The Dynamic Behavior of Soft Gamma Repeaters

Soft Gamma Repeaters (SGRs) undergo changes in their pulse properties and persistent emission during episodes of intense burst activity. Both SGR 1900+14 and SGR 1806-20 have shown significant changes in their spin-down rates during the last several years, yet the bulk of this variability is not correlated with burst activity. SGR 1900+14 has undergone large changes in flux and a dramatic pulse profile change following burst activity in 1998. The flux level of SGR 1627$-$41 has been decreasing since its only recorded burst activity. Here, we review the global properties of SGRs as well as the observed dynamics of the pulsed and persistent emission properties of SGR 1900+14, SGR 1806-20 and SGR 1627-41 during and following burst active episodes and discuss what implications these results have for the burst emission mechanism, the magnetic field dynamics of magnetars, the nature of the torque variability, and SGRs in general.Comment: Invited review to appear in "High Energy Studies of Supernova Remnants and Neutron Stars" (COSPAR 2002). 12 pages, 7 figure

Predicción de un modelo de acidólisis enzimática usando redes neuronales

A model for the acidolysis of trinolein and palmitic acid under the catalysis of immobilized sn-1,3 specific lipase was presented in this study. A neural networks (NN) based model was developed for the prediction of the concentrations of the major reaction products of this reaction (1-palmitoyl-2,3-oleoyl-glycerol (POO) 1,3-dipalmitoyl-2-oleoyl-glycerol (POP) and triolein (OOO)). Substrate ratio (SR), reaction temperature (T) and reaction time (t) were used as input parameters. The optimal architecture of the proposed NN model, which consists of one input layer with three inputs, one hidden layer with seven neurons and one output layer with three outputs, wass able to predict the reaction products concentration with a mean square error (MSE) of less than 1.5 and R2 of 0.999. and explicit formulation of the proposed NN is presented. Considerable good performance is achieved in modeling the acidolysis reaction using neuronal networks.En este estudio se presenta un modelo para la acidólisis de la trilinoleina y el ácido palmítico mediante la catálisis con una lipasa específica sn-1,3 inmovilizada. Un modelo basado en redes neuronales (NN) ha sido desarrollado para la predicción de la concentración de los principales productos de esta reacción (1-palmitoil-2,3-oleoil-glicerol (POO), 1,3-dipalmitoil-2-oleoil-glicerol (POP) y trioleina (OOO)). Se han usado como parámetros de entrada: la proporción del sustrato (SR), la temperatura de reacción (T) y el tiempo de reacción (t). La arquitectura óptima del modelo de NN propuesto, que consiste en una capa de entrada con tres entradas, una capa oculta con siete neuronas y una capa de salida con tres salidas, fue capaz de predecir la concentración de los productos de reacción con un error cuadrático medio (MSE) de menos de 1.5 y una R2 de 0.999 . Se presenta una formulación explícita del modelo NN propuesto. Se obtienen muy buenos resultados en la predicción de la reacciones de acidólisis mediante el uso de las redes neuronales

Síntesis de los triacilglicéridos de la manteca de cacao mediante un sistema modelo de acidolisis

The effects of reaction parameters such as substrate mole ratio, reaction temperature, enzyme load, water content and reaction time were studied in a model enzymatic acidolysis system. Palmitic and stearic acids were incorporated into triolein (OOO) under the catalysis of sn-1,3 specific lipase to produce the three major triacylglycerols (TAGs) in cocoa butter (CB), namely, 1,3-dipalmitoyl-2-oleoyl--glycerol (POP), 1(3)-palmitoyl-3(1)-stearoyl-2-oleoyl-glycerol (POS) and 1,3distearoyl-2-oleoyl-glycerol (SOS). TAG contents of the reaction products were analyzed by High Performance Liquid Chromatograph (HPLC).The best results (15.2% POP, 30.4% POS, 15.2 % SOS) were obtained at 1:3:3 (OOO:palmitic acid:stearic acid) substrate mole ratio and reaction parameters: time 10 h, temperature 45 oC, enzyme load 20 %, water content 5 %. The results obtained in this model system might be used for the optimization and application of lipase catalyzed acidolysis reactions in natural systems to produce cocoa butter equivalents (CBEs).El efecto de parámetros de reacción como el ratio molar de sustratos, carga de enzima, contenido de agua o temperatura de reacción fueron estudiados en un sistema modelo de acidolisis para la síntesis de triglicéridos disaturados. Los ácidos grasos palmítico y esteárico se incorporaron a la molécula de trioleína (OOO) mediante la catálisis con una li-pasa sn-1,3 específica para producir los tres triglicéridos (TAGs) mayoritarios de la manteca de cacao (CB): 1,3-dipalmitil-2-oleoil glicerol (POP), 1(3)-palmitil-3(1)-estearil-2glicerol (POS) and 1,3-diestearil-2-oleoil glicerol (SOS). Los TAGs producidos en cada reacción se analizaron por cromatografía líquida de alta eficacia (HPLC). Los mejores resultados (15.2 %, POP, 30.4 % POS, 15.2 % SOS) se obtuvieron empleando la relación molar de sustratos 1:3:3 (OOO: ácido palmítico:ácido esteárico) y los parámetros de reacción: tiempo 10h, temperatura 45 °C, carga de enzima 20 %, contenido de agua 5 %. Los resultados obtenidos en este modelo podrían usarse para la optimización de la aplicación de la reacción acidolítica catalizada por lipasas en sistemas naturales para producir equivalentes de manteca (CBEs) de cacao

Looking Into the Fireball: ROTSE-III and Swift Observations of Early GRB Afterglows

We report on a complete set of early optical afterglows of gamma-ray bursts (GRBs) obtained with the ROTSE-III telescope network from March 2005 through June 2007. This set is comprised of 12 afterglows with early optical and Swift/XRT observations, with a median ROTSE-III response time of 45 s after the start of gamma-ray emission (8 s after the GCN notice time). These afterglows span four orders of magnitude in optical luminosity, and the contemporaneous X-ray detections allow multi-wavelength spectral analysis. Excluding X-ray flares, the broadband synchrotron spectra show that the optical and X-ray emission originate in a common region, consistent with predictions of the external forward shock in the fireball model. However, the fireball model is inadequate to predict the temporal decay indices of the early afterglows, even after accounting for possible long-duration continuous energy injection. We find that the optical afterglow is a clean tracer of the forward shock, and we use the peak time of the forward shock to estimate the initial bulk Lorentz factor of the GRB outflow, and find 100<Gamma_0<1000, consistent with expectations.Comment: 31 pages, 5 figures, submitted to Ap

Anomalous X-ray Pulsars: Long-Term Monitoring and Soft-Gamma Repeater like X-ray Bursts

We report on long-term monitoring of anomalous X-ray pulsars (AXPs) using the Rossi X-ray Timing Explorer (RXTE). Using phase-coherent timing, we find a wide variety of behaviors among the sources, ranging from high stability (in 1E 2259.1+586 in quiescence and 4U 0142+61), to instabilities so severe that phase-coherent timing is not possible (in 1E 1048.1-5937). We note a correlation in which timing stability in AXPs decreases with increasing $\dot{\nu}$. The timing stability of soft gamma repeaters (SGRs) in quiescence is consistent with this trend, which is similar to one seen in radio pulsars. We find no significant pulse morphology variations in any AXP in quiescence. We considered high signal-to-noise average pulse profiles for each AXP as a function of energy. We show that, as in the timing properties, there is a variety of different behaviors for the energy dependence. We also used the monitoring and archival data to obtain pulsed flux time series for each source. We have found no large changes in pulsed flux for any source in quiescence, and have set $1\sigma$ upper limits on variations ~20-30% depending on the source. We have recently discovered bursts from the direction of two AXPs: 1E 1048.1-5937 the most SGR-like AXP, and 1E 2259.1+586 the most rotationally stable AXP. We compare the temporal, spectral and flux properties of these events to those of SGR bursts, and show that the two phenomena are very similar. These results imply a close relationship between AXPs and SGRs, with both being magnetars.Comment: 10 pages, 7 figures, to appear in the proceedings of the 34th Cospar Scientific Assembl