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ABSTRACT: Studies of the long-term spectral variations have been used to constrain the
emission processes of black hole candidates. However, a common scenario which
is able to explain the emission from soft to hard X-rays has been proposed only
recently. Here, we use XMM and INTEGRAL data on 1E 1740.7-2942 in order to
demonstrate that Comptonization plays an important role in producing high
energy photons, as predicted by the current modeling scenario.
02/2013;
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Sebastian Müller,
Carlo Ferrigno,
Matthias Kühnel,
Gabriele Schönherr,
Peter A. Becker,
Michael T. Wolff,
Dominik Hertel,
Fritz-Walter Schwarm,
Victoria Grinberg,
Maria Obst, [......],
Katja Pottschmidt,
Felix Fürst,
Ingo Kreykenbohm,
Richard E. Rothschild,
Paul Hemphill,
Silvia Martínez Núñez,
José M. Torrejón,
Dmitry Klochkov,
Rüdiger Staubert, Jörn Wilms
[show abstract]
[hide abstract]
ABSTRACT: We report on an outburst of the high mass X-ray binary 4U 0115+63 with a
pulse period of 3.6s in 2008 March/April as observed with RXTE and INTEGRAL.
During the outburst the neutron star's luminosity varied by a factor of 10 in
the 3--50\,keV band. In agreement with earlier work we find evidence for five
cyclotron resonance scattering features at ~10.7, 21.8, 35.5, 46.7, and
59.7keV. Previous work had found an anti-correlation between the fundamental
cyclotron line energy and the X-ray flux. We show that this apparent
anti-correlation is probably due to the unphysical interplay of parameters of
the cyclotron line with the continuum models used previously, e.g., the
negative and positive exponent power law (NPEX). For this model, we show that
cyclotron line modeling erroneously leads to describing part of the exponential
cutoff and the continuum variability, and not the cyclotron lines. When the
X-ray continuum is modeled with a simple exponentially cutoff power law
modified by a Gaussian emission feature around 10keV, the correlation between
the line energy and the flux vanishes and the line parameters remain virtually
constant over the outburst. We therefore conclude that the previously reported
anti-correlation is an artifact of the assumptions adopted in the modeling of
the continuum.
11/2012;
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Peter Kretschmar,
Peter A. Becker,
Dipankar Bhattacharya,
Isabel Caballero,
Thomas Dauser,
Carlo Ferrigno,
Dmitry Klochkov,
Ingo Kreykenbohm,
Osamu Nishimura,
Katja Pottschmidt,
Richard E. Rothschild,
Andrea Santangelo,
Gabriele Schönherr,
Fritz-Walter Schwarm,
Rüdiger Staubert,
Slawomir Suchy,
Brent West, Jörn Wilms,
Michael Wolff,
Kenneth Wolfram
[show abstract]
[hide abstract]
ABSTRACT: Accreting X-ray pulsars are among the best observed objects of X-ray
astronomy with a rich data set of observational phenomena in the spectral and
timing domain. While the general picture for these sources is well established,
the detailed physics behind the observed phenomena are often subject of debate.
We present recent observational, theoretical and modeling results for the
structure and dynamics of the accretion column in these systems. Our results
indicate the presence of different accretion regimes and possible explanations
for observed variations of spectral features with luminosity.
11/2012;
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[hide abstract]
ABSTRACT: Swift J1626.6-5156 is a Be/X-ray binary that was in outburst from December
2005 until November 2008. We have examined RXTE/PCA and HEXTE spectra of three
long observations of this source taken early in its outburst, when the PCA 2-20
keV count rate was >70 counts/s/PCU, as well as several combined observations
from different stages of the outburst. The spectra are best fit with an
absorbed cutoff power law with a ~6.4 keV iron emission line and a Gaussian
optical depth absorption line at ~10 keV. We present strong evidence that this
absorption-like feature is a cyclotron resonance scattering feature, making
Swift J1626.6-5156 a new candidate cyclotron line source. The redshifted energy
of ~10 keV implies a magnetic field strength of ~8.6(1+z) x 10^11 G in the
region of the accretion column close to the magnetic poles where the cyclotron
line is produced. Analysis of phase averaged spectra spanning the duration of
the outburst suggests a possible positive correlation between the fundamental
cyclotron energy and source luminosity. Phase resolved spectroscopy from a long
observation reveals a variable cyclotron line energy, with phase dependence
similar to a variety of other pulsars, as well as the first harmonic of the
fundamental cyclotron line.
11/2012;
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[show abstract]
[hide abstract]
ABSTRACT: We present the analysis of two Suzaku observations of GX 301–2 at two orbital phases after the periastron passage. Variations in the column density of the line-of-sight absorber are observed, consistent with accretion from a clumpy wind. In addition to a cyclotron resonance scattering feature (CRSF), multiple fluorescence emission lines were detected in both observations. The variations in the pulse profiles and the CRSF throughout the pulse phase have a signature of a magnetic dipole field. Using a simple dipole model we calculated the expected magnetic field values for different pulse phases and were able to extract a set of geometrical angles, loosely constraining the dipole geometry in the neutron star. From the variation of the CRSF width and energy, we found a geometrical solution for the dipole, making the inclination consistent with previously published values.
The Astrophysical Journal 01/2012; 745(2):124. · 6.02 Impact Factor
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ABSTRACT: We present an analysis of the highly variable accreting X-ray pulsar 3A 1954+319 using 2005-2009 monitoring data obtained with INTEGRAL and Swift. This considerably extends the pulse period history and covers flaring episodes in 2005 and 2008. In 2006 the source was identified as one of only a few known symbiotic X-ray binaries (SyXBs), i.e., systems composed of a neutron star accreting from the inhomogeneous medium around an M-giant star. The extremely long pulse period of ~5.3 hr is directly visible in the 2008 INTEGRAL-ISGRI outburst light curve. The pulse profile is double peaked and generally not significantly energy dependent although there is an indication of possible softening during the main pulse. During the outburst a strong spin-up of –1.8 × 10–4 hr hr–1 occurred. Between 2005 and 2008 a long-term spin-down trend of 2.1 × 10–5 hr hr–1 was observed for the first time for this source. The 3-80 keV pulse peak spectrum of 3A 1954+319 during the 2008 flare could be well described by a thermal Comptonization model. We interpret the results within the framework of a recently developed quasi-spherical accretion model for SyXBs.
The Astrophysical Journal Letters 10/2011; 742(1):L11. · 5.53 Impact Factor
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ABSTRACT: ESA's hard X-ray and soft gamma-ray observatory INTEGRAL is covering the 3
keV to 10 MeV energy band, with excellent sensitivity during long and
uninterrupted observations of a large field of view (~100 square degrees), with
ms time resolution and keV energy resolution. It links the energy band of
pointed soft X-ray missions such as XMM-Newton with that of high-energy
gamma-ray space missions such as Fermi and ground based TeV observatories. Key
results obtained so far include the first sky map in the light of the 511 keV
annihilation emission, the discovery of a new class of high mass X-ray binaries
and detection of polarization in cosmic high energy radiation. For the
foreseeable future, INTEGRAL will remain the only observatory allowing the
study of nucleosynthesis in our Galaxy, including the long overdue next nearby
supernova, through high-resolution gamma-ray line spectroscopy. Science results
to date and expected for the coming mission years span a wide range of
high-energy astrophysics, including studies of the distribution of positrons in
the Galaxy; reflection of gamma-rays off clouds in the interstellar medium near
the Galactic Centre; studies of black holes and neutron stars particularly in
high- mass systems; gamma-ray polarization measurements for X-ray binaries and
gamma-ray bursts, and sensitive detection capabilities for obscured active
galaxies with more than 1000 expected to be found until 2014. This paper
summarizes scientific highlights obtained since INTEGRAL's launch in 2002, and
outlines prospects for the INTEGRAL mission.
10/2011;
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[show abstract]
[hide abstract]
ABSTRACT: We report on a Spitzer/InfraRed Spectrograph (mid-infrared), RXTE/PCA+HEXTE (X-ray), and Ryle (radio) simultaneous multiwavelength study of the microquasar Cygnus X-1, which aimed at an investigation of the origin of its mid-infrared emission. Compact jets were present in two out of three observations, and we show that they strongly contribute to the mid-infrared continuum. During the first observation, we detect the spectral break—where the transition from the optically thick to the optically thin regime takes place—at about 2.9 × 1013 Hz. We then show that the jet's optically thin synchrotron emission accounts for Cygnus X-1's emission beyond 400 keV, although it cannot alone explain its 3-200 keV continuum. A compact jet was also present during the second observation, but we do not detect the break, since it has likely shifted to higher frequencies. In contrast, the compact jet was absent during the last observation, and we show that the 5-30 μm mid-infrared continuum of Cygnus X-1 stems from the blue supergiant companion star HD 226868. Indeed, the emission can then be understood as the combination of the photospheric Rayleigh-Jeans tail and the bremsstrahlung from the expanding stellar wind. Moreover, the stellar wind is found to be clumpy, with a filling factor f ∞ 0.09-0.10. Its bremsstrahlung emission is likely anti-correlated to the soft X-ray emission, suggesting an anti-correlation between the mass-loss and mass-accretion rates. Nevertheless, we do not detect any mid-infrared spectroscopic evidence of interaction between the jets and Cygnus X-1's environment and/or the companion star's stellar wind.
The Astrophysical Journal 07/2011; 736(1):63. · 6.02 Impact Factor
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[show abstract]
[hide abstract]
ABSTRACT: We present a detailed study of the X-ray dust scattering halo of the black
hole candidate \cygx1 based on two \chandra\ HETGS observations. Using 18
different dust models, including one modified by us (dubbed XLNW), we probe the
interstellar medium between us and this source. A consistent description of the
cloud properties along the line of sight that describes at the same time the
halo radial profile, the halo lightcurves, and the column density from source
spectroscopy is best achieved with a small subset of these models. Combining
the studies of the halo radial profile and the halo lightcurves, we favor a
geometric distance to \cygx1 of $d=1.81\pm{0.09}$\,kpc. Our study also shows
that there is a dense cloud, which contributes $\sim$50% of the dust grains
along the line of sight to \cygx1, located at $\sim1.6$ kpc from us. The
remainder of the dust along the line of sight is close to the black hole
binary.
06/2011;
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[show abstract]
[hide abstract]
ABSTRACT: In 2009, Cygnus X-3 (Cyg X-3) became the first microquasar to be detected in the GeV γ-ray regime, via the satellites Fermi and AGILE. The addition of this new band to the observational toolbox holds promise for building a more detailed understanding of the relativistic jets of this and other systems. We present a rich data set of radio, hard and soft X-ray, and γ-ray observations of Cyg X-3 made during a flaring episode in 2010 May. We detect a ~3 day softening and recovery of the X-ray emission, followed almost immediately by a ~1 Jy radio flare at 15 GHz, followed by a 4.3σ γ-ray flare (E > 100 MeV) ~1.5 days later. The radio sampling is sparse, but we use archival data to argue that it is unlikely the γ-ray flare was followed by any significant unobserved radio flares. In this case, the sequencing of the observed events is difficult to explain in a model in which the γ-ray emission is due to inverse Compton scattering of the companion star's radiation field. Our observations suggest that other mechanisms may also be responsible for γ-ray emission from Cyg X-3.
The Astrophysical Journal Letters 05/2011; 733(2):L20. · 5.53 Impact Factor
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[show abstract]
[hide abstract]
ABSTRACT: In 2009, Cygnus X-3 (Cyg X-3) became the first microquasar to be detected in
the GeV {\gamma}-ray regime, via the satellites Fermi and AGILE. The addition
of this new band to the observational toolbox holds promise for building a more
detailed understanding of the relativistic jets of this and other systems. We
present a rich dataset of radio, hard and soft X-ray, and {\gamma}-ray
observations of Cyg X-3 made during a flaring episode in 2010 May. We detect a
~3-d softening and recovery of the X-ray emission, followed almost immediately
by a ~1-Jy radio flare at 15 GHz, followed by a 4.3{\sigma} {\gamma}-ray flare
(E > 100 MeV) ~1.5 d later. The radio sampling is sparse, but we use archival
data to argue that it is unlikely the {\gamma}-ray flare was followed by any
significant unobserved radio flares. In this case, the sequencing of the
observed events is difficult to explain in a model in which the {\gamma}-ray
emission is due to inverse Compton scattering of the companion star's radiation
field. Our observations suggest that other mechanisms may also be responsible
for {\gamma}-ray emission from Cyg X-3.
04/2011;
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Slawomir Suchy,
Katja Pottschmidt,
Richard E. Rothschild, Jörn Wilms,
Felix Fürst,
Laura Barragan,
Isabel Caballero,
Victoria Grinberg,
Ingo Kreykenbohm,
Victor Doroshenko,
Andrea Santangelo,
Rüdiger Staubert,
Yukikatsu Terada,
Wataru Iwakari,
and Kazuo Makishima
[show abstract]
[hide abstract]
ABSTRACT: We present broadband analysis of the Be/X-ray transient 1A 1118–61 by Suzaku at the peak of its third observed outburst in 2009 January and two weeks later when the source flux had decayed by an order of magnitude. The continuum was modeled with a cutoffpl model as well as a compTT model, with both cases requiring an additional blackbody component at lower energies. We confirm the detection of a cyclotron line at ~55 keV and discuss the possibility of a first harmonic at ~110 keV. Pulse profile comparisons show a change in the profile structure at lower energies, an indication for possible changes in the accretion geometry. Phase-resolved spectroscopy in the outburst data shows a change in the continuum throughout the pulse period. The decrease in the cyclotron resonance scattering feature centroid energy also indicates that the viewing angle on the accretion column is changing throughout the pulse period.
The Astrophysical Journal 04/2011; 733(1):15. · 6.02 Impact Factor
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[show abstract]
[hide abstract]
ABSTRACT: The X-ray luminosity of black holes is produced through the accretion of
material from their companion stars. Depending on the mass of the donor star,
accretion of the material falling onto the black hole through the inner
Lagrange point of the system or accretion by the strong stellar wind can occur.
Cygnus X-1 is a high mass X-ray binary system, where the black hole is powered
by accretion of the stellar wind of its supergiant companion star HDE226868. As
the companion is close to filling its Roche lobe, the wind is not symmetric,
but strongly focused towards the black hole. Chandra-HETGS observations allow
for an investigation of this focused stellar wind, which is essential to
understand the physics of the accretion flow. We compare observations at the
distinct orbital phases of 0.0, 0.2, 0.5 and 0.75. These correspond to
different lines of sights towards the source, allowing us to probe the
structure and the dynamics of the wind.
03/2011;
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[show abstract]
[hide abstract]
ABSTRACT: In 2009, Cygnus X-3 (Cyg X-3) became the first microquasar to be detected in the GeV γ-ray regime, via the satellites Fermi and AGILE. The addition of this new band to the observational toolbox holds promise for building a more detailed understanding of the relativistic jets of this and other systems. We present a rich dataset of radio, hard and soft X-ray, and γ-ray observations of Cyg X-3 made during a flaring episode in 2010 May. We detect a ∼3-d softening and recovery of the X-ray emission, followed almost immediately by a ∼1-Jy radio flare at 15 GHz, followed by a 4.3σ γ-ray flare (E > 100 MeV) ∼1.5 d later. The radio sampling is sparse, but we use archival data to argue that it is unlikely the γ-ray flare was followed by any significant unobserved radio flares. In this case, the sequencing of the observed events is difficult to explain in a model in which the γ-ray emission is due to inverse Compton scattering of the companion star's radiation field. Our observations suggest that other mechanisms may also be responsible for γ-ray emission from Cyg X-3.
01/2011;
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[show abstract]
[hide abstract]
ABSTRACT: IGR J16318‐4848 is the first example, and probably the most extreme case, of a new class of highly absorbed X‐ray binaries that has been discovered by the INTErnational Gamma‐Ray Astrophysics Laboratory (INTEGRAL) in the last years. We report on the analysis of the first joint Suzaku∕INTEGRAL observation of this source, and also on the detection of 1RXS J163120.0–484325 during our observation.
AIP Conference Proceedings. 07/2010; 1248(1):139-140.
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ABSTRACT: GRS1915+105 is a very peculiar black hole binary that exhibits accretion-related states that are not observed in any other stellar-mass black hole system. One of these states, however -- referred to as the plateau state -- may be related to the canonical hard state of black hole X-ray binaries. Both the plateau and hard state are associated with steady, relatively lower X-ray emission and flat/inverted radio emission, that is sometimes resolved into compact, self-absorbed jets. However, while generally black hole binaries quench their jets when the luminosity becomes too high, GRS1915+105 seems to sustain them despite the fact that it accretes at near- or super-Eddington rates. In order to investigate the relationship between the plateau and the hard state, we fit two multi-wavelength observations using a steady-state outflow-dominated model, developed for hard state black hole binaries. The data sets consist of quasi-simultaneous observations in radio, near-infrared and X-ray bands. Interestingly, we find both significant differences between the two plateau states, as well as between the best-fit model parameters and those representative of the hard state. We discuss our interpretation of these results, and the possible implications for GRS 1915+105's relationship to canonical black hole candidates. Comment: accepted for publication in MNRAS
07/2010;
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Felix Fürst,
Ingo Kreykenbohm,
Katja Pottschmidt, Jörn Wilms,
Manfred Hanke,
Richard E. Rothschild,
Peter Kretschmar,
Norbert S. Schulz,
David P. Huenemoerder,
Dmitry Klochkov,
Rüdiger Staubert
[show abstract]
[hide abstract]
ABSTRACT: We investigate the structure of the wind in the neutron star X-ray binary system Vela X-1 by analyzing its flaring behavior. Vela X-1 shows constant flaring, with some flares reaching fluxes of more than 3.0 Crab between 20-60 keV for several 100 seconds, while the average flux is around 250 mCrab. We analyzed all archival INTEGRAL data, calculating the brightness distribution in the 20-60 keV band, which, as we show, closely follows a log-normal distribution. Orbital resolved analysis shows that the structure is strongly variable, explainable by shocks and a fluctuating accretion wake. Analysis of RXTE ASM data suggests a strong orbital change of N_H. Accreted clump masses derived from the INTEGRAL data are on the order of 5 x 10^19 -10^21 g. We show that the lightcurve can be described with a model of multiplicative random numbers. In the course of the simulation we calculate the power spectral density of the system in the 20-100 keV energy band and show that it follows a red-noise power law. We suggest that a mixture of a clumpy wind, shocks, and turbulence can explain the measured mass distribution. As the recently discovered class of supergiant fast X-ray transients (SFXT) seems to show the same parameters for the wind, the link between persistent HMXB like Vela X-1 and SFXT is further strengthened. Comment: 8 pages, 6 figures, accepted for publication in A&A
05/2010;
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[show abstract]
[hide abstract]
ABSTRACT: We present results from simultaneous observations of the high-mass X-ray binary system Cygnus X-1 / HDE 226868 with Suzaku, Chandra-HETGS, XMM-Newton, RXTE, INTEGRAL, and Swift in 2008 April. Performed shortly after orbital phase 0, when our line of sight to the black hole passes through the densest part of the O-star's wind, these obervations show common transient absorption dips in the soft X-ray band. For the first time, however, we detect a simultaneous scattering trough in the hard X-ray light curves. The more neutral clump is thus only the core of a larger ionized blob, which contains a significant fraction of the total wind mass. The diluted wind outside of these clumps is almost completely photoionized. Comment: 2 pages, 4 figures; proceedings of the 3rd Suzaku Conference "The Energetic Cosmos: From Suzaku to Astro-H"
04/2010;
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[show abstract]
[hide abstract]
ABSTRACT: Since the discovery of IGR J16318−4848 in 2003 January, INTEGRAL has accumulated more than 5.8 Ms in IBIS/ISGRI. We present the first extensive analysis of the archival INTEGRAL data (IBIS/ISGRI, and JEM-X when available) for this source, together with the observations carried out by XMM-Newton (twice in 2003, and twice in 2004) and Suzaku (2006). The source is very variable in the long-term, with periods of low activity, where the source is al-most not detected, and flares with a luminosity ∼ 10 times greater than its average value (5.4 cts/s). IGR J16318−4848 is a HMXB containing a sgB[e] star and a compact object (most probably a neutron star) deeply embedded in the stellar wind of the mass donor. The variability of the source (also in the short-term) can be ascribed to the wind of the optical star being very clumpy. We study the variation of the spectral parameters in time scales of INTEGRAL revolutions. The photoelectric absorption is, with N H around 10 24 cm −2 , unusually high. During brighter phases the strong K-alpha iron line known from XMM-Newton and Suzaku observations is also detectable with the JEM-X instrument.
PoS. 01/2010;
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[show abstract]
[hide abstract]
ABSTRACT: Using Suzaku and the Rossi X-ray Timing Explorer (RXTE), we have conducted a series of four simultane-ous observations of the galactic black hole candidate Cyg X-1 in what were historically faint and spectrally hard "low states". Additionally, all of these observations occurred near superior conjunction with our line of sight to the X-ray source passing through the dense phases of the "focused wind" from the mass donating secondary. One of our observations was also simultaneous with observations by the Chandra-High Energy Transmission Grating (HETG). These latter spectra are crucial for revealing the ionized absorption due to the secondary's focused wind. Such absorption is present and must be accounted for in all four spectra. These simultaneous data give an unprecedented view of the 0.8–300 keV spectrum of Cyg X-1, and hence bear upon both corona and X-ray emitting jet models of black hole hard states. Three models fit the spectra well: coronae with thermal or mixed thermal/non-thermal electron populations, and jets. All three models require a soft component that we fit with a low temperature disk spectrum with an inner radius of only a few tens of GM/c 2 . All three models also agree that the known spectral break at 10 keV is not solely due to the presence of reflection, but each gives a different underlying explanation for the augmentation of this break. Thus whereas all three models require that there is a relativistically broadened Fe line, the strength and inner radius of such a line is dependent upon the specific model, thus making premature line-based estimates of the black hole spin in the Cyg X-1 system. We look at the relativistic line in detail, accounting for the narrow Fe emission and ionized absorption detected by HETG. Although the specific relativistic parameters of the line are continuum-dependent, none of the broad line fits allow for an inner disk radius that is > 40 GM/c 2 .
The Astrophysical Journal 01/2010; 18. · 6.02 Impact Factor
