W' B' Atwood

1
Space Based High Ehergy Gamma Ray Astronomy

• W. B. Atwood
• Les Houches, March, 2007

2
Outline

• Lecture 1 Pair Conversion Gamma Ray Telescopes
• Introduction
• The GLAST Concept How to
• The Resulting Instrument
• Lecture 2 High Energy Gamma Ray Science with
  GLAST
• Pulsars
• AGN
• Extra Galactic Background Light
• Extra Galactic Diffuse Emission
• Dark Matter Detection

3
The Thermal Universe What most of Astronomers
Observer
Thermal Radiation Black Body Spectrum
A cool, invisible galactic gas cloud called Rho
Ophiuchi 60 K
Dim, young star near the center of the Orion
Nebula 600 K
Our star the Sun 6000 K
Cluster of very bright stars, Omega Centauri, as
observed from the space 60,000 K
Accretion Disk reach temperatures in
excess of 105 K
4
Wavelength Bands of the Electromagnetic Spectrum
Wavelength in meters
10-14 10-12 10-10 10-8
10-6 10-4 10-2 1
g-rays
x-rays
ultraviolet
infrared
m waves
radio

• Non-Thermal Sources
• Extreme Environments
• High energy particle acceleration

Accretion Disk
SUN
GIANT BLUE STAR
Non-Thermal Sources
ENERGY
Detection Technique
Energy loss mechanisms
Pair Cross-Section saturates at Eg gt 1 GeV
5
Gamma-Rays in Perspective
Sources - Non Thermal - High Energy particle
acceleration - Extreme environments -
Black Holes - Super Nova Remnants
- Gamma-ray Burst - Both Galactic
Extra-Galactic
Diffuse - Galactic (DOMINATES)
High Energy cosmic rays interacting
with the inter-stellar medium -
Extragalactic Primordial?
Galactic Diffuse Emission
Galactic Diffuse Emission Account for
85 of the celestial gamma- ray emission
Zombeck, M. V. 1990, Handbook of Astronomy and
Astrophysics, Second Edition (Cambridge, UK
Cambridge University Press).
6
Jargon PSF, Aeff, and FoV
Point-Spread-Function
Effective Area- Aeff
Not all entering gs pair-convert
2D Point Source Image at 275 MeV
Typically
Field-of-View - FoV
PSF Characterized by 68 95
Containment
Aeff decreases as q increases
Light-Gathering Power
Dq(deg)
7
Brief History of Detectors
COS-B

• 1967-1968, OSO-3 Detected Milky Way as an
  extended g-ray source
• 621 g-rays
• 1972-1973, SAS-2,
• 8,000 g-rays
• 1975-1982, COS-B
• orbit resulted in a large and variable
  background of charged particles
• 200,000 g-rays
• 1991-2000, EGRET
• Large effective area, good PSF, long
  mission life, excellent background rejection
• gt1.4 106 g-rays

SAS-2
SAS-2
OSO-3
COS-B
EGRET
EGRET
8
EGRET Sets the stage
OSO-III 1967-1968
OSO-III (gt50 MeV)

• 1.4x106 g, 60 interstellar emission from the
  MW
• 10 are cataloged (3EG) point sources

9
An essential characteristic VARIABILITY in time!
AGN Flaring
Gamma Ray Bursts (GRBs) Uniform over the
entire sky
Galactic Pulsars
3rd EGRET Catalog 271 Sources
Monitoring sky requires wide Field-of-View and
large effective area
In the GLAST Era daily AGN Flares, hundreds of
pulsars,
GRB every few days
10
We usually see the Gamma Ray sky as .
Created by Tony Johnson, SLAC
http//glast-ground.slac.stanford.edu/sc1/animatio
n/
11
Evolution of GLAST

• April, 1991 CGRO (with EGRET on board) Shuttle
  Launch
• May, 1992 NASA RD Proposal Cycle

2. Make it Modular
1. Select the Technologies
Another lesson learned in the 1980's
monolithic detectors are inferior to Segmented
detectors
Large area SSD systems and CsI Calorimeters result
ed from SSC RD
Original GISMO 1 Event Displays from the first
GLAST simulations
4. Fill-it-up!
3. Pick the Rocket
Cheap, reliable Communication satellite launch
vehicle
Diameter sets transverse size
Rocket Payload Fairing
Throw capacity to LEO sets depth of
Calorimeter
Delta II (launch of GP-B)
12
Overview of GLAST- LAT

• Tracker 18 XY tracking planes with interleaved W
  conversion foils. Single-sided silicon strip
  detectors (228 µm pitch) Measure the photon
  direction gamma ID.
• Calorimeter 1536 CsI(Tl) crystals in 8 layers
  PIN photodiode readouts. Hodoscopic Measure the
  photon energy image the shower.
• Anticoincidence Detector (ACD) 89 plastic
  scintillator tiles. Reject background of charged
  cosmic rays segmentation removes self-veto
  effects at high energy.

Tracker
ACD
Calorimeter

• Electronics System Includes flexible, robust
  hardware trigger and software filters.

13
Tracker Design and Analysis
Pair Conversion Telescope Layout
Angular Resolution Parameters
g converts ½ through radiator
Close spacing of Radiators to SSDs minimizes
multiple scattering effects
Tungsten Radiator
Si Strip Detector
Plane-to-plane spacing and SSD strip pitch
sets meas. precision limit
d
Trim Radiator tiles to match active SSD area
Kalman Tracking/Fitting
Trade Between Aeff PSF
Track parameters (position, angles, error matrix)
at a plane
Source Sensitivity Photon Density
Propagation of parameters
Which doesn't depend on cRad !
Multiple Scattering -- depends on energy!
Propagation of parameters
2-Source Separation pushes for thin
radiators Transient sensitivity pushes for thick
radiators
Measurement with error
Predicted parameters at next plane
New parameters at next plane
Data Analysis Techniques for High Energy Physics,
R. Fruhwirth et al., (Cambridge U. Press , 2000,
2nd Edition)
14
Tracker Production Overview
Module Structure Components SLAC Ti parts,
thermal straps, fasteners. Italy (Plyform)
Sidewalls
SSD Procurement, Testing Japan, Italy (HPK)
SSD Ladder Assembly Italy (GA, Mipot)
10,368
Parts Count
Tracker Module Assembly and Test Italy (Alenia
Spazio)
2592
18
Tray Assembly and Test Italy (GA)
342
342
Electronics Fabrication, burn-in, Test UCSC,
SLAC (Teledyne)
648
Composite Panel, Converters, and Bias
Circuits Italy (Plyform) fabrication SLAC CC,
bias circuits, thick W, Al cores
Readout Cables UCSC, SLAC (Parlex)
15
LAT Silicon Tracker Completion
Team effort involving physicists and
engineers from the United States (UCSC
SLAC), Italy (INFN ASI), and Japan
16
Image Resolution Point Spread Function
Thick Radiator (18) PSF
Thin Radiator (3) PSF
PSF(95)
PSF(68)
3x PSF(68)
On Axis cos(q) lt -.95
log(E)
log(E)
10 MeV
10 GeV
Off Axis cos(q) gt -.7
log(E)
log(E)
17
LAT Calorimeter
Team effort involving physicists and
engineers from the United States (NRL), France
(IN2P3 CEA), and Sweden
Crossed Hodoscope Log design (first proposed by
Per Carlson, 1989) Gives 3D image of energy
depositions 8 Layers deep (1.08 rad.
len./layer) 12 "Logs" per Layer
Each Log (or Xtal Element) is readout from both
ends by 2 Photodiodes 1 - large area, 1
small area
X- Light Asym.
End-to-End Light Ratio
Longitudinal Co-ordinate
Location of Energy Depositions 2 coordinates by
log location 3rd coordinate by end-to-end
light asymmetry
Y-Log Location
Transverse Co-ordinate
18
Energy Determination
Issues Low Energies - Energy loss in Tracker
is critical High Energies - Leakage
compensation is critical
Compensation for the numerous gaps
1 GeV g
Thin Radiator Hits
Gap Between Tracker Towers
Thick Radiator Hits
Blank Radiator Hits
Gap Between CAL. Towers
Calorimeter Xtals
Leakage out CAL. Back
19
Low Energy Combining the Tracker with the
Calorimeter
100 MeV gs on Axis
Tracker Energy Alone (derived from hit counting)
Tracker - Cal (Anti)Correlation
Use Tracker as a (poor) Sampling Calorimeter
Count Hits Apply Correction for
Inter-Tower Gaps
High Energy Shower Leakage Correction
SLAC Test Beam Data
Measured longitudinal profile allows estimation
of shower leakage event-by-event
Longitudinal Shower Profile Model
Shower Tail escapes out backside
b is a scale factor .5 a is the scaled shower
centroid
20
Energy Reconstruction Results
On Axis cos(?) lt -.95
"Best"
log(E)
After cuts to remove tails
Off Axis cos(q) gt -.7
"Best"
"Best"
log(E)
21
Last Piece Background Rejection (by far the
hardest)
First Low Earth Orbit Particle Flux Environment
South Atlantic Anomaly (Hot Spot)
Orbital Flux Rates
Albedo Gammas
Albedo Trapped ee-
Albedo Trapped Protons
Primary Protons
Primary e-
Heavy Ions
Time (min)
22
Instrument Triggering and Onboard Data Flow
Getting data to the Ground
Hardware Trigger
On-board Processing
Onboard filters reduce data to fit within
downlink, provide samples for systematic studies.
Hardware trigger based on special signals from
each tower initiates readout Function did
anything happen? keep as
simple as possible

• flexible, loose cuts
• The FSW filter code is wrapped and embedded in
  the full detector simulation
• leak a fraction of otherwise-rejected events to
  the ground for diagnostics, along with events ID
  for calibration

signal/background can be tuned
? rate a few Hz
Combinations of trigger primitives
Total Downlink Rate lt400 Hzgt
On-board science analysis transient detection
(bursts)
Upon a trigger, all subsystems are read out in
27ms
Spacecraft
Instrument Total Rate lt3 kHzgt
using ACD veto in hardware trigger
current best estimate, assumes compression, 1.2
Mbps allocation.
23
Trigger and Filter Rates
Trigger
Filter

• Gamma filter rate in this configuration is 360 Hz
• Pass any event w/ Egt20 GeV 40 Hz
• Plus other filters for MIPs and Heavy Ions
• Handles to reduce this rate significantly if
  needed

• Operating daily-average rate is 2.9kHz
• Peak rate is 6 kHz (watch dead time)
• For this simulated day, 201 minutes spent in SAA
  (14).

24
Ground Analysis Dealing with the Remainder
Hardware Trigger and On-Board Computers Filter
out a factor of 20 TKR
(200 ACD)
Entry Points for background events
that come to the ground
Ground analysis utilizes the combined information
from ACD, Tracker Cal. via Classification
Trees
Current Results (analysis on-going)
Contour swept out via CT probability
gt 0.
gt .2
gt .4
gt .6
Bkg. Rej. Prob. gt .4
25
The Nature of the Residual Background Events
Handscan of the Residual Background Events.
(Proton Blanket) p0 2g
Large Angle p0 Small Angle p0
(Hi energy tail)

• (e Blanket) 2g
• Annihilation
• Also we have e e-
• Bremstrahlung in the
• Blanket

These Events are Irreducible a g is produced
outside the ACD within the FoV
26
More Background Event Categories
Space Craft Interaction with
Stopping Stub(s)
Proton Space Craft Cal Shower Stubs
in Tracker
Electromagnetic showers from below
Albedo g Cal Shower Stubs in
Tracker
These showers from below as well as the
Horizontal entering Track wall Interactions
These Events are Reducible (could in principle
be eliminated)
27
Irreducible and Reducible Events in Pictures
Irreducible Events - Photons generated within
FoV - Originating particle
typically in FoV - Mostly e and protons -
Not Rejectable - Require incoming flux meas.
and MC to subtract contamination
Reducible Events - Typically back-entering -
Shower by-product appears in Tracker -
Events have non-photon signature - Should be
rejectable - Contaminate topology classes
differently - MC needed to normalize levels
of contamination
28
All Sky Scanning Mode
GLAST "sees" 20 of the Sky Data taking
"Zenith Pointed" mode - first orbit tilted
up 35o - next orbit tilted down -35o All
Sky Scanning mode results in 1/3 the photons on
a given source compared to a "pointed
observation" But it allows detection of AGN
flares within a few orbits.
GMB FoV
29
Unified Gamma-ray Experiment Spectrum
Complementary capabilities ground-based
space-based angular resolution good
good duty cycle low excellent area HUGE
! relatively small field of view small
excellent (20 of sky at
any instant) energy resolution good
good, w/ small systematic
uncertainties back rejection
adequate good-excellent Sky coverage
Limited Full Sky
air shower experiments have excellent duty cycle
and FOV, and poorer energy resolution.
The ground-based and space-based experiments are
well matched.
30
Unified Gamma-ray Experiment Spectrum Rotated S.
Ritz
Contemporary Experments are well matched
Event Yield Conservative
estimate 30x106 per year 5 Year Mission
150x106 gs GLAST 100 x
EGRET!
31
The Real LAT
LAT Now integrated to Space craft at General
Dynamics In Phoenix, Arizona Launch Package
COMPLETE Next Steps 1) Last round of
environmental testing 2) Ship to Cape
Kennedy 3) Integrate onto Delta II Rocket 4)
Launch!
32
16 tower LAT rate 500 Hz
Some Cosmic Ray Events in the Full LAT
33
The Evolving Picture of the Gamma-Ray Universe
OSO-III (gt50 MeV)
34
Science Overview

• A very broad range of topics that
  includes
• Systems with super massive black holes - AGNs
• Probing the era of galaxy formation - EBL
• Gamma-ray bursts (GRBs)
• Dark Matter
• Galactic Sources Pulsars our Sun
• Origin of Cosmic Rays
• Discovery! Hawking Radiation? Other relics from
  the Big Bang? x100 increment in capabilities.

More Details
Less Detail
The recent GLAST Symposium held at Stanford is an
excellent source of GLAST science talks. The
talks can be found at http//glast.gsfc.nasa.go
v/science/symposium/2007/program.html
35
Rotating Dipole Model
PULSARS - The Basics

• Magnetic dipole radiation
• Braking index
• Surface B field
• Characteristic age

Radiation only occurs for a gt 0 Co-aligned
Rotators do not radiate
36
Where does the High Energy Emission come from in
Pulsars?
Classical Electrodynamics is "easily" solved if
the Pulsar (rotating magnetic dipole) is
in a Vacuum Problem comes when a plasma medium
is introduced which feeds back onto the
Electro-Dynamics
Deutsch 1955
3 Locations have been proposed 1)
Emission form the Magnetic Poles
(Polar Cap Model) 2) From the field close
to the Light Cyl. (Outer Gap Model) 3)
From a region between Mag. Pole Light
Cyl. (Slot-Gap Model)
Each Model Predicts a different population as
well as different energy spectra..
37
The Plane
EGRET Pulsars - Young / High E-Dot
Odd Balls
Millesec. Pulsars
Normal Pulsars
NS-NS Binaries
D. Hartman, Glast Symposium 2007
38
Pulsar Models Differ in Predicted Energy Spectra

• Develop analysis methods to quantify this.
• Razzano and Harding - simulations to illustrate
  the ability of LAT observations to distinguish
  between pulsar emission models.
• Additional simulation improvements
• Adding models for binary pulsars
• Including noise and glitches

1 week
1 month
1 week (left) and 1-month Vela observation and 1
year Vela observation.
1 year
This is not very satisfying as the relative shape
(cut-off) is perhaps a bit subtle
However - population counts catagorized by
emission types is.
39
A. Harding, Glast Symposium 2007
Finding the pulsar in the GLAST data alone!
40
A Blind Pulsar Search Method
Problem Event rate from typical Pulsar is small
requires integrating over
years Maintaining Phase coherence becomes
difficult (impossible) Solution Take
time-of-arrival time differences up to a fixed
max. time difference
FFT of Time Difference
(Discrete Fourier Transform of the Truncated
Discrete Auto-correlation Function)
Phase Slippage Caused by the Period Derivative
After N Periods
Phase Slip q (in sec) after N Periods
Relative Phase Slip is
A reasonable value for h can be estimated from a
"typical" light curve...
PHASE
41
MC Test of the Time-Difference Method
Generate Poisson noise plus signal photons from a
single peak in a phase plot (at left), including
a frequency first derivative. Find for each
method the number of signal photons needed to
make a 95 C.L. detection
210 noise photons
W.B. Atwood, M. Ziegler, R.P. Johnson, B.
Baughman, ApJ Lett. 2006, 652, 49.
42
Search Simulated GLAST Data (DC-2)
Detection Limits for Blind Pulsar Searches

• Lower limits on detection at 95 C.L. for a
  14-day viewing period, using 5 different
  time-difference windows.
• The trial factor is taken into account when
  calculating the significance.

Lower limits on the number of photons needed.
Simulation of 55 days of scanning data
Pulsar with lowest flux Off plane
(b11.9) PSR_J1852m2610 flux 310?7 Ph/cm2/s
In plane (b ?0.9) PSR_J1856p0113 flux
710?7 Ph/cm2/s
16 radio-loud and 3 radio-quiet pulsars were
found.
43
Blind Searches in EGRET Data
The bright pulsars Vela and Geminga can be found
using a time-difference window of only 3 hours.
No scan in the frequency derivative is needed.
The time to calculate the FFT is only about 1s.
Geminga 2nd harmonic
harmonics
Pulsars with a large spin down rate like the Crab
pulsar require a scan in the frequency
derivative. Faint pulsars like PSR 1706-44
require a longer time-differencing window (e.g. 3
days).
PSR 1706-44
M. Ziegler et al., Searching for Radio Quiet
Gamma-ray Pulsars, Glast Symposium, 2007
44
Below are the light curves of four EGRET pulsars
found in the blind-search scan. The scan was
performed on the positions given in the 3EG
catalog (3 radius). In each case, the photon
arrival times were folded into phase plots
according to the frequency and f-dot found in the
scan.
Several additional pulsar candidates with fairly
good significance were found. The evaluation of
those pulsars is still in progress. We probably
need to wait for GLAST to determine whether they
are real.
45
Localizing Pulsars using Time Solution
Event times must be corrected to the solar system
bari-center. (Time of arrival of wave front in a
plane passing through the solar system
bari-center) Requires good - excellent knowledge
of source location. Time Differencing mollifies
sensitivity provided that the Time-Diff window is
small compared with the Earth's orbital
period around the Sun. If the direction to the
source is off, phase-folding using the Timing
Solution will fail as it will oscillate around
the correct answer
For the simple case of the barycenter plane
being close the plane of the Earth's orbit
Barycenter Plane
For Geminga (P .1sec) this gives 4
arcsec location!
1 AU
46
Active Galactic Nuclei (AGN)
Active galaxies produce vast amounts of energy
from a very compact central volume. Prevailing
idea powered by accretion onto super-massive
black holes (106 -1010 M?). Different
phenomenology primarily due to the orientation
with respect to us.
HST Image of M87 (1994)
Models include energetic (multi-TeV),
highly-collimated, relativistic particle jets.
High energy g-rays emitted within a few degrees
of jet axis. Mechanisms are speculative g-rays
offer a direct probe.
47
A little bit about Large Black Holes
Mass is usually given in solar Masses M
Event Horizon or Schwarzschild Radius
for the SUN
SGR A - The black hole in the center of the
Milky Way
or about 13x the size of the SUN
(orbit of Mars is 1.5 AU)
108 M AGN black hole
Accretion Disk starts at 3rs or about in the
middle of the Asteroid Belt And extends out to
10rs or about out to the orbit of Saturn And
finally the Accretion Torus extends outwards on
the parsec scale!
MONSTERS
These are indeed
48
A Sketch of the Distance Scalesnot-to-scale
Black Hole Diameter 2rs 4 AU
Accretion Disk 3- 10 rs
parsecs
Furthermore the Keplerian velocities depend only
the ratio rs/r
So the inner edge of accretion disks have v

49
Most AGN that we see in Gamma Rays are BLAZARS
Observer is along line of sight of Jet Axis
Many Questions 1) What causes the initial
acceleration of matter? 2) Is the Jet made up of
protons or electrons? 3) Where do the "seed"
photons which are Inverse Compton
scattered to high energy come from? 4) What
role does shock acceleration play?
Kerr BH MHD Simulation Blue lines are field
lines entraining Plasma. Frame dragging winds
field lines up at poles
Semenov, Dyadechkin, and Punsly, 2004
SSC Model (Synchrotron Self Compton) Present
bias is that the JETs are electronic and the seed
photons are from the JET's electrons synchrotron
emitting in the confining magnetic field.
ERC Model (External Radiation Compton) Seed
photons come from outside the JET (disk, etc.)
50
Acceleration Mechanisms
Shock Acceleration First proposed by
Fermi Occurs when fast moving particles impinge
on a medium. Particles transfer energy to the
medium and vice-versa Results in Power Law
Spectra Some of the initial particles are
boosted to very high energies
Initial Boost from BH Magnetohydrodynamic
(MHD) Both Accretion disk BH are spinning
Drags field lines around Field lines trap
plasma Field lines wound up at poles likes
springs Results in Bulk Lorentz factors G 10-
50?
Jet terminates in a Shock
51
Distinguishing Models Multi-wavelength
signature combined flux information
Spectral Energy Density Plot (SED) Relative
flux in low peak vs high peak SSC Model
AGN time variability requires Simultaneous
Observations across the EM spectrum
3 BLAZARs 1 RadioGalaxy
FACTOR of 30
Example SED Plot for Mkn 501
Synchrotron Peak
IC Peak
GLAST Band-pass and sensitivity
Lott et al, HEAD, 2006
The above is among the better fits to the SSC
model. (most are really awful)
Variability allows for measuring the relative
peak heights!
52
AGNs Up-Close A Remote Possibility
Clover Leaf Quasar
GLAST will see several thousand AGN 10-3
will be Gravitationally Lensed
Chandra
GLAST will not resolve the Individual images as
does CHANDRA or OPTICAL Teles.
HST
However each image will have a different
light path. When an AGN Flares - GLAST
will see the images in succession according to
their Time delays. AGN ECHOES!
Notice the different relative intensities of the
images!
Time delay for echo can be estimated by
where q 1 arcsec D 109 years (300 Mpc)
Question Will the ECHOES have the same temporal
/ spectral composition? If not two
possibilities 1)(Likely) Correlating x-ray and
optical images of lensed AGN is believed
to reveal a magnified view into the AGN
2)(Unlikely) Reveal gravitationally lenses to
be achromatic - a violation of
Lorentz invariance
Realistically the chance of GLAST having a bright
enough flare in a BLAZAR which is gravitational
lensed is quite small
53
AGN, the EBL, and Cosmology
IF AGN spectra can be understood well enough,
they may provide a means to probe the era
of galaxy formation (Stecker, De Jager
Salamon Madau Phinney Macminn Primack)
If gg c.m. energy gt 2mec2, pair creation can take
place The cross-section
where m is cos(q) The cross-section
peaks at For 10 GeV-to-TeV g-rays, this
corresponds to a partner photon energy in the
optical - UV range. Photon Density is sensitive
to time of galaxy formation.
Fluxes will be attenuated by
F F0 e-?(E,z)
54
Optical Depth of the Universe
Nishikov 1962 ??? Gould Schreder 1966 Jelly
1966 Stecker Fazio 1969/70 Stecker et al.
1992 COBE IR bkgrd 1997 Hauser Dwek 2001
Review McMinn Primack 1996 Franceachini 1998
Malkan Stecker 1998, 2001 Kneiske et
al. 2002, 2004 Dwek Krennrich 2005
Due to
Must integrate along line of sight
EBL(z)
55
The Gamma-Horizon ??? 1
Fazio-Stecker Relation
1970 Stecker, Malkan, Scully 2006
TeV
Log E(GeV) 1.4 (3/2) log z
56
Reprocessing of Light The
metagalactic UV-O-IR background
Kneiske, Mannheim, Hartmann. 2000 AA 386, 1
Tinsley 1977, Madau, Primack, Fall, Pei, Dwek,
Krennrich, Malkan, Stecker, Scully,
57
A Simple Test to Distinguish Models
Chen, Reyes, and Ritz, ApJ, Volume 608, pp.
686-691 (2004)
(1) thousands of blazars - instead of
peculiarities of individual sources, look
for systematic effects vs redshift. (2) key
energy range for cosmological distances
(TeV-IR attenuation more local due to opacity).
Caveats
No EBL

• How many blazars have intrinsic roll-offs in
  this energy range (10-100 GeV)? (An important
  question by itself for GLAST!) Power of
  statistics is the key.
• Must measure the red shifts for a large sample of
  these blazars!

Salamon Stecker
Primack Bullock
58
Extra-Galactic Diffuse Gamma Ray Flux
If it exists 1) It is a result of a
cosmologic relic(s) - Gamma Rays could
not propagate in the Universe until
it was pretty cold! - Something
(particle) would have had to persist and then
via interaction (annihilations) produce
the high energy gamma ray flux 2)
It will be subject to the same EBL cut-off as the
AGNs - This could limit the Z from
whence the gamma rays propagated If it doesn't
exists What are the implications for SUSY?
or WIMPs in general?
BUT The diffuse signal is very hard to
measure. 1) Experimental backgrounds
Irreducible Component 2) Large subtractions
- Solar, Galactic, Un-resolved sources

EGRET Team Result
SMR Result
Strong, Moskalenko, Reimer, 2004 ApJ 613, 956
59
Particle Dark Matter
Particle physics models with SUSY could also
solve the dark matter problem. If correct, these
new particle interactions could produce an
observable flux of gamma rays.
c
q
inclusive flux, or gg or Zg lines?
q
c

• Observations of the Galactic Center are
  intriguing
• EGRET detected a gamma-ray source near the
  galactic center, with a small excess GeV flux.
• TeV galactic center source from Whipple K.
  Kosack et al., astro-ph/0403422, HESS,
• Contributions to extragalactic diffuse flux from
  dark matter haloes also possibly observable.
  Ullio et al, astro-ph/0207125

GLAST 2 yrs, Cesarini et al.
Focus on Galactic Center
60
EGRET to GLAST Galactic Diffuse g ray emission
near the GC - PSF is Important
EGRET
61
Gamma Ray Flux From WIMPS
The flux of gamma rays from WIMP annihilation has
many terms Cesarini et al,
astro-ph/0305075
Annihilation Cross Section Thermal Velocity
Branching Fraction Photon Spectrum
WIMP Number Density
Angle away from Galactic Center Line-of-Sight
in direction
l.o.s
Recasting Scaling in terms of nominal values
Units cm-2s-1GeV-1sr-1
With
62
Largest Uncertainty in Predicted Rate
WIMP Density Parameterization
GLAST Angular Resolution per Photon .1o above
10 GeV
r/rc
Navarro-Frenk-White
Kravtsov et al.
Isothermal
GOOD NEWS! Recent evidence from analysis of
INTEGRAL data suggests .4 lt g lt .8
Orders of Magnitude Uncertainty in J(Y)
Boehm et al, astro-ph/0309686 Phys.Rev.Lett. 92
(2004)
63
Diffuse Background at Galactic Center
Galactic Center Region has excess gt GeV g's
compared to conventional galactic
diffuse model (GALPROP)
GALPROP (local CR Spectra)
GALPROP (Optimized CR Spectra)
A.W.Strong, I.V. Moskalenko, O.
Reimer astro-ph/0406254
Good News Diffuse Background small at
Hi-Energy Bad News Reasonable changes to
CR Spectra fit the data well
64
LHC SUSY Reach
LHC is a "SUSY Discovery
Machine" Abe Seiden LHC
Turn On 2007 Covers Most(?) of GLAST
Discovery Space in a very short
time Plausible scenario LHC Discovers
SUSY and sets parameters GLAST
Measures the Role it plays in CDM
Plot courtesy of Abe Seiden from HEPAP
presentation, April 2004
65
Gamma Ray Bursts

• Vela satellite fleet launched to detect nuclear
  weapons test in late 60s
• Multiple satellites flown allowed crude
  position determination and could test for
  coincidence
• In 1969, it was realized that there were other
  signals!
• 16 bursts found between 1969 and 1972

BATSE ERA (1991-1996)
Simulated Distribution for the 20th brightest
burst in a year
Models
GLAST opens a wide window on the study of the
high energy behavior of bursts!
Hyper- Nova
Coalescing Neutron Stars