a future all-sky high duty cycle vhe gamma ray detector gus sinnis/los alamos with a. smith/umd j....
DESCRIPTION
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 TeVTRANSCRIPT
A Future All-Sky High Duty Cycle VHE Gamma Ray Detector
Gus Sinnis/Los Alamoswith
A. Smith/UMdJ. McEnery/GSFC
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?
Milagro: Current State of Art• Moderate altitude: 2200 m asl• Moderate area: 4000 m2
• Sensitivity: Crab ~4-5/sqrt(year)• Threshold for GRBs: ~300 GeV• Median energy: ~2 TeV
ARGO: Next Generation
• High altitude: 4300 m asl• Moderate area: 6500 m2
• Sensitivity: Crab 10/sqrt(year) [before background rejection]
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)
Is Such an Instrument Possible?Approximation B: Effect of altitude
Strawman Design• 40,000 m2 water Cherenkov Detector• High altitude: 4500 m2
• 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
200 m
200
m
Event Timing
Angular Resolution
0.75o resolution
Preliminary resolution function
Milagro
StrawmanTriggered
Fit in Bin
Effective Area vs. Energy: Gamma Rays
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
Gam
mas
Prot
ons
Pulse Heights in Bottom Layer260 GeV
660 GeV 350 GeV
170 GeV 2.5 TeV 2.2 TeV
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
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
Transient Sensitivity
Absorption of TeV Photons
e+
e-
~eV
~TeV
E (TeV)
z (
= 1
)
Effect of IR Absorption on Distant Sources
z = 0.03z = 0.1z = 0.2
z = 0.3
z = 0.0
Energy Distribution of Fit Events
AGN Sensitivity
Gamma Ray Burst Sensitivity
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