GRB Simulations in DC2

Valerie Connaughton with input from

Nicola Omodei and David Band.

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Data Challenges

• “End-to-end” alpha testing of science analysis software.– Exercises the simulation/analysis chain from low level detector simulations to

top level science analysis and data servers.

• Walk before running: design a progression of studies.– DC1. Modest goals. Contains most essential features of a data challenge.

• 1 simulated day all-sky survey simulation• find the sources, including GRBs• a few physics surprises• exercise:

– exposure, orbit/attitude handling, data processing pipeline components, analysis tools

– DC2 in early 2006. More ambitious goals, incorporate lessons learned from DC1. ~One simulated month.

• toy one-month catalog.• add source variability (AGN flares, pulsars).• include GBM.

– DC3 in 2007. Support for flight science production.

see http://www-glast.slac.stanford.edu/software/Workshops/Feb04DC1CloseOut/coverpage.htm

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DC2 Gamma-Ray Bursts, new features

• Bursts are generated randomly in time and in more realistic numbers.

• Improvement of the GRB physical model: cut-off, IC.

• GRB phenomenological model redesign.• New ‘class’ model implemented: GRBtemplate is

able to accommodate any GRB model (it reads a file from someone else)

• GBM synchronization.• No longer have to find all the bursts. Focus of

GRB effort for DC2 is joint LAT/GBM spectral analysis.

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GRB DC2 Activities

• Generation of LAT GRB data –Nicola Omodei• Generation of GBM data – David Band using burst

definition and spectral parameter history input from Nicola. Produces TTE, DRM, background data and CTIME and CSPEC in our Level 1 FITS format according to ICD.

• Analysis of LAT data to extract GRB pha and rsp files – Nicola

• Fitting of LAT/GBM spectra with XSPEC – Nicola• Development of SAE temporal analysis tool• Production of GRB data package – Tom Stephens at

GSSC• Modelling of GRBs – Nicola, Jay Norris, Felix Ryde• Regular VRVS meetings among Francesco, Nicola,

David and Valerie.• Deciding what kind of bursts – models, numbers,

realistic Log N-Log P, “interesting” events -- are included – ???

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GRBs at BATSE energies

Bursts are varied in:• Duration.• Intensity (Peak Flux).• Number, width,

separation of peaks.• Fluence.• Spectral characteristics.

Over the large ensemble of BATSE GRBs (2704) these parameters allow us to characterize the GRB population at energies up to ~ MeV.

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GRB characteristic distributions

Typical GRB spectrum characterized at BATSE energies by the Band parameterization α, β, A, Epeak or some similar function where the physical meaning of these parameters is not specified.

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GRB High-Energy Measurements

-18 - 14s

14 - 47s

47 - 80s

80 - 113s

113 - 211s

High-energy (> tens MeV) might be delayed, sometimes persistent beyond BATSE range, might fall above extrapolation of β inferred from lower-energy spectrum.

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LAT and GBM Gamma-Ray Bursts

• Same bursts generation for LAT and GBM detectors• ASTRO takes care of the position of the burst with

respect to the LAT zenith.

XML library

GRB simulatorFit the GBM

spectrum with the Band function

GRB_xxx.DEFGRB_xxx.PAR

GRB_xxx.lc

GBM simul.sw

PHA,RSP,BKGFor each GBM detectorFlux FluxSvc/GLEAM

observationSim LAT ScienceTools PHA,PHA2,RSP

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Generation of GBM Data Products

• Inputs are outputs of GRB Simulator:• Burst definition file e.g. GRBOBS_050718001.def

– Burst name (for file names, headers, also source of date)– Burst time (assumed to be the same in the LAT data)– Burst location in spacecraft coordinates (to calculate

response) and celestial coordinates (for file headers)

• Burst spectral parameters file e.g. GRBOBS_050718001.lc– Time series of spectral parameters (every 16 ms). This is the

input of the burst model. Currently, Band function is the only parameterization.

• Process is suite of IDL programs written by David Band to generate GBM data products in the correct format for a burst occurring at the same time and sky location as that simulated for the LAT.

• Many simplifications: only burst-facing detectors, background is assumed constant, no S/C slewing, incomplete detector response.

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Generation of GBM Data Products, cont.

• Output (a file for each burst-facing detector):– Time tagged events e.g.

GLG_TTE_N1_BN050718001_V01.FIT– Response matrices e.g.

GLG_CSPEC_B1_BN050718001_V01.RSP– Background spectra e.g.

GLG_BCK_N7_BN050718001_V01.BAK– Rates for trigger 4000 s in two versions with different

spectral and temporal resolution e.g. GLG_CSPEC_N9_BN050718001_V01.FIT and GLG_CTIME_N9_BN050718001_V01.FIT

– Rates for day with burst GLG_CSPEC_N9_050718_V01.FIT and GLG_CTIME_N9_050718_V01.FIT

• The spacecraft is assumed to maintain constant orientation during the burst (i.e., no autonomous repoint) so only 1 DRM per file.

• The GBM response and background models were provided by Marc Kippen a few years ago, and are preliminary. The response does not include scattering off the Earth’s atmosphere.

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GRB Analysis procedure in DC2

Package with LAT event data, pointing/livetime and IRF (FT1, FT2 and entries in CALDB)

And GBM TTE, background and DRM files(.FIT, .BAK, .RSP, burst-facing, 1 DRM per detector)

LAT Event binning with gtbin (PHA) LAT DRM gen with gtrspgen (RSP)

Bin GBM TTE data in time with gtbin (PHA)(LAT binning can be read from file)

Feed GBM & LAT data to XSPEC/RMFIT

for joint spectral fit.Use BGO and brightest NAI

GRB spectralcatalog GRBs in LAT

Sky map

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LAT/GBM Joint Spectral Fit

• Tutorial written by Nicola available at: http://glast.pi.infn.it/Nicola/GRBTests/GRB050718001_LAT_GBM/GBMandLAT.html

• Burst generated with phenomenological model and Band function spectral parameters 0.4, 2.25, 90 keV and positions of peaks varying with energy (spectral evolution).

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GBM Light Curves

• GBM light curves for LAT, BGO and brightest NaI detectors

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LAT/GBM joint spectral fit (cont’d)

• Parameters retrieved in a time-integrated analysis with XSPEC: 0.36 +/- 0.1, 2.26 +/- 0.03, 84 +/- 8 keV with a reduced chi2 < 1.

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Next steps for GRBs in DC2

• Perform time-resolved joint GBM/LAT spectral analysis of simulated burst.

• Develop scripts to allow convenient time-resolved spectral analysis using XSPEC.

• Continue development of temporal analysis tool.• Decide number and nature of events in DC2 data

set.• Design web site interface for easy access to burst

data products.

• Science-tool checkout – tomorrow & next week• Kick-off in January 2006. Close-out 2—3 months

later