Earth occultation imaging of the low energy gamma-ray sky with the Fermi/Gamma-ray Burst Monitor

The hard X-ray/soft gamma-ray sky is highly variable as source intensities can vary on timescales from fractions of a second to years. The type of sources emitting at these energies often include compact objects such as white dwarfs, neutron stars, and black holes interacting with the surrounding environment, which enables the study of the properties and characteristics of these exotic objects. Because the interactions with the environment is often through accretion, most of the emission is in X-rays and gamma-rays Frank et al. 1992 making this energy range critical to understanding the relevant physical processes and mechanisms. Hard X-ray/soft gamma-ray (10 keV - 1 MeV) photons are difficult to focus requiring alternative observing techniques to monitor sources in this energy range. One method is the Earth Occultation Technique (EOT) that uses the rapid change in count rate (~sim 10 sec) due to a source passing behind (or out from behind) the Earth to measure source intensity. The EOT has been applied to the Gamma-ray Burst Monitor (GBM) on board the NASA Fermi satellite since its launch in 2008 and has been performing all-sky monitoring of a predetermined catalog of ~200 hard X-ray/soft gamma-ray sources. Because the EOT requires prior knowledge of a source\u27s position for monitoring, I have developed a tomographic imaging method Imaging with a Differential filter using the Earth Occultation Method (IDEOM) to generate all-sky images in search of sources absent from the input catalog to construct a catalog as complete as possible. A complete catalog is important for reducing a source of systematic error as the flux from an unaccounted-for source can be attributed to a known source thus biasing its flux measurement. Approximately 4 years of GBM data have been analyzed to produce all-sky images covering the 12-50 keV, 50-100 keV, and 100-300 keV energy bands with 16 sources being added to the GBM catalog. All-sky images are shown for each energy range along with a table listing the sources detected by IDEOM. Also, the list of sources detected by IDEOM has been compared to those detected by EOT in each energy band. In addition, spectral analysis was performed in the four persistent sources detected by GBM and the Fermi/Large Area Telescope (LAT) (NGC 1275, 3C 273, Cen A, and the Crab) thus providing energy coverage from ~10 keV to ~100 GeV to study the high energy emission processes of these sources. Spectral results from GBM and LAT are presented and shown to be in agreement with previously proposed models in the literature. Finally, I have also developed a transient search algorithm to search for flares and outbursts in the light curves of GBM sources. This algorithm was applied to the ~200 sources in the GBM catalog to search for transient events during the first four years of the mission in four energy bands covering 12-500 keV. The search resulted in 168 transient events found from 65 sources with 7 events detected above 50 keV and 1 event detected above 100 keV (XTE J1752-223). A table of start and stop times are listed for each event and energy band, and example light curves are shown for GK Per, GX 339-4, and XTE J1752-223

Soft Gamma-Ray Spectral and Time evolution of the GRB 221009A: prompt and afterglow emission with INTEGRAL/IBIS-PICsIT

The gamma-ray burst (GRB) 221009A, with its extreme brightness, has provided the opportunity to explore GRB prompt and afterglow emission behavior on short time scales with high statistics. In conjunction with detection up to very high-energy gamma-rays, studies of this event shed light on the emission processes at work in the initial phases of GRBs emission. Using INTEGRAL/IBIS's soft gamma-ray detector, PICsIT (200-2600 keV), we studied the temporal and spectral evolution during the prompt phase and the early afterglow period. We found a "flux-tracking" behavior with the source spectrum "softer" when brighter. However the relationship between the spectral index and the flux changes during the burst. The PICsIT light curve shows afterglow emission begins to dominate at ~ T0 + 630s and decays with a slope of 1.6 +/- 0.2, consistent with the slopes reported at soft X-rays.Comment: 6 pages, 4 figures, A&A Accepte

Bayesian Neural Networks for Geothermal Resource Assessment: Prediction with Uncertainty

We consider the application of machine learning to the evaluation of geothermal resource potential. A supervised learning problem is defined where maps of 10 geological and geophysical features within the state of Nevada, USA are used to define geothermal potential across a broad region. We have available a relatively small set of positive training sites (known resources or active power plants) and negative training sites (known drill sites with unsuitable geothermal conditions) and use these to constrain and optimize artificial neural networks for this classification task. The main objective is to predict the geothermal resource potential at unknown sites within a large geographic area where the defining features are known. These predictions could be used to target promising areas for further detailed investigations. We describe the evolution of our work from defining a specific neural network architecture to training and optimization trials. Upon analysis we expose the inevitable problems of model variability and resulting prediction uncertainty. Finally, to address these problems we apply the concept of Bayesian neural networks, a heuristic approach to regularization in network training, and make use of the practical interpretation of the formal uncertainty measures they provide.Comment: 27 pages, 12 figure

Three years of Fermi GBM Earth Occultation Monitoring: Observations of Hard X-ray/Soft Gamma-Ray Sources

The Gamma ray Burst Monitor (GBM) on board Fermi has been providing continuous data to the astronomical community since 2008 August 12. In this paper we present the results of the analysis of the first three years of these continuous data using the Earth occultation technique to monitor a catalog of 209 sources. From this catalog, we detect 99 sources, including 40 low-mass X-ray binary/neutron star systems, 31 high-mass X-ray binary neutron star systems, 12 black hole binaries, 12 active galaxies, 2 other sources, plus the Crab Nebula, and the Sun. Nine of these sources are detected in the 100-300 keV band, including seven black-hole binaries, the active galaxy Cen A, and the Crab. The Crab and Cyg X-1 are also detected in the 300-500 keV band. GBM provides complementary data to other sky-monitors below 100 keV and is the only all-sky monitor above 100 keV. Up-to-date light curves for all of the catalog sources can be found at http://heastro.phys.lsu.edu/gbm/.Comment: 24 pages, 12 figures, accepted for publication in ApJ

1,3-Bis(prop-2-yn­yl)-1H-1,3-benzimid­azol-2(3H)-one

In the title compound, C13H10N2O, the fused-ring system is essentially planar, the largest deviation from the mean plane being 0.015 (1) Å. The two propynyl groups are nearly perpendicular to the benzimidazole plane, making dihedral angles of 85 (3) and 80 (2) °, and point in opposite directions. There are two short inter­molecular C—H⋯O contacts to the carbonyl O atom, one involving the acetyl­enic H atom and the other a H atom of the methyl­ene group

Resource Characterization of Sites in the Vicinity of an Island near a Landmass

This is the author accepted manuscript. The final version is available from the publisher via the DOI in this record.Renewable energy technologies are undergoing rapid development, the global aim being to achieve energy security and lower carbon emissions. Of marine renewable energy sources, tidal power has inherent predictability and large theoretical potential, estimated to exceed 8000 (TW h)a−1 in coastal basins. Coastal sites in the vicinity of an island near a landmass are prime candidates for tidal stream power exploitation by arrays of turbines. This paper characterizes numerically the upper limit to power extraction of turbines installed at such sites. It is demonstrated that the maximum power extracted from the strait is generally not well approximated by either the power dissipated naturally at the seabed or the undisturbed kinetic power of flow in the strait. An analytical channel model [C. Garrett and P. Cummins, “The power potential of tidal currents in channels,” Proc. R. Soc. A Math. Phys. Eng. Sci., vol. 461, no. 2060, pp. 2563–2572, Aug. 2005] provides lower predictions than the present numerical model of available power in the strait due to the analytical model not accounting for changes to the driving head resulting from power extraction and flow diversion offshore of the island. For geometrically long islands extending parallel to the landmass, the numerically predicted extracted power is satisfactorily approximated by the power naturally dissipated at the seabed, and there is reasonable agreement with the estimate by the channel analytical model. It is found that the results are sensitive to choice of boundary conditions used for the coastlines, the eddy viscosity, and bed friction. Increased offshore depth and lower blockage both reduce the maximum power extracted from the strait. The results indicate that power extracted from the site can be maximum if extraction is implemented both in the strait and offshore of the island. Presence of the landmass and increasing island dimensions both enhance power extraction.This work was supported by General Electric Renewable Energy with funding from the ETI and the EPSRC through the Industrial Doctoral Centre for Offshore Renewable Energy (EP/J500847/1). The authors would like to thank the Applied Modelling and Computation Group at Imperial College of London for free access to the software Fluidity and their support