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
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