The Universe >100 MeV Brenda Dingus Los Alamos National Laboratory.

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