HAWC (High Altitude Water Cherenkov) A Wide-Field Gamma-Ray Telescope

Transcription

1 HAWC (High Altitude Water Cherenkov) A Wide-Field Gamma-Ray Telescope Los Alamos National Lab

2 Complementarity of TeV Gamma-Ray Detectors Imaging Air Cherenkov Telescopes Extensive Air Shower Arrays IACTs Energy Range TeV TeV Area >10 4 m 2 >10 4 m 2 Background Rejection >99% >95% Angular Resolution 0.05 o o Energy Resolution ~15% ~50% Aperture sr 2 sr Duty Cycle 10% 95% EAS arrays

3 HAWC Detector Design From Milagro to HAWC: Increase Altitude to 4100 m from 2650 m Increase Area to 22,000 m 2 from 4,000 m 2 (top layer) or 2,200m 2 (bottom layer) Reuse 900 Milagro PMTs and front end electronics Cost $7.4M HAWC x Sensitivity e μ of γ Milagro: HAWC: Detect Crab in ~ 1 day (5σ) Milagro: Detects Crab in 3 months

4 HAWC Detector Design 900 water tanks Tanks are 5 meter diameter and 4.3 meter deep Tanks cost $4.1k each (inc. shipping) One 8 PMT/tank Tank array covers area of 150m x 150m with 78% coverage HAWC Tank Array in GEANT 4 DAQ trailer Road

5 Tanks vs Pond Less expensive Build incrementally Develop & debug as we are building Within 2 yrs HAWC will have 4x Milagro sensitivity Expandable & upgradeable GEANT4 Simulation Muon (thinned 1/50) produces up to 100s of pes depending on impact parameter 100 MeV γ ray (thinned 1/200) produces 1pe/60 MeV independent of impact parameter See Poster by John Pretz

6 Site Location is Sierra Negra,, Mexico 4100 m above sea level Easy Access 2 hr drive from Puebla 4 hr drive from Mexico City Existing Infrastructure Few km from the US/Mexico Large Millimeter Telescope Power, Internet, Roads Sierra Negra Scientific Consortium of ~7 projects Excellent Mexican Collaborators ~15 Faculty at 7 institutions have submitted proposal to CONACYT for HAWC Experience in HEP, Auger, and astrophysics (including TeV) See Poster by Alberto Carramiñana

7 HAWC Collaboration USA: Los Alamos National Laboratory, John Pretz, Gus Sinnis University of Maryland Jordan Goodman, Andrew Smith, Greg Sullivan University of Utah Dave Kieda, University of New Mexico John Matthews Michigan State University Jim Linnemann Pennsylvania State University Ty DeYoung NASA/Goddard Space Flight Center Julie McEnery University of New Hampshire James Ryan University of California, Irvine Gaurang Yodh Mexico: Instituto Nacional de Astrofísica Óptica y Electrónica (INAOE) Alberto Carramiñana, Eduardo Mendoza Universidad Nacional Autónoma de México (UNAM) Instituto de Astronomía: Magdalena González, Dany Page, William Lee, Hector Hernández, Deborah Dultzin, Erika Benitez Instituto de Física: Arturo Menchaca, Rubén Alfaro, Andres Sandoval, Ernesto Belmont Instituto de Ciencias Nucleares: Lukas Nellen, G. Medina-Tanco Instituto de Geofísica: José Valdés Galicia, Alejandro Lara Benemérita Universidad Autónoma de Puebla Humberto Salazar, Oscar Martínez, Cesar Álvarez, Arturo Fernández Universidad Michoacana de San Nicolás de Hidalgo Luis Villaseñor CINVESTAV Arnulfo Zepeda Universidad de Guanajuato David Delepine, Gerardo Moreno, Marco Reyes, Luis Ureña, Victor Migenes

8 HAWC Sensitivity is 15x Better than Milagro s (a) Larger Effective Area at Lowest Energies (b) Better Angular Resolution (c) Improved Background Rejection => x improvement in flux sensitivity => (10-15) 15) 2 x faster to observe same flux Hadron Efficiency Ang. Res. (deg) Eff. Area (m 2 ) (a) 100 GeV 1 TeV 10TeV 100 TeV (b) 100 GeV 1 TeV 10TeV 100 TeV (c) e μ γ 100 GeV 1 TeV 10TeV 8 Nov TeV

9 Lateral Distribution of Extensive Air Showers Gammas have NARROW lateral distribution of electrons Protons have BROAD lateral distribution of muons

10 Gamma/Hadron Separation Rejection factor ~ e -<μ> 30 GeV 70 GeV 230 GeV Protons Gammas Size of HAWC 20 GeV 70 GeV 270 GeV Size of Milagro deep layer Energy Distribution at ground level

11 Background Rejection in Milagro Hadronic showers contain penetrating component: μ s & hadrons Cosmic-ray showers lead to clumpier bottom layer hit distributions Gamma-ray showers give smooth hit distributions Proton MC Proton MC γ MC γ MC Data Data

12 Milagro Background Rejection (Cont d) Background Rejection Parameter A 4 = ( ftop + fout ) mxpe nfit mxpe: ftop: fout: nfit: maximum # PEs in bottom layer PMT fraction of hit PMTs in Top layer fraction of hit PMTs in Outriggers # PMTs used in the angle reconstruction S/B increases with increasing A 4 so analysis weights events by S/B as determined by the A 4 value of the event

13 Sensitivity to Crab-like (dn/de( dn/de=e -2.6 ) Point Source E F(>E) (TeV/cm 2 s) 6 TeV 4 TeV HESS/VERITAS, MAGIC, Whipple, CTA sensitivity in 50 hours, (~0.2 sr/year) GLAST sensitivity in 1 year (4π sr) HAWC, Milagro, sensitivity in 1(solid) and 5 (dashed) years (2π sr) HAWC will do better for hard & diffuse sources GeV

14 HAWC s Field of View = 2.6 π sr = 1.8 π sr

15 HAWC Science Objectives Constrain the origin of cosmic rays via HAWC s observations of γ-rays up to 100 TeV from discrete sources and the Galactic plane. Probe particle acceleration in extreme magnetic and gravitational fields via HAWC s observations of transient TeV sources,, such as gamma ray bursts and supermassive black holes. Explore new TeV physics via HAWC s unbiased sky survey with a detection threshold of ~30 mcrab in two years.

16 Cygnus Region HAWC s science objectives build on the discoveries of Milagro Mrk 421 Crab Nebula

17 Cygnus Region 6.5 year data set (July 2000-January 2007) Weighted analysis using A4 parameter Best data from 2004 on with outriggers Crab nebula 15 σ Galactic plane clearly visible Distribution of Excesses in the Galactic Plane cut level Mrk 421 Crab Nebula

18 C4 J MGRO J σ EGRET MGRO J Tibet Excess E. Ona-Wilhelmi, et al., ICRC σ 4.5 σ C2 J C3 J C1 J Geminga Abdo, et al. ICRC 2007

19 GeV Sources Emit TeV Gamma-Rays H H Milagro has discovered 3 new sources & 4 candidates in the Galaxy. 5/7 of these TeV sources have GeV counterparts. Only 13 GeV counterparts in this region - excluding Crab. Probability = 3x10-6 HAWC + GLAST observations survey the sky from 100 MeV to 100 TeV IC443 LS I HESS J Abdo, et al. ApJ Lett 2007

20 Milagro Extension of TeV spectrum of MGRO J Preliminary Median energy for this angle and α=-2.0 is 50 TeV Cut on A4> 4 & 9 gives median E of 60 and 90 TeV 60 90

21 HAWC Energy Resolution Shower Fluctuations Dominate Energy Resolution Higher Altitude of HAWC increases # of particles by ~6x Ability to measure a high energy cut off is a combination of the energy resolution AND the statistical error in the flux

22 HESS J TeV α=-2.3 Highest energy ~20 TeV

23 HESS J TeV α=-2.3 Highest energy ~20 TeV Simulated HAWC data for 1 year with no cutoff

24 HESS J TeV α=-2.3 Highest energy ~20 TeV Simulated HAWC data for 1 year with 40 TeV exponential cutoff

25 Sensitivity vs. Angular Extent S extended S point σ source σ detector σ EAS ~0.5 o σ IACT ~0.1 o EAS large fov of 2 sr: Entire source & background simultaneously observable Background well characterized

26 Galactic Diffuse Emission Probing cosmic ray origin requires distinguishing between electron and hadron produced γ-rays Hadrons are correlated with matter density and the flux is strongly constrained by direct cosmic ray observations Flux from electrons is less constrained, but must decrease at highest energies due to K-N K effects GALPROP Conventional (solid) and Optimized (dashed) Models Hadronic Pion Decay Electron Inverse Compton Scattering Milagro Observation

27 Milagro Observations of Galactic Diffuse Emission Cygnus Region with Matter Density Contours overlaying Milagro Significance Source Subtracted Longitude Profile (see details in poster by Petra Huntemeyer) Huntemeyer, et al. ICRC x GALPROP 1.5x GALPROP Sources Subtracted GALPROP (optimized) Cygnus Region Below Horizon

28 Extragalactic Science: HAWC & Transients AGN and GRBs have bright flares e.g. PKS J (z=0.117) flared to 50x quiescent flux in one hour with dn/de=ke -3.5 which would give 6 σ in HAWC GRB <1 MeV TeV AGN flares GLAST and HAWC sensitivity for a source of spectrum dn/de=ke -2 z=0 no E cutoff z=0.1 Eexp ~700GeV z=0.3 Eexp ~260GeV z=0.5 Eexp ~170GeV

29 AGNs HAWC will obtain duty factors and notify multiwavelength observers of flaring AGN in real time. Milagro has observed 7yr lightcurve of Mrk 421 HAWC s increased sensitivity would result in ~10x smaller error bars and have similar error bars on hour time scale rather than 64 days Milagro - Events/day Milagro and XTE ASM 7 yr lightcurve of Mrk 421 (Smith et al. ICRC 2007) ASM Flux cts/s Crab Flux 1/1/2000 1/1/2001 1/1/2002 1/1/2003 1/1/2004 1/1/2005 1/1/2006 1/1/2007 MJD

30 GRBs Milagro searches data within few seconds for short duration transients and sends alerts to GCN, but has found no significant emission HAWC s low energy response allows dimmer GRBs at more distant redshifts to be observed

31 HAWC sample GRB lightcurve High Energy cut off could occur due to absorption in GRB or in transit via EBL interaction. Measurements of lightcurve reveal information about progenitor and constrains Lorentz invariance. HAWC lightcurve of a bright GRB (1e-4 ergs/cm2 fluence). Weaker burst counts scale with fluence.

32 Surveying the TeV Sky Discovery Potential Many Classes of Potential TeV Sources Extended Sources Dark Matter, Galaxy clusters, AGN Pair Halos, Molecular Clouds,... Variable Sources Compact Binaries, Microquasar Flares, Solar Energetic Particles,...

33 Milagro s s Unexpected Cosmic Ray Anisotropy Observation Anisotropy on 10 deg size scale with a fractional excess of 7e-4 above the cosmic ray background (15 σ) Excess is not gamma rays, but charged cosmic rays (5 σ) Largest excess is not consistent with the locally measured cosmic ray energy spectrum (4 σ), but is harder with a cut off of ~10 TeV Explanations are difficult because the gyroradius of a 10 TeV proton in a 1 μg field is 0.01 parsecs See Poster by Gary Walker

34 Conclusions Milagro technique works Discovery of diffuse TeV gamma rays from Galactic plane & Cygnus region Discovery of new Galactic TeV sources Demonstration of long-term multi-wavelength AGN monitoring Unexpected TeV Cosmic-ray anisotropy observed With HAWC Large improvements are possible times the sensitivity of Milagro ~5 σ/ day on the Crab 3% of Crab flux sensitivity over entire hemisphere (after 2 year operation) Scientific Capabilities Highest energies Extended sources Galactic diffuse emission TeV transients Unbiased Sky survey

35 TeV γ Rays: New Window on the Sky Milagro HESS TeV gamma ray