Jim Hinton MPI-R, Bonn

3.12.04

Ground-Based Gamma Ray AstronomyGround-Based Gamma Ray Astronomy

at Energies > 10 TeVat Energies > 10 TeV

(H.E.S.S. et al. & beyond......)(H.E.S.S. et al. & beyond......)

Gavin Rowell (MPIK Heidelberg) Gavin Rowell (MPIK Heidelberg)

MPI Kernphysik, HeidelbergHumboldt Univ. BerlinRuhr-Univ. BochumUniv. HamburgLandessternwarte HeidelbergUniv. KielEcole Polytechnique, PalaiseauCollege de France, ParisUniv. Paris VI-VIIUniv. Montpellier II

MPI Kernphysik, HeidelbergHumboldt Univ. BerlinRuhr-Univ. BochumUniv. HamburgLandessternwarte HeidelbergUniv. KielEcole Polytechnique, PalaiseauCollege de France, ParisUniv. Paris VI-VIIUniv. Montpellier II

Jim Hinton MPI-R, Bonn

3.12.04Lessons from H.E.S.S. data of 2003/2004

- Hard spectra for most new TeV sources.

- Most skymaps (of galactic sources) are produced using Hard cuts (< 0.1°, image SIZE > 200 pe., >= 2 tels)

--> improved CR bkg rejection --> improved angular resolution (high E events trigger >2 tels)

- Hard spectra motivates further efforts for E > 10 TeV detection

(Astrophysical motivations are clear and discussed this week)

Investigate

- HESS performance at E > 10 TeV at high zenith angles - New dedicated telescopes for E > 10 TeV astronomy

Jim Hinton MPI-R, Bonn

3.12.04

E < 0.6 TeV 0.6 < E < 1.4 E > 1.4 TeV

eg. the hard spectrum of RXJ1713 permits good statistics well above HESS threshold.

Images below have the same gamma excess (overall)

RX J1713.7-3946

Morphology of Gamma-Ray Sources

HESS Preliminary

Jim Hinton MPI-R, Bonn

3.12.04 The Crab Pulsar Wind NebulaThe Crab Pulsar Wind NebulaStrong, steady source at all wavelengths- Standard candle- Spectrum measured up to ~ 70 TeV (HEGRA) --> Particle accel to E > 100 TeV (GeV sync + IC)

Inverse Compton

(various seed photons)

Aharonian et al. 2004 (HEGRA)

Jim Hinton MPI-R, Bonn

3.12.04 Crab: HESS & HEGRA Results Crab: HESS & HEGRA Results

HESS

~ 30 hrs data

E>250 GeV

7-10 gammas/min

~ 30 sigma/sqrt(hr) ZA> 40°

--> spectrum consistent with

HEGRA

dN/dE ~ E -2.6

paper in preparation

HEGRA (1997 - 2002)

- Over 300 hrs data

E > 500 GeV

1-2 gammas/min

~ 10 sigma/sqrt(hr)

H.E.S.S.H.E.S.S.

Aharonian et al. 2004 (HEGRA)

Jim Hinton MPI-R, Bonn

3.12.04

HESS Collection Area: After 'Standard' Cuts (< 0.112°, Image SIZE > 80 pe., >= 2 tels) Energy & Zenith Angle A

eff approaches

1 km2 ZA >= 60°

Zenith angle (ZA)

Use increasing atm.thickness with ZA:

--> EAS/Cerenkov more spread out

--> EAS can trigger further away

> 1000m !

Sommers & Elbert (1987)

Jim Hinton MPI-R, Bonn

3.12.04 HESS Crab: Compare Med/High ZA for E > 10 TeV

Use runs with 4 telescopes & Crab <= 1.0° off-axis

< 0.112° + 'standard' shape cuts, >= 2 tels

ZA <= 40° (medium zenith)

4.10.6 gam/hr 7.0 sigma 5.9 hrs 3.2 sigma/sqrt(hr)

ZA >= 60° (high zenith)

8.11.6 gam/hr 4.9 sigma 2.2 hrs 3.3 sigma/sqrt(hr)

--> High ZA observation definitely viable. Improved evt rate, similar sigma/sqrt(hr)..... Improved angular res for High ZA expected --> even better!

--> Crab has a rather steep spectrum: Better for hard spectra.

Jim Hinton MPI-R, Bonn

3.12.04

Horns et al. (2004), Aharonian et al. (2005)

dN/dE ~ E-2.1+-0.1 exp(-E/3.1+-0.5)

H.E.S.S. Obs. Of Mkn 421 at High ZA

- Apr – May 2004 (9 nights, 10 hours)

- ZA ~ 61° to 65°

- Eth ~ 1.5 TeV

- Aeff

~ 2 km2 (> 10 TeV)

- <rate> ~ 8 gam/min peak 14 gam/min (4 Crab)

- ~7000 gam >100 sigma

- flux change factor 4 to 5 internight.

- also intranight variability

- Good stability of atm.

CR rate constant ~ few % (after run selection)

Night of MJD 53113

CR rate

Gam rate

Jim Hinton MPI-R, Bonn

3.12.04A Dedicated Cerenkov Imaging System for E > 10 TeV Astronomy

Consider an array of Telescopes (we want stereo!):

- Telescope mirror area A

- Camera FoV & pixel size

- Array size/dimension L

Results based on earlier MC simulation study:

Plyasheshnikov et al. (2000) J. Phys. G: Nucl. Part. Phys. v. 26, p183

- employed ALTAI shower simulation code 0.7 to 200 TeV gammas, 1.5 to 300 TeV protons

--> use these results to suggest the fundamental design.......

L

L

Jim Hinton MPI-R, Bonn

3.12.04Lateral Distribution Cerenkov Image pe. 'Size' vs. Impact Param 'R'

Mirror area A x QE = 1 m2

ie. A = 10 m2

QE = 0.1

Infinite FoV camera

--> 10 m2 perfectly adequate for E > 10 TeV

--> sufficient Cerenkov pe. R > 500m

100 pe.

Gamma (solid)Protons (dashed)

Jim Hinton MPI-R, Bonn

3.12.04First Look at Cerenkov Image Centroid 'Dist' vs. Impact Param 'R'

Single Telescope

Gamma EAS (on-axis)

FoV = 9.3°

Pixel Trigger q = 15 pe.

Dist

FoV

Image

--> Need large FoV ~ 9° – 10°

Jim Hinton MPI-R, Bonn

3.12.04Array Dimension & FoV of each Telescope

Detection Efficiency vs. FoV (Cell of 4 telescopes)Gamma EAS (on axis)

L = 333 m L = 500 m

--> FoV ~9° – 10° recommended ...esp. for extended srcs!

L

L

Jim Hinton MPI-R, Bonn

3.12.04 Array Data Analysis

Cerenkov Image Parameters: Hillas (1985) moment approach width, length, major-axes etc

+ image cleaning (tailcuts)

Stereo gamma/hadron separation: Mean-scaled-width (MSW) MSW = w

i / w

expected,i sum over tels

Stereo direction reconstruction: Intersecting pairs of image major axes (Hofmann et al. 1999)

ang. res ~0.15° is achieved

--> apply MSW + direction cuts (CR bkg rejection) same as for HEGRA, HESS, VERITAS .....

Jim Hinton MPI-R, Bonn

3.12.04 Array Performance (E > 8-10 TeV)

Array: 4 telescopes L = 500m, q=10 pe., pixel size 0.3°, FoV = 9.3°

Crab-like flux & spectrum (vertical) Ethres

~ 8 - 10 TeV

before after direction + shape cuts

Rgamma

3.4 1.7 evts/hr R

protons 702 0.2 --> sig/bkg ~ 9

compare to: HESS ~5 gam/hr sig/bkg ~ 20 (ZA>40deg!)(E > 8 TeV) HEGRA ~2 sig/bkg ~4

-> A modest 4-tel array ~ HESS performance (sims used conservative QE, mirror area..)

Jim Hinton MPI-R, Bonn

3.12.04 Summary

High Zenith Angle Obs for E>10 TeV:

Already verified with HEGRA & HESS! (VERITAS...in future) Aeff >= few km2

Interesting Consequence: High ZA Obs. of Southern sources by VERITAS v. useful! (such sources available 2-4 hrs/night)

Vice versa for HESS obs of Northern sources.

Dedicated Array of Cerenkov Imaging Telescopes for E>10 TeV

Require modest mirror area ~10 m2

Large FoV ~ 9 to 10°Telescope spacing large > 300 m

Good sensitivity for a modest 4-tel array - extend to many more telescopes & optimise detector parameters....further work