High Energy All Sky Transient Radiation Observatory HE-ASTRO By V. Vassiliev, S.
Garber, Jim, Host has reference to this Academic Journal, PHwiki organized this Journal High Energy All Sky Transient Radiation Observatory HE-ASTRO By V. Vassiliev, S. Fegan, A. Weinstein Cherenkov 2005 : 27-29 April 2005 – Ecole Polytechnique, Palaiseau, France A E W $ Scientific Motivations in the realm of GLAST epoch + Studies of very high energy transient phenomena In the Universe Studies of the highest energy radiation Galactic sources Cosmological studies of High Energy Transient Phenomena to determine Population properties of AGN in addition to GRBs Redshift evolution of these objects Redshift evolution of EBL (z=0-6) Major contributors to EBL (stars, dust, AGN, Population III objects, relic particles, SFR, GFR, IMF, BH accretion histories, supernovae feedback, merger history) Cosmological magnetic fields in addition to their evolution High energy properties of space-time
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Cosmological Diffuse Background l [mm] nIn nW m-2 sr-1 Universes Opacity Energy of g-ray [TeV] Redshift Z No CDB Evolution is assumed Collecting Area Requirement To resolve ~a few min variability time scale in emission of Mrk 421-like AGN placed at Z=1, the collecting area of the observatory must be ~1 km2. E interval g-Rate [GeV] [min-1] 25 – 50 1.3 50 -100 0.7 100 – 200 0.3 3C273 Energetic Quasar Jet by Ch in addition to ra
Collecting Area Requirement Because the size of the HE-ASTRO, ~1010 cm2, is much larger than the size of the Cherenkov light pool, ~108 cm2, the number of telescopes required is ~102. A Coupling distance: d=80m Area per telescope: A=31/2/ 2 d2 = 5.542x107cm2 Number of telescopes: N=217=3n(n-1) +1; n=9 HE-ASTRO (1st specs) Target Energy Range 20 200 GeV Array of 217 telescopes (n=9) Area ~1.0km2 Effective Area ~1.6km2 (including boundary events) Detection Rates x 100Hz (flaring nearby AGN) x 1-10Hz (quiescent moderately distant AGN) x few per min (cosmologically distant AGN) Total Cost < $200M (approximate cost of satellite mission) Cost per station < $1M Problem 1 (energy vs area) Although large aperture costly telescopes seem to be favored as long as low energy range prerequisite, they are incompatible with collecting area constraint due to cost limitations Solid Angle Requirement Sky Survey Un-localized Source Known Source Observing Mode: RCR ~300 kHz RCR ~30 kHz RCR ~3 kHz Problems 2 & 3 A requirement of large solid angle coverage, ~p, by the system of a few large aperture telescopes possesses a very difficult engineering problem in addition to costly large aperture secondary optics . Sustaining high data rates in non-distributed system, such as a few large aperture telescopes, is another challenging electronics problem HE-ASTRO (2nd specs) Energy Range 20200 GeV Array of 217 telescopes Area ~1.0km2 (~1.6km2) Field of View ~15o FoV area ~177 deg2 Reflector Diameter ~7m Reflector Area ~40 m2 Cost per station < $1M Energy Range Cost per Telescope Galactic HE Astrophysics Max Acceleration Energy Crab Nebula: 1 g/min > 10 TeV; 2 g/hour > 100 TeV HE pulsars in addition to transients If number of sources is a matter of sensitivity in already probed energy domain ,100 GeV 10 TeV, then collecting area of 1km2 is a figure of merit. New Phase Space in E, T: New Phase Space in F: Horan & Weekes HE-ASTRO Challenge Can telescopes be relatively small, have moderately large FoV, be fairly inexpensive, in addition to have differential peak photon detection rate at ~40 GeV Installation at A.E.R.E., Harwell 1962 – Underst in addition to ing Collecting Area Cell Operation Mode QE+Elevation or Dish Size Concept of IACT-cell Aharonian at el. Astroparticle Physics 6 (1997) 343-377
Important Angular Scales Trigger Pixel Size & Trigger Efficiency Image Pixel Size & Reconstruction Efficiency a = a = Challenges Trigger Efficiency at low energies (peak of detection rate around 30 40 GeV) High Data rates Array trigger Low Cherenkov light level regime High angular resolution Background regection efficiency Engineering & cost issues Light Sensors Wide Field of View Optics Costs Trigger Pixel Optimization Simulations
Wavelength Response (assumption) Wavelength [nm] Efficiency Relevant wavelength response window 200 400 nm Range of implied QEs 0.5 1.0 (50% 100 %) Double reflection from aluminized coated mirror Cherenkov Light Spectrum x (300 nm/l)2 Summary of parameters QE: 0.5 1.0 FoV: 10 15 degrees Rnsb 0.1 1.0 kHz Trigger Pixel Size [degree] (nth-Nnsb) / Q Reflector diameter D=7 m NSB integration window t=20 ns NSB differential flux = 0.4 Lowest trigger threshold (Effects of QE, Rnsb, FoV) Trigger Pixel Size [degree] (nth-Nnsb) / Q QE=0.5, FoV=15o, Rnsb=0.1 kHz QE=0.5, FoV=10o, Rnsb=0.1 kHz QE=0.5, FoV=15o, Rnsb=1.0 kHz QE=1.0, FoV=15o, Rnsb=0.1 kHz QE=1.0, FoV=10o, Rnsb=0.1 kHz QE=1.0, FoV=15o, Rnsb=1.0 kHz QE=0.5, FoV=10o, Rnsb=1.0 kHz QE=0.5, FoV=10o, Rnsb=1.0 kHz Number of photons collected by telescope in trigger pixel in 20 ns from a g-ray shower to trigger pixel of a given size Effects: 1) QE 2) Rnsb 3) FoV
Trigger Efficiency vs Pixel Size (central telescope) Parameters: Eg=42 GeV FoV=15o Rnsb=1kHz Trigger Efficiency Trigger Pixel Size [degree] QE: 1.0, D=7m QE: 0.5, D=10m QE: 1.0, D=7m QE: 0.5, D=10m QE: 0.5, D=7m QE: 0.5, D=7m El: 3.5 km El: 4.5 km Optimum Trigger Sensor pixel size range 0.07o-0.25o Weakly Depends on QE, D, El Efficiency versus Pixel Size (Array) Efficiency Photon Energy [GeV] Array Trigger: Three telescopes above operational threshold Array Parameters: Elevation: 3.5 km QE: 0.5 Reflector: 7 m FoV: 15o p=0.05o p=0.08o p=0.10o p=0.13o p=0.16o p=0.20o Efficiency > 50 % p=0.05o 0.25o as long as E > 20-30 GeV Single Telescope Trigger Efficiency Trigger Efficiency Photon Energy [GeV] Photon Energy [GeV] Diff. Rate El=4.5km, QE: 1.0, D=7m El=4.5km, QE: 0.5, D=10m El=3.5km, QE: 1.0, D=7m El=3.5km, QE: 0.5, D=10m El=3.5km, QE: 1.0, D=7m El=3.5km, QE: 0.5, D=10m Parameters: Trigger pixel size: 0.146o Obs. Mode: Un-localized Source (FoV=15o) Rnsb: 1kHz Effects: 1) Cell operation mode 2) Optimum trigger pixel size 3) QE, Reflector Size 4) Elevation 5) Rnsb Diff. spectral index: 2.5 12 GeV 15 GeV 20 GeV 27 GeV
Single Telescope Trigger Efficiency Trigger Efficiency Diff. Rate Diff. spectral index: 2.5 Photon Energy [GeV] Photon Energy [GeV] Rnsb: 100kHz Rnsb: 10kHz Rnsb: 1kHz Parameters: Trigger pixel size: 0.146o Obs. Mode: Known Source (FoV=3.5o) Effects: 1) Cell operation mode 2) Optimum trigger pixel size 3) QE, Reflector Size 4) Elevation 5) Rnsb 14 GeV 17 GeV 22 GeV Array trigger Trigger Pixel size 0.146o Average Number of Telescopes in Trigger Photon Energy [GeV] El=4.5km, QE: 1.0, D=7m El=4.5km, QE: 0.5, D=10m El=3.5km, QE: 1.0, D=7m El=3.5km, QE: 0.5, D=10m Single telescope CR rates
HE-ASTRO (3rd specs) Array of 217 telescopes Elevation 3.5km Telescopes coupling distance 80m Area ~1.0km2 (~1.6km2) Single Telescope Field of View ~15o FoV area ~177 deg2 Reflector Diameter ~7m Reflector Area ~40 m2 QE 50% (200-400 nm) Trigger sensor pixel size 0.146o Trigger Sensor Size ~31.2cm NSB rate per Trigger pixel ~3.2 pe per 20 ns Single Telescope NSB Trigger Rate 1KHz Energy Range 20200 GeV Differential Detection Rate Peak ~30 GeV Single Telescope CR trigger rate ~ 30 kHz Event Reconstruction Angular scales An event g at 42 GeV
Conclusions I Perhaps, sufficiently reach scientific goal, which can justify spending on the scale $100M+, is studying high energy transient phenomena at cosmological distances in addition to galactic phenomena with sensitivity improved by a factor of ten comparing to current IACTAs. Large array of moderate size telescopes may provide a viable cost effective solution to the problem of required large collecting area, large field of view, in addition to low energy threshold at the same time, by combining new in addition to reviving old ideas of using image intensifiers but based on the contemporary technology. Triggering scheme of individual moderate size telescopes with FoV=~15o in addition to trigger pixel size of 0.15o is compatible with operation at 20-30 GeV energy of the peak detection rate if array of telescopes is located at >3.5 km elevation in addition to QE=50% D=7m or QE=25% D=10m. Predicted CR background rates of ~30 kHz can be already maintained with the use of commercially available technology. By using high resolution high speed CMOS imaging an arrival direction of photons can be reconstructed with high accuracy (21 GeV, 16.2 arcmin; 42 GeV 10.2 arcmin; 100 GeV 3.6 arcmin within 50% g-containment radius). The potential of high resolution imaging as long as CR rejection in low energy light poor regime by a factor of 10-100 is very promising as well as accurate integrated g-ray event energy estimation To finalize feasibility of such approach several more detailed design studies are necessary: optics, readout electronics, array trigger, background rejection efficiency, geomagnetic effect, in addition to practicability of real time image processing in hardware or software to reduce data rates There are alternatives which have not been explored yet; those which could require broader international collaboration to accomplish a project with the price tag of ~$200M in addition to utilizing technology that has been viewed as one with the greatest promise of potential advances in the field since its foundation. Conclusions II Sensitivity of IACTAs Small array of very large dish size telescopes sure guarantees low energy One can see development of the field when several such projects might be pursued in the future in Germany in addition to France in US, UK, in addition to Irel in addition to in Japan In with price tag 3-5 times that of VERITAS or HESS each, ~$50M Is this the only option as long as the money Wide field of view, very high image resolution, in addition to super-fast parallel data processing may provide technological basis as long as the next breakthrough ground-based g-ray astronomy. Conclusions III
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