arXiv subjects

A. Decourchelle

Publications and source records attributed to A. Decourchelle.

At least 37 records · Page 2Linked to original sources

arXiv2006

The signature of 44Ti in Cassiopeia A revealed by IBIS/ISGRI on INTEGRAL

We report the detection of both the 67.9 and 78.4 keV 44Sc gamma-ray lines in Cassiopeia A with the INTEGRAL IBIS/ISGRI instrument. Besides the robustness provided by spectro-imaging observations, the main improvements compared to previous measurements are a clear separation of the two 44Sc lines together with an improved significance of the detection of the hard X-ray continuum up to 100 keV. These allow us to refine the determination of the 44Ti yield and to constrain the nature of the nonthermal continuum emission. By combining COMPTEL, BeppoSAX/PDS and ISGRI measurements, we find a line flux of (2.5 +/- 0.3)*10(-5) cm(-2) s(-1) leading to a synthesized 44Ti mass of 1.6 (+0.6-0.3)*10(-4) solar mass. This high value suggests that Cas A is peculiar in comparison to other young supernova remnants, from which so far no line emission from 44Ti decay has been unambiguously detected.

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arXiv2006

The X-ray emission of the supernova remnant W49B observed with XMM-Newton

In the framework of the study of supernova remnants and their complex interaction with the interstellar medium, we report on an XMM-Newton EPIC observation of the Galactic supernova remnant W49B. We investigate the spatial distribution of the chemical and physical properties of the plasma, so as to get important constraints on the physical scenario, on the dynamics of the supernova explosion, and on the interaction of the supernova remnant with the ambient interstellar clouds. We present line images, equivalent width maps, and a spatially resolved spectral analysis of a set of homogeneous regions. The X-ray spectrum of W49B is characterized by strong K emission lines from Si, S, Ar, Ca and Fe. In all the regions studied, the X-ray spectrum is dominated by the emission from the ejecta and there is no indication of radial stratification of the elements. A high overabundance of Ni (Ni/Ni_sun=10^{+2}_{-1}) is required in the bright central region and the previous detection of Cr and Mn line emission is confirmed. Spectra are well described by two thermal components in collisional ionization equilibrium. We observe spatial variations in the temperature, with the highest temperature found in the east and the lowest in the west. Our results support a scenario in which the X-ray emission comes from ejecta interacting with a dense belt of ambient material, but another possibility is that the remnant is the result of an asymmetric bipolar explosion with the eastern jet being hotter and more Fe-rich than the western jet. The eastern jet is confined by interaction with ambient molecular clouds. Comparison of the observed abundances with yields for hypernova and supernova nucleosynthesis does not directly support the association of W49B with a gamma-ray burst, although it remains possible.

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arXiv2006

An INTEGRAL/IBIS view of Young Galactic SNRs through the 44Ti gamma-ray lines

We present preliminary results of INTEGRAL/IBIS observations on Cas A, Tycho and Vela Junior Supernova remnants in the line emission of 44Ti. This radioactive nucleus is thought to be exclusively produced in supernovae during the first stages of the explosion. It has a lifetime of about 87 y and is then the best indicator of young SNRs, as exemplified by the detection of 44Ti in the youngest known Galactic SNR Cas A with GRO/COMPTEL and latter with BeppoSAX. In this paper, we will focus on this SNR for which we confirm the detection of 44Ti and point out the importance to know the nature of the hard X-ray continuum, the Tycho SNR, for which no indication of 44Ti was ever reported, and Vela Junior, for which the claimed detection of 44Ti with COMPTEL is still controversial. The INTEGRAL/IBIS observations bring new constraints on the nature of these SNRs and on the nucleosynthesis which took place during the explosions.

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arXiv2004

INTEGRAL/SPI Limits on Electron-Positron Annihilation Radiation from the Galactic Plane

The center of our Galaxy is a known strong source of electron-positron 511-keV annihilation radiation. Thus far, however, there have been no reliable detections of annihilation radiation outside of the central radian of our Galaxy. One of the primary objectives of the INTEGRAL (INTErnational Gamma-RAy Astrophysics Laboratory) mission, launched in Oct. 2002, is the detailed study of this radiation. The Spectrometer on INTEGRAL (SPI) is a high resolution coded-aperture gamma-ray telescope with an unprecedented combination of sensitivity, angular resolution and energy resolution. We report results from the first 10 months of observation. During this period a significant fraction of the observing time was spent in or near the Galactic Plane. No positive annihilation flux was detected outside of the central region (|l| > 40 deg) of our Galaxy. In this paper we describe the observations and data analysis methods and give limits on the 511-keV flux.

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arXiv2004

XMM-Newton observations of the supernova remnant RX J1713.7-3946 and its central source

We present new results coming from the observations of the supernova remnant (SNR) RX J1713.7--3946 (also G347.3--0.5) performed in five distinct pointings with the EPIC instrument on board the satellite XMM-Newton. RX J1713.7--3946 is a shell-type SNR dominated by synchrotron radiation in the X-rays. Its emission (emission measure and photon index) as well as the absorption along the line-of-sight has been characterized over the entire SNR. The X-ray mapping of the absorbing column density has revealed strong well constrained variations (0.4 10^22 cm^-2 < NH < 1.1 10^22 cm^-2) and, particularly, a strong absorption in the southwest. Moreover, there are several clues indicating that the shock front of RX J1713.7--3946 is impacting the clouds responsible for the absorption as revealed for instance by the positive correlation between X-ray absorption and X-ray brightness along the western rims. The CO and HI observations show that the inferred cumulative absorbing column densities are in excellent agreement with the X-ray findings in different places of the remnant on condition that the SNR lies at a distance of 1.3 +/- 0.4 kpc, probably in the Sagittarius galactic arm, instead of the commonly accepted value of 6 kpc. An excess in the CO emission is found in the southwest suggesting that the absorption is due to molecular clouds. A search for OH masers in the southwestern region has been unsuccessful, possibly due to the low density of the clouds. The X-ray mapping of the photon index has also revealed strong variations (1.8 < Gamma < 2.6). [See the article for the entire abstract]

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arXiv2003

XMM-Newton observation of SNR RX J1713.7-3946

We present the first results of the observations of the supernova remnant RX J1713.7-3946 (also G347.3-0.5) obtained with the EPIC instrument on board the XMM-Newton satellite. We show a 5 pointings mosaiced image of the X-ray synchrotron emission. We characterize this emission by mapping its spectral parameters (absorbing column density NH and photon index). The synchrotron spectrum is flat at the shock and steep in the interior of the remnant. NH is well correlated with the X-ray brightness. A strong NH is found in the southwest rim of RX J1713.7-3946. We suggest that the SNR is interacting with a HI region there.

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arXiv2003

XMM-Newton observation of Kepler's supernova remnant

We present the first results coming from the observation of Kepler's supernova remnant obtained with the EPIC instruments on board the XMM-Newton satellite. We focus on the images and radial profiles of the emission lines (Si K, Fe L, Fe K) and of the high energy continuum. Chiefly, the Fe L and Si K emission-line images are generally consistent with each other and the radial profiles show that the Si K emission extends to a larger radius than the Fe L emission (distinctly in the southern part of the remnant). Therefore, in contrast to Cas A, no inversion of the Si- and Fe-rich ejecta layers is observed in Kepler. Moreover, the Fe K emission peaks at a smaller radius than the Fe L emission, which implies that the temperature increases inwards in the ejecta. The 4-6 keV high energy continuum map shows the same distribution as the asymmetric emission-line images except in the southeast where there is a strong additional emission. A two color image of the 4-6 keV and 8-10 keV high energy continuum illustrates that the hardness variations of the continuum are weak all along the remnant except in a few knots. The asymmetry in the Fe K emission-line is not associated with any asymmetry in the Fe K equivalent width map. The Si K maps lead to the same conclusions. Hence, abundance variations do not cause the north-south brightness asymmetry. The strong emission in the north may be due to overdensities in the circumstellar medium. In the southeastern region of the remnant, the lines have a very low equivalent width and the X-ray emission is largely nonthermal.

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arXiv2003

The X-ray flaring activity of the galactic nucleus observed with XMM-Newton

We report the results of XMM-Newton observations of Sgr A*, the radiative counterpart of the massive black hole at the nucleus of our Galaxy, performed in the frame of the guaranteed time survey program of the Galactic Center region. The discovery of bright X-ray flares from Sgr A* with Chandra in October 2000 have opened new perspectives to understand the processes at work in this object and in general in black holes accreting at low accretion rates. We report here the important results obtained with XMM-Newton on the Sgr A* high-energy flaring activity and we discuss the implications on the models and the future observational perspectives.

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arXiv2003

XMM-Newton observation of the brightest X-ray flare detected so far from SgrA*

We report the high S/N observation on October 3, 2002 with XMM-Newton of the brightest X-ray flare detected so far from SgrA* with a duration shorter than one hour (~ 2.7 ks). The light curve is almost symmetrical with respect to the peak flare, and no significant difference between the soft and hard X-ray range is detected. The overall flare spectrum is well represented by an absorbed power-law with a soft photon spectral index of Gamma=2.5+/-0.3, and a peak 2-10 keV luminosity of 3.6 (+0.3-0.4) x 10^35 erg/s, i.e. a factor 160 higher than the Sgr A* quiescent value. No significant spectral change during the flare is observed. This X-ray flare is very different from other bright flares reported so far: it is much brighter and softer. The present accurate determination of the flare characteristics challenge the current interpretation of the physical processes occuring inside the very close environment of SgrA* by bringing very strong constraints for the theoretical flare models.

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arXiv2003

XMM-Newton study of the persistent X-ray source 1E1743.1-2843 located in the Galactic Center direction

We report the results of an XMM-Newton observation of the persistent X-ray source 1E1743.1-2843, located in the Galactic Center (GC) direction. We determine the position of the source at alpha_J2000=17h46m21.0s, delta_J2000=-28deg43'44" (with an uncertainty of 1.5"), which is the most accurate to date, and will enable cross-identifications at other wavelengths. The source was bright during this observation (L_2-10keV ~ 2.7 x 10^36 d^2_10kpc erg/s for a power-law continuum), with no significant variability. We propose that 1E1743.1-2843 may be explained in terms of a black hole candidate in a low/hard state. There is an indication that the source exhibits different states from a comparison of our results with previous observations (e.g., ART-P, BeppoSAX). However, the present spectral analysis does not rule out the hypothesis of a neutron star low-mass X-ray binary as suggested previously. If 1E1743.1-2843 is actually located in the GC region, we might expect to observe significant 6.4keV fluorescent iron line emission from nearby molecular clouds (e.g., GCM+0.25+0.01).

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arXiv2003

A New X-Ray Flare from the Galactic Nucleus Detected with the XMM-Newton

The compact radio source Sgr A*, believed to be the counterpart of the massive black hole at the Galactic nucleus, was observed to undergo rapid and intense flaring activity in X-rays with Chandra in October 2000. We report here the detection with XMM-Newton EPIC cameras of the early phase of a similar X-ray flare from this source, which occurred on 2001 September 4. The source 2-10 keV luminosity increased by a factor ~ 20 to reach a level of 4 10$^{34}$ erg s$^{-1}$ in a time interval of about 900 s, just before the end of the observation. The data indicate that the source spectrum was hard during the flare and can be described by simple power law of slope ~ 0.7. This XMM-Newton observation confirms the results obtained by Chandra, suggests that, in Sgr A*, rapid and intense X-ray flaring is not a rare event and therefore sets some constraints on the emission mechanism models proposed for this source.

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arXiv2002

A New X-Ray Flare from the Galactic Nucleus Detected with the XMM-Newton Photon Imaging Cameras

Sgr A*, the compact radio source, believed to be the counterpart of the massive black hole at the galactic nucleus, was observed to undergo rapid and intense flaring activity in X-rays with Chandra in October 2000. We report here the detection with XMM-Newton EPIC cameras of the early phase of a similar X-ray flare from this source, which occurred on September 4, 2001. The source 2-10 keV luminosity increased by a factor about 20 to reach a level of 4 10^{34} erg s^{-1} in a time interval of about 900 s, just before the end of the observation. The data indicate that the source spectrum was hard during the flare. This XMM-Newton observation confirms the results obtained by Chandra and suggests that, in Sgr A*, rapid and intense X-ray flaring is not a rare event. This can constrain the emission mechanism models proposed for this source, and also implies that the crucial multiwavelength observation programs planned to explore the behaviour of the radio/sub-mm and hard X-ray/gamma-ray emissions during the X-ray flares, have a good chance of success.

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arXiv2002

XMM-Newton spectral analysis of the Pulsar Wind Nebula within the composite SNR G0.9+0.1

We present a study of the composite supernova remnant G0.9+0.1 based on observations by XMM-Newton. The EPIC spectrum shows diffuse X-ray emission from the region corresponding to the radio shell. The X-ray spectrum of the whole Pulsar Wind Nebula is well fitted by an absorbed power-law model with a photon index Gamma ~ 1.9 and a 2-10 keV luminosity of about 6.5 X 10^34 d^2_10 erg s^-1 (d_10 is the distance in units of 10 kpc). However, there is a clear softening of the X-ray spectrum with distance from the core, which is most probably related to the finite lifetime of the synchrotron emitting electrons. This is fully consistent with the plerionic interpretation of the Pulsar Wind Nebula, in which an embedded pulsar injects energetic electrons into its surrounding region. At smaller scales, the eastern part of the arc-like feature, which was first revealed by Chandra observations, shows indications of a hard X-ray spectrum with a corresponding small photon index (Gamma=1.0 +- 0.7), while the western part presents a significantly softer spectrum (Gamma=3.2 +- 0.7). A possible explanation for this feature is fast rotation and subsequent Doppler boosting of electrons: the eastern part of the torus has a velocity component pointing towards the observer, while the western part has a velocity component in the opposite direction pointing away from the observer.

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arXiv2002

First XMM-Newton results on the Pulsar Wind Nebula in the composite supernova remnant G0.9+0.1

We report the results of the XMM-Newton observation of the Pulsar Wind Nebula (PWN) in the composite supernova remnant G0.9+0.1 located in the Galactic Center region. Thanks to the sensitivity of the EPIC cameras, we focus on the first spectral analysis of large and small-scale structures of this PWN using MOS and PN data in combination. Our spatially resolved spectral analysis at large-scale offers a clear indication of a softening of the photon index with distance from the centroid of the nebula (from Gamma_{core}=1.12^{+0.45}_{-0.48} to Gamma=2.42^{+0.19}_{-0.19}), as observed in other known X-ray plerions. A spectral analysis of the small-scale structures in the central region of this PWN, delineates variations of the spectral index within the arc-like feature observed with Chandra: the eastern part has a hard photon index (Gamma ~ 1.2 pm 0.5), while the south-west part has a softer photon index (Gamma ~ 2.8 pm 0.7).

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arXiv2002

XMM-Newton observation of the bursting pulsar GRO J1744-28 in quiescence

The XMM-Newton X-ray observatory performed a pointed observation of the bursting pulsar GRO J1744-28 in April 2001 for about 10 ks during a program devoted to the scan of the Galactic center region. After the discovery of this source by BATSE in December 1995 during a very active bursting phase, it has been in quiescence since April 1997. We present here the first detection of GRO J1744-28 in its quiescent state at a position which is consistent with previous high-energy positions (but not consistent with a proposed IR counterpart). The observed luminosity of the source in quiescence is about 6 orders of magnitude weaker than the luminosity in outburst.

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arXiv2001

XMM-Newton Observation of the Black Hole Microquasar GRS 1758-258

The XMM-Newton X-ray observatory pointed the galactic black hole candidate and microquasar GRS 1758-258 in September 2000 for about 10 ks during a program devoted to the scan of the Galactic Center regions. Preliminary results from EPIC MOS camera data are presented here. The data indicate that the source underwent a state transition from its standard low-hard state to an intermediate state. For the first time in this source the ultra-soft component of the accretion disk, which black hole binaries display in intermediate or high-soft states, was clearly detected and measured thanks to the high spectral capabilities of XMM-Newton.

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arXiv2001

Impacts of a power-law non-thermal electron tail on the ionization and recombination rates

We have investigated the effects of a non-thermal electron population on the ionization and recombination rates. The considered electron distribution is defined as a Maxwellian function below a break energy E_b and as a power-law function of index alpha above this energy. We have calculated the collisional (direct and excitation autoionization) ionization coefficient rates as well as the (radiative and dielectronic) recombination rates. Practical methods are given to calculate these rates in order to be easily included in a computer code. The ionization rates are very sensitive to the non-thermal electron population and can be increased by several orders of magnitude depending on the temperature and parameters of the power-law function (E_b and alpha). The non-thermal electrons have a much weaker effect on the (radiative and dielectronic) recombination rates. We have determined the mean electric charge of elements C, N, O, Ne, Mg, Si, S, Ar, Ca, Fe and Ni for different values of the break energy and power-law index. The ionization balance is affected significantly, whereas the effect is smaller in ionizing plasmas.

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arXiv2000

XMM-Newton observation of the Tycho Supernova Remnant

We present the observation of the Tycho supernova remnant obtained with the EPIC and RGS instruments onboard the XMM-Newton satellite. We compare images and azimuthally averaged radial profiles in emission lines from different elements (silicon and iron) and different transition lines of iron (Fe L and Fe K). While the Fe XVII L line and Si XIII K line images are globally spatially coincident, the Fe K emission clearly peaks at a smaller radius, indicating a higher temperature toward the reverse shock. This is qualitatively the profile expected when the reverse shock, after travelling through the outer power-law density profile, has entered the central plateau of the ejecta. The high energy continuum map has an overall smooth distribution, with a similar extent to the radio emission. Its radial profile peaks further out than the lines emission. Brighter and harder continuum regions are observed with a rough bipolar symmetry in the eastern and western edges. The spectral analysis of the southeastern knots supports spatial variations of the relative abundance of silicon and iron, which implies an incomplete mixing of the silicon and iron layers.

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