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OUTLINE Milagro Operations Milagro Observations Galactic Plane Solar Energetic Particles

Surveying the Very High Energy Gamma-Ray Sky with Milagro. OUTLINE Milagro Operations Milagro Observations Galactic Plane Solar Energetic Particles. Brenda Dingus dingus@lanl.gov. Detectors in Gamma-Ray Astrophysics. Air Cherenkov Telescopes HESS, MAGIC, CANGAROO, VERITAS.

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OUTLINE Milagro Operations Milagro Observations Galactic Plane Solar Energetic Particles

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  1. Surveying the Very High Energy Gamma-Ray Sky with Milagro OUTLINE • Milagro Operations • Milagro Observations • Galactic Plane • Solar Energetic Particles Brenda Dingus dingus@lanl.gov

  2. Detectors in Gamma-Ray Astrophysics Air Cherenkov Telescopes HESS, MAGIC, CANGAROO, VERITAS Space-Based Detectors EGRET, AGILE, GLAST Extensive Air Shower Detectors Milagro, Tibet AS, ARGO, miniHAWC Large Effective Area of ~105m2 Excellent Background Rejection < 10% Duty Cycle ~0.02 sr Aperture Sensitive at ~100 GeV Small Area of ~1 m2 “Background Free” ~ 90% Duty Cycle > 2 sr Aperture Sensitive at ~1 GeV Moderate Area of 2 x 104 m2 Good Background Rejection > 90% Duty Cycle ~ 2 sr Aperture Sensitive at ~ 1-10 TeV

  3. Water Cherenkov Extensive Air Shower Detectors e m g 8 meters 50 meters 80 meters • Detect Particles in Extensive Air Showers from Cherenkov light created in a covered pond containing filtered water. • Reconstruct shower direction to 0.3-0.7o from the time different photodetectors are hit. • Multi-kHz trigger rate mostly due to Extensive Air Showers created by cosmic rays • Field of view is ~2 sr and the average duty factor is nearly 100% Milagro Cross Section Schematic

  4. Aerial Photo

  5. Milagro 10 m • Water Cherenkov Detector • 2600m (8500’) elevation • 898 photomultiplier tubes • 450 in top layer in pond • 273 in bottom layer in pond • 175 water tank outriggers • Pond Area is 3600 m2 • Outrigger Array area is 30000 m2

  6. Array of 175 Outriggers 8’ dia. x 3’ deep

  7. Curvature Correction Core Location Error vs True Core Distance from Center of Pond • The shower front is not a plane, but is curved about the shower core • Times of individual PMTs are adjusted based on the distance to the shower core Without Outriggers Core Error (meters) Core Distance (meters) Curved Shower Front 7ns/100m With Outriggers Core Error (meters) Core Distance (meters)

  8. Milagro Status and Timeline • Collaboration between Los Alamos National Lab, Univ. of Maryland, U.C. Santa Cruz, U.C. Irvine, NYU, Michigan State, and Univ. of New Hampshire • January 2001 • Began taking science data • Summer 2004 • Began taking science data with outrigger hardware upgrade • Summer 2005 • NSF site review recommends continuing operation until June 2007 • Summer 2007 • Begin transition of Milagro to miniHAWC (High Altitude Water Cherenkov)

  9. Moon for Monitoring • Cosmic Rays are Shadowed by the Moon (0.5o dia.) • Shadow is deflected by Earth’s magnetic field at low energies • Deflection measures Milagro’s energy scale for protons • Shadow size measures Milagro’s angular resolution for protons Moon Shadow in direction with minimum deflection by Earth’s B

  10. Gamma/Hadron Separation Proton MC Proton MC g MC g MC Data Data Cosmic-ray initiated air showers contain penetrating m’s & hadrons • Cosmic-ray showers have clumpier bottom layer hit distributions • Gamma-ray showers have smoother hit distribution

  11. Background Rejection (Cont’d) Parameterize “clumpiness” of the bottom layer hits Compactness  (nb2/mxPE) • Compactness > 2.5 cuts 50% gammas & 10% hadrons to improve sensitivity by 1.6 or A4  (fOut+fTop)*nFit/mxPE • A4 > 3 20% gammas & 1% hadrons to improve sensitivity by 2.2 mxPE: maximum # PEs in bottom layer PMT nb2: # bottom layer PMTs with >=2 PEs fTop: fraction of PMTs hit in Top layer fOut: fraction of Outriggers hit nFit: # PMTs used in the angle reconstruction

  12. Weighted Analysis Test on Crab Nebula Combine A4 with the weighted Analysis on 5 Years of Data A4 > 3.0 , nFit > 40 A4 > 7.0 , nFit > 40 Weight each event by Expected S/B Apply to Crab Nebula Excess Signal = 3397 Background = 221,263 S/B = 1.5 * 10-2 Excess Signal = 519 Background = 11726 S/B = 5.0 * 10-2

  13. Milagro TeV Sky Survey 2001-2006 Preliminary Significance • Crab Nebula: 14 s • Cygnus Region : 12 s • Galactic Ridge clearly visible

  14. A Closer Look at the Galactic Plane Preliminary Significance • GP diffuse excess clearly visible from l=25° to l=90° • Cygnus Region at l=65°-85° and |b|<3° shows extended excess • FCygnus ~ 2 x Fcrab

  15. Cygnus Region Spatial Morphology Galactic Longitude 90o-65o • Contours are model of cosmic-ray interactions • TeV/matter correlation good in Galactic latitude • Crosses are EGRET sources • Brightest TeV Hot Spot • a=304.5od=36.9o (± 0.3o) • Coincident with 2 unidentified EGRET sources • (3EG J2016+3657 and 3EG J2021+3716) • Source is extended with s = 0.37o+/- 0.13o Preliminary

  16. GeV Galactic Diffuse Spectrum GeV Excess Explanations: 1) Cosmic Ray flux near Earth is low NN: cosmic-ray nucleon + nucleus -> po + …-> gs EB: cosmic-ray electron bremstrahlung IC: inverse Compton scattering of cosmic-ray electron on IR or CMB ID: isotropic diffuse g-rays of unknown origin Hunter et al. ApJ (1997) GeV Excess Strong et al. ApJ (2004) 2) Dark Matter de Boer et al. A&A (2005) 3) ???

  17. TeV Flux from Galactic plane E-2.51±0.05 • Milagro Flux Measurement of Inner Galaxy (R1 40o<Gal. Long.<100o) is consistent with the extension of EGRET Spectrum • Milagro Upper Limit on the Outer Galaxy (R2 140o<Gal. Long.<200o) also consistent with EGRET extrapolation • Phys Rev Letter, Atkins et al 2005 • Work in progress to calculate spectrum of Cygnus region

  18. Measuring Energy Spectrum with Milagro Compatible with other measurements • HEGRA: -2.59 ± 0.03 +- 0.05 • Tibet: -2.62 ± 0.17 • Whipple: -2.49 ± 0.06 +- 0.04 • A4 parameter is sensitive to energy of primary gamma-ray • Calculate Milagro excess vs A4 • Compare with Monte Carlo prediction for different spectra Milagro’s Crab Nebula Preliminary

  19. Solar Physics • Coronal mass ejections are an ideal laboratory to study particle acceleration • By monitoring the singles rates in all PMTs we are sensitive to “low”-energy particles (>10 GeV) • Milagro has detected 4 outbursts from the Sun with >10 GeV particles

  20. X7-Class flare Jan. 20, 2005 • GOES proton data • >10 MeV • >50 MeV • >100 MeV • Milagro scaler data • > 10 GeV protons • ~1 min rise-time • ~5 min duration • inset 2 min grid Milagro PMT Rates

  21. Summary of Milagro Observations • Milagro has operated with > 90% duty factor since 2001 • Deepest survey of northern hemisphere (ApJ, Vol. 608, 680, 2004 ) • Detection of inner Galactic Plane(PRL, Vol. 95, 251103, 2005) • Detection of diffuse emission and an extended source in Cygnus region (paper in progress) • Search for Gamma Ray Bursts • Evidence of VHE emission from 1 of 54 GRBs in Milagrito’s field of view(ApJL, Vol. 533, L119, 2000) • Thus far, 72 satellite-detected bursts in Milagro’s field of view, but no VHE emission detected • 5 Solar Energetic Events Detected • (ApJ, Vol. 588, 557, 2003) • Cosmic ray anisotropy

  22. Milagro is Adding a New Slice to the Milky Way 0.1 GeV TeV Map coming soon PRELIMINARY Milagro 10 TeV gamma-ray

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