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FSSC Science Tools Data Selection and Exploration Fermi Data Analysis Workshop ISDC Saas-Fee Course, 14 March 2010 Elizabeth Ferrara - FSSC 1 Science Analysis Tools Overview of capabilities – Maximum likelihood tool—spatial-spectral analysis of region (source detection, flux) • Includes background models – Pulsars—period analysis, blind searches • Includes ephemerides DB (D4 compatible) • .par files available for TEMPO2 use – GRBs—temporal cuts, spectral analysis: Maximum likelihood tool, XSPEC Tools and documentation are released through FSSC website (http://fermi.gsfc.nasa.gov/ssc/) Fermi Data Analysis Workshop ISDC Saas-Fee Course, 14 March 2010 Elizabeth Ferrara - FSSC 2 Science Tools: Documentation Multi-tier Documentation – Full set accompanies software release • Fermi Mission Technical Handbook – Multiple levels: • Detailed analysis description (‘Cicerone’) • Individual tool descriptions (like fhelp) • Analysis threads (cook book examples) Fermi Data Analysis Workshop ISDC Saas-Fee Course, 14 March 2010 Elizabeth Ferrara - FSSC 3 Science Tools: Structure “Atomic” executables – Allows for divergent analysis without task repetition – Scriptable into more complex analysis chains Standard file types – FITS data i/o – IRAF style param files – XML source models – Text-based supporting files Standard toolsets for astronomy – FV, DS9, XSPEC Fermi Data Analysis Workshop ISDC Saas-Fee Course, 14 March 2010 Elizabeth Ferrara - FSSC 4 Science Tools: Flowchart Fermi Data Analysis Workshop ISDC Saas-Fee Course, 14 March 2010 Elizabeth Ferrara - FSSC 5 Parameter Files Contain parameter defaults or previous values Parameters can be: a = prompted h = hidden Hidden parameters must be given on command line. To keep from overwriting files, set clobber=no Fermi Data Analysis Workshop ISDC Saas-Fee Course, 14 March 2010 Elizabeth Ferrara - FSSC 6 Science Tools: Execution Parameters can be input in three ways – Command line entry - useful for scripting • Allows modification of “hidden” parameters (likely not needed for standard analyses) – Last value stored in param file for next use – Interactive prompted entry • No access to hidden parameters Parameter input can be mixed – %gtselect – %gtselect clobber=no – %gtselect clobber=no, infile=events.fits, outfile=events_cut.fits, etc... Fermi Data Analysis Workshop ISDC Saas-Fee Course, 14 March 2010 Elizabeth Ferrara - FSSC 7 Data Access: File types Events File (2 types) – Photon files contain all needed information for science analysis – Extended files contain additional information about each event that is used for specialized analysis • not needed by any science analysis tool – All event classes are available in both file types 1) Transient - Loose quality definition, significant background contamination 2) Source - Moderate quality 3) Diffuse - Highest quality, lowest background contamination, Use this for most analyses Spacecraft File – Spacecraft Orientation and orbit position information – where are we and where are we pointed – One entry every 30 seconds Fermi Data Analysis Workshop ISDC Saas-Fee Course, 14 March 2010 Elizabeth Ferrara - FSSC 8 Data Access: Downloads Download data from: – http://fermi.gsfc.nasa.gov/ssc/data/analysis/scitools/extract_latdata.html • Allows retrieval of data for a specified region • Default values correspond to suggested data selections for most analysis types – http://fermi.gsfc.nasa.gov/cgi-bin/ssc/LAT/WeeklyFiles.cgi • Weekly files contain all event classes • Weekly spacecraft files are also available – FTP: Can be retrieved automatically using wget • Spacecraft: ftp://legacy.gsfc.nasa.gov/fermi/data/lat/weekly/ • Photon: ftp://legacy.gsfc.nasa.gov/fermi/data/lat/queries/ Fermi Data Analysis Workshop ISDC Saas-Fee Course, 14 March 2010 Elizabeth Ferrara - FSSC 9 Data Access: Data Server - 1 For all-sky data, faster to download these Accessible from Data Access menu Will write DSS position keywords Fermi Data Analysis Workshop ISDC Saas-Fee Course, 14 March 2010 Can use “START” and “END” Elizabeth Ferrara - FSSC 10 Data Access: Data Server - 2 Default energies: 100MeV - 300 GeV Select type(s) of data files For questions, contact the Helpdesk Fermi Data Analysis Workshop ISDC Saas-Fee Course, 14 March 2010 Elizabeth Ferrara - FSSC 11 Data Access: Data Server - Results Search was for 3C 454.3 Save this information for future reference Notice the multiple photon files Fermi Data Analysis Workshop ISDC Saas-Fee Course, 14 March 2010 Elizabeth Ferrara - FSSC 12 Preparing your data • Prior to beginning an analysis you must: – Select the event class (Diffuse in almost all cases) – Exclude time intervals where the bright Earth limb comes close to the edge of your region of interest (zenith angle of 105 degrees give 8 degrees of buffer) • Combine photon files if necessary – For large time ranges you will likely have multiple photon files – Combine using @filelist.txt syntax where filelist.txt is a listing of all photon files to be included, one per line • Combine spacecraft files if necessary – Easiest method is to request the full time range from the data server – Can use fappend to concatenate the files together Fermi Data Analysis Workshop ISDC Saas-Fee Course, 14 March 2010 Elizabeth Ferrara - FSSC 13 Data Selection - 1 Hidden parameters defined on the command line Event-specific cuts can be made with gtselect Time range, energy range, position, ROI radius, zenith angle – Or @filelist.txt Keyword values should correspond EXACTLY to values in header (unless selecting a smaller region) Temporal cuts using spacecraft file keywords are made with gtmktime – This MUST be applied if a zenith cut was used with gtselect Applies zenith angle cut from gtselect Fermi Data Analysis Workshop ISDC Saas-Fee Course, 14 March 2010 Elizabeth Ferrara - FSSC 14 Data Selection - 2 Different cuts should be used for different types of data analysis – Point Source analysis • For hard spectrum sources, localization analysis may benefit from a higher minimum energy cut due to energy-dependent PSF – Pulsar Timing analysis • Requires that spacecraft file span a greater time range than event file • Data server automatically pads the spacecraft file, unless you use START or END time keys – GRB analysis (