GammaRay Bursts GRBs and the GLAST Experiment

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Gamma-Ray Bursts (GRBs)and the GLAST Experiment

• G. Tosti
• Physics Dept. INFN Perugia

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What is a GRB?

• Gamma-ray bursts (GRBs), discovered in 1967 by
  the Vela setellites ( Klebesadel et al. 1973),
  are brief (lt seconds), intense flashes of em
  radiation with typical photon energies gt100 keV
  that arrive at Earth from unpredictable locations
  several times daily.

They are the most concentrated and brightest em
explosions in the Universe.
(see the recent review by P. Meszaros
astro-ph/0605208)
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CGRO-BATSE (1991-2000)
The first significant steps in understanding GRBs
started with the 1991 launch of the Compton
Gamma-Ray Observatory.
CGRO/BATSE (25 KeV10 MeV)
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CGRO-BATSE (1991-2000) Spatial Distribution
The all-sky survey from the BATSE instrument
showed that bursts were isotropically
distributed, ? cosmological origin of GRBs
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CGRO-BATSE (1991-2000) Temporal Behaviour
Two categories of GRBs long (t gt 2 s) and
short, (tlt 2 s) were identified
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CGRO-BATSE (1991-2000) Spectral Behaviour
GRB spectra described by the empirical Band
function with parameters a low-energy index,
b high-energy index E0break energy
Ep E0 (2 a) peak energy
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CGRO-EGRET (1991-2000) GeV GRBs

• GRB941017 A distinct higher energy component
  was observed by the EGRET TASC detector, which
  lasts for longer (230s) than the lower energy
  component.
• GRB940217 EGRET detected gamma-rays from this
  GRB for more than an hour after the prompt
  emission.

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BeppoSAX and the Afterglows

• Good Angular resolution (lt arcmin)
• Observation of the X-Afterglow

Costa et al. (1997)

• Optical Afterglow (HST, Keck)
• Direct observation of the host galaxies
• Distance determination

Kippen et al. (1998)
Djorgoski et al. (2000)
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GRBs Host Galaxy
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GRBs-SNs Connection
(first hypothesis? Colgate (1968))
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The Fireball model
The fireball model a GRB is produced when an
ultra-relativistic ejecta from a central engine
is stopped in the interactions between shells of
different velocities (internal shocks, d1014 cm)
or with the external medium (external shocks, d
?1016 cm). In those interactions, the kinetic
energy of the relativistic flow is converted in
internal energy of relativistic electrons that
produce the observed radiation via synchrotron
(and IC) emission.
Nature of the inner engine the GRB progenitor is
electromagnetically hidden from direct
observation because all the radiation is emitted
at d gt 1013 cm.
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GRB Jets
Harrison et al (1999)
T. Piran (Science 295, 986)
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Progenitor Theories

• Collapsars possibly associated with long bursts
  (t90 gt 2 s.)
• NS-NS mergers possibly associated with short
  bursts
• Emission mechanism independent of exact
  progenitor type

C. Freyss cartoon
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Recent results from Swift (2004- )
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Recent results from Swift
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Afterglow Observations

• New multi-component afterglow paradigm
• Basic questions remain open
• Is outflow particle or poynting driven?
• What causes flares and rebrightenings?
• What are jet configurations (long, short GRBs)?
• What are manifestations of off-axis viewings?

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GRB and early Universe studies

• GRBs afterglows are brightest high-z objects
• (opt 17th mag, X-ray 10-9 erg cm-2 s-1)
• Afterglow studies provide
• - Metallicities / abundances
• - Densities
• - Dust ratios

GRB 050904
z 6.29 (12.8 Gyr) T 225 sec Eiso 3.8x1053 erg
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First Short Burst Host Associations
Swift detection of rapidly decaying afterglow
(300s) of short (40ms) GRB 050509b Allowed
host association
Prochaska05 Gorosabel05, Fox05, Pedersen05,
Covino05, Berger05, Soderberg06, Levan06
Gehrels et. al. 2005
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GRB Host Galaxies
Bloom05, Gorosabel05 Gehrels05, Prochaska05
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GRB-SN Connection

• Recent GRB 060218 this z0.03 GRB triggered
  supernova discovery
• GRBs are new tool for SN understanding
  (hypernovae, BH cores, asymmetries, jets)

Long GRBs associated with SN I b/c
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Missing SNe in LSB GRB
060505
060614
Non-observation of SNe in long bursts
GRB z t90 notes
060505 0.089 4s
faint burst 060614 0.125 102s
hard to soft evolution
astro-ph/0608313. Fynbo et.al.
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But were they really long-soft bursts?
GRB 060614
060614
060505

• Canonical 2s is
• Bandpass dependent
• Minimum of N(T90), not 50
• probability point

Short pulse Long flaring New family
Further analysis of SNe missing bursts raises
issues w/ classification
astro-ph/0610635. Gehrels et.al.
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The GLAST mission (Gamma-ray Large Area Space
Telescope)

• The GLAST satellite has two telescopes
• Large Area Telescope
• Pair Conversion
• Detect photons between 20 MeV - 300GeV
• Tracking system
• Silicon Strip Detectors
• Calorimeter
• CsI Cristals (8.5 r.l., hodoscopic)
• Anticoincidence
• Segmented ACD

Launch Vehicle Delta II 2920-10H Launch
Location Kennedy Space Center Orbit Altitude 565
Km Orbit Inclination 24.5 degrees Orbit
Period 95 Minutes Launch Date October 2007
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The GLAST mission (Gamma-ray Large Area Space
Telescope)

• Glast Burst Monitor
• 12 Sodium Iodide (NaI) Scintillation detectors
• Wide Field of View
• Burst trigger
• Coverage of the typical GRB spectrum
• (10 keV-1 MeV)
• 2 Bismunth Germanate (BGO) Scintillation
  detectors
• Spectral overlap with the LAT
• (150 keV-30 MeV)

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GLAST Performance I LAT
For typical observation angle F 40
Aeff(40) 0.75 Aeff(0)
Effective Area
all layers
At 30 (100) MeV single photon Angular resolution
10 (3)
http//www-glast.slac.stanford.edu/software/IS/gla
st_lat_performance.htm
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Mission Operation

• Operational modes
• Sky survey (full coverage every 3 hours)
• Pointing mode
• GBM and LAT can trigger independently
• GBM will detect 200 burst/year
• gt60 burst/year in LAT FoV
• Position resolution
• GBM lt 15o initially, update lt5o
• LAT gt 10 arcmin depending on burst
• Autonomous repoint
• GLAST can slew to put/keep an intense burst in
  the LAT FoV.
• Downlink and communications
• Bursts data on ground in near real-time (TDRSS)
• Burst alerts provided to GCN within 10 sec.
• Full science data 8 times a day (TDRSS)

GLAST
TDRSS
White Sands
GCN
Users community
(N. Omodei)
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GLAST Simulations
Detailed sky Model (Galactic extragalactic
diffuse, thousands of AGNs, hundreds of
pulsars, CR, GRBs)

• GRB MODELS
• Phenomenological
• Use observed distributions from BATSE.
• Must extrapolate to LAT Energies.
• Physical Models
• Example Fireball Model (Piran, 1999)
• Hybrid ThermalPowe law model
  (Ryde)

GLAST LAT simulators GEANT 4 (Full
MC) Parameterized IRF (fast simulator) GBM
simulator
Combined signal from GBM (BGO NaI) and LAT
detectors
Simulated Data (HEASARC)
(N. Omodei)
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The initial distributions

• Start with BATSE Catalog
• Sample GRB characteristics
• Duration, Flux,spec. index, etc.
• Simulate 1 year of GLAST.

BATSE (Green) Simulation (Blue)
(N. Omodei)
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LAT GRB sensitivity

• Consider different min. energies
• Number of GRB/yr vs Number of LAT counts
• EBL attenuation included
• MODEL DEPENDENT COMPUTATION !!!

SFR (Porciani Madau 01) Binary Mergers (Fryer
99)
LAT GRB sensitivity extrapolating the spectrum
from BATSE energies to LAT energies assuming an
annual rate of 650 GRB/yr. EBL attenuation
included.
(N. Omodei)
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Unveiling the GRB High Energy Emission

• LAT is an important tool for understanding the
  high energy (gt 50 MeV) of GRBs
• Wide discovery window
• New energy regime for burst studies
• What we know from EGRET shows an interesting
  behavior
• Separate components
• Extended/ delayed high energy emission
• GLAST can search for high Energy cutoff
• Highest Energy limit intrinsic of the bursts
• EBL Absorption important only for very high
  redshift and intense bursts
• More speculatively measuring GRB at different
  redshift can be used as a probe for Lorentz
  Invariance Violation
• Effects arise in some Quantum Gravity Models.
• Time resolution 10µs
• Energy resolution 10

Reconstructed c.o. 5.51.5 GeV G22060
Simulated GRB with c.o. at 4.5 GeV
(N. Omodei)
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GLAST and SWIFT era

• GLAST can provide alerts to GRBs that Swift can
  point for follow on observations.
• Precise measurements of the position will be
  given by Swift!
• GLAST will frequently scan the position of the
  bursts hours after the Swift alerts, monitoring
  for High energy emission.
• In these cases, we will have a broad spectral
  coverage of the GRB spectrum (from 0.1 keV to
  hundreds of GeV gt 9 decades!!).
• Swift is seeing 100 bursts per yr 20/yr will
  be in the LAT FoV

(N. Omodei)
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Conclusions

• GLAST will open a new window on the gamma-ray
  sky, exploring an uncovered region of the
  electromagnetic spectrum, with big impact on
  science!
• Glast is being integrated with the SC!
• GLAST - GBM will detect 200 bursts per year, gt
  60 suitable for LAT observations.
• GLAST - LAT will independently detect 100
  bursts
• GLAST will provide burst alerts rapidly ( 10
  seconds)
• Burst position is provided by both the GBM (5o)
  and LAT (1o-0.1o) in few seconds and sent to
  ground for afterglows follow-up.
• GLAST can be repointed autonomously.
• Spectral resolution typically 10 important for
  spectral studies (high energy cut-offs, inverse
  Compton peaks).
• Joined LAT and GBM observations will study the
  relationship between GeV emission and keV-MeV
• The large lever-arm is a key point for
  investigating fundamental questions like the
  breaking of the Lorentz Invariance due to Quantum
  Gravity effect.
• Partnership between Swift and GLAST would open a
  new era for the gamma-ray astronomy!

GLAST launch
Simulated data
(N. Omodei)