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Tom's Input (12-11-2007)
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Tom's Data Catalog FAQs Contributions:How do I access/download a single file from a Monte Carlo task? If you run a web browser on a SLAC machine, then go to the dataCatalog, http://glast-ground.slac.stanford.edu/DataCatalog, You can also download files to your home site by running the web browser on one of your own machines. The dataCatalog downloader should just work. How do I tell the simple skimmer which datasets to read? First, navigate to the desired files in the dataCatalog, http://glast-ground.slac.stanford.edu/DataCatalog, by using the left-hand column, e.g. MC-Tasks -> ServiceChallenge -> How do I access/download a single file from a Monte Carlo task? If you run a web browser on a SLAC machine, then go to the dataCatalog, http://glast-ground.slac.stanford.edu/DataCatalog, You can also download files to your home site by running the web browser on one of your own machines. The dataCatalog downloader should just work. How do I tell the simple skimmer which datasets to read? First, navigate to the desired files in the dataCatalog, http://glast-ground.slac.stanford.edu/DataCatalog, by using the left-hand column, e.g. MC-Tasks -> ServiceChallenge ->
Excerpts from: GLAST Data Access and Analysis-PDFLAT Photon and Event Data. Photon and event data will be served through the GSSC’s LAT data server. The GSSC populates the photon database based on event data received from Events are all triggers reconstructed by the LISOC and will include, e.g., electrons and protons in addition to photons. There are about 200 parameters associated with each event. Based on these parameters, a subset of events are classified as gamma-ray photons. We then use only the events classified as photons and extract about 20 of the 200 parameters for each photon that are most useful for scientific analysis to populate the photon database. Most users will only need the photon data, but the event data will be there for those who wish to rescreen the data themselves. New data will be added to the sever as soon as they are received from the LISOC. This will occur within 72 hours of the data being taken but likely in much less time. A variety of source catalogs will be served through Browse. Burst and transient catalogs will be updated on a per event basis. Other catalogs will be updated infrequently. Also available will be an interstellar emission model. This will be refined as the mission progresses and updated infrequently. LAT Data Server. The LAT Data Server will provide users with access to events, photons, and The user enters the desired position with optional energy and time cuts and will then be served a page with the estimated query time and a link to a results page. When the data files are ready (FITS files), they will be made available for download on the results page. The data server is implemented as a small cluster of Linux PCs which operate on event lists stored in FITS files. Based on the user's query, the photons matching the data cuts are extracted and presented to the user as a downloadable FITS file. The photon and event databases will be updated immediately when new data are received by the GSSC from the LAT instrument team. Spacecraft Data. In addition to the science data, various data products dealing with the spacecraft will be available via the GSSC website to help proposers and observers. These Data Properties and Data Analysis. The LAT will detect photons that can be used in data analysis up to ~66º offaxis. The effective area decreases off-axis, but the solid angle increases, and therefore a large fraction of the data will be taken off-axis. The GBM will detect bursts down to the Earth’s limb. While GLAST can point at individual sources, there will rarely be any advantage because of the LAT’s large FOV. Usually GLAST will rock ~35° above and below the orbital plane once per orbit for uniform sky coverage. The LAT’s PSF will be ~3.5º at 100 MeV, <0.15º at 10 GeV (68% containment radius) with significant tails that will decrease as a power law with radius. LAT sources will be observed against a bright spatially varying Galactic and isotropic Extragalactic diffuse background. The average LAT count rate from astrophysical sources (including the background) will be 2-3 counts/s. Most persistent sources will be observed by the LAT at a variety of detector orientations; each count must be analyzed using the response function appropriate for the detector orientation when the count was detected. Counts from different sources, including the diffuse background, will often overlap. The Standard Analysis Environment. The GSSC will provide a suite of data analysis tools and libraries for use in analyzing the GLAST data called the Standard Analysis Environment (SAE) which is being developed by the instrument teams with assistance from the GSSC. General Analysis: The SAE will consist of several general purpose tools to assist in analyzing data including a data sub-selection tool, tools to generate source models and extract source parameters from existing catalogs, and the workhorse of the GLAST data analysis, the Likelihood GRBs: The SAE will provide several tools to assist in the study of Gamma-ray bursts including tools for spectral and temporal data analysis and model fitting as well as tools for generating the necessary response functions and binning events for analyzing GLAST data with existing tools Pulsars: The SAE will provide a number of tools to assist in pulsar analysis including a barycenter arrival time correction tool, period search and profiling tools, and a pulsar ephemeris extraction tool to retrieve pulsar ephemerides from a pulsar database. Data Simulation: The SAE also provides an observation simulator that can simulate LAT data based on an input source model and optional spacecraft orbit profile. FTOOLS—The SAE will be standard FTOOLS. A GUI interface will also be provided. Generic FTOOLS utilities can be used on the GLAST data files. Documentation—The GSSC website will provide online and printable manuals including an Installation Guide, reference manual (description of all inputs to each tool), analysis threads (step-by-step examples), and a detailed manual (the methodology implemented in each tool). Likelihood Tools For a typical analysis the source model must include: all point sources within a few PSF radii of the region of interest; diffuse sources (e.g., supernova remnants); diffuse spatially variable Galactic emission (which must be modeled); and diffuse isotropic extragalactic emission. A very The data consist of both the counts that were detected, and the regions of parameter space where counts were not observed. A comparison of the likelihood for different models (e.g., with and without an additional point source) will indicate which model is preferred. The best-fit model GLAST Data Products - Where to get:from GSSC's LAT Data Server:
from HEASARC's Browse:
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CALDB
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from GSSC's Website:
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