S. Corbel

Paris Diderot University, Lutetia Parisorum, Île-de-France, France

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Publications (288)912.19 Total impact

  • [Show abstract] [Hide abstract]
    ABSTRACT: We report the detection of 48 millisecond pulsars (MSPs) out of 75 observed thus far using the LOFAR in the frequency range 110-188 MHz. We have also detected three MSPs out of nine observed in the frequency range 38-77 MHz. This is the largest sample of MSPs ever observed at these low frequencies, and half of the detected MSPs were observed for the first time at frequencies below 200 MHz. We present the average pulse profiles of the detected MSPs, their effective pulse widths and flux densities, and compare these with higher observing frequencies. The LOFAR pulse profiles will be publicly available via the EPN Database of Pulsar Profiles. We also present average values of dispersion measures (DM) and discuss DM and profile variations. About 35% of the MSPs show strong narrow profiles, another 25% exhibit scattered profiles, and the rest are only weakly detected. A qualitative comparison of the LOFAR MSP profiles with those at higher radio frequencies shows constant separation between profile components. Similarly, the profile widths are consistent with those observed at higher frequencies, unless scattering dominates at the lowest frequencies. This is very different from what is observed for normal pulsars and suggests a compact emission region in the MSP magnetosphere. The amplitude ratio of the profile components, on the other hand, can dramatically change towards low frequencies, often with the trailing component becoming dominant. As demonstrated by Dyks et al. (2010) this can be caused by aberration and retardation. This data set enables high-precision studies of pulse profile evolution with frequency, dispersion, Faraday rotation, and scattering in the interstellar medium. Characterizing and correcting these systematic effects may improve pulsar-timing precision at higher observing frequencies, where pulsar timing array projects aim to directly detect gravitational waves.
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    ABSTRACT: We report on a multiwavelength observational campaign of the black hole X-ray binary Swift J1753.5-0127 that consists of an ESO/X-shooter spectrum supported by contemporaneous Swift/XRT+UVOT and ATCA data. ISM absorption lines in the X-shooter spectrum allows us to determine E(B-V)=0.45+/-0.02 along the line-of-sight to the source. We also report detection of emission signatures of He II at 4686 angstrom, H alpha, and, for the first time, H I at 10906 angstrom and Paschen Beta. The double-peaked morphology of these four lines is typical of the chromosphere of a rotating accretion disk. Nonetheless, the paucity of disk features points towards a low level of irradiation in the system. This is confirmed through spectral energy distribution modeling and we find that the UVOT+X-shooter continuum mostly stems from the thermal emission of a viscous disk. We speculate that the absence of reprocessing is due to the compactness of an illumination-induced envelope that fails to reflect enough incoming hard X-ray photons back to the outer regions. The disk also marginally contributes to the Compton-dominated X-ray emission and is strongly truncated, with an inner radius about a thousand times larger than the black hole's gravitational radius. A near-infrared excess is present, and we associate it with synchrotron radiation from a compact jet. However, the measured X-ray flux is significantly higher than what can be explained by the optically thin synchrotron jet component. We discuss these findings in the framework of the radio quiet versus X-ray bright hypothesis, favoring the presence of a residual disk, predicted by evaporation models, that contributes to the X-ray emission without enhancing the radio flux.
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    ABSTRACT: After 25 years of quiescence, the microquasar V404 Cyg entered a new period of activity in June 2015. This X-ray source is known to undergo extremely bright and variable outbursts seen at all wavelengths. It is therefore an object of prime interest to understand the accretion-ejection connections. These can, however, only be probed through simultaneous observations at several wavelengths. We made use of the INTEGRAL instruments to obtain long, almost uninterrupted observations from the optical V-band, up to the soft gamma-rays. V404 Cyg was extremely variable in all bands, with the detection of 18 flares with fluxes exceeding 6 Crab (20-40 keV) within 3 days. The flare recurrence can be as short as 20~min from peak to peak. A model-independent analysis shows that the >6 Crab flares have a hard spectrum. A preliminary 10-400 keV spectral analysis of the off-flare and flare periods shows that the variation in intensity is likely to be due to variations of a cut-off power law component only. At X-ray and gamma-ray energies the flares are very well correlated. The optical activity is also correlated with the high energy one, although there is no one-to-one correlation. Instead the optical flares seem to be at least of two different types: one occurring in simultaneity with the X-ray flares, the other showing a delay greater than 10 min. The former could be associated with X-ray reprocessing by either an accretion disk or the companion star. We suggest that the latter are associated with plasma ejections that have also been seen in radio.
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    ABSTRACT: We present results from multi-wavelength simultaneous X-ray and radio observations of the black hole X-ray binary V404 Cyg in quiescence. Our coverage with NuSTAR provides the very first opportunity to study the X-ray spectrum of V404 Cyg at energies above 10 keV. The unabsorbed broad-band (0.3-30 keV) quiescent luminosity of the source is 8.9$\times$10$^{32}$ erg s$^{-1}$ for a distance of 2.4 kpc. The source shows clear variability on short time scales in radio, soft X-ray and hard X-ray bands in the form of multiple flares. The broad-band X-ray spectra obtained from XMM-Newton and NuSTAR can be characterized with a power-law model having photon index {\Gamma}=2.13$\pm$0.07 (90% confidence errors); however, residuals at high energies indicate spectral curvature significant at a 3{\sigma} confidence level with e-folding energy of the cutoff to be 19$^{+19}_{-7}$ keV. Such curvature can be explained using synchrotron emission from the base of a jet outflow. Radio observations using the JVLA reveal that the spectral index evolves on very fast time-scales, switching between optically thick and thin synchrotron emission, possibly due to instabilities in the compact jet or stochastic instabilities in accretion rate. We explore different scenarios to explain this fast variability.
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    ABSTRACT: (abridged) We report on multi-wavelength measurements of Swift J1753.5-0127 in the hard state at L=2.7e36 erg/s (assuming d=3 kpc) in 2014. The radio emission is optically thick synchrotron, presumably from a compact jet. We take advantage of the low extinction and model the near-IR to UV emission with a multi-temperature disk model. Assuming a BH mass of M_BH=5 Msun and a system inclination of 40 deg, the fits imply an inner radius for the disk of Rin/Rg>212 d_3 (5Msun/M_BH). The outer radius is R_out/R_g=90,000 d_3 (5Msun/M_BH), which corresponds to 6.6e10 d_3 cm, consistent with the expected size of the disk. The 0.5-240 keV spectrum measured by Swift/XRT, Suzaku, and NuSTAR is relatively well characterized by a power-law with a photon index of Gamma=1.722+/-0.003, but a significant improvement is seen when a second continuum component is added. Reflection is a possibility, but no iron line is detected, implying a low iron abundance. We are able to fit the entire SED with a multi-temperature disk component, a Comptonization component, and a broken power-law, representing the emission from the compact jet. The broken power-law cannot significantly contribute to the soft X-ray emission, and this may be related to why Swift J1753.5-0127 is an outlier in the radio/X-ray correlation. The broken power-law might dominate above 20 keV, which would constrain the break frequency to be between 2.4e10 Hz and 3.6e12 Hz. Although the fits to the full SED do not include significant thermal emission in the X-ray band, previous observations have consistently seen such a component, and we find that there is evidence at the 3.1-sigma level for a disk-blackbody component with a temperature of 150(+30)(-20) eV and an inner radius of 5-14 R_g. If this component is real, it might imply the presence of an inner accretion disk in addition to the strongly truncated (R_in>212 R_g) disk.
    The Astrophysical Journal 06/2015; 808(1). DOI:10.1088/0004-637X/808/1/85 · 6.28 Impact Factor
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    ABSTRACT: We present quasi-simultaneous, multi-epoch radio and X-ray measurements of Holmberg II X-1 using the European VLBI Network (EVN), the Karl G. Jansky Very Large Array (VLA), and the Chandra and Swift X-ray telescopes. The X-ray data show apparently hard spectra with steady X-ray luminosities 4 months apart from each other. In the high-resolution EVN radio observations, we have detected an extended milli-arcsecond scale source with unboosted radio emission. The source emits non-thermal, likely optically thin synchrotron emission and its morphology is consistent with a jet ejection. The 9-GHz VLA data show an arcsecond-scale triple structure of Holmberg II X-1 similar to that seen at lower frequencies. However, we find that the central ejection has faded by at least a factor of 7.3 over 1.5 years. We estimate the dynamical age of the ejection to be higher than 2.1 years. We show that such a rapid cooling can be explained with simple adiabatic expansion losses. These properties of Holmberg II X-1 imply that ULX radio bubbles may be inflated by ejecta instead of self-absorbed compact jets.
    Monthly Notices of the Royal Astronomical Society 06/2015; 452(1). DOI:10.1093/mnras/stv1308 · 5.23 Impact Factor
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    ABSTRACT: We present spectral analysis of five NuSTAR and Swift observations of GX 339-4 taken during a failed outburst in summer 2013. These observations cover Eddington luminosity fractions in the range ~0.9-6%. Throughout this outburst, GX 339-4 stayed in the hard state, and all five observations show similar X-ray spectra with a hard power-law with a photon index near 1.6 and significant contribution from reflection. Using simple reflection models we find unrealistically high iron abundances. Allowing for different photon indices for the continuum incident on the reflector relative to the underlying observed continuum results in a statistically better fit and reduced iron abundances. With a photon index around 1.3, the input power-law on the reflector is significantly harder than that which is directly observed. We study the influence of different emissivity profiles and geometries and consistently find an improvement when using separate photon indices. The inferred inner accretion disk radius is strongly model dependent, but we do not find evidence for a truncation radius larger than 100 r_g in any model. The data do not allow independent spin constraints but the results are consistent with the literature (i.e., a>0). Our best-fit models indicate an inclination angle in the range 40-60 degrees, consistent with limits on the orbital inclination but higher than reported in the literature using standard reflection models. The iron line around 6.4 keV is clearly broadened, and we detect a superimposed narrow core as well. This core originates from a fluorescence region outside the influence of the strong gravity of the black hole and we discuss possible geometries.
    The Astrophysical Journal 06/2015; 808(2). DOI:10.1088/0004-637X/808/2/122 · 6.28 Impact Factor
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    ABSTRACT: Compressed sensing theory is slowly making its way to solve more and more astronomical inverse problems. We address here the application of sparse representations, convex optimization and proximal theory to radio interferometric imaging. First, we expose the theory behind interferometric imaging, sparse representations and convex optimization, and second, we illustrate their application with numerical tests with SASIR, an implementation of the FISTA, a Forward-Backward splitting algorithm hosted in a LOFAR imager. Various tests have been conducted in Garsden et al., 2015. The main results are: i) an improved angular resolution (super resolution of a factor ~2) with point sources as compared to CLEAN on the same data, ii) correct photometry measurements on a field of point sources at high dynamic range and iii) the imaging of extended sources with improved fidelity. SASIR provides better reconstructions (five time less residuals) of the extended emissions as compared to CLEAN. With the advent of large radiotelescopes, there is scope of improving classical imaging methods with convex optimization methods combined with sparse representations.
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    ABSTRACT: MAXI J1836-194 is a Galactic black hole candidate X-ray binary that was discovered in 2011 when it went into outburst. In this paper, we present the full radio monitoring of this system during its `failed' outburst, in which the source did not complete a full set of state changes, only transitioning as far as the hard intermediate state. Observations with the Karl G. Jansky Very Large Array (VLA) and Australia Telescope Compact Array (ATCA) show that the jet properties changed significantly during the outburst. The VLA observations detected linearly polarised emission at a level of ~1% early in the outburst, increasing to ~3% as the outburst peaked. High-resolution images with the Very Long Baseline Array (VLBA) show a ~15 mas jet along the position angle $-21 \pm 2^\circ$, in agreement with the electric vector position angle found from our polarisation results ($-21 \pm 4^\circ$), implying that the magnetic field is perpendicular to the jet. Astrometric observations suggest that the system required an asymmetric natal kick to explain its observed space velocity. Comparing quasi-simultaneous X-ray monitoring with the 5 GHz VLA observations from the 2011 outburst shows an unusually steep hard-state radio/X-ray correlation of $L_{\rm R} \propto L_{\rm X}^{1.8\pm0.2}$, where $L_{\rm R}$ and $L_{\rm X}$ denote the radio and X-ray luminosities, respectively. With ATCA and Swift monitoring of the source during a period of re-brightening in 2012, we show that the system lay on the same steep correlation. Due to the low inclination of this system, we then investigate the possibility that the observed correlation may have been steepened by variable Doppler boosting.
    Monthly Notices of the Royal Astronomical Society 03/2015; 450(2). DOI:10.1093/mnras/stv723 · 5.23 Impact Factor
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    ABSTRACT: Current and future astronomical survey facilities provide a remarkably rich opportunity for transient astronomy, combining unprecedented fields of view with high sensitivity and the ability to access previously unexplored wavelength regimes. This is particularly true of LOFAR, a recently-commissioned, low-frequency radio interferometer, based in the Netherlands and with stations across Europe. The identification of and response to transients is one of LOFAR's key science goals. However, the large data volumes which LOFAR produces, combined with the scientific requirement for rapid response, make automation essential. To support this, we have developed the LOFAR Transients Pipeline, or TraP. The TraP ingests multi-frequency image data from LOFAR or other instruments and searches it for transients and variables, providing automatic alerts of significant detections and populating a lightcurve database for further analysis by astronomers. Here, we discuss the scientific goals of the TraP and how it has been designed to meet them. We describe its implementation, including both the algorithms adopted to maximize performance as well as the development methodology used to ensure it is robust and reliable, particularly in the presence of artefacts typical of radio astronomy imaging. Finally, we report on a series of tests of the pipeline carried out using simulated LOFAR observations with a known population of transients.
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    ABSTRACT: Current and future astronomical survey facilities provide a remarkably rich opportunity for transient astronomy, combining unprecedented fields of view with high sensitivity and the ability to access previously unexplored wavelength regimes. This is particularly true of LOFAR, a recently-commissioned, low-frequency radio interferometer, based in the Netherlands and with stations across Europe. The identification of and response to transients is one of LOFAR's key science goals. However, the large data volumes which LOFAR produces, combined with the scientific requirement for rapid response, make automation essential. To support this, we have developed the LOFAR Transients Pipeline, or TraP. The TraP ingests multi-frequency image data from LOFAR or other instruments and searches it for transients and variables, providing automatic alerts of significant detections and populating a lightcurve database for further analysis by astronomers. Here, we discuss the scientific goals of the TraP and how it has been designed to meet them. We describe its implementation, including both the algorithms adopted to maximize performance as well as the development methodology used to ensure it is robust and reliable, particularly in the presence of artefacts typical of radio astronomy imaging. Finally, we report on a series of tests of the pipeline carried out using simulated LOFAR observations with a known population of transients.
    03/2015; DOI:10.1016/j.ascom.2015.03.002
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    ABSTRACT: The universal link between the processes of accretion and ejection leads to the formation of jets and outflows around accreting compact objects. Incoherent synchrotron emission from these outflows can be observed from a wide range of accreting binaries, including black holes, neutron stars, and white dwarfs. Monitoring the evolution of the radio emission during their sporadic outbursts provides important insights into the launching of jets, and, when coupled with the behaviour of the source at shorter wavelengths, probes the underlying connection with the accretion process. Radio observations can also probe the impact of jets/outflows (including other explosive events such as magnetar giant flares) on the ambient medium, quantifying their kinetic feedback. The high sensitivity of the SKA will open up new parameter space, enabling the monitoring of accreting stellar-mass compact objects from their bright, Eddington-limited outburst states down to the lowest-luminosity quiescent levels, whose intrinsic faintness has to date precluded detailed studies. A census of quiescently accreting black holes will also constrain binary evolution processes. By enabling us to extend our existing investigations of black hole jets to the fainter jets from neutron star and white dwarf systems, the SKA will permit comparative studies to determine the role of the compact object in jet formation. The high sensitivity, wide field of view and multi-beaming capability of the SKA will enable the detection and monitoring of all bright flaring transients in the observable local Universe, including the ULXs, ... [Abridged] This chapter reviews the science goals outlined above, demonstrating the progress that will be made by the SKA. We also discuss the potential of the astrometric and imaging observations that would be possible should a significant VLBI component be included in the SKA.
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    ABSTRACT: We present the highest-quality polarisation profiles to date of 16 non-recycled pulsars and four millisecond pulsars, observed below 200 MHz with the LOFAR high-band antennas. Based on the observed profiles, we perform an initial investigation of expected observational effects resulting from the propagation of polarised emission in the pulsar magnetosphere and the interstellar medium. The predictions of magnetospheric birefringence in pulsars have been tested using spectra of the pulse width and fractional polarisation from multifrequency data. The derived spectra offer only partial support for the expected effects of birefringence on the polarisation properties, with only about half of our sample being consistent with the model's predictions. It is noted that for some pulsars these measurements are contaminated by the effects of interstellar scattering. For a number of pulsars in our sample, we have observed significant variations in the amount of Faraday rotation as a function of pulse phase, which is possibly an artefact of scattering. These variations are typically two orders of magnitude smaller than that observed at 1400 MHz by Noutsos et al. (2009), for a different sample of southern pulsars. In this paper we present a possible explanation for the difference in magnitude of this effect between the two frequencies, based on scattering. Finally, we have estimated the magnetospheric emission heights of low-frequency radiation from four pulsars, based on the phase lags between the flux-density and the PA profiles, and the theoretical framework of Blaskiewicz, Cordes & Wasserman (1991). These estimates yielded heights of a few hundred km; at least for PSR B1133+16, this is consistent with emission heights derived based on radius-to-frequency mapping, but is up to a few times larger than the recent upper limit based on pulsar timing.
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    ABSTRACT: Adding VLBI capability to the SKA arrays will greatly broaden the science of the SKA, and is feasible within the current specifications. SKA-VLBI can be initially implemented by providing phased-array outputs for SKA1-MID and SKA1-SUR and using these extremely sensitive stations with other radio telescopes, and in SKA2 by realising a distributed configuration providing baselines up to thousands of km, merging it with existing VLBI networks. The motivation for and the possible realization of SKA-VLBI is described in this paper.
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    S. Drappeau · J. Malzac · J. Belmont · P. Gandhi · S. Corbel
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    ABSTRACT: In recent years, compact jets have been playing a growing role in the understanding of accreting black hole engines. In the case of X-ray binary systems, compact jets are usually associated with the hard state phase of a source outburst. Recent observations of GX 339-4 have demonstrated the presence of a variable synchrotron spectral break in the mid-infrared band that was associated with its compact jet. In the model used in this study, we assume that the jet emission is produced by electrons accelerated in internal shocks driven by rapid fluctuations of the jet velocity. The resulting spectral energy distribution (SED) and variability properties are very sensitive to the Fourier power spectrum density (PSD) of the assumed fluctuations of the jet Lorentz factor. These fluctuations are likely to be triggered by the variability of the accretion flow which is best traced by the X-ray emission. Taking the PSD of the jet Lorentz factor fluctuations to be identical to the observed X-ray PSD, our study finds that the internal shock model successfully reproduces the radio to infrared SED of the source at the time of the observations as well as the reported strong mid-infrared spectral variability.
    Monthly Notices of the Royal Astronomical Society 12/2014; 447(4). DOI:10.1093/mnras/stu2711 · 5.23 Impact Factor
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    ABSTRACT: Aims: We have analyzed low frequency radio data of tidal disruption event (TDE) Swift J1644+57 to search for a counterpart. We consider how brief transient signals (on the order of seconds or minutes) originating from this location would appear in our data. We also consider how automatic radio frequency interference (RFI) flagging at radio telescope observatories might affect these and other transient observations in the future, particularly with brief transients of a few seconds duration. Methods: We observed the field in the low-frequency regime at 149 MHz with data obtained over several months with the Low Frequency Array (LOFAR). We also present simulations where a brief transient is injected into the data in order to see how it would appear in our measurement sets, and how it would be affected by RFI flagging. Finally, both based on simulation work and the weighted average of the observed background over the course of the individual observations, we present the possibility of brief radio transients in the data. Results: Our observations of Swift J1644+57 yielded no detection of the source and a peak flux density at this position of 24.7 $\pm$ 8.9 mJy. Our upper limit on the transient rate of the snapshot surface density in this field at sensitivities < 0.5 Jy is $\rho < 2.2 \times10^{-2}$ deg$^{-2}$. We also conclude that we did not observe any brief transient signals originating specifically from the Swift J1644+57 source itself, and searches for such transients are severely limited by automatic RFI flagging algorithms which flag transients of less than 2 minutes duration. As such, careful consideration of RFI flagging techniques must occur when searching for transient signals.
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    ABSTRACT: We report on the results of a search for radio transients between 115 and 190\,MHz with the LOw Frequency ARray (LOFAR). Four different fields have been monitored with observational cadences between 15 minutes and several months. These fields have been chosen among the Medium Deep fields observed by the optical survey PanSTARRS. A total of 15 observing runs were performed giving a total survey area of 2275 deg$^2$. We analysed our data using standard LOFAR tools and searched for radio transients using the LOFAR Transient Pipeline (TraP). No credible radio transient candidate has been detected in our survey; however, it enables us to set upper limits on the surface density of radio transient sources at low radio frequencies, where little is yet known compared to frequencies above 1 GHz. To do this we used two new statistical methods. One is free of assumptions on the flux distribution of the sources, while the other assumes a power-law distribution in flux and sets more stringent constraints on the snapshot surface density. Our upper limit on the snapshot surface density of radio transients is $\rho <$ 10$^{-3}$ deg$^{-2}$ with flux densities $>$ 0.5 Jy. The corresponding radio transient rate is $\hat{\rho} <$ 0.3 deg$^{-2}$ yr$^{-1}$. We also analysed the snapshot surface density as a function of the time separation between different observations, providing insight into how this changes for different radio transient time-scales.
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    ABSTRACT: We present follow-up radio observations of ESO 243-49 HLX-1 from 2012 using the Australia Telescope Compact Array (ATCA) and the Karl G. Jansky Very Large Array (VLA). We report the detection of radio emission at the location of HLX-1 during its hard X-ray state using the ATCA. Assuming that the ‘Fundamental Plane’ of accreting black holes is applicable, we provide an independent estimate of the black hole mass of $M_{\rm {BH}}\le 2.8^{+7.5}_{-2.1} \times 10^{6}$ M⊙ at 90 per cent confidence. However, we argue that the detected radio emission is likely to be Doppler-boosted and our mass estimate is an upper limit. We discuss other possible origins of the radio emission such as being due to a radio nebula, star formation, or later interaction of the flares with the large-scale environment. None of these were found adequate. The VLA observations were carried out during the X-ray outburst. However, no new radio flare was detected, possibly due to a sparse time sampling. The deepest, combined VLA data suggest a variable radio source and we briefly discuss the properties of the previously detected flares and compare them with microquasars and active galactic nuclei.
    Monthly Notices of the Royal Astronomical Society 11/2014; 446(4). DOI:10.1093/mnras/stu2363 · 5.23 Impact Factor
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    ABSTRACT: [Abridged] We report on deep, coordinated radio and X-ray observations of the black hole X-ray binary XTE J1118+480 in quiescence. The source was observed with the Karl G. Jansky Very Large Array for a total of 17.5 hrs at 5.3 GHz, yielding a 4.8 \pm 1.4 microJy radio source at a position consistent with the binary system. At a distance of 1.7 kpc, this corresponds to an integrated radio luminosity between 4-8E+25 erg/s, depending on the spectral index. This is the lowest radio luminosity measured for any accreting black hole to date. Simultaneous observations with the Chandra X-ray Telescope detected XTE J1118+480 at 1.2E-14 erg/s/cm^2 (1-10 keV), corresponding to an Eddington ratio of ~4E-9 for a 7.5 solar mass black hole. Combining these new measurements with data from the 2005 and 2000 outbursts available in the literature, we find evidence for a relationship of the form ellr=alpha+beta*ellx (where ell denotes logarithmic luminosities), with beta=0.72\pm0.09. XTE J1118+480 is thus the third system, together with GX339-4 and V404 Cyg, for which a tight, non-linear radio/X-ray correlation has been reported over more than 5 dex in ellx. We then perform a clustering and linear regression analysis on what is arguably the most up-to-date collection of coordinated radio and X-ray luminosity measurements from quiescent and hard state black hole X-ray binaries, including 24 systems. At variance with previous results, a two-cluster description is statistically preferred only for random errors <=0.3 dex in both ellr and ellx, a level which we argue can be easily reached when the known spectral shape/distance uncertainties and intrinsic variability are accounted for. A linear regression analysis performed on the whole data set returns a best-fitting slope beta=0.61\pm0.03 and intrinsic scatter sigma_0=0.31\pm 0.03 dex.
    Monthly Notices of the Royal Astronomical Society 08/2014; 445(1). DOI:10.1093/mnras/stu1599 · 5.23 Impact Factor
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    ABSTRACT: We observed the Ultraluminous X-ray Source IC 342 X-1 simultaneously in X-ray and radio with Chandra and the JVLA to investigate previously reported unresolved radio emission coincident with the ULX. The Chandra data reveal a spectrum that is much softer than observed previously and is well modelled by a thermal accretion disc spectrum. No significant radio emission above the rms noise level was observed within the region of the ULX, consistent with the interpretation as a thermal state though other states cannot be entirely ruled out with the current data. We estimate the mass of the black hole using the modelled inner disc temperature to be $30~\mathrm{M_{\odot}} \lesssim M\sqrt{\mathrm{cos}i}\lesssim200~\mathrm{M_{\odot}}$ based on a Shakura-Sunyaev disc model. Through a study of the hardness and high-energy curvature of available X-ray observations, we find that the accretion state of X-1 is not determined by luminosity alone.
    Monthly Notices of the Royal Astronomical Society 07/2014; 444(1). DOI:10.1093/mnras/stu1471 · 5.23 Impact Factor

Publication Stats

4k Citations
912.19 Total Impact Points

Institutions

  • 2008–2015
    • Paris Diderot University
      Lutetia Parisorum, Île-de-France, France
  • 2008–2014
    • Université de Vincennes - Paris 8
      Saint-Denis, Île-de-France, France
  • 2012
    • Institut Universitaire de France
      Lutetia Parisorum, Île-de-France, France
  • 2006–2011
    • French National Centre for Scientific Research
      • Astrophysique interactions multi-échelles (AIM)
      Lutetia Parisorum, Île-de-France, France
  • 2001–2010
    • Université Paris-Saclay
      Lutetia Parisorum, Île-de-France, France
    • Massachusetts Institute of Technology
      • Department of Physics
      Cambridge, Massachusetts, United States
    • Harvard-Smithsonian Center for Astrophysics
      • Smithsonian Astrophysical Observatory
      Cambridge, Massachusetts, United States
  • 2000–2009
    • DSM Biomedical
      Exton, Pennsylvania, United States
  • 2003–2008
    • Atomic Energy and Alternative Energies Commission
      Fontenay, Île-de-France, France
    • University of Florida
      Gainesville, Florida, United States
  • 2007
    • University of California, San Diego
      • Center for Astrophysics and Space Sciences (CASS)
      San Diego, California, United States
  • 2005
    • Max Planck Institute for Extraterrestrial Physics
      Arching, Bavaria, Germany
    • University of California, Berkeley
      • Space Sciences Laboratory
      Berkeley, California, United States
  • 2004
    • University of Ferrara
      Ferrare, Emilia-Romagna, Italy
  • 1995–1996
    • California Institute of Technology
      • Jet Propulsion Laboratory
      Pasadena, California, United States