# Presentation: 087458

## GBM Simulation and Instrument Response

**R. Marc Kippen**
*Space and Atmospheric Sciences Group*
***Los Alamos National Laboratory***

## GBM Detector / Instrument Response

**GBM Detector / Instrument Response**

**GRB Photon Spectrum**

**Instrument Response**

**Instrument Background**

**Observed Data**

## Simulation and Detector Response Software

**Definition:  **Multi-purpose software suite that computes the physical and instrumental response of the GBM instrument system
**Primary purpose**: generate *detector response functions* critical to the analysis of flight science data
**Other uses**: instrument design; interpretation of calibrations; design of flight and ground analysis algorithms & s/w
**Technique:  **Numerical simulation — Monte Carlo radiation transport
***Verified through, and incorporating results from experimental calibration***

**Major Components**
- Mass model (geometry + composition)
- Incident particle distributions
- Radiation transport physics
- Instrumental/calibration effects
- DRM database
- DRM synthesizer/generator

## Key Functional Specifications

**GBM SIM/DRM S/W Functional Specs**
**	**GBM-SPEC-1025 (reviewed at GSW PDR)
**GBM IODA S/W Functional Specs**
**	**GBM-SPEC-1031 (reviewed at GSW PDR)
**Complete and accurate interaction physics (included in core simulation package — GEANT4)**
**Accurate mass models, environment models, and instrument models (but not overly complex)**
**Later stages of development require S/C models (including LAT model)**

**Verification through comparison with experimental data**
**Final DRMs must include contribution from atmospheric scattering (+direct detector and S/C scattered response)**
**GLAST S/C will have rapid slew capability — different DRMs are required whenever aspect changes by > 1°**
**DRM generation s/w is part of GBM IODA s/w and subject to the same requirements for standards, configuration control, etc.**

## Development Organization

**SIM/DRM software designed and developed at LANL in collaboration with GBM PI and GSW lead**
**Development process falls under GSW Development Plan (GBM-PLAN-1023)**
**Final products (s/w and data) delivered to GBM PI at NSSTC (also available to MPE and other interested parties)**

## Phased Software/Model Development

**Software and models require cross-validation with calibration data**
**Three phases of SIM/DRM sw/model development**
**Design**
**Simulate prototype detectors**
**Calibration**
**Simulate three levels of calibration/test**
*Detector level*
*GBM system level*
*On-spacecraft level*
**Operation**
**In-flight configuration appropriate for analysis of science data**
**DRM generation**

## Implementation: GBM REsponse Simulation System

**Integrated package that will encompass all GBM instrument response software and data needs**
**Configuration controlled as a single deliverable package with component software/data modules**
**All packages (and their dependencies) use GNU compilers — mainly g++**
**All data files have headers with detailed version & job tracking data**
**Final phase package will be a subset of the GBM IODA software, cf. GBM-SPEC-1036 (GSW Arch. Design)**

**gbmsim**
- GBM instrument
- physical simulator

**calsim**
- Instrumental/calibration
- effects & data packager

**atmosim**
- Atmospheric scattering
- simulator

**drmgen**
- Application-specific DRM
- generator

**GRESS**

**arpack**
- Atmospheric scattering
- data packager

## Implementation: GBM REsponse Simulation System

**Implementation:**** ****G****BM ****RE****sponse ****S****imulation ****S****ystem**

**gbmsim**

**calsim**

**atmosim**

**GRESS**

**root**
**files**

**armdb**

**drmdb**

- Mass model

- Mass model

- Cal.
- Params.

- Cmds.

- Cmds.

- Cmds.

- Application
- Specific
- DRM

- Source Location
- Software
- (SSC & IOC)

- Data Analysis
- Software
- (IOC)

**IODA**

- Spectrum
- or DRM

- Spectrum
- or ARM

**caldb**

**drmgen**

- Aux. data

- Note:  a separate, reduced DRM/ARM
- database is used for BAP software
- (based on same simulation data)

**arpack**

**root**
**files**

**GRESS/IODA**
**Overlap Area**

## How – Direct Instrument Response

**How – *****Direct***** Instrument Response**

**gbmsim** — Raw “physical” data

**calsim** — Packaged, instrument-like data

## How – Atmospheric Scattered Response

**atmosim** — Raw “physical” data

**arpack** — Packaged data matrix

- NRLMSISE-2000 atmospheric model used
- to create concentric shell mass model

## How — Putting it all Together

**How — Putting it all Together**

**drmgen** — burst-specific response generator

**Data Analysis** – spectral fitting and localization

## How — Response used for Spectral Analysis

**Model GRB Spectrum**

**rmfit/xspec** — spectral model “hypothesis testing”

- Parameterized spectral models
- Built-in models or “custom” models

**Total Det. Response**

**Background Model**

**Observed/Predicted Counts**

- iterate

- From drmgen
- Updated automatically when S/C pointing changes

- Empirical, time-dependent model based on data before and after burst

- Observed and predicted counts compared via test statistic
- Chi-squared (Gaussian) or Poisson log Likelihood
- Optimize test Stat. iteratively

- Process is extended to simultaneously include multiple GBM detectors (Incl. NaI and BGO) or other instruments (e.g., LAT, Swift, etc.)

## How — Response used for Localization

**How — Response used for Localization**

- Internal
- response
- generator

**caldb**

- Trial Spectral Parameters

- Simultaneous spatial/spectral model “hypothesis testing”

- S/C attitude/ position

- Predicted
- detector counts

- Observed Det. counts

- Chi-square
- evaluation

- Spatial/spectral optimization

- Background model

## Development Status

- SIM/DRM development is affected by:
**Delivery of GBM detector design data/drawings (received June 2004, three months behind original schedule)**
**Delivery of GLAST spacecraft design data/drawings (expected July 2004, three months behind original schedule, initial delivery August 2004)**
**Schedule of GBM calibrations**
**Required to verify SIM/DRM s/w and models**
**Detector level (MPE), system level (NSSTC), spacecraft level (Spectrum) — all slipped due to launch slip.**
- Development status:
**Preliminary versions of GRESS software complete (several months ahead of schedule)**
**Detector model development nearing completion (3 months behind)**
**Spacecraft model development starting (3 months behind)**
- Result:  able to meet required delivery schedule

## SIM/DRM Revised Delivery Schedule

| Milestone  | Date† | Driver | Date |
| --- | --- | --- | --- |
| SIM/DRM Delivery 1
(Det.-level s/w & models) | Nov. 1, 2004
(+4 mo) | Verify s/w & models with GBM detector-level calibrations | Feb. 2005 –
Mar. 2005 |
| SIM/DRM Delivery 2
(Syst.-level s/w & models) | Jun. 15, 2005
(+3 mo) | Verify s/w & models with GBM system-level calibrations | Jul. 2005 –
Sep. 2005 |
| SIM/DRM Delivery 2.1
(preliminary CALDB/DRM) | Nov. 1, 2005
(new) | Support IODA Release 2.2 & 2.3, and Data Challenge 3 | Nov. 1, 2005; Dec. 1, 2005 |
| SIM/DRM Delivery 3
(S/C-level s/w & models) | Jan. 2, 2006
(+3 mo) | Verify s/w & models with GBM spacecraft-level source survey | Feb. 2006 |
| SIM/DRM Delivery 4
(Ops. phase s/w & models) | Apr. 14, 2006
(no change) | Support IODA Release 3
(launch-ready software) | Sept. 1, 2005 |
| SIM/DRM Delivery 5
(Final DRM/CALDB database) | Nov. 1, 2006
(no change) | Support Phase E science/Ops. | Post-launch |

- * All deliveries from LANL to NSSTC
- † Schedule changes from ground s/w CDR reflect changes in
- the GBM calibration schedule (affected by launch slip)

**Stable since GBM System CDR June 2004**

## SIM/DRM Schedule