arXiv subjects
Publications and source records attributed to J. Rodriguez.
We present preliminary results of an observation of Cygnus X-1 with INTEGRAL performed on June 7-11 2003. Both spectral and variability properties of the source indicate that Cygnus X-1 was in an intermediate state. As expected during state transitions, we find an anticorrelation between the 3-10 keV and the 15 GHz radio fluxes and a strong correlation between the 3-200 keV hardness and radio flux.
We report here the first results of the spectral and timing analysis of our simultaneous INTEGRAL/RXTE observations of GRS 1915+105. The first observation ever performed with INTEGRAL revealed a new class of variability, where changes of luminosity seem driven by changes in the Comptonising medium. The spectro-temporal study of our data taken later, in the steady state, could show the influence of the compact jet in the hard X-rays.
The millisecond pulsar PSR B1259-63 and the Be star SS2883 are situated in a highly eccentric binary system, with orbital period ~3.4 years. We report on hard X-ray observations obtained with the INTEGRAL satellite close to the 2004 periastron passage. These are the first imaging observations of this system in the hard X-ray range (>20 keV) and allow the emission of PSR B1259-63 to be separated from that of a nearby unidentified variable source which may have contaminated previous hard X-ray observations of this system. Using the IBIS/ISGRI instrument we measured a flux of ~2--6 mCrab in the 20--200 keV range, with a power law spectrum of photon index of 1.3 +/- 0.5.
IGR J16320-4751 was re-discovered by IBIS/ISGRI on board INTEGRAL in early February 2003 during the observation of the black hole candidate 4U 1630-47 (PI Tomsick). This source, already observed by ASCA and BeppoSAX, belongs to the class of heavily absorbed objects (N_H > 10^23 cm^-2) that populate some arms of the Galaxy. Soon after the rediscovery by IBIS/ISGRI, the source was observed by XMM-Newton: the arcsec position found with XMM allowed ones to find the most likely infrared counterpart. We present here the reanalysis of the high energy emission from IGR J16320-4751 detected by IBIS/ISGRI, including the spectral and temporal characteristics. We also present a reanalysis of the XMM-Newton and optical/IR data.
We report the results of extensive high-energy observations of the X-ray transient and black hole candidate XTE J1720-318 performed with INTEGRAL, XMM-Newton and RXTE. The source, which underwent an X-ray outburst in 2003 January, was observed in February in a spectral state dominated by a soft component with a weak high-energy tail. The XMM-Newton data provided a high column density Nh of 1.2*e22 cm^{-2} which suggests that the source lies at the Galactic Centre distance. The simultaneous RXTE and INTEGRAL Target of Opportunity observations allowed us to measure the weak and steep tail, typical of a black-hole binary in the so-called High/Soft State. We then followed the evolution of the source outburst over several months using the INTEGRAL Galactic Centre survey observations. The source became active again at the end of March: it showed a clear transition towards a much harder state, and then decayed to a quiescent state after April. In the hard state, the source was detected up to 200 keV with a power law index of 1.9 and a peak luminosity of 7*e36 erg s^{-1} in the 20-200 keV band, for an assumed distance of 8 kpc. We conclude that XTE J1720-318 is indeed a new member of the black hole X-ray novae class which populate our galactic bulge and we discuss its properties in the frame of the spectral models used for transient black hole binaries.
We report on the timing analysis of RXTE observations of the Galactic micro-quasar GRS 1915+105 performed in 2003. Out of a total of six times ~20 ks, we focus here only on the three observations during which GRS 1915+105 is found in a steady C-state (referred to as class $χ$) resulting in a total of \~50 ks. During these observations, we detect low frequency quasi-periodic oscillations with high (~14 %) rms amplitude in the 2-40 keV energy range. Contrary to what is usually observed in GRS 1915+105, in most of our observations the QPO frequency presents no correlation with the RXTE/PCA count rate, nor with the RXTE/ASM count rate. We present, for the first time, high resolution (22 spectral channels) 2-40 keV spectral fits of the energy dependence of the QPO amplitude (``QPO spectra''). The QPO spectra are well modeled with a cut-off power law except on one occasion where a single power law gives a satisfactory fit (with no cut-off at least up to ~40 keV). The cut-off energy evolves significantly from one observation to the other, from a value of ~21.8 keV to ~30 keV in the other observations where it is detected. We discuss the possible origin of this behavior and suggest that the compact jet detected in the radio contributes to the hard X-ray (> 20 keV) mostly through synchrotron emission, whereas the X-ray emitted below 20 keV would originate through inverse Compton scattering. The dependence of the QPO amplitude on the energy can be understood if the modulation of the X-ray flux is contained in the Comptonized photons and not in the synchrotron ones.
IGR J19140+0951 (formerly known as IGR J19140+098) was discovered with the INTEGRAL satellite in March 2003. We report the details of the discovery, using an improved position for the analysis. We have performed a simultaneous study of the 5-100 keV JEM-X and ISGRI spectra from which we can distinguish two different states. From the results of our analysis we propose that IGR J19140+0951 is a persistent Galactic X-ray binary, probably hosting a neutron star although a black hole cannot be completely ruled out.
We present the first results of the timing analysis of our RXTE/INTEGRAL monitoring campaign on GRS 1915+105. Over the 6 already performed RXTE observations, we study the presence of Low Frequency QPO (LFQPO), and their energetic dependences. In a view to understand the QPO phenomenon, we compare the QPO properties to the spectral behaviour of the source. We propose that part of the compact jet detected during multi-wavelength observations, could produce a significant amount of hard X-rays, and hence explain the energy dependence of the amplitude of the QPOs.
We report on RXTE observations of the microquasar XTE J1550 during a ~70 day outburst in April-June 2000. We focus here on the temporal properties of the source and study the behavior of low frequency (0.1-10 Hz) quasi periodic oscillations (LFQPO), which seem to be of different types. We focus on the so-called type C (according to the classification of Remillard and collaborators), which corresponds to a strong 0.1-6 Hz LFQPO, found to be present during at least 17 observations. We find that the frequency of the QPO is better correlated with the soft X-ray (< 7 keV) flux than with the hard flux (> 7 keV). If soft X-rays represent the behavior of an accretion disk, the relation shows that the disk may set the LFQPO frequency. In two cases, the identification of the type of QPO is not straightforward. If the QPOs in those two cases are type A (or B), then we may be seeing the QPO type alternate between type C and type A (or B), and this may represent some rapid changes in the physical properties of the accretion flow, before the system stabilizes and slowly decays toward the end of the outburst. On the other hand, if all the QPOs are of type C, we may be observing an inversion in the frequency vs. flux relation, similar to that seen in GRO J1655-40. We discuss the QPO behavior in the framework of theoretical models.
Our collaboration is responsible for the study of a sample of 72 low mass X-ray binaries (LMXRB) using the INTEGRAL Core Programme data. In this paper we describe the monitoring programme we have started and the current variability and spectral results on a sample of 8 persistently bright LMXRBs hosting a neutron star (Z and Atoll sources). Current results show that among our sample of sources there seems to be no important difference in the variability of Z sources with respect to Atolls and the first colour-colour and hardness intensity diagrams built in the "traditional" energy bands display the expected patterns. Z sources seem to be harder than the bright Atolls of our sample (above 20 keV) and present no evident cut-off until about 50 keV. A hint of a non-thermal hard tail is seen in Sco X-1 with ISGRI and SPI, similarly to what was previously detected by D'Amico et al. (2001) with RXTE. These results, even if preliminary, show the importance of such a programme and the potential underlying it to understand these sources as a class.
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.
The INTEGRAL Science Data Centre (ISDC) routinely monitors the Near Real Time data (NRT) from the INTEGRAL satellite. A first scientific analysis is made in order to check for the detection of new, transient or highly variable sources in the data. Of primary importance for this work is the Interactive Quick Look Analysis (IQLA), which produces JEM-X and ISGRI images and monitors them for interesting astrophysical events
We present the international collaboration MINE (Multi-lambda Integral NEtwork) aimed at conducting multi-wavelength observations of X-ray binaries and microquasars simultaneously with the INTEGRAL gamma-ray satellite. We will focus on the 2003 March-April campaign of observations of the peculiar microquasar GRS 1915+105 gathering radio, IR and X-ray data. The source was observed 3 times in the plateau state, before and after a major radio and X-ray flare. It showed strong steady optically thick radio emission corresponding to powerful compact jets resolved in the radio images, bright near-infrared emission, a strong QPO at 2.5 Hz in the X-rays and a power law dominated spectrum without cutoff in the 3-300 keV range. We compare the different observations, their multi-wavelength light curves, including JEM-X, ISGRI and SPI, and the parameters deduced from fitting the spectra obtained with these instruments on board INTEGRAL.
IGR J19140+098 was discovered during the early INTEGRAL observations of GRS1915+105 in March 2003. The following observations by INTEGRAL and RXTE show significant variability on various time scales from 100s to 1ks, but no pulsations. The ISGRI spectra show strong spectral variability in the 20-80keV range. Combined JEMX_2-ISGRI spectra are well fitted by a power-law and a thermal emission model with a rather high temperature. RXTE data also reveal an apparently broad ionised iron line not detected in earlier INTEGRAL observations. These results are compatible with a galactic X-ray binary source.
We present the international collaboration MINE (Multi-lambda INTEGRAL NEtwork) aimed at conducting multi-wavelength observations of microquasars simultaneously with the INTEGRAL satellite. The first results on GRS 1915+105 are encouraging and those to come should help us to understand the physics of the accretion and ejection phenomena around a compact object.
We present the first results of simultaneous INTEGRAL and RXTE observations of the microquasar GRS 1915+105. We focus on the analysis of the unique highly variable observation and show that we might have observed a new class of variability. We then study the energetic dependence of a low frequency QPO from our steady observations.
We present observations with XMM-Newton of M33 X-8, the ultraluminous X-ray source (L_{0.5-10 keV} ~ 2x10^39 erg/s) closest to the centre of the galaxy. The best-fit model is similar to the typical model of Galactic black holes in very high state. Comparison with previous observations indicates that the source is still in a very high state after about 20 years of observations. No state transition has been observed even during the present set of XMM-Newton observations. We estimate the lower limit of the mass of the black hole >6 M_sun, but with proper parameters taking into account different effects, the best estimate becomes 12 M_sun. Our analysis favours the hypothesis that M33 X-8 is a stellar mass black hole candidate, in agreement with the findings of other authors. In addition, we propose a different model where the high luminosity of the source is likely to be due to orientation effects of the accretion disc and anisotropies in the Comptonized emission.
The imager on board INTEGRAL (IBIS) presently provides the most detailed sky images ever obtained at energies above 30 keV. The telescope is based on a coded aperture imaging system which allows to obtain sky images in a large field of view 29deg x 29deg with an angular resolution of 12'. The System Point Spread Function of the telescope and its detailed characteristics are here described along with the specific analysis algorithms used to derive the accurate point-like source locations. The derived location accuracy is studied using the first in-flight calibration data on strong sources for the IBIS/ISGRI system. The dependence of the calibrated location accuracy with the signal to noise ratio of the sources is presented. These preliminary studies demonstrate that the IBIS/ISGRI telescope and the standard scientific analysis software allow source localizations with accuracy at 90% confidence level better than 1' for sources with signal to noise ratios > 30 over the whole field of view, in agreement with the expected performances of the instrument.