GRB Simulations in DC2 Valerie Connaughton with input from Nicola Omodei and David Band.

2 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 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 Support for flight science production. see

3 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.

4 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 – ???

5 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.

6 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.

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

8 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 simulator Fit the GBM spectrum with the Band function GRB_xxx.DEF GRB_xxx.PAR GRB_xxx.lc GBM simul.sw PHA,RSP,BKG For each GBM detector FluxFluxSvc/GLEAM observationSim LAT ScienceTools PHA,PHA2,RSP

9 Generation of GBM Data Products Inputs are outputs of GRB Simulator: Burst definition file e.g. GRBOBS_ 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_ 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.

10 Generation of GBM Data Products, cont. Output (a file for each burst-facing detector): –Time tagged events e.g. GLG_TTE_N1_BN _V01.FIT –Response matrices e.g. GLG_CSPEC_B1_BN _V01.RSP –Background spectra e.g. GLG_BCK_N7_BN _V01.BAK –Rates for trigger  4000 s in two versions with different spectral and temporal resolution e.g. GLG_CSPEC_N9_BN _V01.FIT and GLG_CTIME_N9_BN _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.

11 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 spectral catalog GRBs in LAT Sky map

12 LAT/GBM Joint Spectral Fit Tutorial written by Nicola available at: M/GBMandLAT.html M/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).

13 GBM Light Curves GBM light curves for LAT, BGO and brightest NaI detectors

14 LAT/GBM joint spectral fit (cont’d) Parameters retrieved in a time-integrated analysis with XSPEC: /- 0.1, /- 0.03, 84 +/- 8 keV with a reduced chi2 < 1.

15 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 Close-out 2—3 months later