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One of the scientific objectives of NASA’s Fermi Gamma‐ray Space Telescope is the study of Gamma‐Ray Bursts (GRBs). The Fermi Gamma‐Ray Burst Monitor (GBM) was designed to detect and localize bursts for the Fermi mission. By means of an array of 12 NaI(Tl) (8 keV to 1 MeV) and two BGO (0.2 to 40 MeV) scintillation detectors, GBM extends the energy range (20 MeV to >300 GeV ) of Fermi’s main instrument, the Large Area Telescope (LAT), into the traditional range of current GRB databases. The physical detector response of the GBM instrument to GRBs is determined with the help of Monte Carlo simulations, which are supported and verified by on‐ground individual detector calibration measurements. We present the principal instrument properties, which have been determined as a function of energy and angle, including the channel‐energy relation, the energy resolution and the effective area.

The GLAST Burst Monitor (GBM) will enhance LAT observations of GRBs by extending the spectral coverage from the LAT threshold down to 8 keV, and will provide a trigger for re-orienting the spacecraft to observe delayed emission from selected bursts outside the LAT field of view. GBM consists of twelve NaI scintillation detectors operating in the 8 keV to 1 MeV energy range and two BGO scintillation detectors operating in the 150 keV to 30 MeV energy range. Detector resolution, effective area, and angular response have been determined by calibrations. Analyses indicate that the on-board burst threshold will be 0.7 photons cm-2s-1 and the on-board burst localization accuracy will typically be better than 8deg.

The GLAST Burst Monitor (GBM) is the secondary instrument on NASA's next Gamma-ray mission GLAST. It will enhance the capabilities of GLAST by locating and detecting cosmic gamma-ray bursts at lower energies by the use of 12 NaI detectors (energy range 10 keV to 1 MeV) and 2 BGO-detectors (energy range 150 keV to 30 MeV). GBM was built in a close collaboration between the MPE and the Marshall Space Flight Center (MSFC). The angular and energy response of each GBM detector has been calibrated using various radioactive sources at different incidence angles relative to the detector in a laboratory environment at the MPE in 2005. To facilitate the understanding of the reconstruction of the detector response, a detailed simulation of the whole laboratory environment and the setup of the calibration source were performed. A modified version of the CERN GEANT 4 simulation software (provided by collaborators at the Los Alamos National Laboratory) was used.

Using our new 3‐D relativistic particle‐in‐cell (PIC) code, we investigated long‐term particle acceleration associated with a relativistic electron‐positron jet propagating in an unmagnetized ambient electron‐positron plasma. The simulations were performed using a much longer simulation system than our previous simulations in order to investigate the full nonlinear stage of the Weibel instability and its particle acceleration mechanism. Cold jet electrons are thermalized and ambient electrons are accelerated in the resulting shocks. Acceleration of ambient electrons leads to a maximum ambient electron density three times larger than the original value as predicted by hydrodynamic compression. Behind the bow shock, in the jet shock, strong electromagnetic fields are generated. These fields may lead to time dependent afterglow emission. In order to go beyond the standard synchrotron model used in astrophysical objects we have used PIC simulations and calculated radiation based on first principles. We calcul...

Using our new 3-D relativistic electromagnetic particle (REMP) code parallelized with MPI, we investigated long-term particle acceleration associated with a relativistic electron-positron jet propagating in an unmagnetized ambient electron-positron plasma. We have also performed simulations with electron-ion jets. The simulations were performed using a much longer simulation system than our previous simulations in order to investigate the full nonlinear stage of the Weibel instability for electron-positron jets and its particle acceleration mechanism. Cold jet electrons are thermalized and ambient electrons are accelerated in the resulting shocks for both cases. Acceleration of ambient electrons leads to a maximum ambient electron density three times larger than the original value for pair plasmas. Behind the bow shock in the jet shock strong electromagnetic fields are generated. These fields may lead to time dependent afterglow emission. We calculated radiation from electrons propagating in a uniform parallel magnetic field to verify the technique. We also used the new technique to calculate emission from electrons based on simulations with a small system with two different cases for Lorentz factors (15 and 100). We obtained spectra which are consistent with those generated from electrons propagating in turbulent magnetic fields with red noise. This turbulent magnetic field is similar to the magnetic field generated at an early nonlinear stage of the Weibel instability.

The work focuses on the problem of determination of cutoff frequency of waveguides and resonators of a complex shape. The problem is sold by method of R‐functions. This approach has a lot of advantages, it possesses geometric flexibility, broad capabilities of numerical realization as for the production of the variation problem and for the selection of basis functions system as well. As basis functions the polynomials (trigonometrical, power, Tchebyshev of I and II types, Legendre, Gegenbauer) or local functions (atomic functions, splines) are used. The contrastive analysis of approximate boundary value problem solving is carried out in accordance to the basis functions system selected.

This paper presents a general framework for sensitivity analysis for few‐parameter inverse problems using the Fisher information and the Cramer‐Rao bound. In particular, the one‐dimensional inverse problem of estimating the dispersive parameters of an inhomogeneous dielectric layer with linear spatial variation is studied. The analysis technique is particularly well‐suited for inverse problems using few parameters, and it is anticipated that the framework may be used as a basis for extensive numerical investigations and physical interpretations. The ill‐posedness of the inverse problem can be explicitely quantified by using the Fisher information analysis. As an example, the sensitivity analysis is used together with asymptotic theory to show that the inverse problem becomes extremely ill‐posed when the linear spatial variation vanishes.

Wave analysis is efficient for investigating the interior of objects. Examples are ultra sound examination of humans and radar using elastic and electromagnetic waves. A common procedure is inverse ...

Future generation mobile telecommunication systems are expected to provide high data rate services and improved system performance. Long Term Evolution (LTE) is a project within the Third Generation Partnership Project (3GPP) that aims at improving the current 3G UMTS (Universal Mobile Telecommunications System) standard to cope with future requirements and to maintain competitiveness in the long term. This paper analyzes the requirements for this evolution and evaluates the performance of the Orthogonal Frequency Division Multiplexing (OFDM) UMTS‐LTE system under different propagation impairments (AWGN, Pedestrian and Vehicular multipath fading channels of different speeds) in terms of bit and symbol error rates (BER and SER) for different modulation formats.

What should be the most general macroscopic linear theory of sound propagation in a connected fluidic domain not supporting the propagation of macroscopic transverse waves and defined by a viscothermal fluid in which rigid fixed inclusions of arbitrary shape are placed in periodic or stationary random manner? Based on considerations inspired by the long‐wavelength electromagnetic theory we discuss here what the general answer should be : a nonlocal “Maxwellian” acoustics with constitutive coefficients determined from microgeometry and fluid and solid physical constants. In forthcoming work the explicit construction of the postulated constitutive coefficients will be performed.

A new low-order and causal twisted-pair cable model for the copper access network is derived. From the serial resistance of the widely used, but non-causal, BT0 model, the serial inductance is computed via the Hilbert transform. By doing so, a causal cable model is obtained containing fewer parameters compared to the BT0 model. The deviation between the two models is evaluated for the standardized ETSI cables.

This paper deals with numerical methods for high frequency wave scattering. It introduces a new hybrid technique that couples a directional fast multipole method for a subsection of a scattering surface to an asymptotic formulation over the rest of the scattering domain. The directional fast multipole method is new and highly efficient for the solution of the boundary integral formulation of a general scattering problem but it requires at least a few unknowns per wavelength on the boundary. The asymptotic method that was introduced by Bruno and collaborators requires much fewer unknowns. On the other hand the scattered field must have a simple structure. Hybridization of these two methods retains their best properties for the solution of the full problem. Numerical examples are given for the solution of the Helmholtz equation in two space dimensions.

The Fermi Gamma‐ray Space Telescope launched on June 11, 2008 carries two experiments onboard—the Large Area Telescope (LAT) and the Gamma‐ray Burst Monitor (GBM). The primary mission of the GBM instrument is to support the LAT in observing γ‐ray bursts (GRBs) by providing low‐energy measurements with high temporal and spectral resolution as well as rapid burst locations over a large field‐of‐view (⩾8 sr). The GBM will complement the LAT measurements by observing GRBs in the energy range 8 keV to 40 MeV, the region of the spectral turnover in most GRBs. The GBM detector signals are processed by the onboard digital processing unit (DPU). We describe some of the hardware features of the DPU and its expected limitations during intense triggers.

Solutions of the nonlinear Schrodinger equation for initial conditions in the form of two separated sech‐shaped in‐phase pulses are analyzed. It is found that this initial condition, with appropriate amplitude, may give rise to, not only stationary solitons, but also to symmetrically separating solitons, if the initial distance of separation is large enough. The condition for the generation of a separating soliton pair is derived from the Zakharov‐Shabat eigenvalue problem using a variational approach.

Using our new 3-D relativistic electromagnetic particle (REMP) code parallelized with MPI, we have investigated long-term particle acceleration associated with an relativistic electron-positron jet propagating in an unmagnetized ambient electron-positron plasma. The simulations have been performed using a much longer simulation system than our previous simulations in order to investigate the full nonlinear stage of the Weibel instability and its particle acceleration mechanism. Cold jet electrons are thermalized and ambient electrons are accelerated in the resulting shocks. The acceleration of ambient electrons leads to a maximum ambient electron density three times larger than the original value. Behind the bow shock in the jet shock strong electromagnetic fields are generated. These fields may lead to the afterglow emission. We have calculated the time evolution of the spectrum from two electrons propagating in a uniform parallel magnetic field to verify the technique., Comment: 3 pages, 2 figures, submitted for the Proceedings of The Sixth Huntsville Gamma-Ray Burst Symposium 2008, Huntsville, AL, October 20-23, 2008

This research represents a synthesis of ultra‐wideband antenna hardware, employed for multiple target detection, using time‐reversal processing and the decomposition of the time‐reversal operator to obtain target location. Real‐data examples are presented using a symmetric and asymmetric configuration consisting of two scatterers. A new entropy‐based criterion for stopping the time‐reverse sequence is employed.

We explore preliminary a 3D wave cavity in which the interior complex wave functions are of Berry‐type. Streamlines and novel disc‐like features are uncovered by means of selective and interactive visualization.

A generalization of the modified Cagniard method (‘Cagniard‐DeHoop method’) is used to obtain closed‐form analytic time‐domain expressions for the line‐source excited pulsed acoustic wave pressure associated with the reflection against the mass‐loaded planar boundary of a semi‐infinite fluid. The expressions reveal the generation of anomalous waveforms near the boundary at large offsets from the source. Their occurrence can be interpreted as a surface effect. As the analysis shows, they are, however, not surface waves in the strict sense of the definition.

Modelling the acoustic scattering and absorption at an area expansion in a flow duct requires the incorporation of the flow‐acoustic interaction. One way to quantify the interaction is to study the energy in the incident and the scattered field respectively. If the interaction is strong, energy may be transferred between the acoustic and the main flow field. In particular, shear layers, that may be the result of the flow separation, are unstable to low frequency perturbations such as acoustic waves. The vortex sheet model is an analytical linear acoustic model, developed to study scattering of acoustic waves in duct with sharp edges including the interaction with primarily the separated flows that arise at sharp edges and corners. In the model the flow field at an area expansion in a duct is described as a jet issuing into the larger part of the duct. In this paper, the flow‐acoustic interaction is described in terms of energy flow. The linear convective wave equation is solved for a two‐dimensional, rectangular flow duct geometry. The resulting modes are classified as “hydrodynamic” and “acoustic” when separating the acoustic energy from the part of the energy arising from the steady flow field. In the downstream duct, the set of modes for this complex flow field are not orthogonal. For small Strouhal numbers, the plane wave and the two hydrodynamic waves are all plane, although propagating with different wave speeds. As the Strouhal numbers increases, the hydrodynamic modes changes to get a shape where the amplitude is concentrated near the vortex sheet. In an intermediate Strouhal number region, the mode shape of the first higher order mode is very similar to the damped hydrodynamic mode. A physical interpretation of this is that we have a strong coupling between the flow field and the acoustic field when the modes are non‐orthogonal. Energy concepts for this duct configuration and mean flow profile are introduced. The energy is formulated such that the vortex sheet turns out as a sink for the acoustic field, but a source for the unstable hydrodynamic wave. This model is physical only close to the edge, due to an exponentially growing hydrodynamic mode. In a real flow, non‐linearities will limit the growth, but this is not included in the model.

Quantization of Maxwell’s equations in waveguides is considered together with an analysis of the quantum correlation functions of the radiation field. Both the spatial and temporal dependence of the polarization correlation functions for entangled states are evaluated. Predictions for experiments for the study of the spatial dependence of the polarization correlation functions for entangled photons are given.

A wide‐angle parabolic wave equation solution, using shift‐map and finite‐difference techniques, is presented. The corresponding split‐step Fourier solution is well known. The solution using finite‐difference technique, where the standard parabolic wave equation is modified into the so‐called Claerbout equation allowing propagation angles up to 45° from the paraxial direction, is also well known. Here, we present an extension to that solution in which the shift‐map technique is incorporated into the finite‐difference scheme allowing a varying terrain to be considered. The result is a solution that corresponds to the well known split‐step solution, which is believed to perform well for terrain slopes up to 10°–15°, and discontinuous slope changes on the order of 15°–20°. This solution is of first order with respect to the terrain slope. The resulting difference scheme is for solving a tridiagonal system. When using the finite‐difference technique, it is also possible to find a second order solution with respect to the terrain slope. The resulting difference scheme in this case is for solving a pentadiagonal system. This new solution performs well for slopes up to about 15°–20° and discontinuous slope changes up to about 30°–40°, which is an improvement.

We prove some micro‐local properties of solutions to hypoelliptic pseudo‐differential operators, using wave‐front sets of Fourier Lebesgue types.

In time reversal acoustics (TRA), a signal is recorded by an array of transducers, time reversed, and then retransmitted into the configuration. The retransmitted signal propagates back through the same medium and retrofocuses on the source that generated the signal. If the transducer array is a single, planar (flat) surface, then this configuration is referred to as a planar, one‐sided, time reversal mirror (TRM). In signal processing, for example, in active‐source seismic interferometry, the measurement of the wave field at two distinct receivers, generated by a common source, is considered. Cross correlating these two observations and integrating the result over the sources yield the cross correlation function (CCF). Adopting the TRM experiments as the basic starting point and identifying the kinematically correct correspondences, it is established that the associated CCF signal processing constructions follow in a specific, infinite recording time limit. This perspective also provides for a natural rationale for selecting the Green’s function components in the TRM and CCF expressions. For a planar, one‐sided, TRM experiment and the corresponding CCF signal processing construction, in a three‐dimensional homogeneous medium, the exact expressions are explicitly calculated, and the connecting limiting relationship verified. Finally, the TRM and CCF results are understood in terms of the underlying, governing, two‐way wave equation, its corresponding time reversal invariance (TRI) symmetry, and the absence of TRI symmetry in the associated one‐way wave equations, highlighting the role played by the evanescent modal contributions.

To determine the grain angle under bark for wooden logs, microwaves are suitable in contrast to a laser system that requires that a part of the bark layer is removed. Such measurements can be used to sort out logs in a sawmill in order to avoid problems in the processing, low quality in finished products and unnecessary costs with sawing, drying and transporting. Since the logs are moving with a high speed, the measurements must be done quickly in real time. To get quick algorithms it has been proposed to model the log with a normal surface impedance rather than as a penetrable cylinder. This paper determines the accuracy in such a modelling by comparing results from the two models in two‐dimensions. The comparison is based on measured values of dielectric data for wood. The conclusion is that there exists a region of moisture content, frequency and azimuthal angle for which the relative error is less than 1% for the longitudinal and less than 10% for the tangential component of the electric field, and still lower for a technically interesting narrow angular region. The induced model error in the determination of the grain angle is about 5% which is of the same order or less than the error introduced by measurement noise.

An investigation of time reversal of nonlinear and non‐dissipative or dissipative plane sound waves was made. Propagation and backpropagation is time reversal invariant only when the dissipation is zero and the wave has not been shocked. A wave that has shocked has irretrievably lost part of its content. Still, if the wave and its derivatives are considered continuous there remain in theory forever information about the original signal. Factors like numerical accuracy and noise naturally set limits in practical situations.

An important topic in the area of airborne sound propagation is the prediction of sound propagation above an impedance ground with an atmospheric profile whose sound speed varies with height. Even if this problem is simple in concept, it leads to complications for general velocity profiles. This work illustrates the existence of a large class of realistic atmospheric profiles for which analytical solutions exist to be used as benchmark solutions for numerical methods. Spectral finite element results are discussed for sound propagation in a half‐space situated above a ground surface impedance.

Strong electromagnetic waves can cause upset in and even destruction of electronic equipment. Therefore, the vulnerability of electronic equipment has to be tested. To be able to quantify the test, an unequivocal test parameter has to be defined. In the case that a plane wave is stressed onto the equipment it is easy; the strength of the electric field is an unequivocal test parameter. In an electromagnetically complex environment with electric fields polarized along different directions it is not so obvious what the test parameter should be. A reverberation chamber is an example of such a complex environment. Some people in the community advocate that a rectangular component of the field is the best measure of the strength of the field, but others advocate for that the total field (the vector sum of three orthogonal field components) is the best. The most generic standard, the IEC 61000‐4‐21 prescribes the use of the rectangular component, but others prescribe the use of the total electric field. In this...

The Multilevel Fast Multipole Algorithm (MLFMA) is a well known and very successful method for accelerating the matrix‐vector products required for the iterative solution of Helmholtz problems. The MLFMA is based on an addition theorem which suffers from the so‐called low‐frequency (LF) breakdown, due to numerical roundoff error. Here, a new addition theorem will be developed which does not suffer from an LF breakdown. Instead it suffers from a High‐Frequency (HF) breakdown. The new addition theorem is based on a novel set of distributions, the so called pseudospherical harmonics, closely related to the spherical harmonics. The so‐called translation operators can be calculated in closed form, which allows the easy implementation of an LF‐stable MLFMA.

This study presents a model of transverse vibrations in a log with a weak part. The aim is to use this model for the inverse application to find the weak part from measurements of transverse vibrations. More precisely, an optimization procedure based on the square of the difference, between measurements and simulations from the model is formulated. The error in the location of the weak part, caused by noise in measurements, can be reduced by including the spatial derivative of transverse vibrations in the optimization and by choosing an optimal frequency. It is shown that for a weak part with no spatial extension along the log, a weak layer, the optimal frequency is a resonance frequency. The a priori information that there is a weak part makes it possible to use wavelengths much longer than the size of the weak part.

We numerically solve Schrodinger’s wave equation under boundary conditions which generate strong chaotic dynamics. A particular system of interest is a 2D open stadium cavity. In general, we see ample fluctuations in the transport coefficients as a function of wave number. We have carried out detailed statistical analysis of such fluctuations in a wide range of the wave number. As a result, we have found some statistical transition of the fluctuations and it is intimately related to the degree of coherence of the quantum waves in the chaotic cavity.

This paper addresses modeling of a clamped boring bar using Euler‐Bernoulli beam theory. Euler‐Bernoulli beams with a number of different boundary conditions were used to model a clamped boring bar. Estimates of the boring bar’s natural frequencies and mode shapes were produced with each of the boring bar models. The estimates produced by the distributed‐parameter system models are compared with eigenfrequencies and mode shapes estimated based on experimental modal analysis of the actual boring bar clamped in a lathe.

The seismic imaging/inversion problem in reflection seismology is revisited. It is argued that the complete and correct incorporation of the multiple scattering is pivotal for the development of improved algorithms beyond linearization approaches. To this end, the incorporation of appropriate prior information is a key idea; even the brute force optimization, or model matching, approaches, which incorporate multiple scattering through their repeated numerical solution of the direct problem, require prior information in the form of an initial velocity model to be successful. The basis for the development of a full multiple‐scatter reconstruction algorithm, absent any initial velocity model, is the application of phase space and path integral methods as applied to classical wave propagation theory, computation, and modeling. Taking the operator symbols as the “data,” and using interplays between (1) time‐and frequency‐domain methods and (2) operator symbols and their “wave field representations,” a direct (...

A class of the Schroedinger type equations, with respect to functions defined on the product of [0;∞) (“time”) and of the p‐adic field (“space”), is considered. In the equation a Vladimirov operator substitutes the standard Lalacian. The main aim of the paper is to get representations of solutions of Cauchy problems for such equations by integrals over Feynman pseudomeasures on paths in the p‐adic field (which is spacial domains of the solutions). The significant role is played by some p‐adic analogs of Poisson–Maslov measures which are constructed in the paper and are used to get the representations.

Reliable characterization of the propagation environment and channel modelling of mobile satellite communication systems is necessary in order to provide better quality of service and efficient design of these systems. In this paper, the channel impairments affecting the performance and an overview of the satellite channel models are presented. The statistical distributions of the received signal that can be used to characterize the dynamic nature of these propagation channels are also presented. The main modelling parameters are investigated and simulation results show that the bit error rate (BER) performance is predominantly affected by the shadowing factor. Finally, in order to further test the channel models and the effect of the propagation environment, we investigate a novel application of using satellite diversity in conjunction with compact MIMO (multiple‐input multiple‐output) antenna array configurations in order to enhance the capacity of satellite communication links.

The Fock functions are mainly used in diffraction theory. A problem relating to these functions arises when accurate numerical computation of integrals with certain exponentials is needed. An integration contour that essentially solves this problem for the Fock scattering functions is discussed.

This paper is an attempt to reproduce predictions of quantum mechanics (QM) on probability of detection by starting with classical random field (e.g. random electromagnetic field). Thus it is an attempt to go beyond QM. The crucial point of our approach is that density operators of QM can be represented as covariance operators of classical random fields. Born’s rule can be obtained from measurement theory for classical random field under the assumption that the probability of detection of field is proportional to the power of this field.

We consider the nonlinear equation i partial derivative(t)psi = (root-Delta+m(2) - m)psi - (vertical bar x vertical bar(-1) * vertical bar psi vertical bar(2))psi on R-3 describing the dynamics of ...

Electro-magnetic scattering is studied in a waveguide with varying shape and crosssection. Furthermore, an impedance or admittance condition is applied to two of the waveguide walls. Under the cond ...

The diffraction problem of a plane electromagnetic wave incident on an ideally conducting grating is solved with the Wiener‐Hopf‐Fock method. In contrast to the standard Wiener‐Hopf method having a single integral equation, the boundary value problem is reduced to a system of integral equations. The short wave asymptotic solution of this system is obtained by means of the saddle point method and expressed in terms of the etalon integral. It contains a resonant denominator which determines the eigenfrequencies of the grating. A precision not below the inclusion of tertiary diffractions is provided by using the saddle point method and the etalon integral for the main contribution of the integrals in the solution. The given method has a clear advantage when the grating consists of a finite number of strips.

One method to characterize the radiated microwave field from a high‐power microwave (HPM) source is to measure the radiated high‐level electromagnetic field in several locations at a high sampling rate registering the frequency time dependence, thus being able to determine the radiated pattern and mode. A complete free‐field measurement system for measuring the magnetic field component in high‐level electromagnetic fields has been developed at FOI.The system consists of a B‐dot sensor and a balun, both designed and constructed at FOI. The B‐dot sensor is designed as two cylindrical loop sensors with differential output. The balun is a microstrip design etched on a dual sided PTFE circuit board. Complete systems have been calibrated at SP Technical Research Institute of Sweden. A method to analyze the data from the free‐field systems has been developed.

Nonthermal radiation observed from astrophysical systems containing relativistic jets and shocks e.g. gamma-ray bursts (GRBs) active galactic nuclei (AGNs) and microquasars commonly exhibit power-law emission spectra. Recent PIC simulations of relativistic electron-ion (or electron-positron) jets injected into a stationary medium show that particle acceleration occurs within the downstream jet. In collisionless relativistic shocks particle (electron, positron and ion) acceleration is due to plasma waves and their associated instabilities (e.g. the Weibel (filamentation) instability) created in the shock region. The simulations show that the Weibel instability is responsible for generating and amplifying highly non-uniform small-scale magnetic fields. These fields contribute to the electron's transverse deflection behind the jet head. The resulting ``jitter'' radiation from deflected electrons has different properties compared to synchrotron radiation which assumes a uniform magnetic field. Jitter radiation may be important for understanding the complex time evolution and/or spectra in gamma-ray bursts, relativistic jets in general and supernova remnants., 19 pages,7 figures, contributed talk at Seventh European Workshop on Collisionless Shocks, Paris, 7- 9 November 2007. High resolution version can be obtained at http://gammaray.nsstc.nasa.gov/~nishikawa/shockws07.pdf

Nonthermal radiation observed from astrophysical systems containing relativistic jets and shocks, e.g., gamma-ray bursts (GRBs), active galactic nuclei (AGNs), and microquasars commonly exhibit power-law emission spectra. Recent PIC simulations of relativistic electron-ion (or electron-positron) jets injected into a stationary medium show that particle acceleration occurs within the downstream jet. In collisionless, relativistic shocks, particle (electron, positron, and ion) acceleration is due to plasma waves and their associated instabilities (e.g., the Weibel (filamentation) instability) created in the shock region. The simulations show that the Weibel instability is responsible for generating and amplifying highly non-uniform, small-scale magnetic fields. These fields contribute to the electron's transverse deflection behind the jet head. The resulting "jitter" radiation from deflected electrons has different properties compared to synchrotron radiation, which assumes a uniform magnetic field. Jitter radiation may be important for understanding the complex time evolution and/or spectra in gamma-ray bursts, relativistic jets in general, and supernova remnants., Comment: : 4 pages, 1 figure and 1 table, typos are corrected, submitted for the Proceedings of The 4th Heidelberg International Symposium on High Energy Gamma-Ray Astronomy, July 7-11, 2008, in Heidelberg, Germany

The onboard Data Processing Unit (DPU), designed and built by Southwest Research Institute, performs the high‐speed data acquisition for GBM. The analog signals from each of the 14 detectors are digitized by high‐speed multichannel analog data acquisition architecture. The streaming digital values resulting from a periodic (period of 104.2 ns) sampling of the analog signal by the individual ADCs are fed to a Field‐Programmable Gate Array (FPGA). Real‐time Digital Signal Processing (DSP) algorithms within the FPGA implement functions like filtering, thresholding, time delay and pulse height measurement. The spectral data with a 12‐bit resolution are formatted according to the commandable look‐up‐table (LUT) and then sent to the High‐Speed Science‐Date Bus (HSSDB, speed=1.5 MB/s) to be telemetered to ground. The DSP offers a novel feature of a commandable & constant event deadtime. The ADC non‐linearities have been calibrated so that the spectral data can be corrected during analysis. The best temporal resolution is 2 μs for the pre‐burst & post‐trigger time‐tagged events (TTE) data. The time resolution of the binned data types is commandable from 64 msec to 1.024 s for the CTIME data (8 channel spectral resolution) and 1.024 to 32.768 s for the CSPEC data (128 channel spectral resolution). The pulse pile‐up effects have been studied by Monte Carlo simulations. For a typical GRB, the possible shift in the Epeak value at high‐count rates (∼100 kHz) is ∼1% while the change in the single power‐law index could be up to 5%.

We report on how the the GLAST Burst Monitor (GBM) Flight Software will detect gamma‐ray rate increases, a process known as “triggering”, and on how the Flight Software will locate and classify the causes of the triggers.

The GLAST Burst Monitor (GBM) is designed to provide wide field of view observations of gamma‐ray bursts and other fast transient sources in the energy range 10 keV to 30 MeV. The GBM is composed of several unshielded and uncollimated scintillation detectors (twelve NaI and two BGO) that are widely dispersed about the GLAST spacecraft. As a result, reconstructing source locations, energy spectra, and temporal properties from GBM data requires detailed knowledge of the detectors’ response to both direct radiation as well as that scattered from the spacecraft and Earth’s atmosphere. This full GBM instrument response will be captured in the form of a response function database that is derived from computer modeling and simulation. The simulation system is based on the GEANT4 Monte Carlo radiation transport simulation toolset, and is being extensively validated against calibrated experimental GBM data. We discuss the architecture of the GBM simulation and modeling system and describe how its products will be used for analysis of observed GBM data. Companion papers describe the status of validating the system.

The Gamma Ray Large Area Space Telescope (GLAST), scheduled for launch in 2006, comprises a Large Area Telescope (LAT) and a GLAST Burst Monitor (GBM). The LAT is a pair telescope with unprecedented sensitivity in the 20 MeV to 300 GeV energy range. The GLAST Burst Monitor consists of an array of NaI and BGO scintillation detectors operating in the 10 keV to 25 MeV range and covering a wide field of view. The GBM will enhance LAT observations of GRBs by extending the spectral coverage into the range of current GRB databases, and will provide a trigger for repointing the spacecraft to observe delayed emission from bursts outside the LAT field of view.

The GLAST Burst Monitor (GBM) comprises 12 NaI and 2 BGO detectors dispersed about the GLAST spacecraft. The GBM instrument simulation software must generate an accurate response function database for all detectors in their flight configuration to optimize the mission science return. Before science analysis codes use the response database, we must confirm that our simulation codes and models can reproduce laboratory observations. To validate the simulation effort, Monte Carlo results are compared to calibrated laboratory measurements collected with a variety of radiation sources.

The GLAST Burst Monitor (GBM) consists of 12 NaI detectors and 2 BGO detectors mounted on two sides of the spacecraft. This provides detection capability for energies between 10 keV and 30 MeV, and sensitivity to all directions in the sky. Extensive measurements using radioactive sources have been performed on the isolated detectors. Simulations of these measurements using the GEANT4 Monte Carlo radiation transport simulations toolset have also been preformed. For gamma‐ray burst the spacecraft itself will have a significant impact on the detector response, therefore the final stage of validations involves measuring the detector response to radioactive sources after the spacecraft is fully assembled, and validating the results using simulation. Details of these simulations will be given in this paper.