Transcript GLAST 101 - Santa Cruz Institute for Particle Physics

2003 DoE Site Visit
W. B. Atwood , SCIPP
GLAST Science at SCIPP
• Overview of GLAST Science
• Areas of focus at SCIPP/UCSC
• Contributions to GLAST Analysis Software
2003 DoE Site Visit
W. B. Atwood , SCIPP
Science Overview
GLAST will do fundamental science, with a very broad menu that
includes:
• Systems with super massive black holes
• Probing the era of galaxy formation
• Gamma-ray bursts (GRBs)
• Dark Matter
• Galactic Sources: Pulsars & our Sun
• Origin of Cosmic Rays
• Discovery! Hawking Radiation? Other relics from the Big
Bang? – Huge increment in capabilities.
GLAST draws the interest of both the the High Energy
Particle Physics and High Energy Astrophysics
communities.
2003 DoE Site Visit
W. B. Atwood , SCIPP
UCSC Participation in GLAST SCIENCE
AGNs & Cosmology:
W.B. Atwood, Brian Baughman, R. Johnson, J. Primack,
G. Blumenthal, P. Madau,...
Pulsars:
Steve Thorsett (GLAST IDS)
UCSC Organized a GLAST Pulsar Workshop
(December, 2001)
2003 DoE Site Visit
W. B. Atwood , SCIPP
Unified gamma-ray experiment spectrum
Complementary capabilities
angular resolution
duty cycle
area
field of view
ground-based*
good
low
HUGE !
small
space-based
good
excellent
relatively small
excellent (~20%
of sky at any instant)
energy resolution
good
good, w/ small
systematic
uncertainties
*air shower experiments have excellent
duty cycle and FOV, and poorer energy
resolution.
The next-generation ground-based and
space-based experiments are well matched.
2003 DoE Site Visit
W. B. Atwood , SCIPP
How Many Sources Will GLAST FIND
Some AGN shine brightly in the TeV range, but
are barely detectable in the EGRET range.
GLAST will allow quantitative investigations of
the double-hump luminosity distributions, and
may detect low-state emission:
Mrk 501
EGRET 3rd Catalog: 271 sources
GLAST 1st Catalog: >9000 sources?
+ new source classes also anticipated
2003 DoE Site Visit
W. B. Atwood , SCIPP
Active Galactic Nuclei (AGN)
Very active area of study at UCSC:
W.B. Atwood, Brian Baughman, R. Johnson, J. Primack,
G. Blumenthal, P Madau,...
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
solar masses). Different phenomenology primarily due to the orientation with respect
to us.
HST Image of M87 (1994)
2003 DoE Site Visit
W. B. Atwood , SCIPP
BLAZAR Opacity: The Photosphere
Closeness vs AGN Mass
For various Energies
Log( Z/Rg)
1 TeV
100 GeV
10 GeV
1 GeV
100 MeV
Log( M/Mo)
Calculation: Brandon Allgood
2003 DoE Site Visit
W. B. Atwood , SCIPP
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 > 2me, pair creation will attenuate flux. For a flux of
g -rays with energy, E, this cross-section is maximized when the partner, e, is
e 
1  1TeV 

eV
3 E 
For 10 GeV- TeV g - rays, this corresponds to a partner photon energy
in the optical - UV range. Density is sensitive to time of galaxy formation.
source
source
us
Eg
lower
us
Eg higher
2003 DoE Site Visit
W. B. Atwood , SCIPP
An important energy band for Cosmology
Photons with E>10 GeV are attenuated by the diffuse field of UVOptical-IR extragalactic background light (EBL)
Opacity (Salamon & Stecker, 1998)
EBL over cosmological distances is
probed by gammas in the 10-100 GeV
range.
In contrast, the TeV-IR attenuation
results in a flux that may be limited to
more local (or much brighter) sources.
A dominant factor in EBL models is the
time of galaxy formation -- attenuation
measurements can help distinguish models.
No significant attenuation below ~10 GeV.
2003 DoE Site Visit
W. B. Atwood , SCIPP
More Absorption Effects
The resulting e+e- pair can up scatter on the CMB:
High Energy
g
e+
e-
Pair Creation
Inverse Compton
g
g
Low Energy
Effects:
1)
Time delay of low energy signal
2)
Smearing on source image on the sky: Halo
3)
e+e- deflected in inter-galactic magnetic fields
(Brian Baughman’s Thesis Topic)
2003 DoE Site Visit
W. B. Atwood , SCIPP
Features of the gamma-ray sky
diffuse extra-galactic background
(flux ~ 1.5x10-5 cm-2s-1sr-1)
galactic diffuse (flux ~O(100) times larger)
high latitude (extra-galactic) point
sources (typical flux from EGRET
sources O(10-7 - 10-6) cm-2s-1
galactic sources (pulsars, un-ID’d)
EGRET all-sky map (galactic coordinates) E>100 MeV
An essential characteristic: VARIABILITY in time!
Combined, the improvements in GLAST provide a ~ two order of magnitude
increase in sensitivity over EGRET.
The wide field of view, large effective area, highly efficient duty cycle, and
ability to localize sources in this energy range will make GLAST an important fast trigger
for other detectors to study transient phenomena.
2003 DoE Site Visit
W. B. Atwood , SCIPP
Transients Sensitivity
100 sec
work done by Seth Digel
(updated March 2001)
EGRET Fluxes
1 orbit*
During the all-sky
survey, GLAST will
- GRB940217 (100sec)
have sufficient
- PKS 1622-287 flare
sensitivity after one
- 3C279 flare
day to detect (5s)
- Vela Pulsar
the weakest EGRET
sources.
- Crab Pulsar
- 3EG 2020+40 (SNR g Cygni?)
1 day^
- 3EG 1835+59
- 3C279 lowest 5s detection
- 3EG 1911-2000 (AGN)
- Mrk 421
- Weakest 5s EGRET source
*zenith-pointed,
^“rocking” all-sky scan
2003 DoE Site Visit
W. B. Atwood , SCIPP
GRBs and Deadtime
Distribution for the 20th brightest burst in a year
GLAST
opens a wide
window on
the study of
the high
energy
behavior of
bursts!
Time between consecutive arriving photons
Pulsars
2003 DoE Site Visit
W. B. Atwood , SCIPP
• Can distinguish acceleration models by observing high-energy roll-offs
• Models also predict very different statistics.
• Independent of models, GLAST sensitivity probes further through the
Galaxy.
preliminary
PREDICTED PULSAR POPULATIONS
POLAR CAP
Sturner &
Gonthier et al.
Dermer(1996)
(2000)
SOURCE
EGRET
4
1
Radio-loud
Radio-quiet
GLAST
17
5
132
212
21
Radio-loud
Radio-quiet : point source
: pulsed
(NPSR = 1/100 yr)
OUTER GAP
Yadigaroglu & Zhang, Zhang
Romani (1995) & Cheng (2000)
5
17
10
22
80
1100
(NPSR = 1/100 yr)
(No geometry or spectral effects)
preliminary
Credit: Alice Harding
2003 DoE Site Visit
Particle Dark Matter
W. B. Atwood , SCIPP
If the SUSY LSP is the galactic dark
matter there may be observable
halo annihilations into monoenergetic gamma rays.
X
X
q
or gg or Zg
q
“lines”?
Just an example of what might be
waiting for us to find!
2003 DoE Site Visit
W. B. Atwood , SCIPP
Analysis Development Activities
Contributions Areas
1) Pattern Recognition & Track Fitting
2) Energy Corrections
3) Event level Analysis
a) Resolution Optimization
b) Maximization of Efficiency
c) Background Rejection
2003 DoE Site Visit
W. B. Atwood , SCIPP
Important Terms
Effective area (Light Gathering Power)
(total geometric acceptance) • (conversion probability) • (all detector and
reconstruction efficiencies). Real rate of detecting a signal is (flux) • Aeff
Point Spread Function (PSF)
Angular resolution of instrument, after all detector and reconstruction algorithm
effects. The 2-dimensional 68% containment is the equivalent of ~1.5s (1dimensional error) if purely Gaussian response. The non-Gaussian tail is
characterized by the 95% containment, which would be 1.6 times the 68%
containment for a perfect Gaussian response.
H istogram of D ata
5
2000
lower
68%
95%
upper
y
1000
0
0
5
0
1
2
3
4
5
5
0
x
5
2003 DoE Site Visit
W. B. Atwood , SCIPP
The Importance of Resolution
172 of the 271 sources in the EGRET 3rd catalog are “unidentified”
EGRET source position error circles are
~0.5°, resulting in counterpart confusion.
GLAST will provide much more accurate
positions, with ~30 arcsec - ~5 arcmin
localizations, depending on brightness.
Cygnus region (15x15 deg)
2003 DoE Site Visit
W. B. Atwood , SCIPP
New Directions in Track Reconstruction
UCSC Tracking Team: Bill Atwood, Brain Baughman, Harmut Sadrozinski,
Terry Shalk and Robert Johnson
The GLAST Instrument is essentially
two orthogonal detectors: X & Y
X - Y Ambiguities broken by track
length and/or tower crossings
PDR Analysis code analyzes X & Y
separately
Multiple scattering mixes projections
New approach - try to make track
finding and fitting 3D from the
outset.
Use SSD hits as space points measured well in one projection
poorly in the orthog. Projection
Use detailed track projections:
“Swims” throw the 3D geometry
to integrate material:
Covariance Matrix
Use “missing hits” to veto wrong
track hypotheses
2003 DoE Site Visit
W. B. Atwood , SCIPP
New Pattern Recognition Programs
Combinatoric: Track-by-track
Neural Nets: Analysis at the event level
2003 DoE Site Visit
Track Energies and
2
c
W. B. Atwood , SCIPP
Fewer tracking errors allows determination of track energy from multiple scattering
s = 35%
<Nhits> = 24
<c2>
= 1.0
Almost Perfect c2
Track Energy Scheme
Determine individual track energies via MS
Determine overall event energy (tracker + calorimeter)
Constrain the sum of individual track energies
2003 DoE Site Visit
W. B. Atwood , SCIPP
GLAST’s Fracture Energy
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
2003 DoE Site Visit
Energy Results
Raw Energies
W. B. Atwood , SCIPP
Corrected & Filtered
Energies
Energies generated over 50 MeV
15 GeV
2003 DoE Site Visit
W. B. Atwood , SCIPP
Background Rejection by Classification Trees
GLAST Data an Excellent Match
to Classification Tree Method
1)
2)
Rich Event description
Well defined separation problem
Leaves
Input
Branches
Results: 10% signal loss / Factor of 200 Rejection
2003 DoE Site Visit
Summary
W. B. Atwood , SCIPP
• GLAST will address many important questions:
– What is going on around black holes? How do Nature’s most powerful
accelerators work?
– Are the Black Holes in distant BLAZARs Primordial?
– When did galaxies form?
– What is the origin of the diffuse background?
– What is the high energy behavior of gamma ray bursts?
– Discriminate between models for Pulsars
– What else out there is shining gamma rays? Are there further surprises in
this largely unexplored energy region?
– Large discovery potential
• Large group of Particle + Astrophysicists at UCSC
participating
2003 DoE Site Visit
W. B. Atwood , SCIPP
Measurement techniques
g
Energy loss mechanisms:
~103 g cm-2
~30 km
Atmosphere:
For Eg < ~ O(100) GeV, must
detect above atmosphere
(balloons, satellites, rockets)
For Eg > ~ O(100) GeV,
information from showers
penetrates to the ground
(Cerenkov)
E=mc2.
If 2x the rest energy of an
electron (~0.5 MeV) is available (i.e., if
the photon energy is large enough), in
the presence of matter the photon can
convert to an electron-positron pair.
2003 DoE Site Visit
W. B. Atwood , SCIPP
How Close Can You Go?
Radiation Environment caused by
Accretion is EXTREMELY INTENSE
In fact so intense
High Energy Photons don’t get out!
2003 DoE Site Visit
W. B. Atwood , SCIPP
AGNs by Themselves
GLAST will provide a large statistical sample of AGNS
Goal: By studying the spectra, hope to probe the underlying
Super Massive Black Hole.
- Mass
- Spin
- Accretion Disk Properties
Results will allow for determining the AGN’s Black Hole Mass dependence on
Red Shift:
Results will allow usage of AGN’s as “calibrated” sources of high energy g’s
2003 DoE Site Visit
W. B. Atwood , SCIPP
GLAST Probes the Optical-UV EBL
(1) thousands of BLAZARS - instead of peculiarities of individual sources, look for
systematic effects vs redshift. Favorable aspect ratio important here.
(2) key energy range for cosmological distances (TeV-IR attenuation more local due to
opacity).
Caveats
• Effect is model-dependent (this is good):
No EBL
Salamon & Stecker
Primack &
Bullock
• How many blazars have intrinsic roll-offs
in this energy range (10-100 GeV)? (An
important question by itself for GLAST!)
Again, power of statistics is the key.
• What if there is conspiratorial evolution in
the intrinsic roll-of vs redshift? More
difficult, however there may also be
independent constraints (e.g., direct
observation of integrated EBL).
• Most difficult: must measure the
redshifts for a large sample of these
blazars!
• Intrinsic roll-offs also for pulsar studies.
2003 DoE Site Visit
W. B. Atwood , SCIPP
V  c (1   
E
 ...)
EQG
Amelino-Camelia et al,
Ellis, Mavromatos, Nanopoulos
Effects could be O(100) ms or larger, using
GLAST data alone. But ?? effects intrinsic to bursts??
Representative of window opened by such old
photons.
2003 DoE Site Visit
W. B. Atwood , SCIPP
EGRET and 3C279
Prior to EGRET, the only known extra-galactic point source was
3C273; however, when EGRET launched, 3C279 was flaring and
was the brightest object in the gamma-ray sky!
EGRET discovery image of gamma-ray blazar 3C279 (z=0.54)
E>100 MeV (June 1991)
VARIABILITY: EGRET
has seen only the tip of the
iceberg.
2003 DoE Site Visit
W. B. Atwood , SCIPP
New Source Classes?
• Unidentified EGRET sources are fertile ground. example: midlatitude sources separate population (Gehrels et al., Nature, 23
March 2000)
• Radio (non-blazar) galaxies. EGRET detection of Cen A
(Sreekumar et al., 1999)
• “Gamma-ray clusters”: emission from dynamically forming
galaxy clusters (Totani and Kitayama, 2000)
• Various hypotheses for origin of the extragalactic diffuse, if not
from unresolved blazars.
• SURPRISES ! (most important)
2003 DoE Site Visit
W. B. Atwood , SCIPP
The Dark Matter Problem
Observe rotation curves for galaxies:
r
Begeman/Navarro
For large r, expect:
M
v 2 (r )
G 2 
r
r
v (r ) ~
1
r
see: flat or rising rotation curves
Other signatures: e.g., direct detection, high energy neutrinos from annihilations in the core of the sun
or earth [Ritz and Seckel, Nucl. Phys. B304 (1988); Ellis, Flores, and Ritz, Phys. Lett. 198B(1987)
Kamionkowski, Phys. Rev. D44 (1991) ].
2003 DoE Site Visit
W. B. Atwood , SCIPP
AGN shine brightly in GLAST energy range
Power output of AGN is remarkable. Multi-GeV component can be dominant!
Estimated luminosity
of 3C 279:
~ 1045 erg/s
corresponds to 1011
times total solar
luminosity
just in g-rays!! Large
variability within days.
1 GeV
Sum all the power over the whole electromagnetic spectrum from all the stars of a
typical galaxy: an AGN emits this amount of power in JUST g rays from a very
small volume!
2003 DoE Site Visit
W. B. Atwood , SCIPP
Blanford - Znaek Blazar Model
Power = V I = V2/R
Take R = 377 W (the vacuum)
Current Flow
PAGN = 1038 j/s
V = 2 x 1020 Volts
ACREATION DISK
ACREATION DISK
2003 DoE Site Visit
W. B. Atwood , SCIPP
Experimental Technique
Instrument must measure the direction, energy, and arrival time of high energy
photons (from approximately 20 MeV to greater than 300 GeV):
Energy loss mechanisms:
- photon interactions with matter in GLAST
energy range dominated by pair conversion:
determine photon direction
clear signature for background rejection
- limitations on angular resolution (PSF)
low E: multiple scattering => many thin layers
high E: hit precision & lever arm
g Pair-Conversion Telescope
anticoincidence
shield
conversion foil
particle tracking
detectors
e+
e–
calorimeter
(energy measurement)
• instrument must detect g-rays with
high efficiency and reject the much
higher flux (x ~104) of background
cosmic-rays, etc.;
• energy resolution requires calorimeter
of sufficient depth to measure buildup
of the EM shower. Segmentation useful.
2003 DoE Site Visit
Performance Plots
W. B. Atwood , SCIPP
(As of the PDR)
FOV w/ energy
measurement
due to
favorable
aspect ratio
Effects of
longitudinal
shower
profiling
Derived performance parameter: high-latitude point source sensitivity
(E>100 MeV), 2 year all-sky survey: 1.6x10-9 cm-2 s-1, a factor > 50
better than EGRET’s (~1x10-7 cm-2s-1).
2003 DoE Site Visit
W. B. Atwood , SCIPP
First Results of 3D Tracking
First results from the
Combinatoric PR + 3D Kalman Fits
Tracking mistakes greatly reduced
Improved accuracy reflected in many
aspects of the results
1) Track energy estimation based on
multiple scattering between
segments works!
2) Improved track accuracy PLUS
individual track energies
combine to improve PSF
3D Resolution
PDR
Resolution
ss  27
37 mrad
mrad