the future of ground-based gamma ray astronomy where do we go?
Post on 22-Dec-2015
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The future of ground-based The future of ground-based gamma ray astronomygamma ray astronomy
Where do we go?Where do we go?
1
0.1
0.01
0.001
Experimentalsensitivity in Crab Units
late 1980’s
late 1990’s
mid-2000’s
Theoryprediction (SN 1006)“Heinz Völk Units”
Inefficientinjection
High B, low density
1000000
100000000
Radio
Optical
UV
X-Ray
Gamma
IR
1
100
10000
101210610010-6Energy [eV]
Peak detected flux /Detection threshold
Neutrinos (?)
Flux sensitivityFlux sensitivity
Is there a future of ground-based Is there a future of ground-based gamma ray astronomy ?gamma ray astronomy ? Physics issuesPhysics issues Instruments to address these issuesInstruments to address these issues
Wish listWish list
Improved sensitivity
Improvedangular
resolution
Wider energy coverage
Large solid angle coverage
Larger effectivearea
Sensitivity ~ E-0.8 Aeff1/2 bg
-1/2 -1
Angular resolution:Angular resolution:Source structureSource structure
ChandraSN 1006
Typical TeVbeam sizeJ. Hiraga ASCA/Chandra
Interactionwith extragalacticbackground light(EBL)
Cosmologyand structureof space-time
AGNs
Wide energy coverage:Wide energy coverage:Gamma ray horizon, IR & cosmologyGamma ray horizon, IR & cosmology
Blanch & Martinez 2004
Simulatedmeasurements
Different EBL models
Large solid angle coverageLarge solid angle coverage
Surveys: New sources Surveys: New sources not visible in other not visible in other wavelengthswavelengths
Monitoring of bursts Monitoring of bursts and transients (AGN, and transients (AGN, GRB, GRB, Quasars,…)Quasars,…)
HEGRA unidentifiedCygnus source
Large effective area / rate:Large effective area / rate:MWL correlation of flux and index in AGNsMWL correlation of flux and index in AGNs
Whipple Mkn 421
Need a smart new idea!Need a smart new idea!
If I had one, I wouldn’t tell you …from now on: brute force approach …
will concentrate on future beyond will concentrate on future beyond current generationcurrent generation
A biased view!
Sensitivity, angular resolution:Sensitivity, angular resolution:seems hard to beat Cherenkov telescopesseems hard to beat Cherenkov telescopes
I believe that Cherenkov telescopes are good for I believe that Cherenkov telescopes are good for at another Generation beyond CANGAROO / at another Generation beyond CANGAROO / H.E.S.S. / MAGIC / VERITASH.E.S.S. / MAGIC / VERITAS
Should know: where are the fundamental limits of Should know: where are the fundamental limits of the technique?the technique?
Ultimate limit: use all photonsUltimate limit: use all photons
Fit to distribution(x,y,x,y,t)
here: using cruderepresentation ofdistr. function,can probably dobetter
Shower fluctuations:Shower fluctuations:angular resolution: fit to angular resolution: fit to allall photons photons
0.008O/√ETeV
with geomag. fieldin bending plane
How many photons are needed?How many photons are needed?
relativeto PMTquantumefficiency
1 TeV
100 GeV
10 GeV
1 GeV
shower fluctuations
photonstatistics
Shower fluctuations:Shower fluctuations:background rejectionbackground rejection
1 TeV
2 TeV p
x [m]
y
[m]
Rejection: few 10-4
y
[m]x [m]
y
[m]
100 GeV
200 GeV p
Rejection: ~ 10-2
Conclude:Conclude:
With enough light (few 10 p.e./GeV), should be With enough light (few 10 p.e./GeV), should be able to gain factor ~3 from angular resolutionable to gain factor ~3 from angular resolution
Similar factor from background rejection (p)Similar factor from background rejection (p)
Larger telescopesLarger telescopes (Dense) telescope arrays for low energies(Dense) telescope arrays for low energies Small pixels Small pixels advanced photon detectors advanced photon detectors High altitudeHigh altitude
Bonus at low energy: geomagnetic cutoffBonus at low energy: geomagnetic cutoff
Optimum telescope sizeOptimum telescope size
10 m 20 m 30 m
Cost per area
Fixed costs dominate(Control, camera)
Dish cost dominates
Dish size > shower size, depth of field problem ?
Triggering on low-energyshowers becomes very complex
Focus & depth of fieldFocus & depth of field
Example:Cherenkovimages in a20 m telescope
Focus at infinity Focus on shower head
Optimum focus Focus on shower tail
Practical limitaround 30 mdiameter ?Telescope size =shower width
Practical thresholdsPractical thresholds
A. Plyasheshnikov
30 m telescope
@ 1.8 km
@ 5 km
Effect of geomagnetic cutoff
A. Plyasheshnikov
Improved photon detectorsImproved photon detectors
PMT
GaAs NIM A518, 615
Thinned CCD
PMT GaAs CCDSignal: 1 : 2.2 : 4.5S/√B: 1 : 1.1 : 1.4
Self-quenchingGeiger-modeavalanche cells
Russian groups,MPI Munich/Semicond. Lab
Courtesy NRAO/AUI and ESO
VHE physicists dream ?VHE physicists dream ?
High-resolution modeHigh-resolution mode Survey / monitoring modeSurvey / monitoring mode Large-area modeLarge-area mode Halo of nano-telescopes for 10+ TeVHalo of nano-telescopes for 10+ TeV
Survey instrumentsSurvey instruments
Cherenkov telescopes with Cherenkov telescopes with large cameras and Gascoigne large cameras and Gascoigne aspheric corrector plate … aspheric corrector plate … could imagine 10could imagine 10oo to 15 to 15oo diameterdiameter
Fresnel lens wide-angle Fresnel lens wide-angle instrumentsinstruments
• nontrivial Fresnel lensnontrivial Fresnel lens
• huge focal plane (10huge focal plane (1055+ channels)+ channels)
• would probably want several would probably want several (stereo) instruments of 10 m class(stereo) instruments of 10 m class
HAWC: A Next HAWC: A Next Generation All-Sky VHE Generation All-Sky VHE Gamma-Ray TelescopeGamma-Ray Telescope
from G. Sinnis
Median Energy 180 GeV
(Milagro ~3 TeV)
Angular resolution ~1Angular resolution ~1oo
Sensitivity 50 mCrab / y for steady sources,Sensitivity 50 mCrab / y for steady sources,
~ 10 h for 1-Crab flare ~ 10 h for 1-Crab flare (H.E.S.S.: 30 sec)(H.E.S.S.: 30 sec)
ConclusionsConclusions
Try to get (at least) one Cherenkov telescope Try to get (at least) one Cherenkov telescope system with sub-mCrab sensitivity @ 100 GeV to system with sub-mCrab sensitivity @ 100 GeV to TeV energies, O(10 GeV) thresholdTeV energies, O(10 GeV) threshold
and and
one wide-angle 100 GeV survey instrumentone wide-angle 100 GeV survey instrument
Unite communityUnite community
Develop low-cost, no-frills production techniquesDevelop low-cost, no-frills production techniques
• Honeycomb foil mirrors a la Durham ?Honeycomb foil mirrors a la Durham ?
• ASIC for signal storage, trigger, digitisationASIC for signal storage, trigger, digitisation
• ……
no magnetic field (< few 10 nT)atmospheric depth adjustable from 2 r.l. upcombine perfect angular resolution (no low-energy stragglers) with large detection area