1. A Future All-Sky High Duty Cycle VHE Gamma Ray Detector Gus Sinnis/Los Alamos with A. Smith/UMd J. McEnery/GSFC

2. Scientific Motivation High-Energy (>25 GeV) GRB Spectra –Understanding of acceleration in GRBs –Tests of Lorentz invariance at Planck mass Monitor AGN –Long-term continuous studies –Long-term multi-wavelength correlations –Observe short (<10 minute) flares from many AGN Discover new sources –Source statistics needed to understand AGN –New objects unseen at other wavelengths?

3. Milagro: Current State of Art Moderate altitude: 2200 m asl Moderate area: 4000 m 2 Sensitivity: Crab ~4-5  /sqrt(year) Threshold for GRBs: ~300 GeV Median energy: ~2 TeV

4. ARGO: Next Generation High altitude: 4300 m asl Moderate area: 6500 m 2 Sensitivity: Crab 10  /sqrt(year) [before background rejection]

5. Design Goals GRBs –Complement GLAST –Energy threshold near ~20 GeV Near known energy Able to see large distances (z~1) –Lorentz invariance studies require ability to see prompt emission AGN –Ability to detect/study short (~10-20 minute) flares –Ability to detect distant AGN (z~0.3) –Ability to continuously monitor all AGN Large field of view (~2 sr) ~100% duty cycle Crab sensitivity ~7  /sqrt(day) - 140  /sqrt(year)

6. Is Such an Instrument Possible? Approximation B: Effect of altitude

7. Strawman Design 40,000 m 2 water Cherenkov Detector High altitude: 4500 m 2 Two layers of photodetectors –Top layer for direction and triggering –Bottom layer (calorimeter) for background rejection & energy determination 8” PMTs (same as Milagro) 3 m detector spacing (~10,000 PMTs) 50 PMT trigger (in top layer) Corsika to Generate air shower GEANT in water Use standard Milagro reconstruction for events

8. 200 m

9. Event Timing

10. Angular Resolution 0.75 o resolution Preliminary resolution function

11. Milagro Strawman Triggered Fit in Bin Effective Area vs. Energy: Gamma Rays

12. Background Rejection Estimate total rate (due to background) by scaling proton efficiency from Milagro –120 kHz trigger rate expected As in Milagro use bottom layer information to detect penetrating component of hadronic showers. Small clumps of intense light indicate presence of penetrating component

13. Gammas Protons Pulse Heights in Bottom Layer 260 GeV 660 GeV 350 GeV 170 GeV 2.5 TeV2.2 TeV

14. Background Rejection Use 4 parameters: nTop, nBot2, nBot8, sumPEBot MARS: J. Friedman Reject 95% of protons Accept 55% of gammas 2.5x improvement in sensitivity

15. D.C. Sensitivity: Sky Survey Crab Spectrum: dN/dE = 3.2x10 -7 E -2.49 –0.22 (0.12) Hz of gammas from Crab raw (cut) –Whipple 0.025 Hz –Veritas 0.8 Hz Background rate 80 (4) Hz raw (cut) 3  /sqrt(day) raw data 7.5  /sqrt(day) cut data –140  /sqrt(year) 35 mCrab sensitivity (all sky) in one year –Whipple: 140 mCrab per source –VERITAS: 15 mCrab per source

16. Transient Sensitivity

17. Absorption of TeV Photons e+e+ e-e- ~eV  ~TeV  E  (TeV) z (  = 1)

18. Effect of IR Absorption on Distant Sources z = 0.03 z = 0.1 z = 0.2 z = 0.3 z = 0.0

19. Energy Distribution of Fit Events

20. AGN Sensitivity

21. Gamma Ray Burst Sensitivity

22. Conclusions A large area, high altitude all sky VHE detector can: –Instantaneous sensitivity comparable to Whipple –D.C. sensitivity approaching VERITAS –AGN sensitivity to z = 0.3 –GRB sensitivity to <50 GeV –GRB sensitivity to z~1 Continuing work –Background rejection (low energy) –Improved event reconstruction –Detailed detector design (electronics, DAQ, infrastructure) –Reliable cost estimate needed (~$30M???) –Site survey