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The Spectrum of Markarian 421 Above 100 GeV with STACEE
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  1. The Spectrum of Markarian 421 Above 100 GeV with STACEE Jennifer Carson UCLA / Stanford Linear Accelerator Center February 2006 Space-based 10 MeV 100 MeV 10 GeV 100 GeV 10 TeV 1 GeV 1 TeV 1 MeV Ground-based

  2. Outline I. Science goal for -ray detections from active galaxies • Understanding particle acceleration II. Brief overview of VHE gamma-ray astronomy III. Ground-based detection techniques • Atmospheric Cherenkov technique • Imaging vs. wavefront sampling IV. STACEE V. Markarian 421 • First STACEE spectrum • Detection of high-energy peak? VI. Prospects for the future

  3. Blazars Radio-loud AGN viewed at small angles to the jet axis • bright core •  3% optical polarization • strong multi-wavelength variability

  4. Blazars Radio-loud AGN viewed at small angles to the jet axis 1 eV (IR) 1 keV (X-ray) 1 MeV 1 GeV • bright core •  3% optical polarization • strong multi-wavelength variability • Double-peaked SED: synchrotron emission + ? 10-3 eV (radio) ? Maraschi et al. 1994 synchrotron What physical processes produce the high-energy emission?

  5. Blazar High-Energy Emission Models Is the beam particle an e- or a proton?

  6. Blazar High-Energy Emission Models Is the beam particle an e- or a proton? Leptonic models: • Inverse-Compton scattering off accelerated electrons • Synchrotron self-Compton and/or • External radiation Compton

  7. Blazar High-Energy Emission Models Is the beam particle an e- or a proton? Leptonic models: • Inverse-Compton scattering off accelerated electrons • Synchrotron self-Compton and/or • External radiation Compton Hadronic models: • Accelerated protons • Gamma rays from pion decay or • Synchroton gamma-ray photons

  8. Blazar High-Energy Emission Models Is the beam particle an e- or a proton? Leptonic models: • Inverse-Compton scattering off accelerated electrons • Synchrotron self-Compton and/or • External radiation Compton Hadronic models: • Accelerated protons • Gamma rays from pion decay or • Synchroton gamma-ray photons Gamma-ray observations around 100 GeV can distinguish between models

  9. Compton Gamma Ray Observatory 10 MeV 100 MeV 10 GeV 100 GeV 10 TeV 1 GeV 1 TeV 1 MeV Energy Atm. Cherenkov Wavefront Sampling Atm. Cherenkov Wavefront Sampling Atm. Cherenkov Single Dish Imaging Air shower arrays Exploring the Gamma-ray Spectrum Past Present/Future Atm. Cherenkov Imaging Arrays GLAST

  10. e- e+ … e+ e- e+ e+ Atmospheric Cherenkov Technique g-ray q ~ 1.5o

  11. Single-dish Imaging Telescopes g-ray q ~ 1.5o Whipple 10-meter

  12. Wavefront Sampling Technique g-ray q ~ 1.5o

  13. Wavefront Sampling Technique g-ray q ~ 1.5o

  14. Compton Gamma Ray Observatory 10 MeV 100 MeV 10 GeV 100 GeV 10 TeV 1 GeV 1 TeV 1 MeV Energy Atm. Cherenkov Wavefront Sampling Atm. Cherenkov Wavefront Sampling Atm. Cherenkov Single Dish Imaging Air shower arrays Exploring the Gamma-ray Spectrum Past Present/Future Atm. Cherenkov Imaging Arrays GLAST Whipple 10-meter

  15. 10 MeV 100 MeV 10 GeV 100 GeV 10 TeV 1 GeV 1 TeV 1 MeV Energy Atm. Cherenkov Wavefront Sampling Atm. Cherenkov Wavefront Sampling Atm. Cherenkov Single Dish Imaging Air shower arrays Exploring the Gamma-ray Spectrum STACEE Atm. Cherenkov Imaging Arrays GLAST Whipple 10-meter CELESTE

  16. 10 MeV 100 MeV 10 GeV 100 GeV 10 TeV 1 GeV 1 TeV 1 MeV Energy Atm. Cherenkov Wavefront Sampling Atm. Cherenkov Wavefront Sampling Atm. Cherenkov Single Dish Imaging Air shower arrays Exploring the Gamma-ray Spectrum STACEE Present/Future Atm. Cherenkov Imaging Arrays GLAST

  17. 10 MeV 100 MeV 10 GeV 100 GeV 10 TeV 1 GeV 1 TeV 1 MeV Energy Atm. Cherenkov Wavefront Sampling Exploring the Gamma-ray Spectrum STACEE HESS Present/Future Atm. Cherenkov Imaging Arrays GLAST VERITAS

  18. The High-Energy Gamma Ray Sky 1995  3 sources Mrk421 Mrk501 Crab (2) (1) Pulsar Nebula AGN (0) (0) Other, UNID SNR R.A.Ong Aug 2005

  19. The High-Energy Gamma Ray Sky 2004  12 sources Mrk421 H1426 M87 Mrk501 1ES1959 RXJ 1713 Cas A GC TeV 2032 Crab 1ES 2344 PKS 2155 (7) (1) Pulsar Nebula AGN (2) (1,1) Other, UNID SNR R.A.Ong Aug 2005

  20. The High-Energy Gamma Ray Sky 2005  31 sources! + 8-15 add. sources in galactic plane. 1ES 1218 Mrk421 H1426 M87 Mrk501 PSR B1259 1ES 1101 1ES1959 SNR G0.9 RXJ 1713 RXJ 0852 Cas A LS 5039 GC Vela X TeV 2032 Crab 1ES 2344 HessJ1303 Cygnus Diffuse MSH 15-52 PKS 2155 H2356 PKS 2005 (11) (4+2) Pulsar Nebula AGN (3+4) (3,3+1) Other, UNID SNR R.A.Ong Aug 2005

  21. e- e+ … e+ e- e+ e+ Wavefront Sampling Detectors STACEE & CELESTE Cherenkov light intensity on ground  energy of gamma ray Cherenkov pulse arrival times at heliostats  direction of source

  22. National Solar Thermal Test Facility Albuquerque, NM 5 secondary mirrors & 64 PMTs 64 heliostats STACEE Solar Tower Atmospheric Cherenkov Effect Experiment

  23. National Solar Thermal Test Facility Albuquerque, NM 5 secondary mirrors & 64 PMTs 64 heliostats STACEE Solar Tower Atmospheric Cherenkov Effect Experiment • PMT rate @ 4 PEs: ~10 MHz • Two-level trigger system (24 ns window): - cluster: ~10 kHz - array: ~7 Hz • 1-GHz FADCs digitize each Cherenkov pulse

  24. Ethresh = 165 GeV STACEE Advantages / Disadvantages • 2-level trigger system  good hardware rejection of hadrons • GHz FADCs  pulse shape information • Large mirror area (6437m2)  low energy threshold

  25. Ethresh = 165 GeV STACEE Advantages / Disadvantages • 2-level trigger system  good hardware rejection of hadrons • GHz FADCs  pulse shape information • Large mirror area (6437m2)  low energy threshold But… • Limited off-line cosmic ray rejection  limited sensitivity: 1.4/hour on the Crab Nebula • Compare to Whipple sensitivity: 3/hour above 300 GeV

  26. STACEE Data Observing Strategy: Equal-time background observations for every source observation (1-hour “pairs”) Analysis: Cuts for data quality Correction for unequal NSB levels Cosmic ray background rejection Significance/flux determination

  27. 200 GeV gamma ray 500 GeV proton Energy Reconstruction Idea • Utilize two properties of gamma-ray showers: • Linear correlation: Cherenkov intensity and gamma-ray energy • Uniform intensity over shower area

  28. Energy Reconstruction Method New method to find energies of gamma rays from STACEE data: 1. Reconstruct Cherenkov light distribution on the ground from PMT charges 2. Reconstruct energy from spatial distribution of light Results: fractional errors < 10% energy resolution ~25-35%

  29. Markarian 421 • Nearby: z = 0.03 • First TeV extragalactic source detected (Punch et al. 1992) • Well-studied at all wavelengths except 50-300 GeV • Inverse-Compton scattering is favored • High-energy peak expected around 100 GeV • Only one previous spectral measurement at ~100 GeV (Piron et al. 2003) Blazejowski et al. 2005 STACEE Krawczynski et al. 2001 STACEE ? log (E2 dN/dE / erg cm-2 s-1) log (Energy/eV)

  30. Pairwise distribution of  STACEE Detection of Mkn 421 • Observed by STACEE January – May 2004 • 9.1 hours on-source + equal time in background observations • Non – Noff = 2843 gamma-ray events • 5.8 detection • 5.52  0.95 gamma rays per minute • Energy threshold ~198 GeV for  = 1.8 Eth = 198 GeV  = 1.8

  31. Rate (photons s-1 GeV-1) Spectral Analysis of Mkn 421 • Six energy bins between 130 GeV and 2 TeV • Find gamma-ray excess in each bin • Convert to differential flux with effective area curve Gamma-ray rate (photons s-1 GeV-1) Effective area (m2) Aeff(E) (m2) Energy (GeV) Energy (GeV)

  32. Spectral Analysis of Mkn 421 First STACEE spectrum  = 1.8  0.3stat

  33. Spectral Analysis of Mkn 421 First STACEE spectrum  = 1.8  0.3stat Flat SED

  34. January February March April TeV X-ray 2004 Multiwavelength Campaign PCA data courtesy of W. Cui, Blazejowski et al. 2005

  35. January February March April TeV X-ray 2004 Multiwavelength Campaign STACEE observations PCA data courtesy of W. Cui, Blazejowski et al. 2005 • STACEE coverage: 40% of MW nights • ~90% of STACEE data taken during MW nights • STACEE combines low and high flux states

  36. Multiwavelength Results Blazejowski et al. 2005

  37. Multiwavelength Results STACEE region Blazejowski et al. 2005

  38. STACEE + Whipple Results

  39. STACEE + Whipple Results

  40. Science Interpretation • • STACEE’s first energy bin is ~90 GeV below Whipple’s. • • STACEE result: •  is consistent with a flat or rising SED.  suggests that the high-energy peak is above ~200 GeV. • slghtly is inconsistent with most past IC modeling. • Combined STACEE/Whipple data suggest that the peak is around 200-500 GeV. • • SED peak reflects peak of electron energy distribution.

  41. Gamma-ray spectrum Compton Gamma Ray Observatory Air Cherenkov Wavefront Sampling Air Cherenkov Single Dish Imaging 10 MeV 100 MeV 10 GeV 100 GeV 10 TeV 1 GeV 1 TeV 1 MeV Energy Prospects for the Future • STACEE will operate for another year

  42. Air Cherenkov Wavefront Sampling Prospects for the Future • STACEE will operate for another year • Imaging arrays coming online, Ethreshold 150 GeV - HESS: 5 Crab detection in 30 seconds! - VERITAS: 2 (of 4) dishes completed Gamma-ray spectrum Air Cherenkov Imaging Arrays Compton Gamma Ray Observatory 10 MeV 100 MeV 10 GeV 100 GeV 10 TeV 1 GeV 1 TeV 1 MeV Energy

  43. TIBET MILAGRO MAGIC STACEE VERITAS TACTIC CANGAROO HESS VHE Experimental World TIBET ARGO-YBJ MILAGRO STACEE TACTIC PACT GRAPES

  44. Compton Gamma Ray Observatory Air Cherenkov Wavefront Sampling GLAST Prospects for the Future • STACEE will operate for another year • Imaging arrays coming online, Ethreshold 150 GeV - HESS: 5 Crab detection in 30 seconds! - VERITAS: 2 (of 4) dishes completed • GLAST launch in 2007! Gamma-ray spectrum Air Cherenkov Imaging Arrays 10 MeV 100 MeV 10 GeV 100 GeV 10 TeV 1 GeV 1 TeV 1 MeV Energy

  45. GLAST Large Area Telescope (LAT) Burst Monitor (GBM) GLAST • Two instruments:  LAT: 20 MeV – >300 GeV   GBM: 10 keV – 25 MeV • LAT energy resolution ~ 10% • LAT source localization < 0.5’

  46. EGRET Sources

  47. GLAST Potential

  48. Conclusions • Gamma-ray observations of AGN are key to understanding particle acceleration in the inner jets • Many new VHE gamma-ray detectors & detections • STACEE - “1st-generation” instrument sensitive to ~100 GeV gamma rays - Energy reconstruction is successful - 5.8 detection of Markarian 421 - Preliminary spectrum between 130 GeV and 2 TeV - Second spectrum of Mkn 421 at 100-300 GeV - High-energy peak is above ~200 GeV • Bright future for gamma-ray astronomy

  49. Cosmic Ray Background Rejection What we have: • Hardware hadron rejection (~103) • Off-source observations for subtraction • 2 from shower core reconstruction (‘templates’) • Timing information & 2 from wavefront fit • RMS on average # photons at a heliostat • Limited directional information - reconstruction precision ~0.2°, FOV ~0.6° Some initial success with the Crab nebula… • 5.4 hours on-source after data quality cuts • 3.0 before hadron rejection • Cut on core fit 2 + wavefront fit 2 + direction: 5.7!

  50. Field Brightness Correction Extra light in FOV from stars will increase trigger rate due to promotions of sub-threshold cosmic rays