the universe >100 mev brenda dingus los alamos national laboratory
TRANSCRIPT
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The Universe >100 MeV
Brenda Dingus
Los Alamos National Laboratory
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EGRET
Compton Observatory
1991-2000•BATSE, OSSE, and Comptel
at ~< MeV•EGRET 30 MeV – 30 GeV
•1st proposed in late 1970s•Spark Chamber with NaI
calorimeter
e+ e– calorimeter (energy measurement)
particle tracking detectors
conversion foil
anticoincidenceshield
Pair-Conversion Telescope
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GLAST
16 towers modularity
height/width = 0.4 large field-of-view
Si-strips: fine pitch: 228 µm, high efficiency
0.44 X0 front-end reduce multiple scattering
1.05 X0 back-end increase sensitivity > 1 GeV
CsI: wide energy range 0.1-100 GeV
hodoscopic cosmic-ray rejection
shower leakage correction
XTOT = 10.1 X0 shower max contained <100GeV
segmented plastic scintillator
minimize self-veto
> 0.9997 efficiency & redundant readout
InstrumenInstrumentt
TKRTKR
CALCAL
ACDACD Expected Launch Date 2007
First of 16 towers delivered March 2005 to integrate and test with the spacecraft
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GLAST Instrument Performance
More than 50 times the sensitivity of EGRET
Large Effective Area (20 MeV – > 300 GeV)
Optimized Point Spread Function(0.35o @ 1 GeV)
Wide Field of View(2.4 sr)
Energy Resolution(E/E < 10%, E >100 MeV)
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• Electromagnetic Processes:
• Synchrotron Emission
•E (Ee/mec2)2 B
• Inverse Compton Scattering
•E f ~ (Ee/mec2)2 E i
• Bremmstrahlung
•E ~ 0.5 E e
• Hadronic Cascades
• p + ± +o +… e ± + + +…
• p + p ± +o +… e ±+ + +…
Nature’s Particle Accelerators
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“Exotic” Gamma-Ray Production
• Particle-Antiparticle Annihilation • WIMP called neutralino, is postulated by SUSY • 50 GeV< m< few TeV
• Primordial Black Hole Evaporation• As mass decreases due to Hawking radiation,
temperature increases causing the mass to evaporate faster
• Eventually temperature is high enough to create a quark-gluon plasma and hence a flash of gamma-rays
q
qor or Z
lines?
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Radio Optical X-ray GeV TeV
E 2 dN/dE
or
F
High Energy Gamma-Ray Astronomy
Typical Multiwavelength Spectrum
from High Energy -ray source
[ Energy Emitted]
[ Photon Energy]
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Crab Nebula
Electron Energies
Spinning Neutron Star Fills Nebula with Energetic Electrons Synchrotron Radiation and Inverse Compton Scattering
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Massive Black Hole Accelerates Jet of Particles to Relativistic Velocities
=> Synchrotron Emission and Inverse Compton and/or Proton Cascades
Active Galactic Nuclei
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AGN Theory, e.g. WComae Blazar
Electrons produce gammas via Inverse Compton scattering of synchrotron photons
Protons produce gammas via synchrotron
Boettcher, Mukherjee, & A. Reimer, 2002
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Gamma-Ray Bursts
• EGRET discovered GeV emission from 4 bright GRBs with no evidence of a spectral break at higher energies
• One GRB had GeV emission extending for over an hour
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Typical GRB Broad Band Spectra
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GRB 941017
• M.M. González, B.L. Dingus, Y. Kaneko, R.D. Preece, C.D. Dermer and M.S. Briggs, Nature, 424, 749 (2003)
• This burst is the first observation of a distinct higher energy spectral component in a GRB
• Power released in higher energy component is more than twice the lower energy component
• Higher energy component decays slower than lower energy component
• Peak of higher energy component is above the energy range of the detector
-18 to 14 sec
14 to 47 sec
47 to 80 sec
80 to 113 sec
113 to 200 sec
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GRB GeV-TeV Theories
• Requires GRBs are more energetic phenomena
• Different timescale of low and high energy implies an evolving source environment or different high energy particles
• Shape of high energy component applies tight constraints to ambient densities and magnetic fields
• Or evidence of origin of Ultra High Energy Cosmic Rays
• More and Higher Energy observations are needed
Pe’er & Waxman 2003constrain source parameters for Inverse Compton emission of GRB941017
Milagro Sensitivityz=0.2
z=0.02
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Gamma-Ray Detected Pulsars
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Pulsars
• Extend # of gamma-ray pulsars to of order 100
• Differentiate between different accelerators
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>100 MeV Astrophysical Sources
• Active Galactic Nuclei, Gamma Ray Bursts, and Pulsars are ONLY identified classes of individual sources.
• ~ ¾ of EGRET point sources NOT identified with known objects.
Individual Examples of
Sources:
Solar Flare
Large Magellenic
Cloud
X-ray Binary (?)
Cen A (?)
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Supernova Remnants (SNR)
• SNR are predicted by some to be source of cosmic rays
• 19 EGRET sources are positionally coincident with SNR• Probability of chance coincidents ~10-5
• Several are non-variable and spectra consistent with that expected by SNR
• However, other sources associated with SNR• Pulsars that might not be known at other
wavelengths• Pulsar Wind Nebula accelerate electrons with
energy of pulsar and the electrons radiate gamma-rays.
• See D. Torres et al. Physics Reports 2003 for review.
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Supernova Remnants with GLAST
• Example of GLAST sensitivity to SNR
• Improved spectra to resolve o bump
• Improved localization to resolve correlation with dense proton target of molecular cloud SNR -Cygni
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Galactic Plane
Nucleon-Nucleon
Electron Bremstrahlung
Inverse Compton
Isotropic
Diffuse E-2.1 (Extragalactic)
•Galactic Diffuse Spectrum of Region |b|<10 and 300< l <60
•Nucleon-Nucleon (o decay) component should dominate above 1 GeV and should have the same E-2.7 differential photon spectrum as cosmic rays.
•However, the observed flux >1 GeV is greater resulting in an E-2.4 differential photon spectrum.
•Strong, Moskolenko, Reimer 2004 require cosmic ray flux in galaxy >2 times local flux
•Other theories such as increasing Inverse Compton ruled out by TeV observation of Galactic plane by Milagro
Hunter, et al. ApJ 481,205-240
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Extragalactic Diffuse
• What’s left over?• Unresolved
point sources• Diffuse
sources, both in and out of our galaxy
• No predicted sources can over produce this limit of diffuse emission
(Sreekumar et al. 1998)
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ConclusionsEGRET detected ~300 sources
~1/4 individual identifications•Active Galactic Nuclei•Pulsars•Gamma-ray bursts •Large Magellenic Cloud, Solar Flare•Possibly Cen A and an x-ray binary
Unidentified Source possibilities include•Supernova Remnants•Pulsar Wind Nebula•Galactic Black Holes •Galaxy Clusters•Luminous IR Galaxies
GLAST predicted to detect ~10000 sources