F3: The transient catastrophic Universe
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.
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.
Stéphane Corbel (Professeur des Universités, AIM)
Isabelle Grenier (Professeur des Universités, AIM)
Jean-Luc Starck (Chercheur CEA, AIM) Page web
Julien Girard (Post-doc, LabEx UnivEarthS, AIM) Page web (à venir)
Ming Jiang (Doctorant, CEA, AIM) Page web
Hugh Garsden (LEDA project, Harvard Observatory, ex post-doc LabEx UnivEarthS) Page web
In collaboration with Cyril Tasse (GEPI, Observatoire de Paris) and the LOFAR (TKP), MeerKAT (ThunderKAT) and ASKAP(VAST) collobarations
The SKA pathfinders
Core located in The Netherlands, with international stations located in France, UK, Germany and Sweden
64 antennas of 13.5 m to be operating from 0.6 to 15 GHz
Location: South Africa
7 dishes to be used as a MeerKAT precursor. 0.9 to 1.6 GHz
Location: SOuth Africa
36 antennas of 12-m diameter located in Western Australia operating around 1.4 GHz. Large field of view.
Operational around 2016, with a subset of antennas already working
Publications in refereed journals:
- Hassall et al. 2012, Astronomy & Astrophysics, 543, 66: Wide-band simultaneous observations of pulsars: disentangling dispersion measure and profile variations
- Garsden, Girard, Starck, Corbel et al. 2015, Astronomy & Astrophysics, 575, A90: LOFAR Sparse Image Reconstruction, (link)
- Girard, Jiang, Starck, Corbel et al. (in prep) Sparse aperture synthesis detection of radio transients
- LSS/NenuFAR: The LOFAR Super Station project in Nançay, SF2A-2012: Proceedings of the Annual meeting of the French Society of Astronomy and Astrophysics (link)
- Sparse representations and convex optimization as tools for LOFAR radio interferometric imaging, JINST, (INFIERI 2014, Paris) (in press) (link)
- Compressed Sensing and Radio interferometry, (EUSIPCO 2015, Nice) (in press)
- Detection of radio transients using sparse reconstruction technics, SF2A-2015 (in prep) (link)
Presentations of work during:
- LOFAR TKP (Transient Key Project) meeting – Amsterdam (Nl) – 3 to 5 december 2012. SC + HG attended. talk by HG (website here)
- Joint meeting of LOFAR TKP, ThunderKAT and TRAPUM – Oxford (GB) – 12 to 15 June 2012. HG attended. talk by HG (website here)
- Journée de l’Action Spécifique SKA-LOFAR – SF2A meeting – Nice -6 june 2012. SC + HG attended. talk by SC & HG (website here)
- Techniques for Radio Weak Lensing meeting – Manchester – 6 to 7 october 2014 – Manchester. JLS + JG attended. talk by JG (website here)
- Journée de l’Action Spécifique SKA-LOFAR – SF2A meeting – Toulouse – 5 june 2015. SC + MJ attended. talk by MJ (prepared by JG) (site website here)
Contribution to Schools:
- INFIERI à l’IN2P3 – Paris – 14 to 25 july 2014 – Lecture by JG – 23 Juillet (1h30), Radio Aperture synthesis as a practical example of sparse signal reconstruction – numerica hands-on session by François Lanusse (CosmoStat/AIM) (website here)
- Large Ground-based 21st Century Radio Instrument: ALMA/NOEMA / SKA/LOFAR – CIEP Sèvres – 16 to 20 novembre 2015 (coming soon here)