschild radii) of the GCBH. These electrons are accelerated through second-order Fermi processes by MHD turbulence, as suggested by Liu et al. (2004). Closer to the innermost stable orbit of the ADAF, instabilities and shocks within the flow inject power-law electrons through first-order Fermi acceleration to make synchrotron X-ray flares observed with Chandra, XMM, and INTEGRAL. A subrelativistic MHD wind subtending an ~1 sr cone with power ~1037 erg s-1 is driven by the ADAF from the vicinity of the GCBH. As in pulsar powered plerions, electrons are accelerated at the wind termination shock, at ~1016.5 cm from the GCBH, and Compton-scatter the ADAF and the far infra-red (FIR) dust radiation to TeV energies. The synchrotron radiation of these electrons forms the quiescent X-ray source resolved by Chandra. The radio counterpart of this TeV/X-ray plerion, formed when the injected electrons cool on timescales of ~104 yrs, could explain the origin of nonthermal radio emission in the pc-scale bar of the radio nebula Sgr A West. | |
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| The soft X-ray counterpart of the newly discovered INTEGRAL source IGRJ16195-4945 | |
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L. Sidoli1, S. Vercellone1, S. Mereghetti1, M. Tavani2 1. IASF/CNR Milano 2. IASF/CNR Roma | |
| Accepted for publication in A&A on November 22, 2004 | |
| Abstract. The INTEGRAL satellite, during its regular scanning observations of the Galactic plane, has discovered several new X-ray sources emitting above 20 keV. The nature of the great majority of them is still unknown. Here we report on the likely low energy counterpart, observed with ASCA in 1994 and 1997, of one of these sources, IGRJ16195-4945. The ASCA source is faint (Flux~10-11erg/cm2/s), highly absorbed (NH~1023cm-2) and has a rather hard spectrum (photon index~0.6).These spectral properties are suggestive of a neutron star in a High Mass X-ray Binary. Our analysis of all the public INTEGRAL data of IGRJ16195-4945 shows that this source is variable and was in a high state with a 20-40 keV flux of 17 mCrab in two occasions in March 2003. | |
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| GRB 040403: a faint X-ray rich Gamma-ray Burst discovered by INTEGRAL | |
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S. Mereghetti1, et al. IASF-Milano, CNR | |
| Accepted for publication in A&A on December 1, 2004 | |
| Abstract. GRB 040403 is one of the faintest gamma-ray bursts for which a rapid and accurate localization has been obtained. Here we report on the gamma-ray properties of this burst, based on observations with the IBIS instrument aboard INTEGRAL, and the results of searches for its optical afterglow. The steep spectrum (power law photon index = 1.9 in the 20-200 keV range) implies that GRB 040403 is most likely an X-ray rich burst. Our optical limit of R > 24.2 at 16.5 hours after the burst, indicates a rather faint afterglow, similar to those seen in other relatively soft and faint bursts. | |
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| Investigating the EGRET-radio galaxies link with INTEGRAL: the case of 3EG J1621+8203 and NGC 6251 | |
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L. Foschini1, M. Chiaberge2, P. Grandi1, I.A. Grenier3, et al. 1. IASF-CNR/INAF, Sezione di Bologna. Via Gobetti 101, 40129 Bologna (Italy) 2. IRA-CNR/INAF, Via Gobetti 101, 40129 Bologna (Italy) 3. Universitè Paris VII Denis-Diderot and CEA-Saclay, Paris (France) | |
| Accepted for publication in A&A on December 6, 2004 | |
| Abstract. The analysis of an INTEGRAL AO2 observation of the error contours of the EGRET source 3EG J1621+8203 is presented. The only source found inside the error contours for energies between 20 and 30 keV at 5 sigma detection significance is the FR I radio galaxy NGC 6251. This supports the identification of NGC 6251 with 3EG J1621+8203. The observed flux is higher and softer than observed in the past, but consistent with a variable blazar-like spectral energy distribution. | |
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| Discovery of the INTEGRAL X/γ-ray transient IGR J00291+5934: a comptonised accreting ms pulsar | |
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S.E. Shaw1,4, N. Mowlavi1, J. Rodriguez2,1, P. Ubertini3, F. Capitanio3, et al. 1. INTEGRAL Science Data Centre, ch. d' Ecogia 16, CH-1290 Versoix, Switzerland 2. CEA Saclay, DSM/DAPNIA/SAp (CNRS FRE 2591), F-91191 Gif Sur Yvette Cedex, France 3. Istituto di Astrofisica Spaziale, CNR/INAF, Via Fosso del Cavaliere 100, 00133, Rome, Italy | |
| Submitted to A&A on 14th December 2004 | |
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Abstract. We report the discovery of a high energy transient with the
IBIS/ISGRI detector on board the INTEGRAL observatory. The source,
namely IGR J00291+5934, was first detected on 2nd December 2004 in the
routine monitoring of IBIS/ISGRI images (energy range 20-60 keV) of the
Galactic Plane. The observations were conducted during Galactic Plane Scans,
which are a key part of the INTEGRAL Core Programme observations.
After verifying the basic source behaviour, the discovery was announced on 3
December. The transient shows a hard comptonised spectrum, with peak energy
release at about 20 keV and a total luminosity of ~1.1 x 1036
erg/s in the 5--100 keV range, assuming a distance of 4 kpc. Following the
INTEGRAL announcement of the discovery of IGR J00291+5934, a number of
observations were made by other instruments. We summarise the results of
those observations and, together with the INTEGRAL data, identifiy IGR
J00291+5934 as the 6th member of a class of X-ray accreting millisecond
pulsars.
Note: This paper has not yet been accepted, but has been announced here given the interest surrounding this new source. | |
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