Water Cherenkov Technology in GammaRay Astronomy Gus Sinnis

Water Cherenkov Technology in Gamma-Ray Astronomy Gus Sinnis Los Alamos National Laboratory

Complementarity of Gamma-Ray Detectors Low Energy Threshold EGRET/GLAST High Sensitivity HESS, MAGIC, VERITAS Large Aperture/High Duty Cycle Milagro, Tibet, ARGO, HAWC Space-based (Small Area) Large Area “Background Free” Large Duty Cycle/Aperture Excellent Background Rejection Low Duty Cycle/Small Aperture Good Background Rejection Large Duty Cycle/Aperture Sky Survey High Resolution Spectra Sky Survey AGN Physics Transients (GRBs) Study of known sources Limited Surveys Fast Flaring Distant AGN Extended Sources Transients (AGN, GRB) Highest Energies Galactic Diffuse Emission

Goals of a Te. V Gamma-Ray Survey Instrument • Galactic cosmic-ray origins – Galactic diffuse emission – Highest energies (>10 - 100 Te. V) • Particle acceleration in astrophysical jets – Gamma-ray bursts – Active galaxy transients – Multi-wavelength/messenger campaigns • All-sky survey – Discovery potential – IACT alert system

Galactic Cosmic Rays Cygnus Region EG – Large area (100, 000 m 2) – High duty factor (~100%) – Large field-of-view (~2 sr) RE T • Measure Galactic accelerators to >100 Te. V • Measure diffuse emission spatial and spectrally resolved n ha nc pio Inv Strong & Moskalenko EGRET all sky (100 Me. V) l ne er se ch Co an mp ne to l n Milagro

Extragalactic transients • Absorption by EBL requires • Gamma-Ray Bursts – Low energy threshold – Ge. V ≥ 0. 1 x Me. V fluence – 200 Ge. V for z = 0. 5 horizon – 10 -7 ergs/cm 2 @ 10 sec – 1 -2 Te. V for z = 0. 1 horizon – 4000 m 2 @ 200 Ge. V Fermi/LAT Science. Express 2/19/2009 e. V k 0 G e. V = V MAGIC collab. LAT Ge 10 = e. V k 0 0 1 1 0. GBM

Extensive Air Shower Arrays http: //www. ast. leeds. ac. uk/~fs/photon-showers. html 30 km Tibet AS Milagro meters 7. 7 km Active detectors 4 km gamma: electron ratio ~6: 1 em particles sparse at low energies need enclosed area ~ active detector area 200 m 1 Te. V gamma-ray shower Longitudinal Profile • gammas • electrons

Effect of Altitude on Response 30% eff 7% eff

E-M Energy on Ground 5200 m Observatory ~10% of energy reaches the ground Error on Mean

Background rejection in EAS arrays ’s within a 105 m 2 area of core Large fluctuations of shower size manifest as fluctuations in muon content

Milagro – 1 st Generation • • 2600 m asl 898 detectors – 450(t)/273(b) in pond – 175 water tanks 4000 m 2 (pond) / 4. 0 x 104 m 2 (phys. area) 5 -40 Te. V median energy (analysis dependent) 1700 Hz trigger rate 400 Gbyte/day 0. 3 o-1. 2 o resolution (0. 75 o average) 95% background rejection (at 50% gamma eff. ) e 8 meters 50 meters 80 meters

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

Background Rejection (Cont’d) Background Rejection Parameter Apply a cut on A 4 to reject hadrons: A 4 > 3 rejects 99% of Hadrons retains 18% of Gammas S/B increases with increasing A 4 mx. PE: maximum # PEs in bottom layer PMT f. Top: fraction of hit PMTs in Top layer f. Out: fraction of hit PMTs in Outriggers n. Fit: # PMTs used in the angle reconstruction

Te. V Observations of Fermi Sources Boomerang Cygnus Region MGRO 1908+06 HESS 1908+063 Fermi Sources Geminga Crab Nebula • • 34 Fermi BSL Galactic sources above declination of -5 o 14 detected by Milagro above 3 s – • • FDR Miller 2001 estimates 1% false positive rate 5 new Te. V sources Geminga 6. 3 s as extended source (2. 6 o fwhm)

IC 433 SNR MAGIC VERITAS Radio pulsar J 0631+10 (new Te. V source) G 65. 1+0. 6 (SNR) W 51 HESS J 1923+141 Fermi Pulsar (J 1958) New Te. V sources SNR Geminga Pulsar Milagro C 3 Pulsar (AGILE/Fermi) MGRO 2019+37 un. ID (new Te. V source) Fermi Pulsar Cygni SNR Fermi Pulsar HESS 2032+41 MGRO 2031+41 MAGIC 2032+4130 un. ID (new Te. V source) Fermi Pulsar MGRO 1908+06 HESS 1908+063 Fermi Pulsar Milagro (C 4) 3 EG 2227+6122 Boomerang PWN

HAWC: The Next Generation 15 x Milagro sensitivity 5 x larger active detector area optical isolation of detector elements 10 x larger muon detector improved angular resolution improved energy resolution higher altitude (4100 m) 1/3 median energy of Milagro The base of volcán Sierra Negra • latitude : 18º 59’ • longitude: 97º 18’ • altitude : 4100 m Inside Parque Nacional Pico de Orizaba 2 hours from Puebla (INAOE)

The HAWC Collaboration Los Alamos National Laboratory B. Dingus, J. Pretz, G. Sinnis University of Maryland D. Berley, R. Ellsworth, J. Goodman, A. Smith, G. Sullivan, V. Vasileiou University of New Mexico J. Matthews University of Utah D. Kieda Michigan State University J. Linnemann Pennsylvania State University Ty De. Young NASA/Goddard J. Mc. Enery Naval Research Lab A. Abdo UC Santa Cruz M. Schneider Instituto Nacional de Astrofísica Óptica y Electrónica Alberto Carramiñana, L. Carasco, E. Mendoza, S. Silich, G. T. Tagle, Universidad Nacional Autónoma de México R. Alfaro, E. Belmont, M. Carrillo, M. González, A. Lara, Lukas Nellin, D. Page, V. A. Reese, A. Sandoval, G. Medina Tanco, O. Valenzuela, W. Lee Benemérita Universidad Autónoma de Puebla C. Alvarez, A. Fernandez, O. Martinez, H. Salazar Universidad Michoacana de San Nicolás de Hidalgo L. Villasenor Universidad de Guanajuato David Delepine, Victor Migenes, Gerardo Moreno, Marco Reyes, Luis Ureña UC Irvine G. Yodh University of New Hampshire J. Ryan

HAWC Design 100 Me. V photons shown 900 tank array 4. 3 m high x 5 m diameter tanks 15 0 m 150 m Through-going Muon

Gammas HAWC: Background Rejection Protons Size of HAWC Size of Milagro deep layer Energy Distribution at ground level Rejection Parameter: n. PMT/cx. PE n. PMT = # PMTs in event cx. PE = Maximum # Pes in PMT > 30 m from fit core location

Background rejection gammas hadrons Fraction bkgd remaining • Background rejection improves with increasing energy • S/B 5 x at E> 5 Te. V (with rejection vs. no rejection) • Essentially background free near 100 Te. V Milagro HAWC

HAWC: Effective Area

HAWC DC Sensitivity: 5 -Year Survey 1 yr IACTs 50 hrs (~0. 06 sr/yr) EAS 5 yrs (~2 sr) 2 0 0 20 km r h sr

7 min/fov 1500 hrs/fov 4 min/fov Survey Sensitivity 1500 hrs/fov

Sensitivity vs. Source Size Large, low surface brightness sources require large fov and large observation time to detect. EAS arrays obtain ~1500 hrs/yr observation for every source. Large fov (2 sr): Entire source & background simultaneously observable Background well characterized

AGN Monitoring • Measure Te. V duty factors and notify other observers of flares in real time. • Unbiased survey for Te. V “orphan” flares • All sources within ~2 sr will be observed every day for ~ 5 hrs. • Continuous observations – no gaps due to weather, moon, or solar constraints. • HAWC’s 5 s sensitivity is (10, 1, 0. 1) Crab in (3 min, 5 hrs, 1/3 yr) Worldwide Dataset of Te. V Observations by IACTs of Mrk 421 1 month Brenda Dingus HAWC Review -

Tank Details • PMT at bottom of tank • Non reflective interior surfaces • Roto-molded tank issues – Largest tanks available not deep enough – Too large for road transport (build on site) @ Sierra Negra In CA Steel pipe with bladder No size limitations, easy transportation (in pieces)

Conclusions • • Water Cherenkov Technology enables a “low”-threshold all-sky gamma-ray capability (sub-Te. V) First generation instrument built at moderate altitude demonstrated the capability of the technique – – • Discovery of Galactic diffuse emission at 10 Te. V (large excess observed) Discovery of extended sources of Te. V emission Discovery of an anomalous component to the local cosmic rays Te. V counterparts to Fermi Ge. V sources (5 new Te. V sources) The next generation instrument will have ~15 x greater sensitivity – Build at high altitude (4100 m) • Scientific Goals – Origin of Galactic Cosmic Rays – Understanding Galactic accelerators (Pevatrons) – Extragalactic accelerators via multi-wavlength/messenger study of transients • Active Galaxies (10 x Crab in 3 minutes) • Gamma-ray bursts • Funding received for R&D and site development ($1 M) – 3 tanks operating on site – All permits for full array in place • Proposal at NSF and Do. E awaiting PASAG (Summer 2009)