The Universe 100 Me V Brenda Dingus Los
The Universe >100 Me. V Brenda Dingus Los Alamos National Laboratory
EGRET Compton Observatory 1991 -2000 • BATSE, OSSE, and Comptel at ~< Me. V • EGRET 30 Me. V – 30 Ge. V • 1 st proposed in late 1970 s • Spark Chamber with Na. I calorimeter Pair-Conversion Telescope anticoincidence shield conversion foil particle tracking detectors e+ e– calorimeter (energy measurement)
GLAST Instrument 16 towers modularity height/width = 0. 4 large field-of-view TKR Si-strips: fine pitch: 228 µm, high efficiency 0. 44 X 0 front-end reduce multiple scattering 1. 05 X 0 back-end increase sensitivity > 1 Ge. V CAL Cs. I: wide energy range 0. 1 -100 Ge. V hodoscopic cosmic-ray rejection shower leakage correction XTOT = 10. 1 X 0 shower max contained <100 Ge. V ACD segmented plastic scintillator minimize self-veto > 0. 9997 efficiency & redundant readout 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 Me. V – > 300 Ge. V) Optimized Point Spread Function (0. 35 o @ 1 Ge. V) Wide Field of View (2. 4 sr) Energy Resolution (DE/E < 10%, E >100 Me. V)
Nature’s Particle Accelerators • Electromagnetic Processes: • Synchrotron Emission • E g a (Ee/mec 2)2 B • Inverse Compton Scattering • E f ~ (Ee/mec 2)2 E i • Bremmstrahlung • E g ~ 0. 5 E e • Hadronic Cascades • p + g -> p± +po +… -> e ± + n + g +… • p + p -> p± +po +… -> e ±+ n + g +…
“Exotic” Gamma-Ray Production • Particle-Antiparticle Annihilation • WIMP called neutralino, c, is postulated by SUSY • 50 Ge. V< mc< few Te. V c q c or Z q lines? • 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
High Energy Gamma-Ray Astronomy Typical Multiwavelength Spectrum from High Energy -ray source E 2 d. N/d. E or n. Fn [ Energy Emitted] Radio Optical X-ray [ Photon Energy] Ge. V Te. V
Crab Nebula Electron Energies Spinning Neutron Star Fills Nebula with Energetic Electrons Þ Synchrotron Radiation and Inverse Compton Scattering
Active Galactic Nuclei Massive Black Hole Accelerates Jet of Particles to Relativistic Velocities => Synchrotron Emission and Inverse Compton and/or Proton Cascades
AGN Theory, e. g. WComae Blazar Electrons produce gammas via Inverse Compton scattering of synchrotron photons Protons produce gammas via m synchrotron Boettcher, Mukherjee, & A. Reimer, 2002
Gamma-Ray Bursts • EGRET discovered Ge. V emission from 4 bright GRBs with no evidence of a spectral break at higher energies • One GRB had Ge. V 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) -18 to 14 sec • This burst is the first observation of a distinct higher energy spectral component in a GRB 14 to 47 sec • Power released in higher energy component is more than twice the lower energy component 47 to 80 sec • Higher energy component decays slower than lower energy component • Peak of higher energy component is above the energy range of the detector 80 to 113 sec 113 to 200 sec
GRB Ge. V-Te. V 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 2003 constrain source parameters for Inverse Compton emission of GRB 941017 Milagro Sensitivity z=0. 2 z=0. 02
Gamma-Ray Detected Pulsars
Pulsars • Extend # of gamma-ray pulsars to of order 100 • Differentiate between different accelerators
>100 Me. V 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 po bump • Improved localization to resolve correlation with dense proton target of molecular cloud SNR g-Cygni
Galactic Plane • Galactic Diffuse Spectrum of Region |b|<10 and 300< l <60 Hunter, et al. Ap. J 481, 205 -240 Nucleon-Nucleon • Nucleon-Nucleon (po decay) component should dominate above 1 Ge. V and should have the same E 2. 7 differential photon spectrum as cosmic rays. • However, the observed flux >1 Ge. V 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 Te. V observation of Galactic plane by Milagro Electron Bremstrahlung Inverse Compton Isotropic Diffuse E-2. 1 (Extragalactic)
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)
Conclusions EGRET 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
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