1. Extending the Sensitivity Of Air-Cerenkov Telescopes Steve Biller, Oxford University (de la Calle & Biller – astro-ph/0602284)

2. Most effort in ACTs today is generally directed at lower energies (~200 GeV) using small pixels and, typically, relatively narrow fields of view What about higher energies and wider fields of view ?? IR Background  ~ 5-20 TeV gammas probe IR regime of interest Tests of Lorentz Invariance  want high energies & moderate redshift AGN Jet Dynamics  spectral shape & variability at high energies TeV Sky Survey  wide field of view perhaps as important as threshold

3. Gamma-ray Induced Shower ~ 10km a.s.l. First InteractionShower Maximum Observation Level ~120m Cerenkov Light Pool

4. 10TeV, 15Tev, 20TeV 500GeV, 1Tev, 2TeV 10 Km 5 Km 100400300500200 SHOWER AXIS X (m) 0.57-1.142.29-4.571.14-2.291.72-3.432.86-5.71 (°) :

6. Optical Reflector: Mount: Davis-Cotton design 10 m diameter Mirror Area: ~87 m 2 271 hexagonal facets Focal length: 10 m (f1 optics) Simulation of Single Facets Ray Tracing Facet Shape : Hexagonal Facet Area : ~0.32 m 2 Facet Separation: 0.61 m Facet Diameter : 0.61 m Facet Reflectivity Misalignment : YES 0.61 m Mirror Facet

7. Camera: 935 pixels (PMT) 0.30  /PMT  10  FOV QE according to wavelength Light Cones QADCs and TDCs included in the simulations Light Cones Ray Tracing Hexagonal + Straight PMT Separation : 0.052 m PMT Radius : 0.026 m ( 0.15 ° ) Cone Angle : ~17.3° Cone Height : 0.0125 m Cone Reflectivity : 80% PMT Cone PMT Cone 0.052 m 0.046 m 0.0125 m 0.0012 m 17.3°

9. Length Width TSlope Alpha

10. 2 TeV Gamma-ray shower (0° zenith angle, 125m core distance, using only pixels with > 7 phe) Arrival time of first photon (ns) Radial distance on camera (m)

12.   [m i – m i o (E,R)] 2  i o (E,R)] 2 i=1 3 Fit for E and R as a function of D isplacement, S ummed light and T Slope / D

15. jj  [m i – m i o (E,X,Y)] 2  i o (E,X,Y)] 2 i=1 4 jj   array    j=1 n

17. 10 Km 5 Km 100400300500200 SHOWER AXIS X (m) 0.57-1.142.29-4.571.14-2.291.72-3.432.86-5.71 (°) : r d h max t = (1/c)  (h max 2 + r 2 )  t  (r 2 2 – r 1 2 ) 2 c h max

19. shape orientation time-based “depth” (independent by construction)

21. 50 hours Integral Sensitivity

22. 1 hour Integral Sensitivity

23. 1)That the simulations are accurate and that the analysis techniques applied are valid. In this regard we have verified the simulation by comparing with analytical calculations, alternative simulations and actual experimental data. We have been able to reproduce trends seen in other, independent studies and replicate parameter distributions and published sensitivity curves from existing experiments. 2) That the repeated sampling of showers employed does not lead to significant biases. To this end, we have explicitly tested this with regard to image selection and have found no evidence of any bias to within the limits our statistical uncertainties. Furthermore, throughout this analysis, we have specifically checked to insure that resulting distributions were not unduly influenced by a handful of independent showers with unusually high ``weights.'‘ 3)That the background rejection factor for the tandem WFOV design can be factorised into groups of largely independent contributions which can be separately assessed and combined as a product. However, in addition for there being logical arguments for why this ought to be the case for the parameters used, we have also explicitly verified the independence of these parameters to within the limits of our statistical uncertainties. 4) That the predicted rejection factors due to newly introduced timing parameters are accurate, even though this is yet to be experimentally tested. We find no reason to doubt these factors given that the photon timing is largely governed by basic air-shower development and geometry, though we certainly encourage future experimental efforts to explicitly explore this. Assumptions: (the small print)

24. These results predict the 2-telescope design considered here to be more than 3 times more sensitive than existing/planned arrays in the regime above 300 GeV for continuously emitting sources; up to 10 times more sensitive for hour-scale emission; significantly more sensitive in the regime above 10 TeV; and possessing a sky coverage which is roughly an order of magnitude larger than existing instruments. Conclusions: (the big print!) Next Step: Bigger mirrors, even wider field-of-view, investigate simple array configurations.

25. Controversial Proposals: 3) Should work towards a prototype via modification of one of the HESS telescopes. 1) Telescope performance has NOT been optimised in current instruments. This should be done before designing large arrays. 2) Work towards any “all-sky” instruments should start by actually building at least one wide-angle instrument with conventional methods before looking at radical solutions.

27. Also note: Most of the information we’ve obtained from AGN in the TeV regime has come from data taken during strong flares Not so much background limited! (effective area could buy more than rejection) Note: Lower intensity gamma images means we’re competing with lower energy background showers  Must improve rejection by at least an order of magnitude to be in the ball park!

28. EAS Simulation Code* Observation Level: 2300 m a.s.l. (763 g/cm 2, same as Whipple Observatory ) X CORE (m) Y CORE (m) 800m Distribution of Core Locations TELESCOPE Gammas: ~ 5x10 6 effective Showers 300GeV - 20TeV Crab-like spectrum  = 1.5 (Integral) 0  zenith Angle Core Distance < 800m Protons: 10 6 – 10 7 effective Showers 10 6 – 10 7 effective Showers 200GeV - 20TeV  = 1.7 (Integral) 0  - 15° zenith Angle Core Distance < 800m *by S Biller, based on EGS4 & SHOWERSIM

29. Whipple 10m Crab DataEAS Simulations Length Width Distance Alpha Simulations of the Whipple 10m gamma-ray telescope SC2000

30. C herenkov Signal : ADC i (d.c.) ≡ # detected photoelectrons (pe) Telescope Trigger Condition : at least 2 pixels  20 pe Image Cleaning : RMS Noise = 3 pe Picture Pixel : Signal is 4.25  above RMS Noise (from night sky background) Boundary Pixel: Signal is 2.25  above RMS Noise and borders a picture pixel Image Parameterization : Number of picture pixels in the image  5 Image Moment parameters (Hillas 1985) Background Rejection : Size and distance dependent cuts on: Length(s,d), Width(s,d), Alpha(s,d), TSlope(s,d) so as to arbitrarily keep 95% after each individual cut