Heavy Nuclei Synthesized in Gamma-Ray Burst Outflows as the Source of UHECRs

Recent measurements by the Pierre Auger Observatory suggest that the composition of ultra-high energy cosmic rays (UHECRs) becomes dominated by heavy nuclei at high energies. However, until now there has been no astrophysical motivation for considering a source highly enriched in heavy elements. Here we demonstrate that the outflows from Gamma-Ray Bursts (GRBs) may indeed be composed primarily of nuclei with masses A ~ 40-200, which are synthesized as hot material expands away from the central engine. In particular, if the jet is magnetically-dominated (rather than a thermally-driven fireball) its low entropy enables heavy elements to form efficiently. Adopting the millisecond proto-magnetar model for the GRB central engine, we show that heavy nuclei are both synthesized in proto-magnetar winds and can in principle be accelerated to energies >1e20 eV in the shocks or regions of magnetic reconnection that are responsible for powering the GRB. Similar results may apply to accretion-powered GRB models if the jet originates from a magnetized disk wind. Depending on the precise distribution of nuclei synthesized, we predict that the average primary mass may continue to increase beyond Fe group elements at the highest energies, possibly reaching the A ~ 90 (Zirconium), A ~ 130 (Tellurium), or even A ~ 195 (Platinum) peaks. Future measurements of the UHECR composition at energies >~ 1e20 eV can thus confirm or constrain our model and, potentially, probe the nature of GRB outflows. The longer attenuation length of ultra-heavy nuclei through the extragalactic background light greatly expands the volume of accesible sources and alleviates the energetic constraints on GRBs as the source of UHECRs.Comment: 10 pages, 3 figures, final version now accepted to MNRA

The tribunal of philosophy and its norms: History and philosophy in Georges Canguilhem's historical epistemology

In this article I assess Georges Canguilhem's historical epistemology with both theoretical and historical questions in mind. From a theoretical point of view, I am concerned with the role that history can play in the understanding and evaluation of philosophical concepts. From a historical point of view, I regard historical epistemology, as developed by Gaston Bachelard and Georges Canguilhem, as a conception and practice which came out of the project, elaborated in France from the 1920s to the 1940s, of combining history of science and philosophy. I analyse in particular Canguilhem's epistemology in his theory and practive of history of science. What he called 'normative history' is the focus of my analysis. I evaluate the question of the nature and provenience of the norm employed in normative history, and I compare it with the norm as discussed by Canguilhem in _Le normal et le pathologique_. While I am critical of Canguilhem's treatment of history, I conclude that his philosophical suggestion to analyse the formation of scientific concepts 'from below' represents a useful model for history and philosophy of science, and that it can be very profitably extended to philosophical concepts

Using DL for a Case-Based Explanation System

Colloque avec actes et comité de lecture. internationale.International audienceThis paper presents a knowledge-based system for land use interpretation and prediction. We describe our needs for representing knowledge and data, and for reasoning. We explain our choices : case-based reasoning within the framework of the description logic system RACER. Then, we present the knowledge base and the data we are working with. Data about spatial entities are represented as graphs and represented in the DL system accordingly. An example of graph manipulation is used to illustrate our purpose. Then, we propose a first synthesis of our research work and present an extension of the DL system necessary for going further

Analyse de l'interaction experts -- informaticiens lors de la modélisation de connaissances spatiales

Colloque avec actes et comité de lecture. nationale.National audienceCet article rend compte d'un travail interdisciplinaire autour de la conception d'un système à bases de connaissances pour l'agronomie. Une des séances d'acquisition de connaissances entre agronomes et informaticiens a été filmée et fait l'objet d'une analyse par des psychologues des processus cognitifs. La séance porte sur l'écriture d'organisations spatiales agricoles sous forme de graphes auxquels sont associés des explications. L'article présente tout d'abord le contexte de ce travail et la situation qui a été filmée. Puis nous proposons une analyse d'une séquence interactionnelle en mettant en avant le rôle des inscriptions dans les décisions prises par les acteurs. Enfin nous présentons les premiers éléments du système à bases de connaissances en conception

Modelling and comparing maps with graphs

Colloque avec actes et comité de lecture. internationale.International audienceThis paper is concerned with the modelling of maps with conceptual graphs for the design of a knowledge-based system. We first describe the maps, which are synthetic descriptions of farm territories. We then explain the modelling principles we have used: the spatial objects of the map and the relations are represented into concepts linked with arcs. The reasoning principle of the system are briefly described. We finally focus on an example of graph comparison

The Canada-France deep fields survey-I: 100,000 galaxies, 1 deg^2: a precise measurement of \omega(\theta) to IAB~25

(abridged) Using the UH8K mosaic camera, we have measured the angular correlation function \omega(\theta) for 100,000 galaxies over four widely separated fields totalling ~1\deg^2 and reaching IAB~25.5. With this sample we investigate the dependence of \omega(\theta) at 1', A_\omega(1'), on sample median IAB magnitude in the range 19.5<I(AB-med)<24. Our results show that A_\omega(1') decreases monotonically to IAB~25. At bright magnitudes, \omega(\theta) is consistent with a power-law of slope \delta = -0.8 for 0.2'<\theta<3.0' but at fainter magnitudes we find \delta ~ -0.6. At the 3\sigma level, our observations are still consistent with \delta=-0.8. Furthermore, in the magnitude ranges 18.5<IAB<24.0 and 18.5<IAB<23.0 we find galaxies with 2.6<(V-I)AB<2.9 have A_\omega(1')'s which are ~10x higher than field values. We demonstrate that our model redshift distributions for the faint galaxy population are in good agreement with current spectroscopic observations. Using these predictions, we find that for low-omega cosmologies and assuming r_0=4.3/h Mpc, in the range 19.5<I(AB-med)<22, the growth of galaxy clustering is \epsilon~0. However, at 22<I(AB-med)<24.0, our observations are consistent with \epsilon>1. Models with \epsilon~0 cannot simultaneously match both bright and faint measurements of A_\omega(1`). We show how this result is a natural consequence of the ``bias-free'' nature of the \epsilon formalism and is consistent with the field galaxy population in the range 22.0<IAB<24.0 being dominated by galaxies of low intrinsic luminosity.Comment: 20 pages, 21 figures, requires natbib.sty, accepted for publication in Astronomy and Astrophysic

Evaporation in capillary porous media at the perfect piston-like invasion limit: Evidence of non-local equilibrium effects

The classical continuum modeling of evaporation in capillary porous media is revisited from pore network simulations of the evaporation process. The computed moisture diffusivity is characterized by a minimum corresponding to the transition between liquid and vapor transport mechanisms confirming previous interpretations. Also the study suggests an explanation for the scattering generally observed in the moisture diffusivity obtained from experimental data. The pore network simulations indicate a noticeable nonlocal equilibrium effect leading to a new interpretation of the vapor pressure‐saturation relationship classically introduced to obtain the one‐equation continuum model of evaporation. The latter should not be understood as a desorption isotherm as classically considered but rather as a signature of a nonlocal equilibrium effect. The main outcome of this study is therefore that nonlocal equilibrium two‐equation model must be considered for improving the continuum modeling of evaporation

The Proto-Magnetar Model for Gamma-Ray Bursts

Long duration Gamma-Ray Bursts (GRBs) originate from the core collapse of massive stars, but the identity of the central engine remains elusive. Previous work has shown that rapidly spinning, strongly magnetized proto-neutron stars (`millisecond proto-magnetars') produce outflows with energies, timescales, and magnetizations sigma_0 (maximum Lorentz factor) that are consistent with those required to produce long GRBs. Here we extend this work in order to construct a self-consistent model that directly connects the properties of the central engine to the observed prompt emission. Just after the launch of the supernova shock, a wind heated by neutrinos is driven from the proto-magnetar. The outflow is collimated into a bipolar jet by its interaction with the star. As the magnetar cools, the wind becomes ultra-relativistic and Poynting-flux dominated (sigma_0 >> 1) on a timescale comparable to that required for the jet to clear a cavity through the star. Although the site and mechanism of the prompt emission are debated, we calculate the emission predicted by two models: magnetic dissipation and internal shocks. Our results favor the magnetic dissipation model in part because it predicts a relatively constant `Band' spectral peak energy E_peak with time during the GRB. The jet baryon loading decreases abruptly when the neutron star becomes transparent to neutrinos at t ~ 10-100 seconds. Jets with ultra-high magnetization cannot effectively accelerate and dissipate their energy, suggesting this transition ends the prompt emission and may explain the steep decay phase that follows. We assess several phenomena potentially related to magnetar birth, including low luminosity GRBs, thermal-rich GRBs/X-ray Flashes, very luminous supernovae, and short duration GRBs with extended emission.Comment: 21 pages (plus 2 appendices), 21 figures, 1 table, now accepted to MNRA

Carbon-Rich Mira Variables: Radial Velocities and Distances

Optical radial velocities have been measured for 38 C-type Mira variables. These data together with others in the literature are used to study the differences between optical and CO mm observations for C-Miras and the necessary corrections to the optical velocities are derived in order to obtain the true radial velocities of the variables. The difference between absorption and emission line velocities is also examined. A particularly large difference (+30 km\s) is found in the case of the H-alpha emission line. A catalogue is given of 177 C-Miras with estimated distances and radial velocities. The distances are based on bolometric magnitudes derived in Paper I using SAAO observations or (for 60 of the stars) using non-SAAO photometry. In the latter case the necessary transformations to the SAAO system are derived. These data will be used in paper III to study the kinematics of the C-Miras.Comment: 11 pages, accepted for publication in MNRA

Host galaxies of long gamma-ray bursts in the Millennium Simulation

(abridged) In this work, we investigate the nature of the host galaxies of long Gamma-Ray bursts (LGRBs) using a galaxy catalogue constructed from the Millennium Simulation. We developed an LGRB synthetic model based on the hypothesis that these events originate at the end of the life of massive stars following the collapsar model, with the possibility of including a constraint on the metallicity of the progenitor star. A complete observability pipeline was designed to calculate a probability estimation for a galaxy to be observationally identified as a host for LGRBs detected by present observational facilities. This new tool allows us to build an observable host galaxy catalogue which is required to reproduce the current stellar mass distribution of observed hosts. This observability pipeline predicts that the minimum mass for the progenitor stars should be ~75 solar masses in order to be able to reproduce BATSE observations. Systems in our observable catalogue are able to reproduce the observed properties of host galaxies, namely stellar masses, colours, luminosity, star formation activity and metallicities as a function of redshift. At z>2, our model predicts that the observable host galaxies would be very similar to the global galaxy population. We found that ~88 per cent of the observable host galaxies with mean gas metallicity lower than 0.6 solar have stellar masses in the range 10^8.5-10^10.3 solar masses in excellent agreement with observations. Interestingly, in our model observable host galaxies remain mainly within this mass range regardless of redshift, since lower stellar mass systems would have a low probability of being observed while more massive ones would be too metal-rich. Observable host galaxies are predicted to preferentially inhabit dark matter haloes in the range 10^11-10^11.5 solar masses, with a weak dependence on redshift.Comment: 11 pages, 10 figures, accepted for publication in MNRA