The Universe >100 MeV Brenda Dingus Los Alamos National Laboratory
Jan 21, 2016
The Universe >100 MeV
Brenda Dingus
Los Alamos National Laboratory
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
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
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)
• 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
“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?
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]
Crab Nebula
Electron Energies
Spinning Neutron Star Fills Nebula with Energetic Electrons Synchrotron Radiation and Inverse Compton Scattering
Massive Black Hole Accelerates Jet of Particles to Relativistic Velocities
=> Synchrotron Emission and Inverse Compton and/or Proton Cascades
Active Galactic Nuclei
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
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
Typical GRB Broad Band Spectra
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
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
Gamma-Ray Detected Pulsars
Pulsars
• Extend # of gamma-ray pulsars to of order 100
• Differentiate between different accelerators
>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 (?)
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.
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
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
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)
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