2003 doe site visit w. b. atwood, scipp glast science at scipp overview of glast science areas of...

2003 DoE Site Visit W. B. Atwood , SCIPP

SCIPPSCIPP GLAST Science at SCIPP

• Overview of GLAST Science

• Areas of focus at SCIPP/UCSC

• Contributions to GLAST Analysis Software


SCIPPSCIPP

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 GLAST draws the interest of both the the High Energy

Particle Physics and High Energy Astrophysics Particle Physics and High Energy Astrophysics communities.communities.

Science Overview


SCIPPSCIPP 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)


SCIPPSCIPPUnified gamma-ray experiment spectrum

The next-generation ground-based and space-based experiments are well matched.

Complementary capabilitiesground-based* space-based

angular resolution good goodduty cycle low excellentarea HUGE ! relatively smallfield of view 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.


SCIPPSCIPP

Mrk 501

EGRET 3rd Catalog: 271 sources GLAST 1st Catalog: >9000 sources?

+ new source classes also anticipated

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:

How Many Sources Will GLAST FIND


SCIPPSCIPP 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)


SCIPPSCIPP BLAZAR Opacity: The Photosphere

Calculation: Brandon Allgood

1 TeV

100 MeV

Log( M/Mo)

Log

( Z

/Rg

)

Closeness vs AGN Mass For various Energies

1 GeV

10 GeV

100 GeV


SCIPPSCIPP AGN, the EBL, and Cosmology

IFIF 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 c.m. energy > 2me, pair creation will attenuate flux. For a flux of -rays with energy, E, this cross-section is maximized when the partner, , is

For 10 GeV- TeV - rays, this corresponds to a partner photon energy

in the optical - UV range. Density is sensitive to time of galaxy formation.

eVE

TeV

1

3

1

ussource E

lowerussource

E higher


SCIPPSCIPP

Opacity (Salamon & Stecker, 1998)

No significant attenuation below ~10 GeV.

A dominant factor in EBL models is the time of galaxy formation -- attenuation measurements can help distinguish models.

Photons with E>10 GeV are attenuated by the diffuse field of UV-Optical-IR extragalactic background light (EBL)

An important energy band for Cosmology

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.


SCIPPSCIPP More Absorption Effects

The resulting e+e- pair can up scatter on the CMB:

e+

e-

High Energy

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)

Pair Creation Inverse Compton


SCIPPSCIPPFeatures of the gamma-ray sky

EGRET all-sky map (galactic coordinates) E>100 MeV

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)

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.


SCIPPSCIPPTransients Sensitivity

100 sec

1 orbit**

1 day^̂

work done by Seth Digelwork done by Seth Digel(updated March 2001)

*zenith-pointed, ^“rocking” all-sky scan

EGRET Fluxes

- GRB940217 (100sec)- PKS 1622-287 flare- 3C279 flare- Vela Pulsar

- Crab Pulsar- 3EG 2020+40 (SNR Cygni?)

- 3EG 1835+59- 3C279 lowest 5 detection- 3EG 1911-2000 (AGN)- Mrk 421- Weakest 5 EGRET source

During the all-sky survey, GLAST will have sufficient sensitivity after one day to detect (5) the weakest EGRET sources.


SCIPPSCIPP GRBs and Deadtime

Time between consecutive arriving photons

Distribution for the 20th brightest burst in a year

GLAST opens a wide window on the study of the high energy behavior of bursts!


SCIPPSCIPPPulsars

• Can distinguish acceleration models by observing high-energy roll-offs

Credit: Alice Hardingpreliminary

PREDICTED PULSAR POPULATIONS

POLAR CAP OUTER GAP

Sturner & Gonthier et al. Yadigaroglu & Zhang, ZhangSOURCE Dermer(1996) (2000) Romani (1995) & Cheng (2000)

EGRET Radio-loud 4 17 5 10Radio-quiet 1 5 17 22

GLAST Radio-loud 132 80

Radio-quiet : point source 212 1100 : pulsed 21

(NPSR = 1/100 yr) (NPSR = 1/100 yr)

(No geometry or spectral effects)

• Models also predict very different statistics. • Independent of models, GLAST sensitivity probes further through the Galaxy. preliminary


SCIPPSCIPPParticle Dark Matter

If the SUSY LSP is the galactic dark matter there may be observable halo annihilations into mono-energetic gamma rays.

q

qor or Z

“lines”?

X

X

Just an example of what might be Just an example of what might be waiting for us to find!waiting for us to find!


SCIPPSCIPP Analysis Development Activities

Contributions Areas

1) Pattern Recognition & Track Fitting

2) Energy Corrections

3) Event level Analysisa) Resolution Optimizationb) Maximization of Efficiencyc) Background Rejection


SCIPPSCIPP Important Terms

0 1 2 3 4 50

1000

2000Histogram of Data

lower upper

5 0 55

0

5

y

x

68% 95%

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 ~1.5 (1-dimensional 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.


SCIPPSCIPP

172 of the 271 sources in the EGRET 3rd catalog are “unidentified”

Cygnus region (15x15 deg)

The Importance of Resolution

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.


SCIPPSCIPPNew Directions in Track Reconstruction

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 projectionpoorly 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

UCSC Tracking Team: Bill Atwood, Brain Baughman, Harmut Sadrozinski, Terry Shalk and Robert Johnson


SCIPPSCIPPNew Pattern Recognition Programs

Neural Nets: Analysis at the event levelCombinatoric: Track-by-track


SCIPPSCIPP Track Energies and 2

Fewer tracking errors allows determination of track energy from multiple scattering

Track Energy SchemeDetermine individual track energies via MSDetermine overall event energy (tracker + calorimeter)

Constrain the sum of individual track energies

= 35%<Nhits> = 24

<2> = 1.0

Almost Perfect 2


SCIPPSCIPPGLAST’s Fracture Energy

1 GeV

Thin Radiator Hits

Thick Radiator Hits

Blank Radiator Hits

Calorimeter Xtals

Gap Between Tracker Towers

Gap Between CAL. Towers

Leakage out CAL. Back


SCIPPSCIPP

Raw Energies Corrected & Filtered Energies

Energies generated over 50 MeV 15 GeV

Energy Results


SCIPPSCIPPBackground Rejection by Classification Trees

GLAST Data an Excellent Match to Classification Tree Method

1) Rich Event description2) Well defined separation problem

Results: 10% signal loss / Factor of 200 Rejection

Input

Leaves

Branches


SCIPPSCIPP Summary

• 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 potentialLarge discovery potential

• Large group of Particle + Astrophysicists at UCSC participating


SCIPPSCIPP Measurement techniques

~103 g

cm

-2

~30

km

Atmosphere:

For E < ~ O(100) GeV, must detect above atmosphere (balloons, satellites, rockets)

For E > ~ O(100) GeV, information from showers penetrates to the ground (Cerenkov)

Energy loss mechanisms:

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.


SCIPPSCIPP How Close Can You Go?

Radiation Environment caused byAccretion is EXTREMELY INTENSE

In fact so intense High Energy Photons don’t get out!


SCIPPSCIPP

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 ’s

AGNs by Themselves


SCIPPSCIPP

(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).

• Effect is model-dependent (this is good):

Primack & Bullock

Salamon & Stecker

• 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.

No EBL

GLAST Probes the Optical-UV EBL

Caveats


SCIPPSCIPP

...)1( QGE

EcV 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.


SCIPPSCIPP EGRET and 3C279

EGRET discovery image of gamma-ray blazar 3C279 (z=0.54) E>100 MeV (June 1991)

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! VARIABILITY:

EGRET has seen only the tip of the iceberg.


SCIPPSCIPP New Source Classes?• Unidentified EGRET sources are fertile ground. example: mid-latitude 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 ! SURPRISES ! ((most importantmost important))


SCIPPSCIPPThe Dark Matter Problem

Observe rotation curves for galaxies:

For large r, expect:

GM

r

v r

rv r

r2

2 1

( )( ) ~

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) ].

r

Begeman/Navarro


SCIPPSCIPP 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/scorresponds to 1011 times total solar luminosityjust in -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 rays from a very small volume!


SCIPPSCIPP Blanford - Znaek Blazar Model

ACREATION DISKACREATION DISK

Power = V I = V2/R

Take R = 377 (the vacuum)

PAGN = 1038 j/s

V = 2 x 1020 Volts

Current Flow


SCIPPSCIPP Experimental Technique Instrument must measure the direction, energy, and arrival time of high energy photons (from approximately 20 MeV to greater than 300 GeV):

- photon interactions with matter in GLAST energy range dominated by pair conversion: determine photon direction

clear signature for background rejection

e+ e– calorimeter (energy measurement)

particle tracking detectors

conversion foil

anticoincidenceshield

Pair-Conversion Telescope

• instrument must detect -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.

Energy loss mechanisms:

- limitations on angular resolution (PSF) low E: multiple scattering => many thin layerslow E: multiple scattering => many thin layers high E: hit precision & lever armhigh E: hit precision & lever arm


SCIPPSCIPP Performance Plots

Derived performance parameter: high-latitude point source sensitivity Derived performance parameter: high-latitude point source sensitivity (E>100 MeV), 2 year all-sky survey: (E>100 MeV), 2 year all-sky survey: 1.6x101.6x10-9-9 cm cm-2-2 s s-1-1, a factor > 50 , a factor > 50

better than EGRET’s (~1x10better than EGRET’s (~1x10-7-7 cm cm-2-2ss-1-1).).

(As of the PDR)

FOV w/ energy measurement due to favorable aspect ratio

Effects of longitudinal shower profiling


SCIPPSCIPP

3D Resolutionmrad

First Results of 3D Tracking

First results from the Combinatoric PR + 3D Kalman Fits

Tracking mistakes greatly reduced

Improved accuracy reflected in manyaspects 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

PDR Resolutionmrad

2003 doe site visit w. b. atwood, scipp glast science at scipp overview of glast science areas of...

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