Probe of Lorentz Invariance Violation effects and determination of the distance of PG 1553+113

The high frequency peaked BL Lac object PG 1553+113 underwent a flaring event in 2012. The High Energy Stereoscopic System (H.E.S.S.) observed this source for two consecutive nights at very high energies (VHE, $E>$100~GeV). The data show an increase of a factor of three of the flux with respect to archival measurements with the same instrument and hints of intra-night variability. The data set has been used to put constraints on possible Lorentz invariance violation (LIV), manifesting itself as an energy dependence of the velocity of light in vacuum, and to set limits on the energy scale at which Quantum Gravity effects causing LIV may arise. With a new method to combine H.E.S.S. and Fermi large area telescope data, the previously poorly known redshift of PG 1555+113 has been determined to be close to the value derived from optical measurements.Comment: 2014 Fermi Symposium proceedings - eConf C14102.

H.E.S.S. discovery of very-high-energy gamma-ray emission of PKS 1440-389

Blazars are the most abundant class of known extragalactic very-high-energy (VHE, E>100 GeV) gamma-ray sources. However, one of the biggest difficulties in investigating their VHE emission resides in their limited number, since less than 60 of them are known by now. In this contribution we report on H.E.S.S. observations of the BL Lac object PKS 1440-389. This source has been selected as target for H.E.S.S. based on its high-energy gamma-ray properties measured by Fermi-LAT. The extrapolation of this bright, hard-spectrum gamma-ray blazar into the VHE regime made a detection on a relatively short time scale very likely, despite its uncertain redshift. H.E.S.S. observations were carried out with the 4-telescope array from February to May 2012 and resulted in a clear detection of the source. Contemporaneous multi-wavelength data are used to construct the spectral energy distribution of PKS 1440-389 which can be described by a simple one-zone synchrotron-self Compton model.Comment: In Proceedings of the 34th International Cosmic Ray Conference (ICRC2015), The Hague, The Netherland

Optical-NIR spectroscopy of the puzzling gamma-ray source 3FGL 1603.9-4903/PMN J1603-4904 with X-shooter

The Fermi/LAT instrument has detected about two thousands Extragalactic High Energy (E > 100 MeV) gamma-ray sources. One of the brightest is 3FGL 1603.9-4903, associated to the radio source PMN J1603-4904. Its nature is not yet clear, it could be either a very peculiar BL Lac or a CSO (Compact Symmetric Object) radio source, considered as the early stage of a radio galaxy. The latter, if confirmed, would be the first detection in gamma-rays for this class of objects. Recently a redshift z=0.18 +/- 0.01 has been claimed on the basis of the detection of a single X-ray line at 5.44 +/- 0.05 keV interpreted as a 6.4 keV (rest frame) fluorescent line. We aim to investigate the nature of 3FGL 1603.9-4903/PMN J1603-4904 using optical to NIR spectroscopy. We observed PMN J1603-4904 with the UV-NIR VLT/X-shooter spectrograph for two hours. We extracted spectra in the VIS and NIR range that we calibrated in flux and corrected for telluric absorption and we systematically searched for absorption and emission features. The source was detected starting from ~6300 Ang down to 24000 Ang with an intensity comparable to the one of its 2MASS counterpart and a mostly featureless spectrum. The continuum lacks absorption features and thus is non-stellar in origin and likely non-thermal. On top of this spectrum we detected three emission lines that we interpret as the Halpha-[NII] complex, the [SII] 6716,6731 doublet and the [SIII] 9530 line, obtaining a redshift estimate of z= 0.2321 +/- 0.0004. The equivalent width of the Halpha-[NII] complex implies that PMN J1603-4904 does not follow the observational definition of BL Lac, the line ratios suggest that a LINER/Seyfert nucleus is powering the emission. This new redshift measurement implies that the X-ray line previously detected should be interpreted as a 6.7 keV line which is very peculiar.Comment: Published in Astronomy and Astrophysic

Off-road mobile robot control: An adaptive approach for accuracy and integrity

International audienceThis paper proposes an algorithm dedicated to the control of off-road mobile robots at high speed. Based on adaptive and predictive principles, it first proposes a control law to preserve a high level of accuracy in the path tracking problem. Next, the dynamic model used for grip condition estimation is considered to address also robot integrity preservation thanks to the velocity limitation

High-speed mobile robot control in off-road conditions: a multi-model based adaptive approach

International audienceThis paper is focused on the design of a control strategy for the path tracking of off-road mobile robots acting at high speed. In order to achieve high accuracy in such a context, uncertain and fast dynamics have to be explicitly taken into account. Since these phenomena (grip conditions, delays due to inertial and low-level control properties) are hardly measurable directly, the proposed approach relies on predictive and observer-based adaptive control techniques. In particular, the adaptive part is based on an observer loop, taking advantage of both kinematic and dynamic vehicle models. This multi-model based adaptive approach permits to adapt on-line the grip conditions (represented by cornering stiffnesses), enabling highly reactive sideslip angles observation and then accurate path tracking. The relevance of this approach is investigated through full scale experiments

Algorithmes pour la commande d’une formation de robots mobiles

International audienceLa nécessité de diminuer l'impact sur l'environnement des activités agricoles, tout en préservant le niveau de production pour satisfaire les demandes de population en croissance, exige l'étude de nouveaux outils de production. Des robots mobiles peuvent constituer une solution prometteuse, puisque des dispositifs autonomes peuvent permettre d'accroître les niveaux de production, en préservant l'environnement en raison de leur grande précision. Si le contrôle automatique d'une machine seule offre des améliorations significatives, le contrôle d'une flotte modulaire de véhicules permet d'augmenter les espaces couverts sans utiliser de grandes machines qui provoquent un important compactage du sol. Pour être efficace, le contrôle de plusieurs robots autonomes doit être très précis et capable de gérer les différentes configurations rencontrées pendant une tâche agricole. Pour réaliser ces objectifs, les lois de contrôle simples utilisées dans le contexte routier ne sont pas appropriées dans des conditions tout terrain. Dans cet article, la commande en formation de plusieurs robots est envisagée dans le cadre du suivi de trajectoire. On propose des lois de commande adaptatives et prédictives qui prennent en compte les faibles conditions d'adhérence pour préserver l'exactitude de positionnement global et relatif. Elle permet alors de gérer une formation dans l'environnement naturel, indépendamment des conditions du sol, de la trajectoire à suivre et de la forme choisie pour la formation. Dans une première partie, on considère le modèle du mouvement de formation, en tenant compte des faibles conditions d'adhérence. Dans une deuxième partie, un observateur dédié à l'évaluation en ligne des conditions d'adhérences est conçu. Il permet de calculer les variables manquantes exigées pour un contrôle précis. Finalement, en se référant au modèle et à l'observateur, des lois de commande pour l'asservissement latéral et angulaire sont proposées. Il est basé sur une erreur mélangeant des écarts relatifs et absolus et permet la gestion du contrôle adaptatif. Les capacités de l'approche développée sont alors examinées à travers des expériences à échelle réelle

Motion Control of a heterogeneous fleet of mobile robots: Formation control for achieving agriculture task

International audienceLa nécessité de réduire l'impact environnemental des activités agricoles, tout en préservant le niveau de production pour satisfaire la demande croissante des populations nécessite une étude de nouveaux outils de production. Les robots mobiles peuvent constituer une solution prometteuse, puisque les dispositifs autonomes peuvent permettre une augmentation des niveaux de production, tout en préservant l'environnement grâce à leur grande précision. Dans cet article, l'utilisation de plusieurs robots mobiles autonomes pour effectuer l'opération sur le terrain est étudiée. En particulier, les techniques prédictives sont également proposées pour tenir compte des retards induits par des actionneurs à basse altitude. Les capacités de l'approche proposée sont étudiées au moyen d'expériences de la pleine échelle. / The necessity of decreasing the environmental impact of agricultural activities, while preserving the level of production to satisfy growing population demands requires investigation of new production tools. Mobile robots may constitute a promising solution, since autonomous devices may allow increasing production levels, while preserving the environment thanks to their high accuracy. In this paper, the use of several autonomous mobile robots to perform field operation is investigated. In particular, predictive techniques are also proposed to account for delays induced by low-level actuators. Capabilities of the proposed approach are investigated through full scale experiments

New active safety device dedicated to light all-terrain vehicle stability: Application to quad bike and off-road mobile robot

International audienceAccording to their specific geometric and dynamic characteristics (small weight, huge reachable speeds ), All-Terrain Vehicles (ATVs - as quad bikes) and off-road mobile robots are very compact and driveable. They permit to realize extra agricultural tasks (spreading, spraying ) in an easier way than using once more a heavy farm tractor. However such vehicles require highly accurate control laws, able to preserve their stability even at high speed. In this paper, the prevention of off-road vehicle and mobile robot rollover are addressed by using a new active safety device. It consists in using Predictive Functional Control (PFC) so as to compute, on-line, the maximum vehicle velocity, compatible with a safe motion over some horizon of prediction, and can be applied, if needed, to the vehicle actuator to prevent from rollover. The capabilities of the proposed device are demonstrated and discussed thanks to both advanced simulations and real experimentation