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Kinematics of massive star ejecta in the Milky Way as traced by Al
Context. Massive stars form in groups and their winds and supernova explosions create superbubbles up to kpc in size. The fate of their ejecta is of vital importance for the dynamics of the interstellar medium, for chemical evolution models, and the chemical enrichment of galactic halos and the intergalactic medium. However, ejecta kinematics and the characteristic scales in space and time have not been explored in great detail beyond ~10 Ka. Aims. Through measurement of radioactive 26Al with its decay time constant at ~106 years, we aim to trace the kinematics of cumulative massive-star and supernova ejecta independent of the uncertain gas parameters over million-year time scales. Our goal is to identify the mixing time scale and the spatio-kinematics of such ejecta from the pc to kpc scale in our Milky Way. Methods. We use the SPI spectrometer on the INTEGRAL observatory and its observations along the Galactic ridge to trace the detailed line shape systematics of the 1808.63 keV gamma-ray line from 26Al decay. We determine line centroids and compare these to Doppler shift expectations from large-scale systematic rotation around the Galaxy centre, as observed in other Galactic objects. Results. We measure the radial velocities of gas traced by 26Al, averaged over the line of sight, as a function of Galactic longitude. We find substantially higher velocities than expected from Galactic rotation, the average bulk velocity being ~200 km/s larger than predicted from Galactic rotation. The observed radial velocity spread implies a Doppler broadening of the gamma-ray line that is consistent with our measurements of the overall line width.
[Remainder of abstract truncated due to character limitations]
Publication date: 19 Nov 2013
Tidal disruption of a super-Jupiter by a massive black hole

Aims. A strong, hard X-ray flare was discovered (IGR J12580+0134) by INTEGRAL in 2011, and is associated to NGC 4845, a Seyfert 2 galaxy never detected at high-energy previously. To understand what happened we observed this event in the X-ray band on several occasions.

Methods.

Follow-up observations with XMM-Newton, Swift, and MAXI are presented together with the INTEGRAL data. Long and short term variability are analysed and the event wide band spectral shape modelled.

Results.

The spectrum of the source can be described with an absorbed (NH ~ 7 × 1022 cm-2) power law (Gamma = 2.2), characteristic of an accreting source, plus a soft X-ray excess, likely to be of diffuse nature. The hard X-ray flux increased to maximum in a few weeks and decreased over a year, with the evolution expected for a tidal disruption event. The fast variations observed near the flare maximum allowed us to estimate the mass of the central black hole in NGC 4845 as ~3 × 105 solar masses. The observed flare corresponds to the disruption of about 10% of an object with a mass of 14-30 Jupiter. The hard X-ray emission should come from a corona forming around the accretion flow close to the black hole. This is the first tidal event where such a corona has been observed.

Publication date: 02 Apr 2013
Distribution of High-mass X-Ray Binaries in the Milky Way
Observations of the high-energy sky, particularly with the INTEGRAL satellite, have quadrupled the number of supergiant X-ray binaries observed in the Galaxy and revealed new populations of previously hidden high-mass X-ray binaries (HMXBs), raising new questions about their formation and evolution. The number of detected HMXBs of different types is now high enough to allow us to carry out a statistical analysis of their distribution in the Milky Way. For the first time, we derive the distance and absorption of a sample of HMXBs using a spectral energy distribution fitting procedure, and we examine the correlation with the distribution of star-forming complexes (SFCs) in the Galaxy. We show that HMXBs are clustered with SFCs with a typical cluster size of 0.3 ± 0.05 kpc and a characteristic distance between clusters of 1.7 ± 0.3 kpc. Furthermore, we present an investigation of the expected offset between the position of spiral arms and HMXBs, allowing us to constrain age and migration distance due to supernova kick for 13 sources. These new methods will allow us to assess the influence of the environment on these high-energy objects with unprecedented reliability.
Publication date: 06 Feb 2013
Neutron star masses from hydrodynamical effects in obscured sgHMXBs
Context. A population of obscured supergiant high mass X-ray binaries has been discovered by INTEGRAL. X-ray wind tomography of IGR J17252-3616 inferred a slow wind velocity to account for the enhanced obscuration.
Aims. The main goal of this study is to understand under which conditions high obscuration could occur.
Methods. We have used an hydrodynamical code to simulate the flow of the stellar wind around the neutron star. A grid of simulations was used to study the dependency of the absorbing column density and of the X-ray light-curves on the model parameters. A comparison between the simulation results and the observations of IGR J17252-3616 provides an estimate on these parameters.
Results. We have constrained the wind terminal velocity to 500-600 km/s and the neutron star mass to 1.75-2.15 MSun.
Conclusions. We have confirmed that the initial hypothesis of a slow wind velocity with a moderate mass loss rate is valid. The mass of the neutron star can be constrained by studying its impact on the accretion flow.
Publication date: 01 Nov 2012
Hard X-ray emission lines from the decay of 44_Ti in the remnant of Supernova 1987A
It is assumed that the radioactive decay of 44Ti powers the infrared, optical and UV emission of a supernova remnant since the complete decay of 56Co and 57Co (3-4 years after the explosion) until the beginning of active interaction of the ejecta with the surrounding matter. Simulations show that 44Ti is synthesized in an amount of M44 ~ (0.02-2.5)×10-4 MSun in core-collapse supernovae. Hard X/gamma-rays from this decay have been unambiguously observed from Cassiopeia A only, leading to the suggestion that the high values of M44 occur in exceptional cases. For the Supernova 1987A remnant, an upper limit M44 <= 10-3 MSun was obtained from direct X-ray observations12, and an estimation M44 ~ (1-2)×10-4 MSun - from infrared light-curves and UV spectra by complex model dependent computations. Here we report observations of hard X-rays from SNR 1987A in the narrow band containing two direct-escape lines of 44Ti at 67.9 and 78.4 keV. The measured line fluxes imply sufficient energy to power the remnant at late times. An initial mass of 44Ti was estimated to be (3.1 +/- 0.8)×10-4 MSun, which is near the upper bound of theoretical predictions.
Publication date: 17 Oct 2012
ESA SP-1323: ESA's Report to the 39th COSPAR Meeting

The 39th meeting of the Committee on Space Research (COSPAR) was held 14-22 July 2012 in Mysore, India.

This report to COSPAR on the scientific activities of the European Space Agency was written by members of the Directorate of Earth Observation, the Directorate of Human Spaceflight and Operations and the Directorate of Science and Robotic Exploration.

Contents:

  • Foreword by Jean-Jacques Dordain, Director General, ESA
  • Earth Observation
    1. Introduction
    2. The Living Planet Programme
    3. The Earth Explorer Missions
    4. ERS and Envisat
  • Human Spaceflight and Operations
    1. Introduction
    2. Overview: Columbus and ISS Facilities
    3. Funding Europe's ISS Research: ELIPS
    4. Research on the ISS
    5. Ongoing Research Using Other Platforms
    6. Projects under Development
  • Science and Robotic Exploration
    1. Introduction
    2. Missions in Operation
    3. Missions in the Post-Operations and Archiving Phases
    4. Projects under Development
    5. Missions under Study
Publication date: 30 Jun 2012
Temporal and spectral evolution in X- and gamma-rays of magnetar 1E 1547.0-5408 since its October 2008 outburst: the discovery of a transient hard pulsed component after its January 2009 outburst
The magnetar 1E1547.0-5408 exhibited outbursts in October 2008 and January 2009. In this paper we present in great detail the evolution of the temporal and spectral characteristics of the persistent total and pulsed emission of 1E1547.0-5408 between <1 and 300 keV starting in October 3, 2008, and ending in January 2011. We analyzed data collected with the Rossi X-ray Timing Explorer, the International Gamma-Ray Astrophysics Laboratory and the Swift satellite. We report the evolution of the pulse frequency, and the measurement at the time of the onset of the January 2009 outburst of an insignificant jump in frequency, but a major frequency derivative jump. Before this glitch, a single broad pulse is detected, mainly for energies below ~10 keV. Surprisingly, ~11 days after the glitch a new transient high-energy (up to ~150 keV) pulse appears with a Gaussian shape and width 0.23, shifted in phase by ~0.31 compared to the low-energy pulse, which smoothly fades to undetectable levels in ~350 days. We report the evolution of the pulsed-emission spectra. For energies 2.5-10 keV all pulsed spectra are very soft with photon indices between -4.6 and -3.9. For ~10-150 keV, after the glitch, we report hard non-thermal pulsed spectra, similar to what has been reported for the persistent pulsed emission of some anomalous X-ray pulsars. This pulsed hard X-ray emission reached maximal luminosity 70 ± 30 days after the glitch epoch, followed by a gradual decrease by more than a factor of 10 over ~300 days. These characteristics differ from those of the total emission. [Abstract abbreviated due to character limitations.] We discuss these findings in the framework of the magnetar model.
Publication date: 01 Apr 2012
Extended Hard X-Ray Emission from the Vela Pulsar Wind Nebula
The nebula powered by the Vela pulsar is one of the best examples of an evolved pulsar wind nebula, allowing access to the particle injection history and the interaction with the supernova ejecta. We report on the INTEGRAL discovery of extended emission above 18 keV from the Vela nebula. The northern side has no known counterparts and it appears larger and more significant than the southern one, which is in turn partially coincident with the cocoon, the soft X-ray, and TeV filament toward the center of the remnant. We also present the spectrum of the Vela nebula in the 18-400 keV energy range as measured by IBIS/ISGRI and SPI on board the INTEGRAL satellite. The apparent discrepancy between IBIS/ISGRI, SPI, and previous measurements is understood in terms of the point-spread function, supporting the hypothesis of a nebula more diffuse than previously thought. A break at ~25 keV is found in the spectrum within 6' from the pulsar after including the Suzaku XIS data. Interpreted as a cooling break, this points out that the inner nebula is composed of electrons injected in the last ~2000 years. Broadband modeling also implies a magnetic field higher than 10 mG in this region. Finally, we discuss the nature of the northern emission, which might be due to fresh particles injected after the passage of the reverse shock.
Publication date: 21 Nov 2011
Diffuse emission measurement with the spectrometer on INTEGRAL as an indirect probe of cosmic-ray electrons and positrons

Significant advances have been made in the understanding of the diffuse Galactic hard X-ray continuum emission using data from the INTEGRAL observatory. The diffuse hard power-law component seen with the SPectrometer on INTEGRAL (SPI) has been identified with inverse-Compton emission from relativistic (GeV) electrons on the cosmic microwave background and Galactic interstellar radiation field. In the present analysis, SPI data from 2003 to 2009, with a total exposure time of ~108 s, are used to derive the Galactic ridge hard X-ray spatial distribution and spectrum between 20 keV and 2.4 MeV. Both are consistent with predictions from the GALPROP code. The good agreement between measured and predicted emission from keV to GeV energies suggests that the correct production mechanisms have been identified. We discuss the potential of the SPI data to provide an indirect probe of the interstellar cosmic-ray electron distribution, in particular for energies below a few GeV.

Publication date: 01 Sep 2011
Reflection in Seyfert Galaxies and the Unified Model of AGN
We present a deep study of the average hard X-ray spectra of Seyfert galaxies. We aim to test the unified model of active galactic nuclei, and constrain differences and similarities between different classes of objects. We analyzed all public INTEGRAL IBIS/ISGRI data available on all the 165 Seyfert galaxies detected at z < 0.2. Our final sample consists of 44 Seyfert 1s, 29 Seyfert 1.5s, 78 Seyfert 2s, and 14 narrow-line Seyfert 1s. For each subsample, we stacked all the images, and derived their average hard X-ray spectra in the 17-250 keV energy range. We performed a detailed spectral analysis using both a model-independent and a model-dependent approach. All classes of Seyfert galaxies show on average the same nuclear continuum, as foreseen by the zeroth order unified model, with a cutoff energy of EC >~ 200 keV, and a photon index of Gamma~1.8. The average optical depth of the Comptonizing medium is consistent for the different classes (tau~0.8). Compton-thin Seyfert 2s show a reflection component stronger than Seyfert 1s and Seyfert 1.5s. Most of this reflection is due to mildly obscured (1023 cm-2 <= NH < 1024 cm-2) Seyfert2s, which have a significantly stronger reflection component (R = 2.2+4.5-1.1) than Seyfert 1s (R <= 0.4), Seyfert 1.5s (R <= 0.4) and lightly obscured (NH < 1023 cm-2) Seyfert 2s (R <= 0.5). This cannot be explained easily by the unified model. The absorber/reflector in mildly obscured Seyfert 2s might cover a large fraction of the X-ray source, and contain clumps of Compton-thick material. The large reflection found in the spectrum of mildly obscured Seyfert 2s reduces the amount of Compton-thick objects needed to explain the peak of the cosmic X-ray background. Our results are consistent with the fraction of Compton-thick sources being ~10 percent.
- The remainder of the abstract is truncated -
Publication date: 02 Aug 2011
Constraints on Lorentz Invariance Violation using integral/IBIS observations of GRB041219A
One of the experimental tests of Lorentz invariance violation is to measure the helicity dependence of the propagation velocity of photons originating in distant cosmological obejcts. Using a recent determination of the distance of the gamma-ray burst GRB 041219A, for which a high degree of polarization is observed in the prompt emission, we are able to improve by four orders of magnitude the existing constraint on Lorentz invariance violation, arising from the phenomenon of vacuum birefringence.
Publication date: 28 Jun 2011
Polarized Gamma-ray Emission from the Galactic Black Hole Cygnus X-1

Published online in Science Express, 24 March 2011.

Because of their inherently high flux allowing the detection of clear signals, black hole x-ray binaries are interesting candidates for polarization studies, even if no polarization signals have been observed from them before. Such measurements would provide further detailed insight into these sources' emission mechanisms. We measured the polarization of the gamma-ray emission from the black hole binary system Cygnus X-1 with the INTEGRAL/IBIS telescope. Spectral modeling of the data reveals two emission mechanisms: The 250-400 keV data are consistent with emission dominated by Compton scattering on thermal electrons and are weakly polarized. The second spectral component seen in the 400keV-2MeV band is by contrast strongly polarized, revealing that the MeV emission is probably related to the jet first detected in the radio band.

Publication date: 24 Mar 2011
X-ray wind tomography of the highly absorbed HMXB IGR J17252–3616
Context. About ten persistently highly absorbed super-giant high-mass X-ray binaries (sgHMXB) have been discovered by INTEGRAL as bright hard X-ray sources lacking bright X-ray counterparts. Besides IGR J16318-4848, which has peculiar characteristics, the other members of this family share many properties with the classical wind-fed sgHMXB systems.
Aims. Our goal is to understand the characteristics of highly absorbed sgHMXB and in particular the companion stellar wind, which is thought to be responsible for the strong absorption.
Methods. We monitored IGR J17252-3616, a highly absorbed system featuring eclipses, with XMM-Newton to study the variability of the column density and the Fe K-alpha emission line along the orbit and during the eclipses. We also compiled a 3D model of the stellar wind to reproduce the observed variability.
Results. We first derive a refined orbital solution based on INTEGRAL, RXTE, and XMM-Newton data. We find that the XMM-Newton monitoring campaign reveals significant variations in the intrinsic absorbing column density along the orbit and the Fe K-alpha line equivalent width around the eclipse. The origin of the soft X-ray absorption is associated with a dense and extended hydrodynamical tail, trailing the neutron star. This structure extends along most of the orbit, indicating that the stellar wind has been strongly disrupted.
The remainder of the abstract is truncated.
Publication date: 01 Feb 2011
Radioactive 26Al from the Scorpius-Centaurus association

Context. The Scorpius-Centaurus association is the most-nearby group of massive and young stars. As nuclear-fusion products are ejected by massive stars and supernovae into the surrounding interstellar medium, the search for characteristic g-rays from radioactivity is one way to probe the history of activity of such nearby massive stars on a My time scale through their nucleosynthesis. 26Al decays with a radioactivity lifetime t~1 My, 1809 keV g-rays from its decay can be measured with current g-ray telescopes.

Publication date: 01 Nov 2010
INTEGRAL/IBIS 7-year All-Sky Hard X-Ray Survey – Part II: Catalog of Sources
This paper is the second in a series devoted to the hard X-ray (17-60 keV) whole sky survey performed by the INTEGRAL observatory over seven years. Here we present a catalog of detected sources which includes 521 objects, 449 of which exceed a 5 sigma detection threshold on the time-averaged map of the sky, and 53 were detected in various subsamples of exposures. Among the identified sources with known and suspected nature, 262 are Galactic (101 low-mass X-ray binaries, 95 high-mass X-ray binaries, 36 cataclysmic variables, and 30 of other types) and 219 are extragalactic, including 214 active galactic nuclei (AGNs), 4 galaxy clusters, and galaxy ESO 389-G 002. The extragalactic (|b|>5 deg) and Galactic (|b|<5 deg) persistently detected source samples are of high identification completeness (respectively ~96% and ~94%) and valuable for population studies.
Publication date: 23 Jun 2010
INTEGRAL/IBIS 7-year All-Sky Hard X-Ray Survey – Part I: Image Reconstruction
This paper is the first in a series devoted to the hard X-ray whole sky survey performed by the INTEGRAL observatory over seven years. Here we present an improved method for image reconstruction with the IBIS coded mask telescope. The main improvements are related to the suppression of systematic effects which strongly limit sensitivity in the region of the Galactic Plane (GP), especially in the crowded field of the Galactic Center (GC). We extended the IBIS/ISGRI background model to take into account the Galactic Ridge X-ray Emission (GRXE). To suppress residual systematic artifacts on a reconstructed sky image we applied nonparametric sky image filtering based on wavelet decomposition. The implemented modifications of the sky reconstruction method decrease the systematic noise in the ~20 Ms deep field of GC by ~44%, and practically remove it from the high-latitude sky images. New observational data sets, along with an improved reconstruction algorithm, allow us to conduct the hard X-ray survey with the best currently available minimal sensitivity 3.7E-12 erg/s/cm2 ~0.26 mCrab in the 17-60 keV band at a 5 sigma detection level. The survey covers 90% of the sky down to the flux limit of 6.2E-11 erg/s/cm2 (~4.32 mCrab) and 10% of the sky area down to the flux limit of 8.6E-12 erg/s/cm2 (~0.60 mCrab).
Publication date: 20 May 2010
ISOC Newsletter #22
This Newsletter is based on inputs from members of ISOC, and edited by Guillaume Bélanger with the help of Suzanne Philipsen.

Contents:

  • Foreword
  • AO-7 Results
  • AO-8 Timetable
  • Science Operations
  • 7th INTEGRAL Workshop
  • Science Highlights
  • Changes at ISOC
  • Contacting ISOC

Publication date: 22 Dec 2009
Untwisting magnetospheres of neutron stars
Magnetospheres of neutron stars are anchored in the rigid crust and can be twisted by sudden crustal motions ("starquakes"). The twisted magnetosphere does not remain static and gradually untwists, dissipating magnetic energy and producing radiation. The equation describing this evolution is derived, and its solutions are presented.
Publication date: 04 Sep 2009
Using population synthesis of massive stars to study the interstellar medium near OB associations

Aims. We study the massive stars in OB associations and their surrounding interstellar medium environment, using a population synthesis code.

Methods. We developed a new population synthesis code for groups of massive stars, where we model the emission of different forms of energy and matter from the stars of the association. In particular, the ejection of the two radioactive isotopes 26Al and 60Fe is followed, as well as the emission of hydrogen ionizing photons, and the kinetic energy of the stellar winds and supernova explosions. We investigate various alternative astrophysical inputs and the resulting output sensitivities, especially effects due to the inclusion of rotation in stellar models. As the aim of the code is the application to relatively small populations of massive stars, special care is taken to address their statistical properties. Our code incorporates both analytical statistical methods applicable to small populations, as well as extensive Monte Carlo simulations.

Publication date: 16 Jul 2009
ISOC Newsletter #21
Contents:
  • Foreword
  • AO-6 and AO-7
  • The 7th INTEGRAL Workshop
  • Science Operations
  • Contacting ISOC
Publication date: 15 Dec 2008
 
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