# Presentation: 376174

## GLAST Science Simulations

**Julie McEnery**
**NASA/GSFC**

**GLAST Science Simul****ations**

## Flow of Simulation

## Reconstruction Overview

**Goal of the reconstruction:**
**Determine the incident gamma direction and energy**
**Provide tools for suppressing background**
**Follow a two pass approach for Cal and Tracker**
**Best energy from Calorimeter needs tracking information**
**Best tracks from Tracker needs best energy reconstruction**
**Solve by breaking into two passes**
**Background suppression**
**ACD Recon**
**MIP Finder**
**Analysis step at end of reconstruction**
**Create output ntuple for detailed performance studies**
**Event Classification – determine the particle type and quality**
**Create FT1 output for analysis (convert to RA/DEC etc)**

## Background Model

**The background model consists of several components**
**Gamma-ray albedo from the Earth**
**Electron, positron and proton albedo (splash and reentrant)**
**Primary cosmic-ray (Electons, positrons, protons and heavy ions)**
**Background spectra and flux model includes orbit position and direction dependencies.**

## Astrophysical sources

**The sources are defined by creating input files which specify location, flux, spectrum, spatial extent etc**
**Blazar Populations (provide flux, spectra and redshift) **
**Modified version of Chiang and Mukerjee**
**Stecker**
**Giommi (astro-ph/0508034) – this also provides optical - X-ray fluxes**
**Variability models**
**Simple red noise model**
**Inverted PSDs (Timmer and Konig 1995) **
**Shot noise model (Terrel and Olsen 1972)**
**Non-linearity (Uttley et al 2005)**
**Spectral models (for variabilty studies have been fairly simple – power-laws, broken power laws or log-parabola**

## Astrophysical Sources

**Extragalactic background light: for source classes that have been specified with a redshift we can apply a choice of EBL models to attenuate the spectra.**
**Kneiske best fit model (Kneiske et al 2004)**
**Kneiske high-UV (Kneiske et al 2004)**
**Primack99 (Primack et al 1999)**
**Primack05 (Primack et al 2005)**
**Salamon and Stecker 1998**
**Stecker 2005**
**It is relatively straightforward to mix and match population, variability and EBL models.**

## Astrophysical Sources

**Pulsar populations generated using code developed by Alice Harding and Peter Gonthier. Given a pulsar emission model it provides flux, spectra, timing properties and location for populations of radio-loud and radio quiet pulsars.**
**The simulated pulsar spectra are parameterised as**
**The lightcurves are either randomly generated (useful for making a population of pulsars) or can be explicitly specified.**

- Nel and De Jager, 1995

## Astrophysical Sources

**GRB **
**Phenomological: Specify alpha, beta, flux duration and the package will generate a GRB.**
**Physical model: more complete physical simulation**
**Extended sources**
**Individual sources modeled as 2 or 3 d maps (Galactic diffuse, SNR, dark matter etc) **

## Data Challenges 

**A series of end-to-end studies: **
**Produce 1 day; ****one precession period (55 days);**** release this to the collaboration for science analysis.**
**Drives instrument performance studies, exercises detector simulation software.**
**Science input – include in the simulation science/astrophysical features we expect to see in the GLAST gamma-ray sky, verify that the analysis tools can find them.**
**Tests data servers, user level documentation and more...**
**DC1.  Modest goals.   1 simulated day.**
**DC2****, start March 06.  More ambitious goals.  Encourage further development, based on lessons from DC1.  55 day simulation.**

## Data Challenge 2 (March – May 2006)

**55 days of simulated GLAST data**
**Brings together many elements Including: **
**Full (Geant4) detector simulation**
**Realistic detector description (electronic deadtime, some small imperfections)**
**Realistic orbit and attitude profile**
**Updated particle background model (including orbit variations)**
**Updated event reconstruction and event classification analysis**
**Updated instrument response functions**
**Data formats for input to high level tools**
**Plausible model of the gamma-ray sky (This is kept a secret until the close of DC2)**
**Generation of datasets (Level 1 pipeline)**
**Populate and exercise dataservers at GSSC and LAT**
**Alpha test high level science tools and documentation**
**The challenge is for the DC2 participants to figure out the properties of the simulated gamma-ray sky. **

## The DC2 Sky

**DC2 sky in galactic coordinates**

- Plot by Seth Digel

## DC2 Catalog

- Catalog analysis pipeline developed by Jean Ballet and collaborators, runs a source detection algorithm and then runs more detailed analysis on each source to produce a table of the basic gamma-ray properties of each source.
- Released at the beginning of DC2, provides a starting point for more detailed analyses.

- 380 sources

- Verifies the automated pipeline processing from low-level data to source characterization.

## More on Catalogs

- Cross reference the catalog sources against other catalogs to produce identifications.
- Displays the catalog data in an interactive way and links in data from other wavelengths.

- Produced by ASDC group – Giommi and collaborators

## Lightcurves and Spectra

- From the catalog at ASDC, there are links from each source to DC2 data products

- “Quicklook” lightcurves have been produced by Benoit Lott for every source in the catalog.

- Spectral fits for each source were produced by Luis Reyes. These are simple power-law fits, but provide a plot which can guide users to different models if needed.

## More on lightcurves

- The LAT PSF varies rapidly as a function of energy. A simple binned analysis will can only be an approximation because the fractional background level will be a function of source spectrum, and there may be confusion from other nearby sources
- Jennifer Carson and Jim Chiang have been looking at systematic effects associated with using simple binned analysis rather than likelihood to make lightcurves.

- Source flux

- Extragalactic diffuse flux

- Spectral index

- Lightcurve produced with Likelihood analysis

- Comparing flux estimates from likelihood and simple binned analysis

##  Spectral studies of Blazars – Intergalactic Radiaton fields.

- The DC2 data support more sophisticated spectral analyses. Luis Reyes has searched for evidence of attenuation of the gamma-ray flux due to  the EBL background. He looks for high energy cutoffs in blazar spectra which vary in a systematic way with redshift. He uses the results to set constraints on the DC2 EBL model.

## GRB simulations

**In addition to LAT data. Simulated GBM data was generated for a population of bursts.**
**This included all the burst data products and also included a “GCN-like” notice to provide summary GBM information.**
**This allows us to more fully explore the possibilities of GRB studies in the GLAST era. Where we will have data from 10 keV to 300 GeV for many GRB.**

- 64 GBM bursts

## GRB Analyses

- Joint spectral fits –  This illustrates the very broad energy range (10 keV to >300 GeV that GLAST will measure for the prompt phase of GRB (Nukri Komin)

- A search for high energy gamma-ray afterglows discovered a hard bright component occuring several hours after the prompt  emission in one of the simulated bursts (Nicola Omodei)

## GRB Analyses

- A search for bursts in the LAT data found a short, very hard burst which produced a significant signal in the LAT (>5 GeV) but did not trigger the GBM. (Nukri Komin)

- David Band has compared the difference between the LAT determined and GBM determined locations and compared that with the quoted statistical uncertainties to look for systematic offsets.

## Pulsars

- One of the DC2 data products was pulsar ephemerides to describe the subset of “known” pulsars in the DC2 sky.
- Many people have run the GLAST timing tools on the DC2 data – and discovered a bug in the simulation (now fixed).
- Damien Parent wrote a set of scripts to automatically process all the pulsars in the DC2 ephemeris and produce phase plots.

## More Pulsars

-  Markus Ziegler performed a blind search for periodicity in candidate pulsars in the DC2 data (i.e. not using an ephemeris). He found significant periodicity in several of the sources listed in the ephemeris (which is reassuring), and also identified a few “radio-quiet” pulsars.
-  Composite sources:  Riccardo Rando found a source that appears to consist of two components – a steady power-law component and a hard pulsed component

- Power-law point source + background model is a very poor fit to the data

- Phase vs energy plot shows that the pulsed emission dominates above 1 GeV

- Refit with a composite source consisting of a power-law and a log normal component

## Comparing the simulated data with the Model

- Blue line is the sum of the modeled galactic diffuse and extragalactic diffuse emission. The red points are the DC2 data. Differences between them could be due to contributions from point sources, residual particle background or unmodeled diffuse components (from eg dark matter).

- Excess at ~60 GeV!

- Analysis by Andy Strong

## Connecting to VHE energies

**Possibility of extrapolating the source spectra to higher energies to get an estimate of the number of sources detectable by both GLAST and ground-based instruments for given luminosity/redshift distributions and EBL model.**
**For some source classes, the extension of the spectrum to higher energies may need to be more careful than a simple extrapolation.**
**To get an estimate of how many would actually be detected by both, we would need to simulate an observing schedule.**
**All of the astrophysical sources in the GLAST simulation can also be used in a “fast” simulation**
**Skip the full detector simulation and instead produce high level results by convolving source descriptions with parameterisations of effective area, energy and angular resolution. Could this be extended to include VHE instruments?**

## Summary

**All of the results shown here are simulated figments of our imagination. However, they illustrate phenomena that GLAST might and could see after launch.**
**Describing astrophysical source models in a consistent way is extremely useful.**
**An excellent test of our processing pipelines and data handling infrastructure**
**200,000 cpu hours/400 cpus**
**~5 TB of data**
**Provided an opportunity for an early, realistic test of science tools usability. **
**Improve the analysis software and documentation based on user feedback.**
**DC2  closeout will be May 31 – June 2 at GSFC. **
**Participants can present their analyses of the DC2 data.**
**Organisers will reveal the “true” contents of the simulation.**
**The GLAST users committee will beta test the science tools using DC2 data in November 2006.**