Prompt thermal emission in gamma-ray bursts

GRB spectra appear non-thermal, but recent observations of a few bursts with Fermi GBM have confirmed previous indications from BATSE of the presence of an underlying thermal component. Photospheric emission is indeed expected when the relativistic outflow emerging from the central engine becomes transparent to its own radiation, with a quasi-blackbody spectrum in absence of additional sub-photospheric dissipation. However, its intensity strongly depends on the acceleration mechanism - thermal or magnetic - of the flow. We aim to compute the thermal and non-thermal emissions produced by an outflow with a variable Lorentz factor, where the power injected at the origin is partially thermal (fraction epsilon_th) and partially magnetic (fraction 1-epsilon_th). The thermal emission is produced at the photosphere, and the non-thermal emission in the optically thin regime. Apart from the value of epsilon_th, we want to test how the other model parameters affect the observed ratio of the thermal to non-thermal emission. If the non-thermal emission is made by internal shocks, we self-consistently obtained the light curves and spectra of the thermal and non-thermal components for any distribution of the Lorentz factor in the flow. If the non-thermal emission results from magnetic reconnection we were unable to produce a light curve and could only compare the respective non-thermal and thermal spectra. In the different considered cases, we varied the model parameters to see when the thermal component in the light curve and/or spectrum is likely to show up or, on the contrary, to be hidden. We finally compared our results to the proposed evidence for the presence of a thermal component in GRB spectra. Focussing on GRB 090902B and GRB 10072B, we showed how these observations can be used to constrain the nature and acceleration mechanism of GRB outflows.Comment: 11 pages, 5 figures, accepted for publication in A&

Origin of the bright prompt optical emission in the naked eye burst

The huge optical brightness of GRB 080319B (the "Naked Eye Burst) makes this event really challenging for models of the prompt GRB emission. In the framework of the internal shock model, we investigate a scenario where the dominant radiative process is synchrotron emission and the high optical flux is due to the dynamical properties of the relativistic outflow: if the initial Lorentz factor distribution in the jet is highly variable, many internal shocks will form within the outflow at various radii. The most violent shocks will produce the main gamma-ray component while the less violent ones will contribute at lower energy, including the optical range.Comment: 3 pages, 1 figure, proceedings of the conference "Deciphering the Ancient Universe with Gamma-Ray Bursts", Kyoto, Japan. Editors: N. Kawai, S. Nagatak

Toolpaths Programming in an Intelligent Step-NC Manufacturing Context

The current language for CNC programming is G-code which dates from the beginning of the eighties with the norm ISO 6983. With the new technologies, G-code becomes obsolete. It presents drawbacks that create a rupture in the numerical chain at the manufacturing step. A new standard, STEP-NC, aims to overtake these lacks. A STEP-NC file includes all the information for manufacturing, as geometry description of the entities, workplan, machining strategies, tools, etc. For rough pocket milling, the ISO norms propose different kind of classical strategies as bidirectional, parallel or spiral contour, etc. This paper describes a new way of toolpath programming by the repetition of a pattern all along a guide curve. It presents several advantages as building fastness and easiness. The integration of pattern strategies in STEP-NC standard is an other step for the development of these strategies but also for the enrichment of STEP-NC possibilities. A complete STEP-NC numerical chain was built, integrating these pattern strategies. The implementation of this approach of building pattern strategies was made by the development of tools for the complete manufacturing cycle, from the CAD file to the machined part. Several application cases were experimented on machine tool to validate this approach and the efficiency of the developped tools

Do Fermi-LAT observations imply very large Lorentz factors in GRB outflows ?

Recent detections of GeV photons in a few GRBs by Fermi-LAT imply huge bulk Lorentz factors to avoid a large gamma gamma optical depth at high energy. Estimates can be as high as Gamma ~ 1000 in the most extreme cases. This puts severe constraints on models of the central engine and the jet acceleration in GRBs. These estimates are however obtained from a simplified single zone model. We present here a more realistic calculation which takes into account the time, space and direction dependent photon field existing in an outflow with several relativistically moving emitting zones. The formalism is general and can be applied to many models of the prompt GRB emission. We present results obtained for a numerical implementation in the framework of the internal shock model. We show that (i) the minimum Lorentz factor Gamma_min in bright LAT GRBs is reduced by a factor ~ 2-3 compared to previous estimates if the GeV and MeV emission are produced in the same region, and by an additional factor ~ 2-8 if the GeV emission is produced at larger radii. We provide an improved approximate formula for Gamma_min which is in good agreement with our numerical results and can be directly applied to LAT GRB data; (ii) a delayed GeV onset can be due to the time evolution of the opacity. As an illustration of these two first results, we present a synthetic GRB that reproduces most features of GRB 080916C with a mean Lorentz factor of ~ 340, an optically thin regime for gamma gamma opacity at 3GeV in bin 'b', a variability timescale of 0.5s in the MeV lightcurve and a delayed onset of ~ 5s of the GeV emission; (iii) the gamma gamma opacity can smooth the short timescale variability in the GeV lightcurve. This last result implies that the observed variability at high energy is not necessarily a good test to distinguish between an internal and an external origin for the GeV emission in GRBs. [abridged]Comment: 23 pages, 11 figure

Pulse Dynamics in a Chain of Granules With Friction

We study the dynamics of a pulse in a chain of granules with friction. We present theories for chains of cylindrical granules (Hertz potential with exponent $n=2$) and of granules with other geometries ($n>2$). Our results are supported via numerical simulations for cylindrical and for spherical granules ($n=5/2$).Comment: Submitted to PR

Épuisay - La Cousinière

Lien Atlas (MCC) : http://atlas.patrimoines.culture.fr/atlas/trunk/index.php?ap_theme=DOM_2.01.02&ap_bbox=0.887;47.869;0.973;47.925 En février 1998, les travaux d'élargissement de la R.D. 957 entre Épuisay et Vendôme (Loir-et-Cher) ont nécessité, au lieu-dit de la Cousinière, la réalisation d'une opération d'évaluation archéologique, motivée par la présence de matériel lithique recueilli en prospection dans l'environnement des travaux. Il a pu être constaté que le mobilier, exclusivement cons..

Manufacturing complexity evaluation at the design stage for both machining and layered manufacturing

International audienceIn this paper, a methodology to estimate manufacturing complexity for both machining and layered manufacturing is proposed in order to realize tools (dies or molds) by a combination of a subtractive and an additive process. Manufacturability indexes are calculated at the tool design stage, these indexes provide an accurate view of which areas of the tool will advantageously be machined or manufactured by an additive process. In this case, tools are not seen as single pieces but as 3-D puzzles with modules, manufactured aside by the best process and further assembled

Beauvilliers - La Sablonnière

Lien Atlas (MCC) : http://atlas.patrimoines.culture.fr/atlas/trunk/index.php?ap_theme=DOM_2.01.02&ap_bbox=1.601;48.276;1.710;48.323 Cette carrière de calcaire de Beauce a fait l’objet de deux opérations d’évaluation archéologique en 1998, respectivement pour des surfaces de 1,5 et 3,7 ha. Située dans un secteur à forte implantation gallo-romaine, cette exploitation se trouve non loin de la voie antique reliant Orléans à Chartres. Environ 5 % de la surface a été sondée mécaniquement, révélant ..