0000000000327783
AUTHOR
M. Van Der Klis
showing 24 related works from this author
Presence of a soft excess between 0.6 keV and 0.9 keV in the energy spectrum of Cir X-1
2004
Abstract We report on the results of a new BeppoSAX (0.12–200 keV) observation of the peculiar X–ray binary source Circinus X–1 (Cir X–1) near the apastron. We produced a color-color diagram and selected seven different zones. We fitted the spectra obtained from each zone using a model consisting of a blackbody component, at a temperature of ∼0.5 keV, and a Comptonized component, with a seed-photon temperature of ∼1 keV, electron temperature of ∼2.7 keV and optical depth of ∼11. A soft excess between 0.6 keV and 0.9 keV is present in four out of the seven extracted spectra. To fit the soft excess we tried several continuum emission models, and we find good results only adding a further blac…
Discovery of a redshifted X-ray emission line in the symbiotic neutron star binary 4U 1700+24
2005
We present the spectral analysis of an XMM-Newton observation of the X-ray binary 4U 1700+24, performed during an outburst in August 2002. The EPIC-PN spectrum above 1 keV can be modeled by a blackbody plus Comptonization model, as in previous observations. At lower energies, however, we detect a prominent soft excess, which we model with a broad Gaussian centered at ~0.5 keV. In the high resolution RGS spectrum we detect a single emission line, centered at 19.19^{+0.05}_{-0.09} \AA. We discuss two possible interpretations for this line: O VIII at redshift z=0.012^{+0.002}_{-0.004} or Ne IX at redshift z~0.4.
Coupling Between Periodic and Aperiodic Variability in SAX J1808.4-3658
2003
We detect a significant broadening in the wings of the 401 Hz peak in the power spectrum of the accreting millisecond binary pulsar SAX J1808.4-3658. This feature is consistent with the convolution of the red noise present in the power spectrum with the harmonic line. We conclude that the flux modulated by the spin period shows aperiodic variability similar to the red noise in the overall flux, suggesting such variability also originates at the magnetic caps close to the neutron star surface. This is analogous to the results found in some longer period, higher magnetic field pulsators in high mass X-ray binaries.
A new BeppoSAX observation of the Z Source GX 349+2
2004
Abstract We report on the results from two BeppoSAX observations of the Z source GX 349+2 performed in February 2001 and covering the broad energy range 0.12–200 keV. The average spectrum is well described by a soft blackbody (kTBB∼0.5 keV) and a Comptonized component having a seed-photon temperature of kT0∼1 keV, an electron temperature of kTe∼2.7 keV, and optical depth τ∼11. To well fit the energy spectrum three gaussian lines are needed at 1.2 keV, 2.6 keV, and 6.7 keV with corresponding equivalent widths of 13 eV, 10 eV, and 39 eV, probably associated to L-shell emission of Fe XXIV, Lyα S XVI, and Fe XXV, respectively. These lines may be produced at different distances from the neutron …
On the Spectral Evolution of Cygnus X-2 along its Color-Color Diagram
2002
We report on the results of a broad band (0.1-200 keV) spectral study of Cyg X-2 using two BeppoSAX observations taken in 1996 and 1997, respectively, for a total effective on-source time of ~100 ks. The color-color (CD) and hardness-intensity (HID) diagrams show that the source was in the horizontal branch (HB) and normal branch (NB) during the 1996 and 1997 observation, respectively. Five spectra were selected around different positions of the source in the CD/HID, two in the HB and three in the NB. These spectra are fit to a model consisting of a disk blackbody, a Comptonization component, and two Gaussian emission lines at ~1 keV and ~6.6 keV, respectively. The addition of a hard power-…
LOFT: the Large Observatory For X-ray Timing
2012
The LOFT mission concept is one of four candidates selected by ESA for the M3 launch opportunity as Medium Size missions of the Cosmic Vision programme. The launch window is currently planned for between 2022 and 2024. LOFT is designed to exploit the diagnostics of rapid X-ray flux and spectral variability that directly probe the motion of matter down to distances very close to black holes and neutron stars, as well as the physical state of ultra-dense matter. These primary science goals will be addressed by a payload composed of a Large Area Detector (LAD) and a Wide Field Monitor (WFM). The LAD is a collimated (<1 degree field of view) experiment operating in the energy range 2-50 keV,…
Linking Jet Emission, X‐Ray States, and Hard X‐Ray Tails in the Neutron Star X‐Ray Binary GX 17 \documentclass{aastex} \usepackage{amsbsy} \usepackag…
2007
We present the results from simultaneous radio (Very Large Array) and X-ray (Rossi-X-ray Timing Explorer) observations of the Z-type neutron star X-ray binary GX~17+2. The aim is to assess the coupling between X-ray and radio properties throughout its three rapidly variable X-ray states and during the time-resolved transitions. These observations allow us, for the first time, to investigate quantitatively the possible relations between the radio emission and the presence of the hard X-ray tails and the X-ray state of the source. The observations show: 1) a coupling between the radio jet emission and the X-ray state of the source, i.e. the position in the X-ray hardness-intensity diagram (HI…
Does GRS 1915+105 exhibit "canonical" black-hole states?
2003
We have analysed RXTE data of the superluminal source GRS 1915+105 in order to investigate if, despite its extreme variability, it also exhibits the canonical source states that characterise other black-hole candidates. The phenomenology of GRS 1915+105 has been described in terms of three states (named A, B and C) based on their hardness ratios and position in the colour-colour diagram. We have investigated the connection between these states and the canonical behaviour and found that the shape of the power spectral continuum and the values of the best-fit model parameters to the noise components in all three states indicate that the source shows properties similar to the canonical very hi…
XMM-Newton X-ray spectroscopy of the high mass X-ray binary 4U 1700-37 at low flux
2004
We present results of a monitoring campaign of the high-mass X-ray binary system 4U 1700-37/HD 153919, carried out with XMM-Newton in February 2001. The system was observed at four orbital phase intervals, covering 37% of one 3.41-day orbit. The lightcurve includes strong flares, commonly observed in this source. We focus on three epochs in which the data are not affected by photon pile up: the eclipse, the eclipse egress and a low-flux interval in the lightcurve around orbital phase phi ~0.25. The high-energy part of the continuum is modelled as a direct plus a scattered component, each represented by a power law with identical photon index (alpha ~1.4), but with different absorption colum…
The broad-band spectrum of Cyg X-2 with INTEGRAL
2005
We study the broad band (3-100 keV) spectrum of Cygnus X-2 with INTEGRAL. We find that the spectrum is well fitted by a Comptonized component with a seed-photons temperature of ~1 keV, an electron temperature of ~3 keV and an optical depth tau ~ 8. Assuming spherical geometry, the radius of the seed-photons emitting region is ~17 km. The source shows no hard X-ray emission; it was detected only at a 3 sigma level above 40 keV. We also analyzed public ISGRI data of Cyg X--2 to investigate the presence of a hard X-ray component. We report the possible presence of hard X-ray emission in one data set.
High Resolution Spectroscopy of 4U 1728-34 from a Simultaneous Chandra-RXTE Observation
2004
We report on a simultaneous Chandra and RossiXTE observation of the LMXB atoll bursting source 4U 1728-34 performed on 2002 March 3-5. We fitted the 1.2-35 keV continuum spectrum with a blackbody plus a Comptonized component. An overabundance of Si by a factor of ~2 with respect to Solar abundance is required for a satisfactory fit. Large residuals at 6-10 keV can be fitted by a broad (FWHM ~ 1.6 keV) Gaussian emission line, or, alternatively, by absorption edges associated with Fe I and Fe XXV at ~7.1 keV and ~9 keV, respectively. In this interpretation, we find no evidence of a broad, or narrow Fe Kalpha line, between 6 and 7 keV. We tested our alternative modeling of the iron Kalpha regi…
Disappearance of Hard X-Ray Emission in the Last BeppoSAX Observation of the Z Source GX 349+2
2003
We report on the results from two BeppoSAX observations of the Z source GX 349+2 performed in February 2001 and covering the broad energy range 0.12-200 keV. The light curve obtained from these observations shows a large flaring activity, the count rate varying from ~130 to ~260 counts/s, indicating that the source was in the flaring branch during these observations. The average spectrum is well described by a soft blackbody and a Comptonized component. To well fit the energy spectrum three gaussian lines are needed at 1.2 keV, 2.6 keV, and 6.7 keV with corresponding equivalent widths of 13 eV, 10 eV, and 39 eV, probably associated to L-shell emission of Fe XXIV, Ly-alpha S XVI, and Fe XXV,…
X-ray spectroscopy of the high-mass X-ray binary 4U 1700-37
2004
We present the first results of a monitoring campaign of the high-mass X-ray binary system 4U 1700-37/HD 153919, carried out with XMM-Newton.We have observed the high-mass X-ray binary (HMXB) 4U 1700-37 with XMM-Newton at four orbital phases in February 2001. 4U 1700-37 is powered by the dense stellar wind of the O supergiant HD 153919. Numerous X-ray flares are observed with a typical duration, of the order of half an hour. We focus on three intervals in which the data are not affected by pile up: the eclipse, the eclipse egress and a low-flux part around orbital phase ϕ ~ 0.28.
A Hard X-Ray View of Scorpius X-1 with INTEGRAL : Nonthermal Emission?
2006
We present here simultaneous INTEGRAL/RXTE observations of Sco X-1, and in particular a study of the hard X-ray emission of the source and its correlation with the position in the Z-track of the X-ray color-color diagram. We find that the hard X-ray (above about 30 keV) emission of Sco X-1 is dominated by a power-law component with a photon index of ~3. The flux in the power-law component slightly decreases when the source moves in the color-color diagram in the sense of increasing inferred mass accretion rate from the horizontal branch to the normal branch/flaring branch vertex. It becomes not significantly detectable in the flaring branch, where its flux has decreased by about an order of…
The Large Observatory For x-ray Timing
2014
The Large Observatory For x-ray Timing (LOFT) was studied within ESA M3 Cosmic Vision framework and participated in the final down-selection for a launch slot in 2022-2024. Thanks to the unprecedented combination of effective area and spectral resolution of its main instrument, LOFT will study the behaviour of matter under extreme conditions, such as the strong gravitational field in the innermost regions of accretion flows close to black holes and neutron stars, and the supra-nuclear densities in the interior of neutron stars. The science payload is based on a Large Area Detector (LAD, 10 m 2 effective area, 2-30 keV, 240 eV spectral resolution, 1 deg collimated field of view) and a WideFi…
A broad iron line in the Chandra/HETG spectrum of 4U 1705-44
2004
We present preliminary results from a Chandra 30 ks observation of the atoll sourco 4U 1705 44. In particular we concentrate on the study of the iron Kα line, using the HEG spectrometer. The iron Kα line at ~ 6.6 keV is found to be intrinsically broad (FWHM ~ 1.7 keV); its width can be explained by reflection from a cold accretion disk extending down to ~ 17 km from the neutron star center or by Compton broadening in the hotter (~ 3 – 4 keV) corona.
Inhomogeneous Accretion Flow in X-ray Binary Pulsars
2005
We analyze the power spectrum of SAX J1808.4‐3658, the first accreting millisecond binary pulsar discovered, to look for a broadening in the wings of the harmonic line, in analogy to what had been previously found in some high mass X‐ray binaries. We indeed detect a broadening at the base of the 401 Hz peak, which is consistent with the convolution of the low frequency noise present in the power spectrum with the harmonic line. We interpret this as the result of a coupling between a fraction of the aperiodic and periodic variability, suggesting that at least part of the noise originates in a region close to the neutron star surface at the magnetic poles.
Study of the Temporal Behavior of 4U 1728−34 as a Function of Its Position in the Color‐Color Diagram
2001
We study the timing properties of the bursting atoll source 4U 1728-34 as a function of its position in the X-ray color-color diagram. In the island part of the color-color diagram (corresponding to the hardest energy spectra), the power spectrum of 4U 1728-34 shows several features such as a band-limited noise component present up to a few tens of Hz, a low-frequency quasi-periodic oscillation (LFQPO) at frequencies between 20 and 40 Hz, a peaked noise component around 100 Hz, and one or two QPOs at kHz frequencies. In addition to these, in the lower banana (corresponding to softer energy spectra) we also find a very low frequency noise (VLFN) component below ∼1 Hz. In the upper banana (co…
A Broad Iron Line in the Chandra High Energy Transmission Grating Spectrum of 4U 1705-44
2005
We present the results of a Chandra 30 ks observation of the low-mass X-ray binary and atoll source 4U 1705-44. Here we concentrate on the study of discrete features in the energy spectrum at energies below ~3 keV, as well as on the iron Kalpha line, using the High Energy Transmission Grating Spectrometer on board the Chandra satellite. Below 3 keV, three narrow emission lines are found at 1.47, 2.0, and 2.6 keV. The 1.47 and 2.6 keV lines are probably identified with Lyalpha emission from Mg XII and S XVI, respectively. The identification of the feature at ~2.0 keV is uncertain because of the presence of an instrumental feature at the same energy. The iron Kalpha line at ~6.5 keV is found …
The iron K-shell features of MXB 1728-34 from a simultaneous Chandra-RXTE observation
2005
We report on a simultaneous Chandra and RossiXTE observation of the low-mass X-ray binary atoll bursting source MXB 1728-34 performed on 2002 March 3-5. We fit the 1.2-35 keV continuum spectrum with a blackbody plus a Comptonized component. Large residuals at 6-10 keV can be fitted by a broad (FWHM ~ 2 keV) Gaussian emission line or, alternatively, by two absorption edges associated with lowly ionized iron and Fe XXV/XXVI at ~7.1 keV and ~9 keV, respectively. In this interpretation, we find no evidence of broad, or narrow, emission lines between 6 and 7 keV. We test our alternative modelling of the iron K shell region by reanalysing a previous BeppoSAX observation of MXB 1728-34, finding a …
Timing Properties and Spectral States in Aquila X‐1
2003
We have analyzed five X-ray outbursts of the neutron-star soft X-ray transient Aql X-1 and investigated the timing properties of the source in correlation with its spectral states as defined by different positions in the color-color and hardness-intensity diagrams. The hard color and the source count rate serve as the distinguishing parameters giving rise to three spectral states: a low-intensity hard state, an intermediate state and a high-intensity soft state. These states are respectively identified with the extreme island, island and banana states that characterize the atoll sources. The large amount of data analyzed allowed us to perform for the first time a detailed timing analysis of…
The BeppoSAX 0.1–18 keV spectrum of the bright atoll source GX 9+1: an indication of the source distance
2005
We report the results of a long, 350 ks, BeppoSAX observation of the bright atoll source GX 9+1 in the 0.12-18 keV energy range. During this observation GX 9+1 showed a large count rate variability in its lightcurve. From its color-color diagram we selected six zones and extracted the source energy spectrum from each zone. We find that the model, composed of a blackbody plus a Comptonized component absorbed by an equivalent hydrogen column of ~1.4 ¿ 1022 cm-2, fits the spectra in the energy range 1-18 keV well; however, below 1 keV a soft excess is present. We find that the spectrum of GX 9+1, in the 0.12-18 keV energy range, is well fitted by the model above, if we use an equivalent hydrog…
On the soft excess in the x-ray spectrum of circinus X-1: Revisitation of the distance to circinus X-1
2005
We report on a 300 ks BeppoSAX (0.12-200 keV) observation of Circinus X-1 (Cir X-1) at phases between 0.62 and 0.84 and on a 90 ks BeppoSAX observation of Cir X-1 at phases 0.11-0.16. Using the canonical model adopted until now to fit the energy spectrum of this source, large residuals appear below 1 keV. These are well fitted using an equivalent hydrogen column of 0.66¿1022 cm-2, adding absorption edges of O VII, O VIII, and Ne IX in the spectra extracted from the observation at phases 0.62-0.84 and adding absorption edges of O VII, O VIII, Mg XI, and Mg XII and absorption lines of O VIII and Mg XII in the spectra extracted from the observation at phases 0.11-0.16. During the observation a…
The BeppoSAX 0.1 - 18 keV Spectrum of the Bright Atoll Source GX 9+1: an Indication of the Source Distance
2005
We report the results of a long, 350 ks, BeppoSAX observation of the bright atoll source GX 9+1 in the 0.12 - 18 keV energy range. During this observation GX 9+1 showed a large count rate variability in its lightcurve. From its color - color diagram we selected six zones and extracted the source energy spectrum from each zone. We find that the model, composed of a blackbody plus a Comptonized component absorbed by an equivalent hydrogen column of similar to 1.4 x 10(22) cm(-2), fits the spectra in the energy range 1 - 18 keV well; however, below 1 keV a soft excess is present. We find that the spectrum of GX 9+1, in the 0.12 - 18 keV energy range, is well fitted by the model above, if we us…