F3: The transient catastrophic Universe

> Read the articles connected to the project.


  • The capability to study transient phenomena on time scales from milliseconds to years has recently increased and shown large discovery potential. Yet, the time domain of the sky has been sparsely explored. Fermi and Swift are now showing the way at high energies, the former by mapping the whole sky every 3 hours, the latter by its rapid follow-up across many wavelengths. With the construction of wide field imagers dedicated to sky surveys on a daily timescale in the radio (Lofar, ASKAP, MeerKAT), optical (Pan-STARRS, LSST), infrared (Akari), and X-ray (eRosita/SRG), and with the ongoing surveillance in gamma rays from Fermi, there are new motivations to explore transients. Discovering new classes of fast transients is one, as it could represent new exotic or explosive events out to cosmological distances, such as merging neutron stars or evaporating black holes.


    Over the next decade, a combination of increased sensitivity, larger field of view, and algorithmic developments will open up the time domain to a wide range of astronomical fields, from stellar flares and supernovae to neutron-star and black-hole births, quakes and instabilities. Near-coincidence searches with high-energy neutrino and gravitational wave signals will be actively pursued across the world. The dynamic and bursting events represent the new terra incognita.


    Radio astronomy is leading this effort. Transient science is identified as a key goal for LOFAR (Europe), ASKAP (Autralia) and MeerKAT (South Africa) that are the precursor instruments of the major international SKA facility to be developed for the 2020+. The synchrotron radio emission probes with unequalled angular resolution the cooling in the ambient magnetic field of the relativistic particles ejected by compact accretors or explosions. It also constrains the kinetic feedback of such events on their environment.


    Artistic view of a small part of the SKA kilometer array.


    Algorithmic improvements for transient detection would yield improved use of the different combinations of fields-of-view and unprecedented sensitivities offered by these instruments. The vast storage and computational requirements of transient searches, in particular for imaging interferometers, also requires the development of near real-time detection pipelines. The LOFAR project is engaged in the development of first-generation pipelines. The characterization of transients and their identification at other wavelengths represents another challenge.


    LOFAR is a radio telescope currently being built in The Netherlands and neighboring countries


    Image from one of the Lofar low frequency station in Nançay (France)


    In this context, the Frontier project F3 targets innovative algorithmic improvement of radio software (Compressed Sensing framework and sparse representations, Direction-Dependent Effects,…) along the scientific exploitation of the forthcoming large flow of data originating from this new generation of radio telescopes.


    WP leader Corbel Stéphane AIM Professor, University Paris Diderot
    WP co-leader Grenier Isabelle AIM Professor, University Paris Diderot
    WP co-leader Starck Jean-Luc AIM Researcher/CEA
    WP member Girard Julien AIM Ass. Prof., University Paris Diderot
    WP member Migliori Giulia AIM Post-doc, LabEx UnivEarthS (Dec 14-Dec 17)
    WP member Loh Alan LESIA Post-doc at LESIA/OP (former AIM PhD)
    WP member Jiang Ming AIM PhD Student (Start Oct 14)
    WP member Evangelia Tremou AIM New post-doc (Start Nov 17)
    WP member Floriane Cangemi AIM New PhD Student (Start Oct 17)
    WP member Pires Sandrine AIM Researcher/CEA
    WP member Bobin Jérôme AIM Researcher/CEA
    WP member Rodriguez Jérôme AIM Researcher/CEA

    In collaboration with Cyril Tasse (GEPI, Observatoire de Paris) and the LOFAR (TKP), MeerKAT (ThunderKAT) and ASKAP(VAST) collobarations

  • New and large radio telescopes, that are currently developped and built, will observe the whole radio spectrum with an improved spectral, angular and especially an unprecedented time resolution. They represent a huge technical improvement over the past technologies and a data processing challenge for users that would require comparable performances, similar to what is developped for “big data” problems. At an early stage, the Frontier Project FP3 carried out the development of tools to produce robust 2D radio maps and extended the scope of application to produce two supplementary imagers working on 3D data: one dedicated to transient detection and imaging, the other on hyperspectral radio imaging. On its final stage, FP3’s main aim is to apply these new tools to a wide scope of applications in radio interferometry to generate scientific products and study the associated physical processes (either in time or in frequency).


    Algorithmic developments:

    In the current 2010-2020 era, the scientific teams that exploit the large datasets generated by continental-scaled instrument (such as LOFAR, MeerKAT, the South African precursors or SKA1-MID) have to face a huge radio data calibration and imaging challenge. On the imaging/deconvolution side, we have demonstrated with the past products generated by the FP3, that the compressed sensing framework could bring better image reconstruction with low residuals [Garsden et al., 2015; Girard et al., 2015], while taking into account some of the Direction Dependent Effects through W-Projection and A-Projections.


    Scientific developments

    After this large effort on the algorithmic side of the project, we also continued pursuing the scientific exploitation of various radio and high energy facilities in order to probe the transient emission from a wide range of astrophysical objects (galactic or extragalactic). The physics of relativistic jets represents a main axis of our research (being frequently associated with transient radio emission). Adopting an observational approach, we aim at understanding how in stellar and supermassive black holes jets are formed, evolve and interact with their environment.



    The past and current theoretical and numerical groundwork carried on 2D, 2D-1D and hyperspectral deconvolution, benefited from the support of the UnivEarthS Labex funding allocated to Human Ressource and to participation to specialized workshops (Jiang, Girard), conferences (Girard, Jiang, Starck, Corbel) on the topics of Compressed Sensing, Radio interferometry Imaging & image processing. The LabEx allowed two very different teams to bring their own expertise in this innovative project. During 2015/2016, JG was offered a post-doctoral fellowship and has worked at SKA South Africa, on the integration of our developped CS code in one the SKA imager candidate (DDFacet, C. Tasse, in rev.) and benefited from regular interactions with the project team (supervision of Jiang PhD Thesis, production of results for the 2D-1D study). He was hired as Ass. Prof. at Univ. Paris Diderot.

    Current effort is being put on applying all the described methods on real dataset for scientific production. We especially aim at the following science case:

    • Imaging of Fast-transient:
    • Code acceleration:
    • From sparse imaging to sparse calibration
    • Scientific exploitation of various radio facilities (with specific focus on MeerKAT and NenuFAR).


    Therefore, in the final funding period, we will carry out the studies in the direction of the scientific exploitation of MeerKAT and NenuFAR and the application of the 2D-1D, hyperspectral method which should open up new prospects (like the electromagnetic counterpart of gravitational wave events or other type of transients to be discovered with MeerKAT) to follow-up after UnivEarthS.




    • Curran, P.A. …Corbel, S. et al. The evolving polarized jet of black hole candidate Swift J174526, 2014, MNRAS, 437, 3265
    • Bassa, C. … Corbel, S. et al. A state change in the low-mass X-ray binary XSS J122704859 2014, MNRAS, 441, 1825
    • Marlowe, H. … Corbel, S. et al. Spectral state transitions of the Ultraluminous X-ray Source IC 342 X-1, 2014, MNRAS, 444, 642
    • Gallo, E. … Corbel, S. et al. The radio/X-ray domain of black hole X-ray binaries at the lowest radio luminosities, 2014, MNRAS, 445, 290
    • Cseh, D. …, Corbel, S. et al. On the radio properties of the intermediate mass black hole ESO 243-49 HLX-1 2014, MNRAS, 446, 3268



    • Garsden, H., Girard, J., Starck, J.L., Corbel, S. et al. “LOFAR Sparse Image Reconstruction, 2015, A&A 575, A90.
    • Swinbank, J.D., … Garsden, H., Corbel, S. et al. “The LOFAR transients pipeline”, A&C, 2015, 11, 25
    • Cseh, D. …, Corbel, S. et al. “The evolution of a jet ejection of the ultraluminous X-ray source Holmberg II X-1”, 2015, MNRAS, 452, 24.
    • Rahoui, F, … Corbel, S. et al. “Optical and near-infrared spectroscopy of the black hole Swift J1753.5-0127”, 2015, ApJ, 810, 161.
    • Tomsick, J.A., … Corbel, S. et al. “The Accreting Black Hole Swift J1753.5–0127 from Radio to Hard X-Ray”, 2015, ApJ, 808, 85.
    • Russell, T. D. … Corbel, S. et al. “Radio monitoring of the hard state jets in the 2011 outburst of MAXI J1836−194”, 2015, MNRAS, 450, 1745.
    • Rodriguez, J., … Corbel, S. et al. “Correlated optical, X-ray, and gamma-ray flaring activity seen with INTEGRAL during the 2015 outburst of V404 Cygni”, A&A, 581, L9.



    • Loh,, Corbel, S., Dubus, G., Rodriguez, J., Grenier, I., Hovatta, T., Pearson, T., Readhead, A., Fender, R., Mooley, K. “High-energy gamma-ray observations of the accreting black hole V404 Cygni during its 2015 June outburst”, 2016, MNRAS, 462, L111.
    • Carbone, D., ., … Corbel, S. et al. “New methods to constrain the radio transient rate: results from a survey of four fields with LOFAR”, MNRAS, 459, 316.
    • Broderick, J.W., … Corbel, S. et al. “Low-radio-frequency eclipses of the redback pulsar J2215+5135 observed in the image plane with LOFAR», 2016, MNRAS, 459, 2681.
    • Del Santo, M., … Corbel, S, … Rodriguez, J. et al. “Spectral and timing evolution of the bright failed outburst of the transient black hole Swift J174510.8-262411» 2016, MNRAS, 456, 3585.
    • Stewart, A. … Corbel, S. et al. “LOFAR MSSS: detection of a low-frequency radio transient in 400 h of monitoring of the North Celestial Pole» 2016, MNRAS, 456, 2321.
    • Marcotte, B. … Corbel, S. et al. “Orbital and superorbital variability of LS I +61 303 at low radio frequencies with GMRT and LOFAR», 2016, MNRAS, 456, 1791.
    • Migliori, G., …, Loh, A., Corbel, S. et al. « First Detection in Gamma-Rays of a Young Radio Galaxy: Fermi-LAT Observations of the Compact Symmetric Object PKS 1718-649» 2016, ApJ, 821, 103.
    • Rana, V., Loh, A., Corbel, S. et al. “Characterizing X-Ray and Radio Emission in the Black Hole X-Ray Binary V404 Cygni during Quiescence», 2016, ApJ, 821, 103.
    • Girard, J., … Corbel, S. et al., “Imaging Jupiter’s radiation belts down to 127 MHz with LOFAR”, 2016, A&A, 587, 3.
    • Kondratiev, V.I. … Corbel, S. et al. “A LOFAR Census of Millisecond Pulsars”, 2016, A&A, 585, 128.
    • Siemiginowska, A., … Migliori G. et al. “X-Ray properties of the youngest radio sources and their environments”, 2016, ApJ, 823, 57.
    • Migliori, G, « The high-energy view of young radio sources: X-ray and gamma-ray observations» 2016, AN, 337, 52.
    • Füerst, F. …Corbel, S., … Loh, A. et al. “GRS 1739-278 observed at very low luminosity with XMM-Newton and NuSTAR», 2016, ApJ, 832, 115.



    • Migliori, G., Corbel, S., Tomsick, J. A., Kaaret, P., Fender, R. P., Tzioumis, A. K., Coriat, M., Orosz, J. A. 2017, Mon. Not. R. Astron. Soc. 472, 141, “ Evolving morphology of the large-scale relativistic jets from XTE J1550-564”
    • Egron, E. et al. (incluant S. Corbel) 2017, Mon. Not. R. Astron. Soc., 471, 2703, « Single-dish and VLBI observations of Cygnus X-3 during the 2016 giant flare episode”
    • Loh, A., Corbel, S., Dubus, G., 2017, Mon. Not. R. Astron. Soc., 467, 4462, « Fermi/LAT detection of a transient gamma-ray flare in the vicinity of the binary star DG CVn »
    • Coughlam, C.P. et al. (incluant S. Corbel) 2017, Astrophys. J., 834, 206 «  A LOFAR Detection of the Low-mass Young Star T Tau at 149 MHz »
    • Margutti, R.… Migliori, G. et al « X-rays from the location of the Double-humped Transient ASASSN-15lh », 2017, ApJ, 836, 25