arXiv subjects

Ph. Durouchoux

Publications and source records attributed to Ph. Durouchoux.

18 recordsLinked to original sources

arXiv2005

Characterizing a new class of variability in GRS 1915+105 with simultaneous INTEGRAL/RXTE observations

We report on the analysis of 100 ks INTEGRAL observations of the Galactic microquasar GRS 1915+105. We focus on INTEGRAL Revolution number 48 when the source was found to exhibit a new type of variability as preliminarily reported in Hannikainen et al. (2003). The variability pattern, which we name $ξ$, is characterized by a pulsing behaviour, consisting of a main pulse and a shorter, softer, and smaller amplitude precursor pulse, on a timescale of 5 minutes in the JEM-X 3-35 keV lightcurve. We also present simultaneous RXTE data. From a study of the individual RXTE/PCA pulse profiles we find that the rising phase is shorter and harder than the declining phase, which is opposite to what has been observed in other otherwise similar variability classes in this source. The position in the colour-colour diagram throughout the revolution corresponds to State A (Belloni et al. 2000) but not to any previously known variability class. We separated the INTEGRAL data into two subsets covering the maxima and minima of the pulses and fitted the resulting two broadband spectra with a hybrid thermal--non-thermal Comptonization model. The fits show the source to be in a soft state characterized by a strong disc component below ~6 keV and Comptonization by both thermal and non-thermal electrons at higher energies.

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arXiv2004

SPI observations of positron annihilation radiation from the 4th galactic quadrant: Spectroscopy

The status of the analysis of the electron/positron annihilation radiation performed by INTEGRAL/SPI in the 4th GALACTIC QUADRANT is reported. We use data from the first two Galactic Center Deep Exposures (GCDE) and from the Galactic Plane Scans (GPS). The analysis presented here is focused on the spectroscopic aspects of the electron/positron annihilation radiation. Background substraction and model fitting methods are described, and the parameters of the 511 keV line (flux, energy, and width) are deduced.

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arXiv2004

SPI observations of positron annihilation radiation from the 4th galactic quadrant: sky distribution

During its first year in orbit the INTEGRAL observatory performed deep exposures of the Galactic Center region and scanning observations of the Galactic plane. We report on the status of our analysis of the positron annihilation radiation from the 4th Galactic quadrant with the spectrometer SPI, focusing on the sky distribution of the 511 keV line emission. The analysis methods are described; current constraints and limits on the Galactic bulge emission and the bulge-to-disk ratio are presented.

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arXiv2004

GRS 1915+105: The first three months with INTEGRAL

GRS 1915+105 is being observed as part of an Open Time monitoring program with INTEGRAL. Three out of six observations from the monitoring program are presented here, in addition to data obtained through an exchange with other observers. We also present simultaneous RXTE observations of GRS 1915+105. During INTEGRAL Revolution 48 (2003 March 6) the source was observed to be in a highly variable state, characterized by 5-minute quasi-periodic oscillations. During these oscillations, the rise is faster than the decline, and is harder. This particular type of variability has never been observed before. During subsequent INTEGRAL revolutions (2003 March-May), the source was in a steady or ''plateau'' state (also known as class $χ$ according to Belloni et al. 2000). Here we discuss both the temporal and spectral characteristics of the source during the first three months of observations. The source was clearly detected with all three gamma-ray and X-ray instruments onboard INTEGRAL.

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arXiv2003

First INTEGRAL observations of GRS 1915+105

We present data from the first of six monitoring Open Time observations of GRS 1915+105 undertaken with the orbiting INTEGRAL satellite. The source was clearly detected with all three X-ray and gamma-ray instruments on board. GRS 1915+105 was in a highly variable state, as demonstrated by the JEM X-2 and ISGRI lightcurves. These and simultaneous RXTE/PCA lightcurves point to a novel type of variability pattern in the source. In addition, we fit the combined JEM X-2 and ISGRI spectrum between 3-300 keV with a disk blackbody + powerlaw model leading to typical parameter values found earlier at similar luminosity levels. A new transient, IGR J19140+098, was discovered during the present observation.

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arXiv2003

Early SPI/INTEGRAL measurements of galactic 511 keV line emission from positron annihilation

We report the first measurements of the 511 keV line emission from the Galactic Centre (GC) region performed with the spectrometer SPI on the space observatory INTEGRAL (International Gamma-Ray Astrophysics Laboratory). Taking into account the range of spatial distribution models which are consistent with the data, we derive a flux of $9.9^{+4.7}_{-2.1} \times 10^{-4}$ ph cm$^{-2}$ s$^{-1}$ and an intrinsic line width of $2.95^{+0.45}_{-0.51}$ keV (FWHM). The results are consistent with other high-spectroscopy measurements, though the width is found to be at the upper bound of previously reported values.

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arXiv2002

BeppoSAX observations of the EXS 1737.9-2952 region II: Analysis of sources

(Abridged) Spectral and time variability analysis of the region of the hard X-ray transient EXS 1737.9-2952 near the Galactic Centre (GC), using data from the Narrow Field Instruments of BeppoSAX is reported. The main results are the MECS spectra of the 10 identified sources. Fluxes obtained with spectral fits are 1.7-4.8E-12 erg / cm2 s. The absorption is in the range N_H=0.5-6.7E22 / cm2, indicating that the sources are at least at the distance of the GC, and thus have L_x > 2-5E34 erg/s (2-10 keV). A powerlaw with photon index 1.1-1.8 generally gives a fair fit, but a strong iron line (at 6-7 keV) is evident for 5 sources and exists at lower confidence in the others. The fits indicate differences in line position in the range 6.1-7.0 keV suggesting that the ionisation state and/or emission mechanism may not be the same in all sources. The time-binned data indicates that two sources are variable on a time scale of hours at confidence > 99.99%, and one at 99.67%. These sources could be low-mass X-ray binaries. The other sources are most probably X-ray binaries or SNRs. A MECS spectrum from a subfield including 8 of the new sources and a major contribution of diffuse emission yielded a fairly good fit to a power-law spectrum with photon index 1.3 and a strong iron line at 6.8 keV. Another field with only residual emission and no point sources yielded spectral parameters close to the diffuse emission near GC observed by other investigators, except for the high interstellar absorption. The PDS spectrum of the same region is more difficult to interpret due to lack of spatial resolution and a larger FOV that contains the bright hard X-ray source 1E1740.7-2942. The source for the hard X-ray transient EXS 17137.9-2952 cannot be identified from the present observations.

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arXiv2002

Accretion-ejection instability and QPO in black hole binaries. I. Observations

This is the first of two papers in which we address the physics of the low-frequency Quasi-Periodic Oscillation (QPO) of X-ray binaries, in particular those hosting a black hole. We discuss and repeat the recent analysis and spectral modelling of the micro-quasar GRO J1655 by Sobczak et al (2000, hereafter SMR), and compare it with GRS 1915; this leads us to confirm and analyze in more detail the different behavior noted by SMR, between GRO J1655 and other sources, when comparing the correlation between the QPO frequency and the disk inner radius. In a companion paper (Varniere et al., 2002, hereafter Paper II) we will show that these opposite behaviors can be explained in the context of the Accretion-Ejection Instability recently presented by Tagger and Pellat (1999). We thus propose that the difference between GRO J1655 and other sources comes from the fact that in the former, observed in a very high state, the disk inner radius always stays close to the Last Stable Orbit. In the course of this analysis, we also indicate interesting differences between the source properties, when the spectral fits give an anomalously low inner disk radius. This might indicate the presence of a spiral shock or a hot point in the disk.

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arXiv2002

Energy Dependence of a Low Frequency QPO in GRS 1915+105

We analyze a set of three RXTE Target of Opportunity observations of the Galactic microquasar GRS 1915+105, observed on April 2000, during a multi-wavelength campaign. During the three observations, a strong, variable low frequency (2-9 Hz) quasi periodic oscillation (hereafter QPO), often referred to as the ubiquitous QPO, is detected together with its first harmonic. We study the spectral properties of both features, and show that : 1) their frequency variations are better correlated with the soft X-ray flux (2-5 keV), favoring thus the location of the QPO in the accretion disk; 2) the QPO affects more the hard X-rays, usually taken as the signature of an inverse compton scattering of the soft photons in a corona; 3) the fundamental and its harmonic do not behave in the same manner: the fundamental sees its power increase with the energy up to 40 keV, whereas the harmonic increases up to $\sim 10$ keV. The results presented here could find an explanation in the context of the Accretion-Ejection Instability, which could appear as a rotating spiral or hot point located in the disk, between its innermost edge and the corotation radius. The presence of the harmonic could then be a signature of the non-linear behavior of the instability. The high-energy (>40 keV) decrease of the fundamental would favor an interpretation where most or all of the quasi-periodic modulation at high energies comes, not from the comptonized corona as usually assumed, but from a hot point in the optically thick disk

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arXiv2002

Chandra Observation of SNR G54.1+0.3 -- a Close Cousin of the Crab Nebula

We present a {\it Chandra} ACIS observation of SNR G54.1+0.3. This supernova remnant is resolved into several distinct X-ray emitting components: a central bright point-like source (CXOU J193030.13+185214.1), a surrounding ring, bipolar elongations, plus low surface brightness diffuse emission. The spectra of these components are all well described by power-law models; the spectral index steepens with increasing distance from the point-like source. We find no evidence for any thermal plasma emission that would correspond to shocked interstellar medium or ejecta. The observed morphological and spectral characteristics suggest that G54.1+0.3 is the closest ``cousin'' of the Crab Nebula -- a pulsar wind nebula driven by a combination of equatorial and polar outflows from the putative pulsar represented by the point-like X-ray source.

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arXiv2001

Evolution of Iron K$_α$ Line Emission in the Black Hole Candidate GX 339-4

GX 339-4 was regularly monitored with RXTE during a period (in 1999) when its X-ray flux decreased significantly (from 4.2$\times 10^{-10}$ erg cm$^{-2} s^{-1}$ to 7.6$\times 10^{-12}$ erg cm$^{-2}$s$^{-1}$ in the 3--20 keV band), as the source settled into the ``off state''. Our spectral analysis revealed the presence of a prominent iron K$_α$ line in the observed spectrum of the source for all observations. The line shows an interesting evolution: it is centered at $\sim$6.4 keV when the measured flux is above 5$\times 10^{-11}$ erg cm$^{-2} s^{-1}$, but is shifted to $\sim$6.7 keV at lower fluxes. The equivalent width of the line appears to increase significantly toward lower fluxes, although it is likely to be sensitive to calibration uncertainties. While the fluorescent emission of neutral or mildly ionized iron atoms in the accretion disk can perhaps account for the 6.4 keV line, as is often invoked for black hole candidates, it seems difficult to understand the 6.7 keV line with this mechanism, because the disk should be less ionized at lower fluxes (unless its density changes drastically). On the other hand, the 6.7 keV line might be due to recombination cascade of hydrogen or helium like iron ions in an optically thin, highly ionized plasma. We discuss the results in the context of proposed accretion models.

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arXiv2000

The Accretion Ejection Instability : Observationnal Tests

The Accretion Ejection Instability (hereafter AEI), has been proposed to explain, the energy and angular momentum transport from the innermost parts of accretion disks in the X-Ray Binaries (XB), (permitting thus the accretion), toward a coronal medium, which is thought to be the base of jets (Tagger & Pellat, 1999; Tagger 1999, Varnière et al., 2000; Corbel, phD Thesis, 1999). The low frequency QPO often observed in the XB's, are theorically predicted with the AEI; furthemore theorical calculations in a strong gravitationnal field (Varnière, Rodriguez & Tagger, 2000) lead to an unexpected behavior when looking at the QPO frequency variations vs. the disk radius. We the analysed a set of public observations of GRO J1655-40 and GRS 1915+105, in order to verify the theorical predictions. We 'll see in particular that they have different behavior, and will point out interesting differences between the two sources when the model gives unrealistic low values of the disk radius.

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arXiv1999

Space Positronium Detection by Radio Measurements

The possibility of positronium detection at radio wavelengths is investigated in detail. For orthopositronium, the fine structure lines of the n = 2 level (1.62 cm, 2.30 cm and 3.48 cm) may be probably detected by radiotelescopes of next generations with the sensitivity around 1 microJansky. The spin-flip line of the ground state (0.147 cm) may be observed from sources with a narrow annihilation line by modern telescopes with the sensitivity around 10 microJansky. In the fine structure and spin-flip lines a maser effect is produced. The expected radio fluxes in the spin-flip line can reach detected limits for certain source geometries and optimal physical conditions inside the source.

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arXiv1999

Simultaneous Observations of GRS 1758-258 in 1997 by VLA, IRAM, SEST, RXTE and OSSE: Spectroscopy and Timing

We report the results of our multi-wavelength observations of GRS 1758-258 made in August 1997. The energy bands include radio, millimeter, X-ray, and gamma-ray. The observations enable us to obtain a complete spectrum of the source over an energy range of 2 - 500 keV. The spectrum shows that GRS 1758-258 was in its hard state. It is well fitted by the Sunyaev-Titarchuk (ST) Compton scattering model. The spectrum is also fit by a power law with an exponential cutoff (PLE) plus a soft black-body component. The temperature of the soft component is about 1.2 keV, and the energy flux is less than 1.5% of the total X- and gamma-ray flux. The deduced hydrogen column density is in the range of (0.93 - 2.0) 10^{22} cm^{-2}. No significant iron lines are detected. The radio emission has a flat energy spectrum. The daily radio, X-ray and gamma-ray light curves show that GRS 1758-258 was stable during the observation period, but was highly variable on smaller time scales in X- and gamma-rays. The power density spectra are typical for the low-state, but we find the photon flux for the 5 to 10 keV band to be more variable than that in the other two energy bands (2 - 5 keV and 10 - 40 keV). Harmonically spaced quasi-periodic oscillations (QPOs) are observed in the power spectra. The phase lags between the hard photons and the soft photons have a flat distribution over a wide range of frequencies. A high coherence of about 1.0 (0.01 - 1 Hz) between the hard photons and the soft photons is also obtained in our observations. We compare these results with two variation models. Our millimeter observations did not reveal any conclusive signatures of an interaction between the jet from GRS 1758-258 and the molecular cloud that lies in the direction of GRS 1758-258.

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arXiv1998

Observations of GX 339-4 in 1996

GX 339-4 is an unusual black hole candidate in that it is a persistent source, being detected by X-ray telescopes most of the time, but it also has nova-like flaring states. In 1996 we performed radio, optical, X-ray, and gamma-ray observations of GX 339-4 when it was in a hard state (= soft X-ray low state). Here we present a brief summary of some of the results.

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arXiv1998

Multiwavelength Observations of GX 339-4 in 1996. I. Daily Light Curves and X-ray and Gamma-Ray Spectroscopy

As part of our multiwavelength campaign of GX 339-4 observations in 1996 we present our radio, X-ray, and gamma-ray observations made in July, when the source was in a hard state (= soft X-ray low state). The radio observations were made at the time when there was a possible radio jet. We show that the radio spectrum was flat and significantly variable, and that the radio spectral shape and amplitude at this time were not anomalous for this source. Daily light curves from our pointed observation July 9-23 using OSSE, from BATSE, and from the ASM on RXTE also show that there was no significant change in the X- and gamma-ray flux or hardness during the time the possible radio jet-like feature was seen. The higher energy portion of our pointed RXTE observation made July 26 can be equally well fit using simple power law times exponential (PLE) and Sunyaev-Titarchuk (ST) functions. An additional soft component is required, as well as a broad emission feature centered on 6.4 keV. This may be an iron line that is broadened by orbital Doppler motions and/or scattering off a hot medium. Its equivalent width is 600 eV. Our simplistic continuum fitting does not require an extra reflection component. Both a PLE and a ST model also fit our OSSE spectrum on its own. Although the observations are not quite simultaneous, combining the RXTE and CGRO spectra we find that the PLE model easily fits the joint spectrum. However, the ST model drops off too rapidly with increasing energies to give an acceptable joint fit.

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arXiv1997

Two-phase spectral modelling of 1E1740.7-2942

Combined ASCA and SIGMA data of 1E1740.7-2942 during the standard state (September 1993 and 1994) were fitted with two-phase models (ISMBB/Poutanen at al. and ADAF/Narayan et al.). In ISMBB's, the radius of the spherical hot (Te = 150 - 200 KeV) corona lies between 200 - 250 km where it joins the classical inner disc. The disc radiates 40 per cent of the total luminosity with 1.7 per cent of the Eddington accretion rate of 10 solar mass black hole. ADAF's need an extra component to reproduce the soft part of the spectrum. However, the origin of the soft excess remains somewhat uncertain, although special care was taken in the background elimination.

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arXiv1996

The Great Annihilator 1E1740.7-2942: Molecular cloud connection and coronal structure

Using 12CO and 13CO observations we present column density maps of the molecular cloud (V = -135 km/s) in the direction of 1E1740.7-2942. Hydrogen column densities of the cloud scatter between (3.5 - 11) 10**22 cm-2, depending on the method used. From this we conclude, deriving first a simple analytic formula, that despite of the weakness of the iron fluorescent 6.4 keV line (Churazov et al. 1996), the source may lie inside the cloud, or at least close to its edge. The combined ASCA/BATSE spectrum from September 1993 and 1994 can be modelled with a two-phase accretion disc corona model, where the hot region is detached from the cold disc. Geometrically, the hot phase can be interpreted e.g. as a number of active regions (magnetic loops) above the disc, or as a spherical hot cloud around the central object.

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