S. Corbel

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

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Publications (270)881.85 Total impact

  • [Show abstract] [Hide abstract]
    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.
    12/2014;
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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.
    11/2014;
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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 $M_{\rm{BH}}\leq2.8^{+7.5}_{-2.1} \times 10^{6}$ M$_{\odot}$ at 90% 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 suggests a variable radio source and we briefly discuss the properties of the previously detected flares and compare them with microquasars and active galactic nuclei.
    11/2014;
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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.
    08/2014;
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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). · 5.52 Impact Factor
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    ABSTRACT: Here we report on Swift and Suzaku observations near the end of an outburst from the black hole transient 4U 1630-47 and Chandra observations when the source was in quiescence. 4U 1630-47 made a transition from a soft state to the hard state ~50 d after the main outburst ended. During this unusual delay, the flux continued to drop, and one Swift measurement found the source with a soft spectrum at a 2-10 keV luminosity of L = 1.07e35 erg/s for an estimated distance of 10 kpc. While such transients usually make a transition to the hard state at L/Ledd = 0.3-3%, where Ledd is the Eddington luminosity, the 4U 1630-47 spectrum remained soft at L/Ledd = 0.008/M10% (as measured in the 2-10 keV band), where M10 is the mass of the black hole in units of 10 solar masses. An estimate of the luminosity in the broader 0.5-200 keV bandpass gives L/Ledd = 0.03/M10%, which is still an order of magnitude lower than typical. We also measured an exponential decay of the X-ray flux in the hard state with an e-folding time of 3.39+/-0.06 d, which is much less than previous measurements of 12-15 d during decays by 4U 1630-47 in the soft state. With the ~100 ks Suzaku observation, we do not see evidence for a reflection component, and the 90% confidence limits on the equivalent width of a narrow iron Kalpha emission line are <40 eV for a narrow line and <100 eV for a line of any width, which is consistent with a change of geometry (either a truncated accretion disk or a change in the location of the hard X-ray source) in the hard state. Finally, we report a 0.5-8 keV luminosity upper limit of <2e32 erg/s in quiescence, which is the lowest value measured for 4U 1630-47 to date.
    The Astrophysical Journal 07/2014; 791(1). · 6.73 Impact Factor
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    ABSTRACT: Millisecond radio pulsars acquire their rapid rotation rates through mass and angular momentum transfer in a low-mass X-ray binary system. Recent studies of PSR J1824-2452I and PSR J1023+0038 have observationally demonstrated this link, and they have also shown that such systems can repeatedly transition back-and-forth between the radio millisecond pulsar and low-mass X-ray binary states. This also suggests that a fraction of such systems are not newly born radio millisecond pulsars but are rather suspended in a back-and-forth state switching phase, perhaps for giga-years. XSS J12270-4859 has been previously suggested to be a low-mass X-ray binary, and until recently the only such system to be seen at MeV-GeV energies. We present radio, optical and X-ray observations that offer compelling evidence that XSS J12270-4859 is a low-mass X-ray binary which transitioned to a radio millisecond pulsar state between 2012 November 14 and 2012 December 21. Though radio pulsations remain to be detected, we use optical and X-ray photometry/spectroscopy to show that the system has undergone a sudden dimming and no longer shows evidence for an accretion disk. The optical observations constrain the orbital period to 6.913+-0.002 hr.
    02/2014; 441(2).
  • John A. Tomsick, Stephane Corbel
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    ABSTRACT: The black hole candidate X-ray transient MAXI J1828-249 was discovered on 2013 October 15 (ATEL#5474). While it may have briefly been in the hard state (ATEL#5476, ATEL#5483), it soon made a transition to a soft state, and both thermal disk-blackbody and power-law components were detected (ATEL#5479, ATEL#5492). The source has not been observable with Swift since mid-November because of a sun angle constraint, but it just became visible again.
    01/2014;
  • Stéphane Corbel, John A. Tomsick, Tasso Tzioumis
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    ABSTRACT: Following the recent detection of MAXI J1828-249 in the hard state by Swift/XRT (ATel #5886), we report on radio observations conducted on 2014 February 16 with the ATCA and the CABB backend.
    01/2014;
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    ABSTRACT: Some of the most significant questions concerning the physics of accreting black holes (BHs) are addressed by studying BH transients at low mass accretion rates. This is where radio observations indicate the presence of steady and powerful jets, and quiescence is where significant accretion energy may be advected across the BH event horizon. While quiescent BHs have been studied previously at soft X-rays, the Nuclear Spectroscopic Telescope Array (NuSTAR) provides the first opportunity to extend coverage to energies above 10 keV. In 2013 October, we will observe V404 Cyg with NuSTAR (3-79 keV), XMM-Newton (0.3-12 keV), and VLA at radio frequencies. Of the known BH transients, V404 Cyg is known to have the highest quiescent flux, primarily due to its proximity (2.39+/-0.14 kpc). We will report on the broadband X-ray spectrum and a search for correlations between the hard X-ray, soft X-ray, and radio light curves.
    01/2014;
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    ABSTRACT: -In Press. Submitted to A&A. See http://adsabs.harvard.edu/abs/2014arXiv1406.7242G -. Context. The LOFAR Radio Telescope is a giant digital phased array interferometer with multiple antennas gathered in stations placed throughout Europe. As other interferometers, it provides a discrete set of measured Fourier components of the sky brightness. With these samples, recovering the original brightness distribution with aperture synthesis forms an inverse problem that can be solved by different deconvolution and minimization methods. Aims. Recent papers have established a clear link between the discrete nature of radio interferometry measurement and "compressed sensing" theory, which supports sparse recovery methods to reconstruct an image from the measured visibilities. We aimed at the implementation and at the scientific validation of one of these methods. Methods. We evaluated the photometric and resolution performance of the sparse recovery method in the framework of the LOFAR instrument on simulated and real data. Results. We have implemented a sparse recovery method in the standard LOFAR imaging tools, allowing us to compare the reconstructed images from both simulated and real data with images obtained from classical methods such as CLEAN or MS-CLEAN. Conclusions.We show that i) sparse recovery performs as well as CLEAN in recovering the flux of point sources, ii) performs much better on extended objects (the root mean square error is reduced by a factor up to 10), and iii) provides a solution with an effective angular resolution 2-3 times better than the CLEAN map. Applied to a real LOFAR dataset, the sparse recovery has been validated with the correct photometry and realistic recovered structures of Cygnus A, as compared to other methods. Sparse recovery has been implemented as an image recovery method for the LOFAR Radio Telescope and it can be used for other radio interferometers.
    Astronomy and Astrophysics. 01/2014;
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    ABSTRACT: Following the discovery of the new X-ray transient MAXI J1421-613 (ATel #5750, #5751), we conducted a radio observation on 2014 January 11/12 (23:15-01:00 UT) with the Australia Telescope Compact Array in the 1.5B configuration (maximum baseline 4.3 km). We observed at 5.5 GHz and 9 GHz simultaneously and detected a faint radio source at the following coordinates:
    12/2013;
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    ABSTRACT: Following our initial detection of a candidate radio counterpart of the newly discovered neutron star X-ray binary MAXI J1421-613 (ATel #5750, #5751, #5759, #5780), we observed the source again on 2014 January 17 (23:15-01:00 UT) with the Australia Telescope Compact Array. The source was detected with the following flux densities:
    12/2013;
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    ABSTRACT: We report on the discovery of an apparent triple radio structure hidden inside the radio bubble of the ultraluminous X-ray source Holmberg II X-1. The morphology is consistent with a collimated jet structure, which is observed to emit optically thin synchrotron radiation. The central component has a steep radio spectrum and is brighter than the outer components indicating a renewed radio activity. We estimate a minimum time-averaged jet power of 2 x 10^{39} erg/s that is associated with a time-averaged isotropic X-ray luminosity of at least 4 x 10^{39} erg/s. Our results suggest that Holmberg II X-1 is powered by a black hole of M_BH \geq 25 M_sun, that is inferred to be accreting at a high Eddington rate with intermittent radio activity.
    Monthly Notices of the Royal Astronomical Society 11/2013; · 5.52 Impact Factor
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    ABSTRACT: The black hole candidate XTE J1908+094, currently in outburst (Krimm et al. ATel #5523, Atel #5529; Miller-Jones et al. Atel #5530; Rushton et al. Atel #5532), recently started a hard-to-soft state transition (Negoro et al. Atel #5549). Rushton et al. (ATel #5551) reported a significant increase of the radio flux density at 16.3 GHz from 0.93 mJy on 2013-11-04T14:22-18:19 to 7.3 mJy on 2013-11-05T14:27-20:24 UT suggesting the ejection of optically thin radio-emitting plasma as usually associated with a hard-to-soft state transition.
    The Astronomer's Telegram. 11/2013;
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    ABSTRACT: The microquasar GX 339-4 was observed by Suzaku five times, spaced by a few days, during its transition back to the hard state at the end of its 2010-2011 outburst. The 2-10 keV source flux decreases by a factor ~10 between the beginning and the end of the monitoring. Simultaneous radio and OIR observations highlighted the re-ignition of the radio emission just before the beginning of the campaign, the maximum radio emission being reached between the two first Suzaku pointings, while the IR peaked a few weeks latter. A fluorescent iron line is always significantly detected. Fits with a gaussian or Laor profiles give statistically equivalent results. In the case of a Laor profile, fits of the five data sets simultaneously agree with a disk inclination angle of ~20 degrees. The disk inner radius is <10-30 R_g in the first two observations but almost unconstrained in the last three. A soft X-ray excess is also present in these two first observations. Fits with a multicolor disk component give disk inner radii in agreement with those obtained with the iron line fits. The use of a physically more realistic model, including a blurred reflection component and a comptonization continuum, give some hints of the increase of the disk inner radius but the significances are always weak. Interestingly, the addition of warm absorption significantly improves the fit of OBS1 while it is not needed in the other observations. The radio-jet re-ignition occurring between OBS1 and OBS2, these absorption features may indicate the natural evolution from a disk wind and a jet. The comparison with a long 2008 Suzaku observation of GX 339-4 in a persistent faint hard state where a narrow iron line clearly indicates a disk recession, is discussed.
    Astronomy and Astrophysics 10/2013; 564. · 5.08 Impact Factor
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    ABSTRACT: Swift J1745-26 is an X-ray binary towards the Galactic Centre that was detected when it went into outburst in September 2012. This source is thought to be one of a growing number of sources that display "failed outbursts", in which the self-absorbed radio jets of the transient source are never fully quenched and the thermal emission from the geometrically-thin inner accretion disk never fully dominates the X-ray flux. We present multi-frequency data from the VLA, ATCA, and KAT-7 radio arrays, spanning the entire period of the outburst. Our rich data set exposes radio emission that displays a high level of large scale variability compared to the X-ray emission and deviations from the standard radio--X-ray correlation that are indicative of an unstable jet and confirm the outburst's transition from the canonical hard state to an intermediate state. We also observe steepening of the spectral index and an increase of the linear polarization to a large fraction (~50%) of the total flux, as well as a rotation of the electric vector position angle. These are consistent with a transformation from a self-absorbed compact jet to optically-thin ejecta -- the first time such a discrete ejection has been observed in a failed outburst -- and may imply a complex magnetic field geometry.
    Monthly Notices of the Royal Astronomical Society 09/2013; 437(4). · 5.52 Impact Factor
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    ABSTRACT: The LOFAR Radio Telescope is a radio interferometer with multiple antennas placed throughout Europe. A radio interferometer samples the image of the sky in the Fourier domain; recovering the image from these samples is an inverse problem. In radio astronomy the CLEAN method has been used for many years to find a solution. Recent papers have established a link between radio interferometry and compressed sensing, which supports sparse recovery methods to reconstruct an image from interferometric data. The goal of this paper is to study sparse recovery methods on LOFAR data by comparing the accuracy of CLEAN and compressed sensing when applied to simulated LOFAR observations.
    Proc SPIE 09/2013;
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    ABSTRACT: We obtained multi-epoch Very Large Telescope (VLT) optical spectroscopic data in 2011 and 2012 on the ultraluminous X-ray source (ULX) NGC 5408 X-1. We confirm that the HeII\lambda4686 line has a broad component with an average FWHM of v=780\pm64 km/s with a variation of ~13% during observations spanning over 4 years, and is consistent with the origin in the accretion disc. The deepest optical spectrum does not reveal any absorption line from a donor star. Our aim was to measure the radial velocity curve and estimate the parameters of the binary system. We find an upper limit on the semi-amplitude of the radial velocity of K=132\pm42 km/s. A search for a periodic signal in the data resulted in no statistically significant period. The mass function and constraints on the binary system imply a black hole mass of less than ~510 M_sun. Whilst, a disc irradiation model may imply a black hole mass smaller than ~431-1985 M_sun, depending on inclination. Our data can also be consistent with an unexplored orbital period range from a couple of hours to a few days, thus with a stellar-mass black hole and a subgiant companion.
    Monthly Notices of the Royal Astronomical Society 08/2013; 435(4). · 5.52 Impact Factor
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    ABSTRACT: This White Paper, submitted to the recent ESA call for science themes to define its future large missions, advocates the need for a transformational leap in our understanding of two key questions in astrophysics: 1) How does ordinary matter assemble into the large scale structures that we see today? 2) How do black holes grow and shape the Universe? Hot gas in clusters, groups and the intergalactic medium dominates the baryonic content of the local Universe. To understand the astrophysical processes responsible for the formation and assembly of these large structures, it is necessary to measure their physical properties and evolution. This requires spatially resolved X-ray spectroscopy with a factor 10 increase in both telescope throughput and spatial resolving power compared to currently planned facilities. Feedback from supermassive black holes is an essential ingredient in this process and in most galaxy evolution models, but it is not well understood. X-ray observations can uniquely reveal the mechanisms launching winds close to black holes and determine the coupling of the energy and matter flows on larger scales. Due to the effects of feedback, a complete understanding of galaxy evolution requires knowledge of the obscured growth of supermassive black holes through cosmic time, out to the redshifts where the first galaxies form. X-ray emission is the most reliable way to reveal accreting black holes, but deep survey speed must improve by a factor ~100 over current facilities to perform a full census into the early Universe. The Advanced Telescope for High Energy Astrophysics (Athena+) mission provides the necessary performance (e.g. angular resolution, spectral resolution, survey grasp) to address these questions and revolutionize our understanding of the Hot and Energetic Universe. These capabilities will also provide a powerful observatory to be used in all areas of astrophysics.
    06/2013;

Publication Stats

2k Citations
881.85 Total Impact Points

Institutions

  • 2008–2014
    • Paris Diderot University
      Lutetia Parisorum, Île-de-France, France
    • Université de Vincennes - Paris 8
      Saint-Denis, Île-de-France, France
  • 2011
    • French National Centre for Scientific Research
      • Astrophysique interactions multi-échelles (AIM)
      Lutetia Parisorum, Île-de-France, France
  • 2010
    • University of Iowa
      • Department of Physics and Astronomy
      Iowa City, IA, United States
  • 2003–2009
    • Campus Paris Saclay
      Lutetia Parisorum, Île-de-France, France
  • 2003–2008
    • Cea Leti
      Grenoble, Rhône-Alpes, France
  • 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
  • 2002
    • Atomic Energy and Alternative Energies Commission
      Fontenay, Île-de-France, France
  • 2001
    • Harvard-Smithsonian Center for Astrophysics
      • Smithsonian Astrophysical Observatory
      Cambridge, Massachusetts, United States
    • Massachusetts Institute of Technology
      • Department of Physics
      Cambridge, Massachusetts, United States
  • 1995–1996
    • California Institute of Technology
      • Jet Propulsion Laboratory
      Pasadena, California, United States
    • University of Helsinki
      Helsinki, Southern Finland Province, Finland