| No. 19 - 27 March 2006 | Edited by Marc Türler & Pierre-Olivier Petrucci |
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Spring finally arrived, INTEGRAL's AO-4 is open (deadline: April
21) and INTEGRAL results are getting published at a rate never reached before
(about 1 publication every 3 days). The abstracts of thirteen of them are included in the Science News section together with two PhD Thesis summaries.
The growing impact of INTEGRAL is also shown in a science
article by K. Hurley reporting the interactions between INTEGRAL and other
satellites or ground facilities.
INTEGRAL scientific highlights are not included here as they were already well
covered by ESA press releases:
Late January and early February INTEGRAL performed exceptional
manoeuvres to look down to the Earth. The aim of the series of four Earth
observations was mainly to use the Earth as a mask to study the cosmic X-ray
background (see ESA's press
release). The results of this successful campaign will soon be published.
All this would not have been possible without the work done by the ISDC and the Instrument Teams to provide rapidly the best possible tools for INTEGRAL data analysis. A significant improvement is the release today of four new ancillary response files (ARFs) for IBIS/ISGRI analysis and the update of the INTEGRAL Source Results with lightcurves, images and spectra of sources now processed with OSA 5.1. Developments for OSA 6.0 - to be released before the next INTEGRAL Data Analysis Workshop - are on-going, for instance concerning the ISGRI spectral response. Finally, P. Lubinski is giving us new hope for getting soon much better IBIS/PICsIT scientific results. There are therefore many good reasons to continue (or start) working with INTEGRAL data and this for many years to come as ESA has extended the INTEGRAL mission until the end of 2010.
Since almost two years, Pierre-Olivier Petrucci is editing this Newsletter. In
the future, he will leave this task to Jérôme Rodriguez, who
replaced Thierry Montmerle as the French Co-I of the ISDC Consortium. Until then,
we wish you a lot of success with your INTEGRAL scientific analysis and future
proposals.
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| What's New on the Integral Source Results Pages ? | ||
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P. Kubánek (Astron. Inst. Czech Republic & ISDC); M. Beck, P. Binko, M. Meharga, S. Paltani (ISDC); and D. Willis (Univ. Southampton & ISDC) |
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The INTEGRAL Source Results (ISR) provide lightcurves, images and spectra of sources detected by INTEGRAL (see article in Newsletter No. 17). The data set includes all public data of the mission and the pages allow to easily download all public data of a given source through a W3 Browse query. A new version of the ISR tool is now available on-line. The major difference is that the data are now reprocessed with the latest Off-line Scientific Analysis (OSA 5.1) instead of OSA 4.2.
As more public data were available for OSA 5.1 reprocessing, this new version contains data spanning a larger time interval. New public data for revolutions greater than 250 will be processed only with OSA 5.1. They will be added to the database as soon as they become public.
The reprocessing with OSA 5.1 used a new version of the INTEGRAL Reference Catalogue (v. 23 for ISGRI and v. 24 for JEM-X). Consequently, some faint sources which were not flagged as detected in the old catalogue version 15, are now present on the ISR pages (see for example NGC 4151).
In version 1 data were filtered after OSA processing, before they were inserted to the ISR database. In particular for ISGRI, data with a big off-set angle, i.e. when the source was in the border of the field-of-view, were not included. In version 2, there is no more any filtering between OSA processing and storing in thedatabase. As a consequence, there are now more data points in the lightcurves of some sources. Users should however be cautious when using low countrate values or strange features in the lightcurves, as they can be caused by random background fluctuations.
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Some other differences and notes are listed below:
| New Instrument Characteristics with four new IBIS/ISGRI ARFs | ||
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IBIS Team & ISDC |
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The IBIS Team has released a set of new Ancillary Response Files (ARFs). Instead of the single ARF of OSA 5.1 (isgr_arf_rsp_0010.fits), there are now four ARFs to better describe the evolution of the IBIS/ISGRI instrument with time. Their validity corresponds to four periods delimited by changes in the ISGRI low energy threshold and the very strong solar flare of revolution 128:
Figure: Comparison of the four new IBIS/ISGRI ARFs (period 1: red; period 2: blue; period 3: green; period 4: yellow) with the previous single ARF (black) of OSA 5.1. In the most important ISGRI range between 35 and 140 keV the differences are very small. However, the strong features at low energy and between 150 and 200 keV are now much reduced with the new ARFs. The main differences among the four new ARFs are found in the 17-20 keV and 200-400 keV ranges.
OSA 5.1 was already able to deal with multiple ISGRI ARFs. In particular, spe_pick finds the ARFs of the individual spectra in the header of these spectra and combines them on the fly when creating the summed spectrum. It is therefore important not to specify the "response" and "ancrfile" when launching spe_pick, unless one really wants to bypass the multiple ARFs and the RMF that are included in this IC release. Note that in case of an average spectrum spanning across two or more validity periods, the corresponding ARFs are then also averaged by spe_pick.
The new ARFs are part of the Instrument Characteristics (IC 5.1.1) available
from the software download page.
The new version of the IC file contains also new JEM-X ARFs, but only applying
to the redundant JEM-X instrument during Crab calibration observations. This
does therefore not impact on scientific results obtained currently with OSA 5.1.
Finally, there are also updated SPI line calibrations and new OMC flat-fields
for recent observations.
| ISGRI Spectral Response: Status & Developments | ||
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F. Lebrun (CEA Saclay, France) |
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A paper by Mineo et al. (2006, A&A in press, astro-ph/0601641) recently appeared claiming that an ancillary response file (ARF) and a look-up table 2 (LUT2) better than those used in the Off-line Scientific Analysis (OSA) are available. Although it is true that the ISGRI spectral response can be improved, things are not that simple and a New LUT2 and a new ARF cannot alone solve the problem.
In fact, we are facing a degenerate problem: different energy deposits can produce the same pulses in ISGRI (hopefully not always). Any LUT2 attributes a definite energy to a pulse and the reconstructed spectrum is distorted since different input energies are restored at the same output energy. But this is not a serious problem. The real problem is that these wiggles in the spectrum are not predicted by the OSA RMF (produced using GEANT 3 Monte-Carlo simulations). As a result, there are wiggles or "snakes" in the residuals at a few-percent level.
This does not mean that things cannot be improved. First it should be possible
to apply a charge loss to the energy deposits predicted by the Monte-Carlo
simulation and then correct them with the OSA LUT2. If done accurately, with the
proper charge loss simulation, this should get rid of the "snakes" in the
residuals. We are facing difficulties in actually doing it but the principle is
absolutely clear. Second it should be possible to minimize the wiggles in the
ISGRI raw spectrum if instead of assigning a single energy to a given pulse, one
actually takes into account the spectrum of events that can produce this pulse.
This means a 3D LUT2 and we are working on it.
| Science with PICsIT: a New Hope | ||
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P. Lubinski (CAMK, Warsaw & ISDC) |
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PICsIT data analysis is currently possible only for a few bright sources and stronger GRBs [1]. This limitation is the result of a very small signal-to-noise ratio characterizing PICsIT data. For example, in the 252-336 keV band there are on average about 1000 photons from Crab after 2 ks exposure, whereas the total background is about 1.2 millions, giving SNR = ~0.001. Because PICsIT is in fact an array of 4096 detectors, a single pixel collects usually less than 1 count per Science Window. Therefore, a too simple method applied during deconvolution of the image may appear to be not sufficient to give a good measure of the source count rate and its uncertainty. A Bayesian inference framework gives a good solution to this type of problems, with the Poisson probability density function (PDF) used to model the data with a low number of counts [2]. The efficiency of such an approach was already proved in case of the average AGN spectra from ASCA satellite [3]: the PDF method was the only one reproducing an iron line shape assumed in simulations.
Recently a modified version of the PDF method have been applied to PICsIT data,
to test if it is possible to obtain results better than those extracted with the
standard OSA 5.1 software. This alternative procedure is used for spectral
extraction based on an energy-dependent model of the Pixel Illumination Fraction
(PIF). The background was also modeled in a different way than implemented in
OSA, because very long exposure standard background maps were replaced by summed
shadowgrams from a given observation. This allows to take into account the
variability of the background. New approach was tested first with the
shadowgrams simulated for 1, 0.2 and 0.05 Crab strength source of the same
spectral shape (power-law with the slope 2.15). Tests show that the 200 mCrab
source can be detected up to 1 MeV after 270 ks exposure and up to about 2 MeV
after 1350 ks exposure. In case of the 50 mCrab source and 270 ks exposure, the
detection is feasible up to about 500 keV. Nevertheless, even at higher
energies the PDF method gives upper limits consistent with the assumed model.
The standard imaging software from OSA is not able to give so tight limits.
Figure: Data-to-model ratios obtained for IBIS and SPI high-energy spectra of Crab, Cyg X-1 and NGC 4151. Model (power-law for Crab, cut-off power-law for others) was fitted to ISGRI data. SPI spectra are renormalized, PICsIT spectra are shown without any renormalization. For only comparison's sake, PICsIT PDF method results are plotted always as a mean and symmetric 1 SD errors. Otherwise, both the highest energy points for Crab and Cyg X-1, and all points for NGC 4151 should be presented as upper limits. (Error bars in case of STD method applied to NGC 4151 seem to be too small, they were determined from the mosaic variance maps done with the varmosaic tool.)
The software for the alternative PICsIT data analysis is still in rather early stage of development, being not automatized enough to allow fast extraction of spectra. Up to now, it was used only for Crab, Cyg X-1 and NGC 4151. The results are quite promising, as it is shown in the Figure. For Crab the new method gives spectra more consistent with the model fitted to ISGRI spectra than the spectra extracted from the mosaic image made with OSA 5.1. The accuracy of the count rates determined with the PDF method is also better than for the standard software, due to the correct modeling of Poisson type data. Above ~300 keV PICsIT becomes more accurate than ISGRI, and above ~500 keV more accurate than SPI (please note that the absolute normalization of PICsIT response in still uncertain, varying usually between 0.8-0.9 when compared to ISGRI). Crab spectra from different observations, extracted with the new method are in very good agreement in entire PICsIT energy range, whereas those from the standard mosaics are much more scattered. In case of Cyg X-1 also a much better agreement between ISGRI and PICsIT spectra is observed for the PDF method. Extension of Cyg X-1 spectrum above 1 MeV seems now possible after merging more than two-revolutions data used in current studies. At last, in case of very weak object, NGC 4151, (10 mCrab at ~300 keV), the PDF method demonstrated its power, giving very tight upper limits fully consistent with the extrapolation of ISGRI spectrum. In this case signal-to -noise ratio is only 10-5 in the 252-336 keV band and the object was observed only once, with ~300 ks exposure.
In summary, the method based on Poisson PDFs produces much better PICsIT spectra, precise enough to allow deeper studies of high-energy spectra of even relatively weak objects. The elements of this new approach are planned to be implemented gradually in future OSA releases, presumably starting with a new tool for making the background maps. Taking into account that there are still other possibilities to improve the model of the detector, the uniqueness of PICsIT as the only instrument (with some credit to SPI) operating currently in 0.17 - 10 MeV range should firm up the position of INTEGRAL among similar satellites on orbit.
References
[1] F. Schiavone, PICsIT sources web page
[2] T.J. Loredo, The Promise of Bayesian Inference for Astrophysics,
Statistical Challenges in Modern Astronomy, ed. E.D. Feigelson and G.J. Babu
(New York: Springer-Verlag) pp. 275-297 (1992).
[3] P. Lubinski, Averaging Spectral Shapes, MNRAS 350, 596L (2004).
| Announcement of the 3rd INTEGRAL Data Analysis Workshop | ||
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A. Neronov (ISDC) |
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The third INTEGRAL Data Analysis Workshop will take place at the ISDC on October 18-20, 2006. The main goals of the workshop will be to introduce basic data analysis techniques and new developments in the 6th version of Offline Science Analysis (OSA) software package. A special attention will be given to the improved interface of the INTEGRAL data archive, which in its new form will contain a large amount of "ready-to-use" data (images, spectra, lightcurves) on most of the galactic and extragalactic hard X-ray sources detected by INTEGRAL over the 4-year operation time.
The workshop will be organized as a series of presentations on
each of the INTEGRAL instruments (ISGRI, SPI, JEM-X and OMC) followed by the
hands-on practical sessions. Participants will be able to use the computer
facilities at ISDC and/or to get support for OSA software installation and
set-up. For more details visit the web-page
of the Workshop.
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| INTEGRAL Interactions with Other Observatories | ||
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K. Hurley (Space Science Laboratory, Berkeley) |
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This image summaries the interactions between INTEGRAL and other space missions
and ground based observatories. For each link, the number of interactions is
shown on the figure.
The interactions I considered with the corresponding sources of information are:
| X-Gamma Ray Imaging of HMXRB with INTEGRAL | |
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Silvia Martínez Núñez GACE/ICMUV Valencia University P.O. Box 22085 E-46071 Valencia, Spain | |
| Ph.D. thesis directed by Víctor Reglero, Peter Kretschmar and Pablo Reig at the Valencia University | |
| Ph.D. degree awarded on March 12, 2005 | |
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Summary.
This thesis is the result of my involvement on the development of scientific
analysis software for the X-ray monitor (JEM-X) on-board the INTErnational
Gamma-Ray Astrophysics Laboratory (INTEGRAL) mission and the reduction and
analysis of data provided by the high-energy instruments of INTEGRAL.
INTEGRAL is a gamma-ray telescope (15 keV - 10 MeV) including simultaneous monitoring in the X-ray band (4 - 35 keV) and in the optical band (500 - 600 nm). The three high-energy instruments are coded mask telescopes, thus the reduction of INTEGRAL data is complex, requiring a deep knowledge of the instruments and the tools to analyse the data. This thesis has been divided in two main parts. In the first part I describe the JEM-X scientific analysis software. An important work in this part has been the study of the JEM-X software, the scientific validation of the software during the early phases of the INTEGRAL mission and the development and maintenance of the scientific analysis scripts of the X-ray monitor. In the second part, I present the results of a detailed study of the enigmatic X-ray binary system Cygnus X-3. This system has been observed since the early times of the X-ray astronomy, but its nature is still unknown. This work gives new clues to solve the mysterious nature of the system. The outline of this thesis is as follows: the first part starts with an overview of the INTEGRAL mission, its instruments and the technique of coded mask imaging, the observing programme and the ground segment. In chapter 2 the main concepts to reduce INTEGRAL data are given, followed by a detailed scientific description of each of the defined analysis level of JEM-X software. The JEM-X software has evolved since launch to handle changes in the instrument configuration in space. The main changes and how they were implemented are described in chapter 3. The second part of this thesis starts with an introduction to X-ray binary systems (chapter 4), where I describe the main accretion mechanisms and main radiation processes that take place in these systems. Finally, in chapter 5 I present the results of a detailed imaging, timing and spectral analysis from the soft to the hard X-rays of Cygnus X-3, using the three high-energy instruments on-board INTEGRAL. Orbital phase variability is clearly detected from 5 to 40 keV. The source becomes harder when the luminosity decreases. The spectral analysis reveals that the source was mainly in the high/soft state, except during a couple of days. During the high state, orbital phase variability is apparent. | |
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E-mail contact | Thesis access |
| Individual studies of newly (re-)discovered Galactic Sources: a study with INTEGRAL and XMM-Newton | |
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Juan A. Zurita Heras INTEGRAL Science Data Centre, ch. d' Ecogia 16, CH-1290 Versoix, Switzerland | |
| Ph.D. thesis directed by Thierry J.-L. Courvoisier at the Geneva University | |
| Ph.D. degree awarded on February 23, 2006 | |
Summary. The IGR sources are bright hard X-rays sources that were unknown or poorly studied with previous high energy missions. The combination of XMM and INTEGRAL analysis were useful to understand the nature of the detected objects. The following results were found during our studies:
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E-mail contact | |
| Swift, INTEGRAL, RXTE, and Spitzer reveal IGR J16283-4838 | |
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V. Beckmann1, J. A. Kennea2, C. Markwardt1, A. Paizis3, S. Soldi3, et al. 1. NASA Goddard Space Flight Center, Exploration of the Universe Division, Greenbelt, MD 20771, USA 2. Department of Astronomy and Astrophysics, Pennsylvania State University, 525 Davey Laboratory, University Park, PA 16802, USA 3. INTEGRAL Science Data Centre, ch. d' Ecogia 16, CH-1290 Versoix, Switzerland | |
| Accepted for publication in ApJ on June 8, 2005 | |
| Abstract. We present the first combined study of the recently discovered source IGR J16283-4838 with Swift, INTEGRAL, and RXTE. The source, discovered by INTEGRAL on April 7, 2005, shows a highly absorbed (variable NH = 0.4 - 1.7 x 1023 cm-2) and flat (Γ = 1) spectrum in the Swift/XRT and RXTE/PCA data. No optical counterpart is detectable (V > 20 mag), but a possible infrared counterpart within the Swift/XRT error radius is detected in the 2MASS and Spitzer/GLIMPSE survey. The observations suggest that IGR J16283-4838 is a high mass X-ray binary containing a neutron star embedded in Compton thick material. This makes IGR J16283-4838 a member of the class of highly absorbed HMXBs, discovered by INTEGRAL. | |
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E-mail contact | Preprint access |
| A large spin-up rate measured with INTEGRAL in the High Mass X-ray Binary Pulsar SAXJ2103.5+4545 | |
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L. Sidoli1, S. Mereghetti1, S. Larsson2, M. Chernyakova3, I. Kreykenbohm3,4 et al. 1. IASF/INAF, sez.Milano, I-20133 Milano, Italy 2. Department of Astronomy, Stockholm University, Sweden 3. INTEGRAL Science Data Center, Versoix, Switzerland | |
| Accepted for publication in A&A on May, 2005 | |
| Abstract. The High Mass X-ray Binary Pulsar SAXJ2103.5+4545 has been observed with INTEGRAL several times during the last outburst in 2002-2004. We report a comprehensive study of all INTEGRAL observations, allowing a study of the pulse period evolution during the recent outburst. We measured a very rapid spin-up episode, lasting 130days, which decreased the pulse period by 1.8s. The spin-up rate, dP/dt = -1.5 x 10-7 s/s, is the largest ever measured for SAXJ2103.5+4545, and it is among the fastest for an accreting pulsar. The pulse profile shows evidence for temporal variability, apparently not related to the source flux or to the orbital phase. The X-ray spectrum is hard and there is significant emission up to 150keV. A new derivation of the orbital period, based on RXTE data, is also reported. | |
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E-mail contact | Preprint access |
| The High Energy Spectrum of NGC 4151 | |
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V. Beckmann1,2, C. R. Shrader1, N. Gehrels1, S. Soldi3, et al. 1. NASA Goddard Space Flight Center, Exploration of the Universe Division, Greenbelt, MD 20771, USA 2. Joint Center for Astrophysics, Department of Physics, University of Maryland, Baltimore County, MD 21250, USA 3. INTEGRAL Science Data Centre, ch. d' Ecogia 16, CH-1290 Versoix, Switzerland | |
| Accepted for publication in ApJ on August 15, 2005 | |
| Abstract. We present the first INTEGRAL observations of the type 1.5 Seyfert galaxy NGC 4151. Combining several INTEGRAL observations performed during 2003, totaling about 400 ks of exposure time, allows us to study the spectrum in the 2 - 300 keV range. The measurements presented here reveal an overall spectrum from X-rays up to soft gamma-rays that can be described by an absorbed (NH = 6.9 x 1022 cm-2) model based on a Compton continuum from a hot electron population (kTe = 94 keV) from an optically thick (τ = 1.3) corona, reflected on cold material (R=0.7), consistent with earlier claims. The time resolved analysis shows little variation of the spectral parameters over the duration of the INTEGRAL observations. The comparison with CGRO/OSSE data shows that the same spectral model can be applied over a time span of 15 years, with flux variations of the order of a factor of 2 and changes in the underlying continuum reflected by the temperature of the electron population (kTe = 50 - 100 keV). When modeled with an exponentially cut-off power law plus Compton reflection this results in photon indices ranging from Γ = 1.5 to Γ = 1.9 and a cut-off energy in the range 100 - 500 keV. | |
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E-mail contact | Preprint access |
| INTEGRAL observations of AGN in the Galactic Plane | |
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S. Soldi1, V. Beckmann2, L. Bassani3, T. J.-L. Courvoisier1, R. Landi3, et al. 1. INTEGRAL Science Data Centre, ch. d'Ecogia 16, 1290 Versoix, Switzerland 2. NASA Goddard Space Flight Center, Exploration of the Universe Division, Greenbelt, MD 20771, USA 3. IASF, CNR/INAF, via Gobetti 101, 40129 Bologna, Italy | |
| Accepted for publication in A&A on August 22, 2005 | |
| Abstract. We present results on approximately one year of INTEGRAL observations of six AGN detected during the regular scans of the Galactic Plane. The sample is composed by five Seyfert 2 objects (MCG -05-23-16, NGC 4945, the Circinus galaxy, NGC 6300, ESO 103-G35) and the radio galaxy Centaurus A. The continuum emission of each of these sources is well represented by a highly absorbed (NH > 1022 cm-2) power law, with average spectral index Γ = 1.9 ± 0.3. A high energy exponential cut-off at Ec ~ 50 keV is required to fit the spectrum of the Circinus galaxy, whereas a lower limit of 130 keV has been found for NGC 4945 and no cut-off has been detected for NGC 6300 in the energy range covered by these INTEGRAL data. The flux of Centaurus A was found to vary by a factor of ~ 2 in 10 months, showing a spectral change between the high and low state, which can be modelled equally well by a change in the absorption (NH from 17 to 33 x 1022 cm-2) or by the presence of a cut-off at ≥ 120 keV in the low state spectrum. A comparison with recently reprocessed BeppoSAX/PDS data shows a general agreement with INTEGRAL results. The high energy cut-off in the hard X-ray spectra appears to be a common but not universal characteristic of Seyfert 2 and to span a wide range of energies. | |
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E-mail contact | Preprint access |
| The First INTEGRAL AGN Catalog | |
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V. Beckmann1,2, N. Gehrels1, C. R. Shrader1 & S. Soldi3 1. NASA Goddard Space Flight Center, Exploration of the Universe Division, Code 661, Greenbelt, MD 20771, USA 2. Joint Center for Astrophysics, Department of Physics, University of Maryland, Baltimore County, MD 21250, USA 3. INTEGRAL Science Data Centre, ch. d' Ecogia 16, CH-1290 Versoix, Switzerland | |
| Accepted for publication in ApJ on October 18, 2005 | |
| Abstract. We present the first INTEGRAL AGN catalog, based on observations performed from launch of the mission in October 2002 until January 2004. The catalog includes 42 AGN, of which 10 are Seyfert 1, 17 are Seyfert 2, and 9 are intermediate Seyfert 1.5. The fraction of blazars is rather small with 5 detected objects, and only one galaxy cluster and no star-burst galaxies have been detected so far. A complete subset consists of 32 AGN with a significance limit of 7σ in the INTEGRAL/ISGRI 20-40 keV data. Although the sample is not flux limited, the distribution of sources shows a ratio of obscured to unobscured AGN of 1.5 - 2.0, consistent with luminosity dependent unified models for AGN. Only four Compton-thick AGN are found in the sample. Based on the INTEGRAL data presented here, the Seyfert 2 spectra are slightly harder (Γ = 1.95 ± 0.01) than Seyfert 1.5 (Γ = 2.10 ± 0.02) and Seyfert 1 (Γ = 2.11 ± 0.05). | |
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E-mail contact | Preprint access |
| Properties of the energetic particle distributions during the October 28, 2003 solar flare from INTEGRAL/SPI observations | |
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J. Kiener1, M. Gros2, V. Tatischeff1, G. Weidenspointner3 1. CSNSM Orsay, IN2P3-CNRS et Université Paris-Sud, 91405 Campus Orsay, France 2. DSM/DAPNIA/Service d'Astrophysique, CEA Saclay, 91191 Gif-sur-Yvette, France 3. Centre d'Etude Spatiale des Rayonnements, 9, avenue du Colonel Roche, 31028 Toulouse, France | |
| Accepted for publication in A&A on September 6, 2005 | |
| Abstract. Analysis of spectra obtained with the gamma-ray spectrometer SPI onboard INTEGRAL of the GOES X17-class flare on October 28, 2003 is presented. In the energy range 600 keV - 8 MeV three prominent narrow lines at 2.223, 4.4 and 6.1 MeV, resulting from nuclear interactions of accelerated ions within the solar atmosphere could be observed. Time profiles of the three lines and the underlying continuum indicate distinct phases with several emission peaks and varying continuum-to-line ratio for several minutes before a smoother decay phase sets in. Due to the high-resolution Ge detectors of SPI and the exceptional intensity of the flare, detailed studies of the 4.4 and 6.1 MeV line shapes was possible for the first time. Comparison with calculated line shapes using a thick target interaction model and several energetic particle angular distributions indicates that the nuclear interactions were induced by downward-directed particle beams with alpha-to-proton ra! tios of the order of 0.1. There are also indications that the 4.4 MeV to 6.1 MeV line fluence ratio changed between the beginning and the decay phase of the flare, possibly due to a temporal evolution of the energetic particle alpha-to-proton ratio. | |
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E-mail contact | |
| INTEGRAL and XMM-Newton observations of the X-ray pulsar IGR J16320-4751/AX J1631.9-4752 | |
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J. Rodriguez1, A. Bodaghee2, P. Kaaret3 et al. 1. CEA Saclay, DSM/DAPNIA/Sap (CNRS UMR AIM), F-91191 Gif Sur Yvette, FRANCE 2. ISDC, ch. d' Ecogia 16, CH-1290 Versoix, Switzerland 3. Dept for Physics and Astronomy, University of Iowa, Iowa City, USA | |
| Accepted for publication in MNRAS on November, 10 2005 | |
| Abstract. We report on observations of the X-ray pulsar IGR J16320-4751 (a.k.a. AX J1631.9-4752) performed simultaneously with INTEGRAL and XMM-Newton. We refine the source position and identify the most likely infrared counterpart. Our simultaneous coverage allows us to confirm the presence of X-ray pulsations at ~1300 s, that we detect above 20 keV with INTEGRAL for the first time. The pulse fraction is consistent with being constant with energy, which is compatible with a model of polar accretion by a pulsar. We study the spectral properties of IGR J16320-4751 during two major periods occurring during the simultaneous coverage with both satellites, namely a flare and a non-flare period. We detect the presence of a narrow 6.4 keV iron line in both periods. The presence of such a feature is typical of supergiant wind accretors such as Vela X-1 or GX 301-2. We inspect the spectral variations with respect to the pulse phase during the non-flare period, and show that the pulse is solely due to variations of the X-ray flux emitted by the source and not to variations of the spectral parameters. Our results are therefore compatible with the source being a pulsar in a High Mass X-ray Binary. We detect a soft excess appearing in the spectra as a blackbody with a temperature of ~0.07 keV. We discuss the origin of the X-ray emission in IGR J16320-4751: while the hard X-rays are likely the result of Compton emission produced in the close vicinity of the pulsar, based on energy argument we suggest that the soft excess is likely the emission by a collisionally energised cloud in which the compact object is embedded. | |
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E-mail contact | Preprint access |
| Testing the inverse-Compton catastrophe scenario in the intra-day variable blazar S5 0716+71. I. Simultaneous broadband observations during November 2003 | |
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L. Ostorero1,2, S. J. Wagner1, J. Gracia3, E. Ferrero1, T. P. Krichbaum, et al. 1. Landessternwarte Heidelberg-Königstuhl, Königstuhl, 69117 Heidelberg, Germany 2. Tuorla Observatory, University of Turku, Väisäläntie 20, 21500 Piikkiö, Finland 3. Section of astrophysics, Astronomy & Mechanics, Department of Physics, University of Athens, Panepistimiopolis, 157 84 Zografos, Athens, Greece | |
| Accepted for publication in A&A on January 16, 2006 | |
| Abstract. Some intra-day variable, compact extra-galactic radio sources show brightness temperatures severely exceeding 1012 K, the limit set by catastrophic inverse-Compton (IC) cooling in sources of incoherent synchrotron radiation. The violation of the IC limit, actually possible under non-stationary conditions, would lead to IC avalanches in the soft-γ-ray energy band during transient periods. For the first time, broadband signatures of possible IC catastrophes were searched for in a prototypical source, S5 0716+71. A multifrequency observing campaign targetting S5 0716+71 was carried out during November 06-20, 2003. The observations, organized under the framework of the European Network for the Investigation of Galactic nuclei through Multifrequency Analysis (ENIGMA) together with a campaign by the Whole Earth Blazar Telescope (WEBT), involved a pointing by the soft-γ-ray satellite INTEGRAL, optical, near-infrared, sub-millimeter, millimeter, radio, as well as Very Long Baseline Array (VLBA) monitoring. S5 0716+71 was very bright at radio frequencies and in a rather faint optical state (R=14.17-13.64) during the INTEGRAL pointing; significant inter-day and low intra-day variability was recorded in the radio regime, while typical fast variability features were observed in the optical band. No obvious correlation was found between the radio and optical emission. The source was not detected by INTEGRAL, neither by the X-ray monitor JEM-X nor by the γ-ray imager ISGRI, but upper limits to the source emission in the 3-200 keV energy band were estimated. A brightness temperature Tb>2.1·1014 K (violating the IC limit) was inferred from the variability observed in the radio regime, but no corresponding signatures of IC avalanches were recorded at higher energies. In the most plausible scenario of negligible contribution of the interstellar scintillation to the observed radio variability, the absence of the signatures of IC catastrophes provides either a lower limit δ≥8 to the Doppler factor affecting the radio emission or strong constraints for modelling of the Compton-catastrophe scenario in S5 0716+71. | |
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| The faint 2005 hard state outburst of Aquila X-1 seen by INTEGRAL and RXTE | |
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J. Rodriguez1, S. E. Shaw2,3, S. Corbel1 1. AIM - Unite Mixte de Recherche CEA - CNRS - Universite Paris VII - UMR 7158, CEA Saclay, Service d'Astrophysique, F-91191 Gif sur Yvette, France 2. School of Physics and Astronomy, University of Southampton, SO 17 1BJ, UK 3. INTEGRAL Science Data Centre, ch. d' Ecogia 16, CH-1290 Versoix, Switzerland | |
| Accepted for publication in A&A on February 07, 2006 | |
| Abstract. We report on the spectral analysis of RXTE and INTEGRAL data of the 2005 April outburst of the transient Atoll source Aql X-1. Although this outburst is one of the faintest ever detected for this source in the soft X-rays (RXTE/ASM), one of our INTEGRAL observations, taken close to the soft X-ray peak, shows that the source flux was quite high, with a 20-200 keV flux of 2.05 x 10-9 erg cm-2 s-1. On this occasion we detect the source up to 150 keV for the first time. We compare and discuss the similarity of the source behavior with that of black hole transients especially XTE J1550-564. | |
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| A Short Hard X-ray Flare from the Blazar NRAO 530 Observed by INTEGRAL | |
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L. Foschini1, E. Pian2, L. Maraschi3, et al. 1. INAF/IASF-Bologna, Via Gobetti 101, 40129 Bologna (Italy) 2. INAF, Osservatorio Astronomico di Trieste, Via G.B. Tiepolo 11, 34131, Trieste (Italy) 3. INAF, Osservatorio Astronomico di Brera, Via Bianchi 46, 23807, Merate (Italy) | |
| Accepted for publication in A&A on Jan 5, 2006 | |
| Abstract. We report about a short flare from the blazar NRAO 530 occurred on 17 February 2004 and detected serendipitously by the IBIS/ISGRI detector on board INTEGRAL. In the 20-40 keV energy range, the source, that is otherwise below the detection limit, is detected at a level of ~2x10-10 erg cm-2 s-1 during a time interval of less than 2000 s, which is about a factor 2 above the detection threshold. At other wavelengths, only nearly-simultaneous radio data are available (1 observation at 2 cm on 11 February 2004), indicating a moderate increase of the polarization. This appears to be the shortest time variability episode ever detected in a high luminosity blazar at hard X-rays, unless the blazar is contaminated by the presence of an unknown unresolved rapidly varying source. | |
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| INTEGRAL observations of the blazar 3C454.3 in outburst | |
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E. Pian1, L. Foschini2, V. Beckmann3, et al. 1. INAF, Osservatorio Astronomico di Trieste, Via G.B. Tiepolo 11, I-34131 Trieste, Italy 2. INAF, IASF-Bologna, Via Gobetti 101, I-40129 Bologna, Italy 3. NASA Goddard Space Flight Center, Code 661, Greenbelt, MD 20771, USA | |
| Accepted for publication in A&A on February 13, 2006 | |
| Abstract. In Spring 2005, the blazar 3C 454.3 underwent a dramatic outburst at all wavelengths from mm to X-rays. This prompted INTEGRAL observations, accomplished in 15-18 May 2005. The source was detected by the INTEGRAL instruments from 3 to 200 keV in a bright state (∼ 5 x 10−10 erg s−1 cm−2), at least a factor of 2-3 higher than previously observed. This is one of the brightest blazar detections achieved by INTEGRAL. During the 2.5 days of INTEGRAL monitoring, we detected a ∼20% decrease in the hard X-rays (20-40 keV), indicating that we have sampled the decaying part of the flare. The decrease is less apparent in the soft X-rays (5-15 keV). The simultaneous optical variations are weakly correlated with those at soft X-rays, and not clearly correlated with those at hard X-rays. The spectral energy distribution exhibits two components, as typically seen in blazars, which can be modeled with synchrotron radiation and inverse Compton scattering occurring in a region external to the broad line region. | |
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| IGR J17252-3616: an accreting pulsar observed by INTEGRAL and XMM-Newton | |
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J. A. Zurita Heras1,2, G. De Cesare3, R. Walter1,2, A. Bodaghee1,2, et al. 1. INTEGRAL Science Data Centre, Ch. d'Écogia 16, 1290 Versoix, Switzerland 2. Observatoire de Genève, Ch. des Maillettes 51, 1290 Sauverny, Switzerland 3. IASF-INAF, via Fosso del Cavaliere 100, 00133 Roma, Italy | |
| Accepted for publication in A&A on September 25, 2005 | |
| Abstract. The discovery of the X-ray source IGR J17252-3616 by INTEGRAL was reported on 9 February 2004. Regular monitoring by INTEGRAL shows that IGR J17252-3616 is a persistent hard X-ray source with an average count rate of 0.96 counts s-1 (~6.4 mCrab) in the 20-60 keV energy band. A follow-up observation with XMM-Newton, which was performed on March 21, 2004, showed that the source is located at R.A.(2000.0)=17h25m11s.4 and Dec.=-36o 16' 58''.6 with an uncertainty of 4''. The only infra-red counterpart to be found within the XMM-Newton error circle was 2MASS J17251139-3616575, which has a Ks-band magnitude of 10.7 and is located 1'' away from the XMM position. The analysis of the combined INTEGRAL and XMM-Newton observations shows that the source is a binary X-ray pulsar with a spin period of 413.7 s and an orbital period of 9.72 days. The spectrum can be fitted with a flat power law plus an energy cut off (Γ ~ 0.02, Ec ~ 8.2 keV) or a Comptonized model (kTe ~ 5.5 keV, τ ~ 7.8). The spectrum also indicates a large hydrogen column density of NH ~ 15x1022 atoms cm-2 suggesting an intrinsic absorption. The Fe Kα line at 6.4 keV is clearly detected. Phase-resolved spectroscopy does not show any variation in the continuum except the total emitted flux. The absorption is constant along the pulse phase. This source can be associated with EXO 1722-363 as both systems show common timing and spectral features. The observations suggest that the source is a wind-fed accreting pulsar accompanied by a supergiant star. | |
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| A historic jet-emission minimum reveals hidden spectral features in 3C 273 | |
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M. Türler1,2, M. Chernyakova1,2, T. J.-L. Courvoisier1,2, et al. 1. INTEGRAL Science Data Centre, ch. d' Ecogia 16, CH-1290 Versoix, Switzerland 2. Geneva Observatory, ch. des Maillettes 51, CH-1290 Versoix, Switzerland | |
| Accepted for publication in A&A Letters on March 20, 2006 | |
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Abstract.
Aims. The aim of this work is to identify and study spectral features in
the quasar 3C 273 usually blended by its strong jet emission. Method. A historic minimum in the sub-millimetre emission of 3C 273 triggered coordinated multi-wavelength observations in June 2004. X-ray observations from the INTEGRAL, XMM-Newton and RXTE satellites are complemented by ground-based optical, infrared, millimetre and radio observations. The overall spectrum is used to model the infrared and X-ray spectral components. Results. Three thermal dust emission components are identified in the infrared. The dust emission on scales from 1 pc to several kpc is comparable to that of other quasars, as expected by AGN unification schemes. The observed weakness of the X-ray emission supports the hypothesis of a synchrotron self-Compton origin for the jet component. There is a clear soft-excess and we find evidence for a very broad iron line which could be emitted in a disk around a Kerr black hole. Other signatures of a Seyfert-like X-ray component are not detected. | |
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| IGR J16393-4643: A New Heavily-Obscured X-Ray Pulsar | |
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A. Bodaghee1,2, R. Walter1,2, J.A. Zurita Heras1,2, A.J. Bird3, T.J.-L. Courvoisier1,2, et al. 1. INTEGRAL Science Data Centre, ch. d' Ecogia 16, CH-1290 Versoix, Switzerland 2. Geneva Observatory, ch. des Maillettes 51, CH-1290 Sauverny, Switzerland 3. School of Physics and Astronomy, University of Southampton, Highfield, Southampton, SO17 1BJ, UK | |
| Accepted for publication in A&A on September 27, 2005 | |
| Abstract. An analysis of the high-energy emission from IGR J16393-4643 (=AX J1639.0-4642) is presented using data from INTEGRAL and XMM-Newton. The source is persistent in the 20-40 keV band at an average flux of 5.1x10-11 ergs/cm2/s, with variations in intensity by at least an order of magnitude. A pulse period of 912.0±0.1 s was discovered in the ISGRI and EPIC light curves. The source spectrum is a strongly-absorbed (NH=(2.5±0.2)x1023 atoms/cm2) power law that features a high-energy cutoff above 10 keV. Two iron emission lines at 6.4 and 7.1 keV, an iron absorption edge ≥7.1 keV, and a soft excess emission of 7x10-15 ergs/cm2/s between 0.5-2 keV, are detected in the EPIC spectrum. The shape of the spectrum does not change with the pulse. Its persistence, pulsation, and spectrum place IGR J16393-4643 among the class of heavily-absorbed HMXBs. The improved position fro! m EPIC is R.A. (J2000)=16:39:05.4 and Dec.=-46:42:12 (4" uncertainty) which is compatible with that of 2MASS J16390535-4642137. | |
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