Diapositiva 1

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The GLAST observatory

• Talk overview
• instrument design
• the LAT Tracker
• science goals
• conclusions

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Precision Si-strip Tracker (TKR) 18
XY tracking planes Single-sided silicon strip
detectors 228 ?m pitch, 8.8 105 channels Measure
the photon direction
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Experimental Technique
Instrument must measure the direction, energy,
and arrival time of high energy photons (from
approximately 20 MeV to greater than 300 GeV)
- photon interactions with matter in GLAST
energy range dominated by pair conversion
determine photon direction clear signature for
background rejection
Energy loss mechanisms
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EGRET vs. GLAST - LAT

• Energy Range
• Energy Resolution
• Effective Area
• Field of View
• Angular Resolution
• Sensitivity
• Source Location
• Lifetime

20 MeV - 30 GeV 10 1500 cm 2 0.5 sr 5.8o _at_ 100
MeV 10-7 cm-2 s-1 5 - 30 arcmin 1991 - 1997
20 MeV -300 GeV 10 8000 cm 2 gt 2 sr 3o _at_ 100
MeV 0.15o gt 10 GeV lt6 x 10-9 cm-2 s-1 0.5 - 5
arcmin 2007 2012
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Covering the Gamma-Ray Spectrum

• Broad spectral coverage is crucial for studying
  and understanding most astrophysical sources.
• GLAST and ground-based experiments cover
  complimentary energy ranges and performances
  (wide FOV and alert capabilites for GLAST, large
  effetive area and energy reach for ground-based)
• The improved sensitivity of GLAST is necessary
  for matching the sensitivity of the next
  generation of ground-based detectors.
• GLAST fill the energy gap between space-based and
  ground-based detectorsthere will be overlap for
  the brighter sources

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Sensitivity and Sky Map
EGRET (1991-2000) - map based on 5 years data
GLAST one year sky-survey - based on the
extrapolation of the number of sources versus
sensitivity of EGRET
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LAT Sensitivity During All-sky Scan Mode
100 sec
During the all-sky survey, LAT will have
sufficient sensitivity after one day to detect
(5s) the weakest EGRET sources.
EGRET Fluxes

• - GRB940217 (100sec)
• - PKS 1622-287 flare
• - 3C279 flare
• - Vela Pulsar
• - Crab Pulsar
• - 3EG 202040 (SNR g Cygni?)
• - 3EG 183559
• - 3C279 lowest 5s detection
• - 3EG 1911-2000 (AGN)
• - Mrk 421
• - Weakest 5s EGRET source

1 orbit
1 day
zenith-pointed rocking all-sky scan
alternating orbits point above/below the orbit
plane
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Glast Physics
First year dedicated to the all-sky survey
Sources identification and diffuse emission
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Identifying Sources
GLAST 95 C.L. radius on a 5? source, compared
with a similar EGRET observation of 3EG 1911-2000
Counting stats not included.

• GLAST high resolution and sensitivity will
• resolve gamma-ray point sources at arc-minute
  level
• detect typical signatures (e.g. spectra, flares,
  pulsation) for identification with known source
  types

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Active Galactic Nuclei

• AGN signature
• vast amounts of energy (1049 erg/s) from a very
  compact central volume
• large luminosity fluctuations in fractions of a
  day
• energetic (multi-TeV), highly-collimated,
  relativistic particle jets
• Prevailing idea accretion onto super-massive
  black holes (106 - 1010 solar masses)

• AGN physics to-do list
• catalogue AGN classes with a large data sample
  (gt3000 new AGNs)
• identify contributions from leptonic (SSC/ESC)
  and/or hadronic (?0 decay) emissions in the
  spectra multiwavelength campaigns
• resolve diffuse background and study redshift
  dependence of cut-off to probe EBL
• track flares (? minutes)

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AGN EBL Studies
Photons with Egt10 GeV are attenuated by the
diffuse field of UV-Optical-IR extragalactic
background light (EBL)
Opacity (Salamon Stecker, 1998)
only e-t of the original source flux reaches us
EBL over cosmological distances is probed by
gammas in the 10-100 GeV range. Important
science for GLAST! In contrast, the TeV-IR
attenuation results in a flux that may be limited
to more local (or much brighter) sources.
opaque
A dominant factor in EBL models is the time of
galaxy formation -- attenuation measurements can
help distinguish models.
No significant attenuation below 10 GeV.
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LAT studies EBL cutoff

• Probe history of star formation to z 4 by
  determining spectral cutoff in AGN due to EBL

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CR production and acceleration in SNR

• SNR widely believed to be the source of CR
  proton acceleration after shell interaction with
  interstellar medium
• ?0 bump in the galactic spectrum detected by
  EGRET

• GLAST simulations showing SNR ?-Cygni spatially
  and spectrally resolved from the compact inner
  gamma-ray pulsar a clear ?0 decay signature
  from the shell would indicate SNR as a source of
  proton CR

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Dark Matter a short review

• Evidence
• Rapidly moving galaxies in clusters
• Rotation curves of galaxies
• Hot gas in galaxy clusters
• Gravitational lensing
• Stability of rotating spiral galaxies
• Types
• Baryonic vs. non-baryonic
• Cold vs. Hot

Hot gas in Galaxy Cluster
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Searching for dark matter

• The lightest supersymmetric particle c is a
  leading candidate for non-baryonic CDM
• It is neutral (hence neutralino) and stable if
  R-parity is not violated
• It self-annihilates in two ways
• c c ? gg where Eg Mc c2
• c c ? Zg where Eg Mc c2(1-Mz2/4Mc2)
• Gamma-ray lines possible 30 GeV - 10 TeV

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Road Map for Photons from Dark Matter
Type Line XX gg, gZ0 (Small Br, Line
Spectra) Inclusive XX g Anything (Large
Br, Continuum Spectra)
Where Galactic Center Known Location Intensity
Dependence Diffuse Character Extra
Galactic Associated with AGN Point Like Character
Particle Source SUSY X c0 (LSP - many
models parameter space large) LIMP X Heavy
nR (Signal to weak too be observed by GLAST)
Focus on Galactic Center
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Diffuse emission from Relic decay

• Set limits on relic mass, density and lifetime

Unresolved AGNs WIMPs Total
GLAST
EGRET
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GLAST WIMP Search Regions

• Galactic center
• Galactic satellites
• Galactic halo
• Extra-galactic

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known gamma-ray pulsars

• direct pulsation search in the ?-ray band
• high time resolution
• detect new gamma-ray pulsars (250)
• precise test of polar cap vs outer gap emission
  models
• large effective area

?
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Gamma-Ray Bursts and GLAST

• spectral studies for
• non-thermal emission model (synchrotron, ICS)
• fireball baryon fraction
• high energy resolution

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Gamma-Ray Bursts
GBM
Simulated one-year GLAST scan, assuming a various
spectral indexes.
LAT
LAT GBM complimentarity
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Conclusions

• The large statistics that GLAST will collect in
  the first year of operations will address many
  important questions- origin of CRs- AGN and
  EBL studies- Dark Matter- GRB- study of
  unidentified EGRET sources
• Importance of multiwavelength observations