| No. 21 - 28 September 2007 | Edited by Marc Türler & Jérôme Rodriguez |
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This issue of the ISDC Newsletter announces the release of version 7.0 of the INTEGRAL off-line scientific analysis (OSA). It is a major step forward for the two main instruments of INTEGRAL.
OSA 7.0 for IBIS/ISGRI provides crucial improvements on the
energy calibration and the spectral response that now gives a slope of the Crab
Nebula in excellent agreement with what is measured on average by other missions
and in particular by SPI. In addition, the usable ISGRI energy range is now
extended towards low energies down to 18 keV for spectral analysis and even 15
keV for source detection. This is expected to allow the detection of new faint
and soft sources such as cataclysmic variables, which could add to the still
increasing number of IGR sources discovered by INTEGRAL.
OSA 7.0 for SPI includes a new alternative analysis method that gives promising results in very good agreement with the standard method and that allowed the creation of a new web page with SPI Revolution-wise Point Source Results. This is an interesting complement to the INTEGRAL Source Results web pages maintained at the ISDC. The changes and improvements for the other instruments (IBIS/PICsIT, JEM-X and OMC) are also reported in this Newsletter.
INTEGRAL is now almost five years in orbit and completed recently its 600th revolution. The evolution of the sky coverage of INTEGRAL observations is illustrated by the animated image. As this only shows the fully coded field of view, by now, almost every spot on the sky is virtually covered by INTEGRAL observations. Nevertheless, many extragalactic fields are still underexposed to allow the detection of their hard X-ray source population.
The ISDC activities are progressively broadening towards providing data analysis
tools and products for other missions than INTEGRAL. Work is starting to acquire
the competence for TeV data analysis for the European Cherenkov Telescope Array
(CTA) project. Two job offers are posted here in relation to
this development of expertise.
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| IBIS/ISGRI Data Analysis in OSA 7.0 | ||
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François Lebrun (CEA Saclay) & Roland Walter (ISDC) |
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OSA-7 brings two main improvements for the IBIS/ISGRI data analysis:
The main improvement in the ISGRI calibration is a more accurate correction of the spectral drift. This gain drift results from an increase of the charge carrier trapping in the CdTe detectors under the cosmic-ray and solar particles irradiation. The gain drift induces a loss at low energy that can mimic an increase of the lower threshold. A correction for this lower threshold drift has been implemented in OSA-7.
While in OSA-6 the gain-drift correction was done as a function of time, OSA-7 takes into account cumulative particle dose received by the detector. In addition events with ill-measured long rise-time are better taken into account. As irradiation affects mainly the electron transport, long rise-time pulses suffer less drift, so these events drift can be under-corrected. This effect is accounted for in OSA-7. Indeed the resulting calibration law is independent of the pulse rise- time up to a dynamic energy threshold which depends on rise-time (nominal value is around 50 keV). Overall, the OSA-7 spectral resolution is improved with respect to OSA-6.
The new ISGRI energy correction, together with a better correction for the
pixel low thresholds allows to use ISGRI down to 18 keV for spectral analysis
and down to 15 keV for source detection. The image quality below 22 keV has
improved as a result of a better background correction due to the more stable
spectral response. Because of the new energy correction, the count rate of a
source in a specific energy-band changes slightly from the OSA-6 results.
The Mont-Carlo simulation has been improved to better reproduce the observed pulse rise-time distribution. This resulted in a new basic ancillary response fonction (ARF). Tested with XSPEC on Crab spectra, it shows a significant improvement (less residuals) with regard to the OSA-6 basic ARF particularly at low energy (down to 16 keV). The Crab spectrum obtained with OSA-7 is harder (photon power law index Γ = 2.10 for E < 100 keV) than that obtained with OSA-6 (Γ = 2.25). The shape of the Crab spectrum is more stable with this new basic ARF but still shows some variation. The basic ARF has then been modified as a function of time to correct for these variations.
Figure: Simultaneous fit of the Crab spectrum with data from ISGRI (14 spectra from various calibration campaigns) and SPI (grey points). The best fit model is composed of a broken powerlaw with photon indices 2.108 ± 0.002 and 2.34 ± 0.01, a break energy of 103 ± 2 keV and a normalization at 1 keV of 10.2 ± 0.1 ph cm-2 s-1 keV-1 for a reduced χ2 of 0.74 (with a systematic uncertainty of 2%).
As an example, we show in the Figure a fit of the Crab Nebula with both
IBIS/ISGRI and SPI data from various calibration campaigns. There are now very
little systematic differences in the residuals from one observation to the
other and a very good match between IBIS/ISGRI and SPI.
| IBIS/PICsIT Data Analysis in OSA 7.0 | ||
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Luigi Foschini & Valentina Bianchin (INAF/IASF-Bologna, Italy) |
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The main novelty of the OSA 7.0 release is the possibility to perform a
scientifically sound analysis of gamma-ray bursts (GRB) detected in
spectral-timing mode. As known, to save telemetry, PICsIT is set to work by
integrating on-board data into histograms. Data are simultaneously stored in the
spectral imaging data set (64x64 pixels, 256 energy channels, 1 histogram per
ScW) and in the spectral timing data set (no spatial information, only 8 energy
bands, but high time resolution, from 1 to 500 ms). In every standard science
window (ScW), the data are available in both modes.
Spectral-timing data have already given good results by detecting dozens of GRB (see IBIS/PICsIT Source Catalog and the Figure), but the response matrices (RMF/ARF) for this mode, prepared by P. Laurent (CEA/Saclay) are only available now with this OSA 7.0 release (see Di Cocco et al. (2007) for more details).
Figure: GRB 041219 as observed in the spectral-timing data of IBIS/PICsIT [Fig 3. of Di Cocco et al. (2007)].
In addition, the executable for the lightcurve extraction from spectral timing data has been improved to include an automatic alert message in output when the rate is greater than a certain value, which in turn can be set by the user.
Other improvements in OSA 7.0 for IBIS/PICsIT concerns an update of the mosaic
tool (correction of source positioning) and of the calculation of energy bands
from HEPI-LUT for spectral imaging data. Although OSA for PICsIT has a
predefined set of energy band (8 for single events and 8 for multiple events),
it is possible for the user to select his/her own set of energy bands. However,
the main problem is the preparation of a proper set of background maps. OSA for
PICsIT includes in IC (instrument characteristics) files a set of maps for the 8
standard energy bands. Users wishing to change the energy bands shall therefore
prepare themselves a corresponding new set of background maps.
| SPI Data Analysis in OSA 7.0 | ||
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Ingo Kreykenbohm (IAA Tübingen & ISDC) |
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There are three important new features introduced for SPI in OSA 7.0:
First of all a third background estimation method has been added: in addition to
flatfields and using background tracers the user can now use background
templates to derive a background. The background templates are provided by the
SPI instrument team in Toulouse. The background templates are part of the SPI
IC-tree (Instrument Characteristics) and therefore available to all users.
Different templates exist depending on the purpose of the user. In the graphical
user interface (GUI) of the spi_science_analysis, the templates can be
selected simply via a drop-down menu. The default background method in the SPI
science analysis pipeline remains, however, the flatfield method, but users are
encouraged to also try the background templates.
Figure: Image of the GRS 1915 region while the transient 4U 1901+03 is in outburst obtained using the timing-imaging mode of spiros in OSA 7.0.
Secondly, the main engine of the SPI analysis pipeline, spiros has also been updated to version 9.3 which provides apart from general improvements a highly sought-after feature: a timing-imaging mode! This mode allows to construct images even when strongly variable sources are in the field of view. Previously, when this happened, it was necessary to use the timing mode or the spectral-timing mode to derive light curves or spectra, but no images could be obtained. With spiros 9.3 it is now possible to derive images with variable sources in the field of view.
The third important addition is the inclusion of a new tool called spimodfit developed at MPE, Munich. This tool is an alternative to spiros that allows to derive spectra for sources in the field of view and most importantly to study the diffuse emission. Spectra obtained by spiros and spimodfit are found to agree generally very well. The spimodfit tool is not yet included in the standard SPI science analysis, but is a stand alone, advanced tool for experienced users. The documentation how to use this new tool is included.
Apart from these major improvements, all other software components have been
updated and improved. The IC files have also been updated, the bad
pointing filter now covers all revolutions up to Rev. 539.
| JEM-X Data Analysis in OSA 7.0 | ||
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Stéphane Paltani (ISDC) |
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In this release efforts have been made to consolidate image processing with JEM-X and direct extraction of fluxes from the images. The main imaging tool, j_ima_iros, has been the subject of important revisions. An astrometric problem has been detected, which resulted in a measurable misalignment of the images. This has been fixed, and astrometry has been verified to be considerably improved for both JEM-X instruments. Parameters defining the area of the detector to be used have also been optimized in order to maximize signal-to-noise ratio. Outside of the imaging step, a new algorithm to detect and remove hotspots has been implemented. This may also contribute to improve the quality of the images when some hotspot activity is present.
Another important modification implemented in the imaging process is related to source detection. The JEM-X imaging process being based on the IROS algorithm (Iterative Removal Of Sources), source detection is a fundamental component of image reconstruction. Coincidence of excesses in at least two separate bands is a criterion to decide about the reality of a detection. In previous releases, source detection was performed by j_ima_iros in all the energy bands provided by the user. This could cause problems for source detection in at least two particular cases. In the first case, the user uses overlapping bands, for instance several narrow bands to get fluxes and one or more large bands to get deep images. Therefore, excesses in different bands are correlated, which resulted in spurious detections. In the second case, the user uses many narrow bands, which increases the chances of coincident excesses, leading again to spurious detections. In OSA 7, j_ima_iros uses three optimized, non-overlapping bands to perform source detection, irrespectively of the user's choice. Then, imaging is performed in the bands requested by the user using only the sources found in the three previous bands, This is completely transparent, and, apart from a moderately extended computation time, there's no visible difference in the output for the user.
Spectral extraction with JEM-X is still problematic, with the main tool suffering from several shortcomings. One of these is the possibility of contamination of weak-source spectra in the presence of nearby bright sources. To alleviate this problem, we introduced in OSA 6 the possibility to extract spectra directly from the JEM-X images using the tool mosaic_spec. We have performed very extensive tests of the quality of spectral extraction with this method, and we are now able to give clear recommendation on how best to use mosaic_spec for this purpose. These tests showed in particular that we achieved very good consistency in the Crab fluxes and spectral indices between the standard spectral method and the mosaic_spec method. While standard spectral extraction is still the reference method for isolated or bright sources, it is recommended to use spectral extraction from images in complex fields. It has also been observed that fluxes derived by j_ima_iros itself, while providing useful rough flux estimates, should not be used for quantitative studies.
With the size of the archive growing and spectral extraction from images becoming a standard approach, the necessity to combine several JEM-X mosaics together is becoming more apparent. The mosaic tool, j_ima_mosaic, is now able to do this in a very straightforward manner, irrespectively of the fact that images have been obtained with JEM-X 1 or JEM-X 2. This will certainly become a very important feature, allowing to reach the faintest possible fluxes with JEM-X.
Finally, once images have been created, the next logical step is source detection. While this was done at the Science Window level by j_ima_iros, nothing existed for the JEM-X mosaics. OSA 7 introduces a new component, j_ima_src_locator, which is able to analyze any JEM-X image in order to produce sources lists that can be matched with a catalogue later on.
Significant development efforts are still on-going within the JEM-X team. Good
progress has been made towards a new spectral extraction tool, which would in
particular incorporate the electronic efficiency curve obtained from calibration
of the JEM-X instruments. These developments are not yet ripe, but we do hope
that the next major OSA release will be to a large extent dedicated to releasing
them to the community.
| OMC News in OSA 7.0 | ||
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Albert Domingo Garau (LAEFF-INTA, Madrid) |
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The new method introduced in OSA 6.0 (see article in Newsletter No. 20) to calculate the fluxes by re-centering on the catalogued positions is now the default (IMA_wcsFlag=yes). As a consequence, the OMC analysis needs by default the OMC Input Catalogue. The location of the catalogue must be passed to the analysis scripts by using the $ISDC_OMC_CAT environment variable. Note that the analysis will fail if the OMC catalogue can not be found by the OMC executables.
One advantage of this is that the mosaics of sub-windows are properly analyzed by using the default parameters, if the source coordinates in the OMC Input Catalogue are accurate enough. In addition, in crowded fields, source confusion can be better managed by the analysis software.
With OSA 7.0 users can also re-process old data when more accurate positions are
available, by making their own local copy of the OMC Input Catalogue with
updated coordinates, or downloading a new version from ISDC.
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| Some Statistics on IGR Sources | ||
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Jérôme Rodriguez (CEA Saclay) |
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Since the launch of INTEGRAL many new sources were discovered, mainly with IBIS
above 20 keV. A lot of attention has been given to these so-called INTEGRAL
Gamma-Ray (IGR) sources, in particular
because INTEGRAL (thanks to the hard X-ray survey above 20 keV) has allowed the
discovery of new and/or poorly known classes of sources: the so-called highly
absorbed sources and Supergiant Fast X-ray Transients.
Figure: All-sky distribution of INTEGRAL Gamma-Ray (IGR) sources detected up to December 1st, 2006. Different point types and colors are used for different types of sources. The grey-scaled background represents the exposure map of IBIS from revolutions 30 to 484. Courtesy: A. Bodaghee In an in depth analysis of all sources detected by IBIS, Bodaghee et al. (2007) have shown that similar numbers of galactic X-ray binaries and extra-galactic sources were detected by IBIS and that many IGRs are active galactic nuclei (AGN) (see the Figure). Together with the increasing number of IGR sources, the attention on these sources has not fallen since the discovery of the first one: IGR J16318-4848. This is illustrated by the still increasing numbers of refereed publications related to IGR sources per year, while the number of Astronomer's Telegrams (ATels) and IAU Circulars referring to IGR sources remained roughly constant (see the list of circulars):
| Year | 2003 | 2004 | 2005 | 2006 | 2007 |
|---|---|---|---|---|---|
| Refereed Publications | 7 | 8 | 25 | 32 | 25+ |
| Telegrams & Circulars | 49 | 51 | 47 | 45 | 28+ |
| New SPI Housekeeping & Source Results Web Pages | ||
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Dirk Petry (MPE, ISDC) & Xiao-Ling Zhang (MPE) |
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The Max Planck Institute for extraterrestrial Physics (MPE) hosts the home page of the INTEGRAL / SPI Spectrometer Team which is meant as a portal for all information on SPI.
Scientists from MPE are now in particular providing a new service for the scientific community which consists of two sister webpages: one for SPI Science Housekeeping (created by Xiao-Ling Zhang) and one for SPI Revolution-wise Point Source Results (created by Dirk Petry). Both are meant to help the general user to judge the quality of a given dataset and understand the achieved sensitivity. They also provide a quick-look analysis for bright point sources.
This page is available since the end of 2006. The SPI science house keeping page
provides a quick look of the status of the SPI data in each revolution, as well
as a link to the underlying SPI science house keeping database (FITS format)
which can be downloaded for comprehensive checking. This database collects
various information for each science window, including house keeping data,
environmental data (e.g. GOES), pointing information etc., in 349 columns. It
can be used in studying the correlation between parameters and selecting good
science windows/pointings.
Figure 1 (left): SPI exposure map for revolution 237 taken from the SPI science housekeeping web page.
Figure 2 (right): Set of single events spectra for revolution 237 for the 17 live SPI detectors taken from the SPI science housekeeping web page.
In the webpage for each revolution, the following information is shown:
This page went online on 26 Sept 2007. In its first version, the page provides spectra for all potentially bright known point sources in the SPI field of view for each individual revolution. This is of course limited to those revolutions for which all data is public.
The user can select a revolution of interest and is then
presented with a table of point sources which were in the
field of view (maximum radius = 20 degrees) during the good
observation time of that revolution.
The table is sorted by equatorial position and provides
differential fluxes (or upper limits) for 30 keV, 100 keV,
300 keV, and 1000 keV. It also gives the effective exposure
at 30 keV taking into account the SPI response and finally a
link to a spectral plot and an ASCII table of flux points, error
bars and upper limits. The range of the spectrum covers the
entire SPI range from 20 to 8000 keV.
Figure 3 (left):
The SPI spectrum of Cyg X-1 observed in revolution
159 as provided by the SPI source results page. A powerlaw fit is applied by
default to the significant points below 100 keV.
Figure 4 (right): The SPI spectrum of the low-mass X-ray binary GX 339-4 as observed in revolution 223 and shown on the SPI source results page.
The results are obtained by an automatic pipeline based on the spimodfit software developed by A.W. Strong (MPE, Garching) and H. Halloin (formerly MPE, now at APC, Paris). The spimodfit software is also included in OSA 7 (see article above). A description of the analysis pipeline can be found on the front page.
The purpose of the results presented here is to provide a quicklook point source analysis for public SPI data. The user can find answers to questions such as
The results on these pages are not intended to be used as a source for publication-ready point source spectra. Still, the spectra are also provided in numerical form such that the user can better make quantitative estimations to plan his/her detailed analysis or proposals of future observations.
The page is also aimed at scientists doing multi-wavelength analysis who want to complement their spectral energy distribution with hard X-ray/soft gamma-ray points.
Over the next few months, the features of this page will continuously be improved and extended and in particular spectra integrated over longer time scales and light curve plots will be provided. Feedback is welcome.
Acknowledgements. All authors were supported by the German Bundesministerium für Bildung, Wissenschaft, Forschung und Technologie (BMBF/DLR) under contract No. FKZ 50 OG 0502.
| The 1 keV to 200 keV X-ray Spectrum of NGC 2992 and NGC 3081 | |
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V. Beckmann1,2, N. Gehrels3 and J. Tueller3 1. INTEGRAL Science Data Centre, ch. d' Ecogia 16, CH-1290 Versoix, Switzerland 2. University of Maryland Baltimore County, 1000 Hilltop Circle, Baltimore, MD 21250, USA 3. Astrophysics Science Division, NASA/GSFC, Code 661, Greenbelt, MD 20771, USA | |
| Accepted for publication in ApJ on April 19, 2007 | |
| Abstract. The Seyfert 2 galaxies NGC 2992 and NGC 3081 have been observed by INTEGRAL and Swift. We report about the results and the comparison of the spectrum above 10 keV based on INTEGRAL IBIS/ISGRI, Swift/BAT, and BeppoSAX/PDS. A spectrum can be extracted in the X-ray energy band ranging from 1 keV up to 200 keV. Although NGC 2992 shows a complex spectrum below 10 keV, the hard tail observed by various missions exhibits a slope with Γ = 2, independent on the flux level during the observation. No cut-off is detectable up to the detection limit around 200 keV. In addition, NGC 3081 is detected in the INTEGRAL and Swift observation and also shows an unbroken Γ = 1.8 spectrum up to 150 keV. These two Seyfert galaxies give further evidence that a high-energy cut-off in the hard X-ray spectra is often located at energies EC ≫ 100 keV. In NGC 2992 a constant spectral shape is observed over a hard X-ray luminosity variation by a factor of 11. This might indicate that the physical conditions of the emitting hot plasma are constant, while the amount of plasma varies, due to long-term flaring activity. | |
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E-mail contact | Preprint access |
| Cygnus X-3 transition from the ultrasoft to the hard state | |
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V. Beckmann1,2,3, S. Soldi1,2, G. Bélanger, S. Brandt, et al. 1. INTEGRAL Science Data Centre, ch. d' Ecogia 16, CH-1290 Versoix, Switzerland 2. Observatoire Astronomique de l'Université de Genève, ch. des Maillettes 51, CH-1290 Sauverny, Switzerland 3. CSST, University of Maryland Baltimore County, 1000 Hilltop Circle, Baltimore, MD 21250, USA | |
| Accepted for publication in A&A on August 3, 2007 | |
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Abstract. Aims: The nature of Cygnus X-3 is still not well understood.
This binary system might host a black hole or a neutron star. Recent
observations by INTEGRAL showed that Cygnus X-3 was again in an extreme
ultrasoft state. Here we present the analysis of the transition from the ultra
soft state, dominated by blackbody radiation at soft X-rays plus non-thermal
emission in the hard X-rays, to the low hard state. Methods: INTEGRAL observed Cyg X-3 six times during three weeks late May and early June 2007. Data from IBIS/ISGRI and JEM-X1 are analysed to show the spectral transition. Results: During the ultrasoft state the soft X-ray spectrum is well described by an absorbed (NH = 1.5 x 1022 cm-2) black body model, whereas the X-ray spectrum above 20 keV appears to be extremely low and hard (Γ = 1.7). During the transition the radio flux rises to a level of >1 Jy, the soft X-ray emission drops by a factor of 3, while the hard X-ray emission rises by a factor of 14 and becomes steeper (up to Γ = 4). Conclusions: The ultra soft state is apparently preceding the emission of a jet, which is apparent in the radio and hard X-ray domain. | |
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E-mail contact | Preprint access |
| IGR J16194-2810: a new symbiotic X-ray binary | |
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N. Masetti1, R. Landi1, M.L. Pretorius2 et al. 1. INAF - Istituto di Astrofisica Spaziale e Fisica Cosmica di Bologna, via Gobetti 101, I-40129 Bologna, Italy 2. School of Physics & Astronomy, University of Southampton, Southampton, Hampshire, SO17 1BJ, United Kingdom | |
| Accepted for publication in A&A, 470, 331 on April 24, 2007 | |
| Abstract. We here report on the multiwavelength study which led us to the identification of X-ray source IGR J16194-2810 as a new Symbiotic X-ray Binary (SyXB), that is, a rare type of Low Mass X-ray Binary (LMXB) composed of a M-type giant and a compact object. Using the accurate X-ray position allowed by Swift/XRT data, we pinpointed the optical counterpart, a M2 III star. Besides, the combined use of the spectral information afforded by XRT and INTEGRAL/IBIS shows that the 0.5-200 keV spectrum of this source can be described with an absorbed Comptonization model, usually found in LMXBs and, in particular, in SyXBs. No long-term (days to months) periodicities are detected in the IBIS data. The time coverage afforded by XRT reveals shot-noise variability typical of accreting Galactic X-ray sources, but is not good enough to explore the presence of X-ray short-term (seconds to hours) oscillations in detail. By using the above information, we infer important parameters! for this source such as its distance (about 3.7 kpc) and X-ray luminosity (about 1.4e35 erg/s in the 0.5-200 keV band), and we give a description for this system (typical of SyXBs) in which a compact object (possibly a neutron star) accretes from the wind of its M-type giant companion. We also draw some comparisons between IGR J16194-2810 and other sources belonging to this subclass, finding that this object resembles SyXBs 4U 1700+24 and 4U 1954+31. | |
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E-mail contact | Preprint access |
| A Hard X-Ray View of Scorpius X-1 with INTEGRAL: Nonthermal Emission? | |
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T. Di Salvo1, P. Goldoni 2, L. Stella3, et al. 1. Dipartimento di Scienze Fisiche ed Astronomiche, Università di Palermo, via Archirafi 36, 90123 Palermo, Italy 2. APC, Laboratoire Astroparticule et Cosmologie, UMR 7164, 11 Place Marcelin Berthelot, 75231 Paris Cedex 05, France 3. Osservatorio Astronomico di Roma, via Frascati 33, 00040 Monteporzio Catone (Roma), Italy | |
| Accepted for publication in ApJ in 2006 | |
| Abstract. We present here simultaneous INTEGRAL/RXTE observations of Sco X-1 and in particular a study of the hard X-ray emission of the source and its correlation with the position in the Z track of the X-ray color-color diagram. We find that the hard X-ray (above about 30 keV) emission of Sco X-1 is dominated by a power-law component with a photon index of 3. The flux in the power-law component slightly decreases when the source moves in the color-color diagram in the sense of increasing inferred mass accretion rate from the horizontal branch to the normal branch/flaring branch vertex. It becomes not significantly detectable in the flaring branch, where its flux has decreased by about an order of magnitude. These results present close analogies to the behavior of GX 17+2, one of the so-called Sco-like Z sources. Finally, the hard power law in the spectrum of Sco X-1 does not show any evidence of a high-energy cutoff up to 100-200 keV, strongly suggesting a nonthermal origin of this component. | |
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E-mail contact | Preprint access |
| South-West extension of the hard X-ray emission from the Coma cluster | |
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D. Eckert 1, A. Neronov 1, T. J.-L Courvoisier1 & N. Produit1 INTEGRAL Science Data Centre, ch. d' Ecogia 16, CH-1290 Versoix, Switzerland | |
| Accepted for publication in A&A on May 14, 2007 | |
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Abstract. Aims: We explore the morphology of hard (18-30 keV) X-ray
emission from the Coma cluster of galaxies. Methods: We analyse a deep (1.1 Ms) observation of the Coma cluster with the ISGRI imager on board the INTEGRAL satellite. Results: We show that the source extension in the North-East to South-West (SW) direction ( 17') significantly exceeds the size of the point spread function of ISGRI, and that the centroid of the image of the source in the 18-30 keV band is displaced in the SW direction compared to the centroid in the 1-10 keV band. To test the nature of the SW extension we fit the data assuming different models of source morphology. The best fit is achieved with a diffuse source of elliptical shape, although an acceptable fit can be achieved assuming an additional point source SW of the cluster core. In the case of an elliptical source, the direction of extension of the source coincides with the direction toward the subcluster falling onto the Coma cluster. If the SW excess is due to the presence of a point source with a hard spectrum, we show that there is no obvious X-ray counterpart for this additional source, and that the closest X-ray source is the quasar EXO 1256+281, which is located 6.1' from the centroid of the excess. Conclusions: The observed morphology of the hard X-ray emission clarifies the nature of the hard X-ray excess emission from the Coma cluster, which is due to the presence of an extended hard X-ray source SW of the cluster core. | |
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E-mail contact | Preprint access |
| Hard X-ray Variability of AGN | |
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V. Beckmann1,2, S. D. Barthelmy3, T.J.-L. Courvoisier1,2, N. Gehrels3, S. Soldi1,2, et al. 1. INTEGRAL Science Data Centre, ch. d' Ecogia 16, CH-1290 Versoix, Switzerland 2. Observatoire Astronomique de l'Université de Genève, Chemin des Maillettes 51, 1290 Sauverny, Switzerland 3. Astrophysics Science Division, NASA Goddard Space Flight Center, Code 661, MD 20771, USA | |
| Accepted for publication in A&A on September 12, 2007 | |
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Abstract. Aims: Active Galactic Nuclei are known to be variable
throughout the electromagnetic spectrum. An energy domain poorly studied in this
respect is the hard X-ray range above 20 keV. Methods: The first 9 months of the Swift/BAT all-sky survey are used to study the 14 - 195 keV variability of the 44 brightest AGN. The sources have been selected due to their detection significance of > 10σ. We tested the variability using a maximum likelihood estimator and by analysing the structure function. Results: Probing different time scales, it appears that the absorbed AGN are more variable than the unabsorbed ones. The same applies for the comparison of Seyfert 2 and Seyfert 1 objects. As expected the blazars show stronger variability. 15% of the non-blazar AGN show variability of >20% compared to the average flux on time scales of 20 days, and 30% show at least 10% flux variation. All the non-blazar AGN which show strong variability are low-luminosity objects with L(14-195 keV) < 1044 erg s-1. Conclusions: Concerning the variability pattern, there is a tendency of unabsorbed or type 1 galaxies being less variable than the absorbed or type 2 objects at hardest X-rays. A more solid anti-correlation is found between variability and luminosity, which has been previously observed in soft X-rays, in the UV, and in the optical domain. | |
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E-mail contact | Preprint access |
| Hard X-ray colours of Neutron Star and Black Hole Low Mass X-ray Binaries with INTEGRAL | |
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Simon E. Shaw1,2, Ada Paizis3, Nami Mowlavi1, Stéphane Paltani
1, Thierry J.-L. Courvoisier1 et. al. 1. INTEGRAL Science Data Centre, ch. d' Ecogia 16, CH-1290 Versoix, Switzerland 2. School of Physics and Astronomy, University of Southampton, SO17 1BJ, UK. 3. INAF-IASF Sezione di Milano, Via Bassini 15, 20133 Milano, Italy | |
| Accepted for publication in JASR - proceedings of COSPAR meeting, Beijing. on 1 June 2007 | |
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Abstract. The X-ray spectra of Low Mass X-ray Binaries (LMXB) can change
on short time-scales, making it difficult to follow their spectral
characteristics in detail through model fitting. Colour-colour (C-C) diagrams
are therefore often used as alternative, model independent, tools to study the
spectral variability of these sources. The INTEGRAL mission, with its
high sensitivity, large field of view and good angular resolution, is well
suited to study the hard X-ray properties of LMXBs. In particular the ISGRI
imager on board of INTEGRAL allows the regular monitoring of the sources
in the less frequently studied domain above 20 keV. In this proceeding, C-C
diagrams have been made with data from the INTEGRAL public archive; a
search is made for systematic differences in the C-C diagrams between black hole
candidates (BH) and neutron stars (NS) in LMXBs using a moments analysis
method.
Using a small sample from the INTEGRAL Source Results web page at the ISDC, containing 6 BH and 7 NS LMXBs, we find that the hard X-ray colours generated above and below 30 keV seem less well correlated for systems containing NS than those with BH. The C-C diagrams indicate that the average spectra of BH are more `power law like' when compared with NS. The centroids of the NS C-C plots are grouped more tightly than BH, which would arise if the spectra of NS had a feature such as a break or cut-off around 30 keV. | |
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E-mail contact | Preprint access |
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The Astrophysics and Space Forum of Sabanci University in Istanbul, Turkey, invite applications for a postdoctoral position funded by the European Commission Marie Curie Transfer of Knowledge Project, ASTRONS (ASTROphysics of Neutron Stars). For details, please see the Job Register. Sabanci University also has short term visiting positions for more experienced researchers. Please contact Dr. Emrah Kalemci for details.
Immediate vacancy of a shared Postdoctoral Position at ETH Zurich and University of Geneva.
ETH Zurich as a member of the MAGIC Collaboration and the University of Geneva, operating the INTEGRAL Science Data Center, are working together towards a Science Data Center for TeV Astronomy.
The rather young field of TeV Astronomy is developing very fast since the commissioning of the current Imaging Air Cherenkov Telescopes H.E.S.S., MAGIC and VERITAS in the past three years. Additionally, the planning for CTA, a major Pan-European next generation facility for TeV Astronomy has already started. While the actual Cherenkov Telescopes are operated in a closed collaboration manner, the shear amount of newly detected sources will soon mandate to make data available to a broader community.
The goal is to combine the experience gained by ETH Zurich in analysing MAGIC data and by the University of Geneva in operating the Science Data Centre of the INTEGRAL satellite. The successful candidate will have to play a leading role in the design of such a centre. Additionally, participation in the scientific programme of MAGIC is encouraged.
Candidates are expected to have a PhD in Astro-Particle Physics or Astronomy. Experience in data analysis of Cherenkov Telescopes, multiwavelength analysis or a theoretical background in TeV Astronomy would be an advantage.
The initial term of this position is limited to two years with the
possibility of an extension. Interested candidates should provide a
curriculum vitae together with a letter of motivation, and arrange to
have three letters of recommendation sent to
Dr. Adrian Biland Dr. Roland Walter
ETH Zurich INTEGRAL Science Data Centre
Institute for Particle Physics Chemin d'Ecogia 16
CH-8093 Zurich CH-1290 Versoix
Switzerland Switzerland
E-mail: Adrian Biland E-mail: Roland Walter
Applications are accepted until the position is filled.
Immediate vacancy of a PhD student position shared between University of Geneva and ETH Zurich
ETH Zurich as a member of the MAGIC Collaboration and the University of Geneva, operating the INTEGRAL Science Data Center, are working together towards a Science Data Center for TeV Astronomy.
The rather young field of TeV Astronomy is developing very fast since the commissioning of the current Imaging Air Cherenkov Telescopes H.E.S.S., MAGIC and VERITAS in the past three years. The number of sources detected in the TeV domain increases very fast and a couple of hundred sources could be expected when MAGIC II and HESS II will be operating (from 2008 on).
A PhD student position is available to conduct research on TeV detected sources, with MAGIC (and possibly other TeV data) and data from other astronomical facilities (in particular GLAST and INTEGRAL). Emphasis will be on variability studies of AGN and X-ray binaries and TeV source counterpart identification.
Candidates are expected to have a Master in Astrophysics or Physics. The PhD degree will be awarded by the Geneva Observatory/University of Geneva.
Interested candidates should e-mail a curriculum vitae together with
marks obtained through the studies, a letter of motivation, and a few
references to one of the address below:
Dr. Adrian Biland Dr. Roland Walter
ETH Zurich INTEGRAL Science Data Centre
Institute for Particle Physics Chemin d'Ecogia 16
CH-8093 Zurich CH-1290 Versoix
Switzerland Switzerland
E-mail: Adrian Biland E-mail: Roland Walter
Applications are accepted until the position is filled.
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