Do Magnetic Fields drive high-energy explosive transients?

I will review the current state-of-the-art in real-time, rapid response optical imaging and polarimetric followup of transient sources such as Gamma Ray Bursts. I will interpret current results within the context of the external shock model and present predictions for future mm- and cm-wave radio observatories. Recent observational results from new radio pilot studies will also be presented

The Central Kiloparsec of Seyfert and Inactive Host Galaxies: a Comparison of Two-Dimensional Stellar and Gaseous Kinematics

We investigate the properties of the two-dimensional distribution and kinematics of ionised gas and stars in the central kiloparsecs of a matched sample of nearby active (Seyfert) and inactive galaxies, using the SAURON Integral Field Unit on the William Herschel Telescope. The ionised gas distributions show a range of low excitation regions such as star formation rings in Seyferts and inactive galaxies, and high excitation regions related to photoionisation by the AGN. The stellar kinematics of all galaxies in the sample show regular rotation patterns typical of disc-like systems, with kinematic axes which are well aligned with those derived from the outer photometry and which provide a reliable representation of the galactic line of nodes. After removal of the non-gravitational components due to e.g. AGN-driven outflows, the ionised gas kinematics in both the Seyfert and inactive galaxies are also dominated by rotation with global alignment between stars and gas in most galaxies. This result is consistent with previous findings from photometric studies that the large-scale light distribution of Seyfert hosts are similar to inactive hosts. However, fully exploiting the two-dimensional nature of our spectroscopic data, deviations from axisymmetric rotation in the gaseous velocity fields are identified that suggest the gaseous kinematics are more disturbed at small radii in the Seyfert galaxies compared with the inactive galaxies, providing a tentative link between nuclear gaseous streaming and nuclear activity.Comment: Accepted for publication in MNRAS, 34 pages, 20 figure

Molecular gas in Arp 94: Implications for intergalactic star formation

We present $^{12}$CO(1-0) observations of the interacting galaxy system Arp 94, which contains the Seyfert galaxies NGC 3227 and NGC 3226 as well as the star-forming candidate dwarf galaxy J1023+1952. We mapped the CO distribution in J1023+1952 with the IRAM 30m telescope and found molecular gas across the entire extent of the neutral hydrogen cloud -- an area of about 9 by 6 kpc. The region where star formation (SF) takes place is restricted to a much smaller ($\sim$ 1.5 by 3 kpc) region in the south where the narrow line width of the CO shows that the molecular gas is dynamically cold. Neither the molecular nor the total gas surface density in the SF region are significantly higher than in the rest of the object suggesting that an external trigger is causing the SF. The fact that CO is abundant and apparently a good tracer for the molecular gas in J1023+1952 indicates that its metallicity is relatively high and argues for a tidal origin of this object.Comment: 5 pages, to appear in the proceedings of "The fate of gas in galaxies", held in Dwingeloo, July 200

Imaging large fields of small targets with shaped EM fields, adaptive beam steering and dynamic constellation antennas

Space debris is an increasing problem, with ca. 18,000 objects large enough to be tracked from the ground and conservative estimates of 670,000 small (1 – 10 cm) debris. Collisions have become a key issue in operation and decommissioning of spacecraft, adding costs and risks to space missions in all orbits, with the added threat of collisional cascading if some debris fields become dense enough. Their accurate mapping in 3-D, and their evolutionwith time, therefore become paramount, but in-flight approaches are constrained by limited fields of view and limited spatial resolutions. The shapes of debris are of interest as it might affect long-term movements, and thelarger ones will be of interest for retrieval missions and in the emerging field of debris exploitation. Leveraging on developments in acoustic imaging of complex subsea targets (e.g. Guigné, 1986; Blondel and Caiti, 2006; Guignéand Blondel, 2017), we propose an approach based on a collection of transducers acting as both EM transmitters and EM receivers, imaging debris fields in 4 dimensions (space and time) and using techniques such as beam steering and waveform inversion to retrieve as much information as possible on their shape and size distributions. Accurately located nanosatellites (as a constellation or in very small swarms) are positioned dynamically to image a particular volume in space. Individual sources are repeatedly actuated, with the other nanosatellites in the swarm acting as receivers. This gives access to a potentially large series of multistatic scattering measurements of any target. These are processed in real-time within each node, reducing the overall computation burden. The first result is a volumetric image of debris within the field of view aggregated from all nodes. Beam steering focuses on diffractions, creating virtual pencil beams from which high-resolution imagery can be formed, yielding information on sizes of individual targets and on shapes (via multi-angle diffraction patterns). This requires accurate positioning of the individual transducer nodes (nanosatellites), achievable using global positioning networks and EM time-of-flight checks between nodes. By varying the relative positions of nodes in the swarm, it is also possible to adapt the focusing toregions of particular interest. By using several nodes as transmitters, positive/destructive interference between sources can also be used to induce high signals in places of interest and null signals in other places (for example toavoid interference with or detection by instruments within the field of view). This enabling technology is adaptive, as the number of individual nodes can be adapted to suit operational requirements, from small groups to largerconstellations of nanosatellites. It is also dynamic as the virtual antenna they create can be changed very fast, either by repositioning them or only activating particular transmitters/receivers, making for responsive space missions. Onboard data processing allows fast, distributed processing, making individual nodes more affordable, and the modular aspect allow growing constellations or re-deploying subsets as mission profiles evolve. Beyond Earth orbit, thisapproach can also be used to map planetary environments and assist future asteroid mining operations

The promises of gravitational-wave astronomy

No abstract available

Gas and stellar dynamics in NGC 1068. Probing the galactic gravitational potential

We present Sauron 2D spectrography of the central 1.5 kpc of the nearby Sey2 galaxy NGC1068, encompassing the well-known NIR inner bar. We have successively disentangled the respective contributions of the ionized gas and stars, thus deriving their 2D distribution and kinematics. The [OIII] and Hbeta emission lines exhibit very different spatial distribution and kinematics, the latter following inner spiral arms with clumps associated with star formation. Strong inwards streaming motions are observed in both the Hbeta and [OIII] kinematics. The stellar kinematics also exhibit clear signatures of a non-axisymmetric tumbling potential, with a twist in both the velocity and h3 fields. We re-examined the long-slit data of Shapiro et al (2003) using pPXF: a strong decoupling of h3 is revealed, and the central decrease in h4 hinted in the Sauron data is confirmed. These data also suggest that NGC1068 is a good candidate for a so-called sigma-drop. We confirm the possible presence of two pattern speeds. We also examine the stellar kinematics of bars formed in N-body+SPH simulations built from axisymmetric initial conditions. These successfully reproduce a number of properties observed in the 2D kinematics of NGC1068, and the long-slit data, showing that the kinematic signature of the NIR bar is imprinted in the stellar kinematics. The remaining differences between the models and the observed properties are mostly due to the exclusion of star formation and the lack of the primary large-scale oval/bar in the simulations. These models suggest that the inner bar could drive a significant amount of gas down to a scale of ~300 pc. This is consistent with the interpretation of the sigma-drop in NGC1068 being the result of central gas accretion followed by an episode of star formation.Comment: accepted for publication in MNRAS, 20 pages, 17 figures (high res version available at www-obs.univ-lyon1.fr/eric.emsellem/preprints/NGC1068_Emsellemetal_final.pdf

Imaging large fields of small targets with shaped EM fields, adaptive beam steering and dynamic constellation antennas

Space debris is an increasing problem, with ca. 18,000 objects large enough to be tracked from the ground and conservative estimates of 670,000 small (1 – 10 cm) debris. Collisions have become a key issue in operation and decommissioning of spacecraft, adding costs and risks to space missions in all orbits, with the added threat of collisional cascading if some debris fields become dense enough. Their accurate mapping in 3-D, and their evolutionwith time, therefore become paramount, but in-flight approaches are constrained by limited fields of view and limited spatial resolutions. The shapes of debris are of interest as it might affect long-term movements, and thelarger ones will be of interest for retrieval missions and in the emerging field of debris exploitation. Leveraging on developments in acoustic imaging of complex subsea targets (e.g. Guigné, 1986; Blondel and Caiti, 2006; Guignéand Blondel, 2017), we propose an approach based on a collection of transducers acting as both EM transmitters and EM receivers, imaging debris fields in 4 dimensions (space and time) and using techniques such as beam steering and waveform inversion to retrieve as much information as possible on their shape and size distributions. Accurately located nanosatellites (as a constellation or in very small swarms) are positioned dynamically to image a particular volume in space. Individual sources are repeatedly actuated, with the other nanosatellites in the swarm acting as receivers. This gives access to a potentially large series of multistatic scattering measurements of any target. These are processed in real-time within each node, reducing the overall computation burden. The first result is a volumetric image of debris within the field of view aggregated from all nodes. Beam steering focuses on diffractions, creating virtual pencil beams from which high-resolution imagery can be formed, yielding information on sizes of individual targets and on shapes (via multi-angle diffraction patterns). This requires accurate positioning of the individual transducer nodes (nanosatellites), achievable using global positioning networks and EM time-of-flight checks between nodes. By varying the relative positions of nodes in the swarm, it is also possible to adapt the focusing toregions of particular interest. By using several nodes as transmitters, positive/destructive interference between sources can also be used to induce high signals in places of interest and null signals in other places (for example toavoid interference with or detection by instruments within the field of view). This enabling technology is adaptive, as the number of individual nodes can be adapted to suit operational requirements, from small groups to largerconstellations of nanosatellites. It is also dynamic as the virtual antenna they create can be changed very fast, either by repositioning them or only activating particular transmitters/receivers, making for responsive space missions. Onboard data processing allows fast, distributed processing, making individual nodes more affordable, and the modular aspect allow growing constellations or re-deploying subsets as mission profiles evolve. Beyond Earth orbit, thisapproach can also be used to map planetary environments and assist future asteroid mining operations

Imaging Space Debris and Small Targets with Space-Based Radars and Dynamic Satellite Constellations – First Tests

Space debris is causing steadily increasing risks but many objects are not identified, limiting the scope of removal missions. We propose a dynamic satellite constellation with multiple EM receivers and transmitters, enabling multiaspect imaging of targets through bespoke signal processing (beam-steering, synthesis of virtual apertures and dynamic beamforming to create virtual pencil beams to interrogate volumes of interest). This adaptive and modular architecture is used to build the first experimental stage toward a scaled demonstrator, using different radar transceivers and adaptive processing of echoes from moving targets. The algorithms developed are intended to be used aboard satellite nodes, with potential distribution of the most demanding tasks amongst neighboring nodes. This laboratory work is supplemented with analyses of US and European orbital debris databases, to identify the LEO portions most at risk from collisions, and to match the expected orbits and velocities of debris with the detection capabilities of the satellite constellation (ranges, fields of view, reaction times afforded by different configurations). These calculations inform the types of radars needed (frequencies, powers), whether in space and part of the constellations, or ground-based and usedas sources of opportunities. Orbital constraints are used to match the number of nodes in the dynamic constellations with their respective positions, depending on propulsion modes and other considerations (general situational awareness).Focused on Near-Earth application, this method can be adapted to other areas (e.g. space mining). This approach aims to make future missions more affordable, de-risking space activities, protecting assets and preparing for future regulations

Dynamical evolution of AGN host galaxies -— gas in/out-flow rates in seven NUGA galaxies

To examine the role of the host galaxy structure in fueling nuclear activity, we estimated gas flow rates from several kpc down to the inner few 10 pc for seven nearby spiral galaxies, selected from the NUclei of GAlaxies sample. We calculated gravitational torques from near-infrared images and determined gas in/out-flow rates as a function of radius and location within the galactic disks, based on high angular resolution interferometric observations of molecular (CO using Plateau de Bure interferometer) and atomic (H I using the Very Large Array) gas. The results are compared with kinematic evidence for radial gas flows and the dynamical state of the galaxies (via resonances) derived from several different methods. We show that gravitational torques are very efficient at transporting gas from the outer disk all the way into the galaxies centers at ~100 pc; previously assumed dynamical barriers to gas transport, such as the corotation resonance of stellar bars, seem to be overcome by gravitational torque induced gas flows from other nonaxisymmetric structures. The resulting rates of gas mass inflow range from 0.01 to 50 M⊙ yr^(–1) and are larger for the galaxy center than for the outer disk. Our gas flow maps show the action of nested bars within larger bars for three galaxies. Noncircular streaming motions found in the kinematic maps are larger in the center than in the outer disk and appear to correlate only loosely with the in/out-flow rates as a function of radius. We demonstrate that spiral gas disks are very dynamic systems that undergo strong radial evolution on timescales of a few rotation periods (e.g., 5 × 10^8 yrs at a radius of 5 kpc), due to the effectiveness of gravitational torques in redistributing the cold galactic gas