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GLAST Science at SCIPP

GLAST Science at SCIPP. Overview of GLAST Science Areas of focus at SCIPP/UCSC Contributions to GLAST Analysis Software. 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

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GLAST Science at SCIPP

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  1. GLAST Science at SCIPP • Overview of GLAST Science • Areas of focus at SCIPP/UCSC • Contributions to GLAST Analysis Software

  2. 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.

  3. 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)

  4. Unified gamma-ray experiment spectrum Complementary capabilities ground-based* space-based angular resolution good good duty cycle lowexcellent area HUGE ! relatively small field 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. The next-generation ground-based and space-based experiments are well matched.

  5. 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

  6. 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)

  7. BLAZAR Opacity: The Photosphere Closeness vs AGN Mass For various Energies 1 TeV 100 GeV Log( Z/Rg) 10 GeV 1 GeV 100 MeV Log( M/Mo) Calculation: Brandon Allgood

  8. 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 For 10 GeV- TeV g - rays, this corresponds to a partner photon energy in the optical - UVrange. Density is sensitive to time of galaxy formation. us source Eg lower us source Eg higher

  9. An important energy band for Cosmology Photons with E>10 GeV are attenuated by the diffuse field of UV-Optical-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.

  10. More Absorption Effects The resulting e+e- pair can up scatter on the CMB: g High Energy e+ g Low Energy e- g Pair Creation Inverse Compton • Effects: • Time delay of low energy signal • Smearing on source image on the sky: Halo • e+e- deflected in inter-galactic magnetic fields • (Brian Baughman’s Thesis Topic)

  11. 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.

  12. Transients Sensitivity 100 sec work done by Seth Digel (updated March 2001) EGRET Fluxes During the all-sky survey, GLAST will have sufficient sensitivity after one day to detect (5s) the weakest EGRET sources. • - GRB940217 (100sec) • - PKS 1622-287 flare • - 3C279 flare • - Vela Pulsar • - Crab Pulsar • - 3EG 2020+40 (SNR g Cygni?) • - 3EG 1835+59 • - 3C279 lowest 5s detection • - 3EG 1911-2000 (AGN) • - Mrk 421 • - Weakest 5s EGRET source 1 orbit* 1 day^ *zenith-pointed, ^“rocking” all-sky scan

  13. 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

  14. Pulsars • Models also predict very different statistics. • Independent of models, GLAST sensitivity probes further through the Galaxy. preliminary Credit: Alice Harding preliminary • Can distinguish acceleration models by observing high-energy roll-offs

  15. Particle Dark Matter If the SUSY LSP is the galactic dark matter there may be observable halo annihilations into mono- energetic gamma rays. X q or gg or Zg q “lines”? X Just an example of what might be waiting for us to find!

  16. Analysis Development Activities • Contributions Areas • Pattern Recognition & Track Fitting • Energy Corrections • Event level Analysis • Resolution Optimization • Maximization of Efficiency • Background Rejection

  17. 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 ~1.5 (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. 68% 95%

  18. 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)

  19. 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. 3D GLAST Tracking 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

  20. New Pattern Recognition Programs Combinatoric: Track-by-track Neural Nets: Analysis at the event level

  21. Track Energies andc2 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

  22. 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

  23. Energy Results Corrected & Filtered Energies Raw Energies Energies generated over 50 MeV 15 GeV

  24. Background Rejection by Classification Trees • GLAST Data an Excellent Match • to Classification Tree Method • Rich Event description • Well defined separation problem Leaves Input Branches Results: 10% signal loss / Factor of 200 Rejection

  25. 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 potential • Large group of Particle + Astrophysicists at UCSC participating

  26. Measurement techniques g Energy loss mechanisms: Atmosphere: ~103 g cm-2 ~30 km 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.

  27. How Close Can You Go? Radiation Environment caused by Accretion is EXTREMELY INTENSE In fact so intense High Energy Photons don’t get out!

  28. 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 ARE THESE BLACK HOLES PRIMOIDIAL?

  29. GLAST Probes the Optical-UV EBL • (1) thousands of BLAZARS - instead of peculiarities of individual sources, look for systematiceffects 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): Caveats • 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 Salamon & Stecker Primack & Bullock

  30. 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.

  31. 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! VARIABILITY: EGRET has seen only the tip of the iceberg. EGRET discovery image of gamma-ray blazar 3C279 (z=0.54) E>100 MeV (June 1991)

  32. 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 ! (most important)

  33. The Dark Matter Problem Observe rotation curves for galaxies: r For large r, expect: Begeman/Navarro 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) ].

  34. 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!

  35. Blanford - Znaek Blazar Model Power = V I = V2/R Take R = 377 W (the vacuum) PAGN = 1038 j/s V = 2 x 1020 Volts Current Flow ACREATION DISK ACREATION DISK

  36. Energy loss mechanisms: Pair-Conversion Telescope  anticoincidence shield conversion foil particle tracking detectors e– • calorimeter • (energy measurement) e+ Experimental Technique Instrument must measure the direction, energy, and arrivaltime 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: determinephoton direction clear signature for background rejection - limitations on angular resolution (PSF) low E: multiple scattering => many thin layers high E: hit precision & lever arm • 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.

  37. FOV w/ energy measurement due to favorable aspect ratio Effects of longitudinal shower profiling Performance Plots (As of the PDR) 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).

  38. 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 s = 27 mrad PDR Resolution s = 37 mrad

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