Clumpy Wind Studies and the Nondetection of a Cyclotron Line in OAO 1657–415
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Pragati Pradhan↗
Engineering topics
Peter Kretschmar
Publications and source records attributed to Peter Kretschmar.
HILIGT, Upper Limit Servers II - Implementing the Data Servers
The High-Energy Light curve Generator(HILIGT) is a new web-based tool which allows the user to generate long-term light curves of X-ray sources. It provides historical data and calculates upper limits from image data in real-time. HILIGT utilizes data from twelve satellites, both modern missions such as XMM-Newton and Swift, and earlier facilities such as ROSAT, EXOSAT, Einstein or Ariel V. Together, this enables the user to query 50 years of X-ray data and, for instance, study outburst behavior of transient sources. In this paper we focus on the individual back-end servers for each satellite, detailing the software layout, database design, catalog calls, and image footprints. We compile all relevant calibration information of these missions and provide an in-depth summary of the details of X-ray astronomical instrumentation and data.
Ole Konig↗
INTEGRAL reloaded: Spacecraft, instruments and ground system
The European Space Agency’s INTErnational Gamma-Ray Astrophysics Laboratory (ESA/INTEGRAL) was launched aboard a Proton-DM2 rocket on 17 October 2002 at 06:41 CEST, from Baikonur in Kazakhstan. Since then, INTEGRAL has been providing long, uninterrupted observations (up to about 47 h, or 170 ksec, per satellite orbit of 2.7 days) with a large field-of-view (FOV, fully coded: 100 deg), millisecond time resolution, keV energy resolution, polarization measurements, as well as additional wavelength coverage at optical wavelengths. This is realized by two main instruments in the 15 keV to 10 MeV energy range, the spectrometer SPI (spectral resolution 3 keV at 1.8 MeV) and the imager IBIS (angular resolution: 12 arcmin FWHM), complemented by X-ray (JEM-X; 3–35 keV) and optical (OMC; Johnson V-band) monitor instruments. All instruments are co-aligned to simultaneously observe the target region. A particle radiation monitor (IREM) measures charged particle fluxes near the spacecraft. The Anti-coincidence subsystems of the main instruments, built to reduce the background, are also very efficient all-sky γ-ray detectors, which provide virtually omni-directional monitoring above ~75 keV. Besides the long, scheduled observations, INTEGRAL can rapidly (within a couple of hours) re-point and conduct Target of Opportunity (ToO) observations on a large variety of sources. INTEGRAL observations and their scientific results have been building an impressive legacy: The discovery of currently more than 600 new high-energy sources; the first-ever direct detection of (56)Ni and (56)Co radio-active decay lines from a Type Ia supernova; spectroscopy of isotopes from galactic nucleo-synthesis sources; new insights on enigmatic positron annihilation in the Galactic bulge and disk; and pioneering gamma-ray polarization studies. INTEGRAL is also a successful actor in the new multi-messenger astronomy introduced by non-electromagnetic signals from gravitational waves and from neutrinos: INTEGRAL found the first prompt electromagnetic radiation in coincidence with a binary neutron star merger. Up to now more than 1750 scientific papers based on INTEGRAL data have been published in refereed journals. In this paper, we will give a comprehensive update of the satellite status after more than 18 years of operations in a harsh space environment, and an account of the successful Ground Segment.
Erik Kuulkers↗
Dust and gas absorption in the High Mass X-ray Binary IGR J16318−4848
Context. With an absorption column density on the order of 10(exp 24)per sq. cm, IGR J16318-4848 is one of the most extreme cases of a highly obscured High Mass X-ray Binary. Besides the overall continuum absorption, the source spectrum exhibits a strong iron and nickel fluorescence line complex at 6.4 keV. Previous empirical modeling of these features and comparison with radiative transfer simulations raised questions about the structure and covering fraction of the absorber and the profile of the fluorescence lines. Aims. We aim at a self-consistent description of the continuum absorption, the absorption edges and the fluorescent lines to constrain properties of the absorbing material, such as ionization structure and geometry. We further investigate the effects of dust absorption on the observed spectra and the possibility of fluorescent emission from dust grains. Methods. We use XMM-Newton and NuSTAR spectra to first constrain empirically the incident continuum and fluorescence lines. Next, we use XSTAR to construct a customized photoionization model where we vary the ionization parameter, column density, and covering fraction. In a third step, we model the absorption and fluorescence in a dusty olivine absorber and employ both, a simple analytical model for the fluorescent line emission and Monte Carlo radiative transfer, spectral shapes and line fluxes that are very close to the data are generated. Results. Our empirical spectral modeling is in agreement with previous works. Our second model, the single gas absorber does not describe the observational data. In particular, irrespective of the ionization state or column density of the absorber, a much higher covering fraction than previously estimated is needed to produce the strong fluorescence lines and the large continuum absorption. A dusty, spherical absorber (modeled as consisting of olivine dust, although the nature of dust cannot be constrained) is well able to produce the observed continuum absorption and edges. Conclusions. A dense, dusty absorber in the direct vicinity of the source consisting of dust offers a consistent description of both the strong continuum absorption and the strong emission features in the X-ray spectrum of IGR J163184848. In particular, for low optical depth of individual grains the dust will contribute significantly to the fluorescent emission, which is the case for typical densities and grain size distribution models.
Ralf Ballhausen↗
Advances in Understanding High-Mass X-ray Binaries with INTEGRAL and Future Directions
High mass X-ray binaries are among the brightest X-ray sources in the Milky Way, as well as in nearby Galaxies. Thanks to their highly variable emissions and complex phenomenology, they have attracted the interest of the high energy astrophysical community since the dawn of X-ray Astronomy. In more recent years, they have challenged our comprehension of physical processes in many more energy bands, ranging from the infrared to very high energies. In this review, we provide a broad but concise summary of the physical processes dominating the emission from high mass X-ray binaries across virtually the whole electromagnetic spectrum. These comprise the interaction of stellar winds with the high gravitational and magnetic fields of compact objects, the behaviour of matter under extreme magnetic and gravity conditions, and the perturbation of the massive star evolutionary processes. We highlight the role of the INTEGRAL mission in the discovery of many of the most interesting objects in the high mass X-ray binary class and its contribution in reviving the interest for these sources over the past two decades. We show how the INTEGRAL discoveries have not only contributed to significantly increase the number of high mass X-ray binaries known, thus advancing our understanding of the population as a whole, but also have opened new windows of investigation that stimulated the multi-wavelength approach nowadays common in most astrophysical research fields. We conclude the review by providing an overview of future facilities being planned from the X-ray to the very high energy domain that will hopefully help us in finding an answer to the many questions left open after more than 18 years of INTEGRAL scientific observations.
Peter Kretschmar↗
The Giant Outburst of 4U 0115+634 in 2011 with Suzaku and RXTE
We present an analysis of X-ray spectra of the high mass X-ray binary 4U 0115+634 as observed with Suzaku and RXTE in 2011 July, during the fading phase of a giant X-ray outburst. We used a continuum model consisting of an absorbed cutoff power-law and an ad-hoc Gaussian emission feature centered around 8.5 keV, which we discuss to be due to cyclotron emission. Our results are consistent with a fundamental cyclotron absorption line centered at keV for all observed flux ranges. At the same time we rule out significant influence of the 8.5 kev Gaussian on the CRSF parameters, which are not consistent with the cyclotron line energies and depths of previously reported flux-dependent descriptions. We also show that some continuum models can lead to artificial line-like residuals in the analyzed spectra, which are then misinterpreted as unphysically strong cyclotron lines. Specifically, our results do not support the existence of a previously claimed additional cyclotron feature at keV. Apart from these features, we find for the first time evidence for a He-like Fe XXV emission line at keV and weak H-like Fe XXVI emission close to keV.
Matthias Bissinger né Kühnel↗
An Evolving Broad Iron Line from the First Galactic Ultraluminous X-Ray Pulsar Swift J0243.6+6124
We present a spectral study of the ultraluminous Be/X-ray transient pulsar Swift J0243.6+6124 using Neutron Star Interior Composition Explorer (NICER) observations during the system's 2017–2018 giant outburst. The 1.2–10 keV energy spectrum of the source can be approximated with an absorbed cutoff power-law model. We detect strong, luminosity-dependent emission lines in the 6–7 keV energy range. A narrow 6.42 keV line, observed in the sub-Eddington regime, is seen to evolve into a broad Fe-line profile in the super-Eddington regime. Other features are found at 6.67 and 6.97 keV in the Fe-line complex. An asymmetric broad-line profile, peaking at 6.67 keV, is possibly due to Doppler effects and gravitational redshift. The 1.2–79 keV broadband spectrum from Nuclear Spectroscopic Telescope Array (NuSTAR) and NICER observations at the outburst peak is well described by an absorbed cutoff power law plus multiple Gaussian lines and a blackbody component. Physical reflection models are also tested to probe the broad iron-line feature. Depending on the mass accretion rate, we found emission sites that are evolving from ~5000 km to a range closer to the surface of the neutron star. Our findings are discussed in the framework of the accretion disk and its implication on the magnetic field, the presence of optically thick accretion curtain in the magnetosphere, jet emission, and the massive, ultrafast outflow expected at super-Eddington accretion rates. We do not detect any signatures of a cyclotron absorption line in the NICER or NuSTAR data.
Gaurava K. Jaisawal↗
Hitomi observations of the LMC SNR N 132 D: Highly redshifted X-ray emission from iron ejecta
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Hitomi Collaboration, Felix Aharonian↗
Two Giant Outbursts of V0332+53 Observed with INTEGRAL
Context. In July 2015, the high-mass X-ray binary V0332+53 underwent a giant outburst, a decade after the previous one. V0332+53 hosts a strongly magnetized neutron star. During the 2004-2005 outburst, an anti-correlation between the centroid energy of its fundamental cyclotron resonance scattering features (CRSFs) and the X-ray luminosity was observed. Aims. The long ( 100 d) and bright (Lx approx. 10(exp 38) ergs(exp -1)) 2015 outburst offered the opportunity to study during another outburst the unique properties of the fundamental CRSF and its dependence on the X-ray luminosity. Methods. The source was observed by the INTEGRAL satellite for approximately 330 ks. We exploit the spectral resolution at high energies of the SPectrometer on INTEGRAL (SPI) and the Joint European X-ray Monitors to characterize its spectral properties, focusing in particular on the CRSF-luminosity dependence. We complement the data of the 2015 outburst with those collected by SPI in 2004-2005 and left unpublished so far. Results. We find a highly significant anti-correlation of the centroid energy of the fundamental CRSF and the 3-100 keV luminosity of E1 alpha -0:095(8)L(sub 37) keV. This trend is observed for both outbursts. We confirm the correlation between the width of the fundamental CRSF and the X-ray luminosity previously found in the JEM-X and IBIS dataset of the 2004-2005 outburst. By exploiting the RXTE/ASM and Swift/BAT monitoring data we also report on the detection of a approximately 34 d modulation superimposed on the mean profiles and roughly consistent with the orbital period of the pulsar. We discuss possible interpretations of such variability.
X-rays: binaries↗