GRBSimulation, Triggers and Alerts Studies with GLAST

1
GRBSimulation, Triggers and Alerts Studies with
GLAST

• Pisa Group Report
• N. Omodei, J.Cohen-Tanugi

2
Overview

• GRB Source simulation package
• Current status
• Gleam and GRB
• Validation and calibration of the Model
• Trigger and alerts studies
• New Design ( almost done)
• Improvement clarity
• Extension to other models
• Analysis tools development
• U13 GUI
• A10 Physical fitting engine

3
Gleam GRB

• The LAT team has set up a complete simulation
  chain
• Simulation of the incoming flux
• Background Albedo, Cosmics, Diffuse gamma
• 2 different GRB model approaches
• physical model from shells to photons
• phenomenological model extrapolated from BATSE
• The detector is illuminated in the correct way,
  taking into account the orbit and the tilting of
  the satellite (FluxSvc)
• Simulation of the Detector
• Geant4, Digitization, Reconstruction
• Triggers and GRB Alerts
• The onboard trigger are taken into account
• All the algorithms can be tested on the simulated
  data

4
GRB Simulations The physical model

• The photon list is extracted according with the
  fireball model (Internal Shocks)
• Changing the parameters of the model (Number of
  shells, geometry of the shells,) we can
  reproduce the wild variety of light curves
  observed.
• Synchrotron emission is the prominent radiation
  process used in this model
• The first extension to high energy is the SSC
  emission,
• The physical description of GRB permits to
  investigate the signature of different physical
  phenomena.

5
Validation Calibration of the physical model

• We explore the parameter space obtaining
  different burst with different properties.
• We select a burst duration from the T90
  distribution observed by BATSE
• The bimodal distribution is reproduced.

• We compare the fluences in the BATSE catalog
  with the simulated.
• Scale laws are in this way reproduced (HR vs T90,
  Intensity vs T90)

• This can be useful for
• Calibrating the physical parameters of the model
• We are planning to extend this approach to
  different physical models (External Shock
  scenario, Cannonball model,) !!

Data from BATSE catalog
Simulated Burst catalog
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LAT Trigger Design

• Test of the trigger efficiency (without
  background)
• GRB With different fluences gt 100 MeV
• Number of incident gamma for a given simulated
  burst
• Number of gammas triggered (L1)
• Number of gammas that have been reconstructed
  (Cal recon, Tkr recon)

7
LAT GRB alerts

• LAT can trigger and locate GRB !!
• On board -gt No full reconstruction available.
  -gt Cuts light algorithms (hopefully clever)
• 1 algo already exists Strawman Real-time,
  Unbinned Trigger Algorithm
• Search sliding 20-event window forming their
  N?(N-1)/2 distances.
• Look for clusters of events within 35 cirle
• Form joint spatial and temporal Likelihood for
  events within circle
• L - log ?(??) ? ?(?t) .
• Set threshold such that GLAST sees lt 1 false
  trigger per week.
• Results
• Triggers on 85 of BATSE-like bursts, 233 /
  270 (number per year).
• Triggers on 78 of these bursts visible to
  GLAST in less than one second,
• With fewer than one false trigger per 3 days
• ON GOING WORK
• How to fast determine the direction of a photon ?
• How to select good events ?
• How to fast determine the position of a GRB on
  Board ?
• Are there other triggers more efficient ?

8
New Design Overview
Engine

• The code has to be redesigned
• Improve clarity
• Better organization of the classes
• Separation between co- moving frame and observed
  frame
• Physics processes as separate classes
• Extension to other model and to other scenarios
• Different shells geometry descriptions
• External shock model
• Fireworks model (Barbiellini, Longo Celotti)

Shell
Shock
Physical Processes
SpectObj
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New design The engine

• The engine fill the shock vector, different way
  to do it
• Evolution of the shell
• Positioning the shocks at fixed observed time
  (loosing the knowledge of the shell evolution)

Engine
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New design The Shells
Shells

• Different geometry of the shells
• Spherical fireball
• Jet fireball (collimated)

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New design The Shocks
Shocks
The shocks vector contain all the information
needed to compute the emission.
Internal energy available Density of Particle
accelerated by the shock wave Distribution of
electron accelerated Magnetic field in the
shocked material Thickness of the emitting region
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New design The Physical processes
Redesign of the radiative processes (Syn,
IC) Accessibility to the physics both in the
co-moving frame (shell) in observer Frame
Physical processes
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New design The SpectObj
Spectrum Object
The Spectrum Object is an interface that carries
all the information and methods that permit the
manipulation of a spectrum Algebra of fluxes
( - /), units conversions, Draw photon from
spectrum
Time t
GRBSimulation
SpectObj
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Analysis tools development

• U13 GRB Visualization -gt GUI
• A5 GRB event binning
• A6 GRB rebinning
• Plot Light curves and spectra
• Time histories of the spectral parameters
• Data and model spectra
• A7 GRB Temporal analysis
• Fourier analysis
• Wavelet
• Cross correlations
• Pulse decomposition
• A8 GRB Spectral Analysis (binned)
• Fit and standard spectral analysis
• XSPEC ?
• A9 GRB Spectral Analysis (unbinned)
• A10 Spectral temporal GRB physical modeling
• Estimation of the goodness of fit, using the
  physical model
• Parameter estimator using data
• Put constrains on the different theoretical
  models

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Analysis Tools development GUI

• Prototype of GUI based on Root
• TDSReadFluxAlg -gt Save the incident events in a
  Root file
• (GLAST and Galactic direction, energy time)
• -gt Save the recon events in a Root file
• (GLAST and Galactic direction, energy time)
• Note not only for GRB, but for every kind of
  Gleam based spectrum !!
• Graphical User Interface -gt Reads the Root file
• -gt Displays results
• -gt Applies analysis
• -gt Gathers tools
• Could became a workbench for future analysis
  development !!

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GUI Snapshot
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Conclusion

• GRB package up and running
• Two models already implemented
• Currently redesigned for improved
  clarity/extension
• Alert studies started, based on it
• A GUI analysis tool prototyped (U13)
• Goodies to come
• Physical model fitting engine (A10)
• Quantum Gravity effect Flux(E) Flux(E(z))
• GBM Integration?