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The Experimental Status at TeV Energies Jim Hinton University of Leeds

The Experimental Status at TeV Energies Jim Hinton University of Leeds. Outline. Non-thermal radiation Ground-based g -ray Techniques Current Instruments A quick introduction to the TeV source classes Supernova remnants Pulsar wind nebulae Unidentified galactic sources AGN. Stars. Dust.

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The Experimental Status at TeV Energies Jim Hinton University of Leeds

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  1. The Experimental Status at TeV EnergiesJim HintonUniversity of Leeds

  2. Outline • Non-thermal radiation • Ground-based g-ray Techniques • Current Instruments • A quick introduction to the TeV source classes • Supernova remnants • Pulsar wind nebulae • Unidentified galactic sources • AGN

  3. Stars Dust The ‘Non-Thermal Windows’ Cherenkov Telescopes Satellites • Tracers for ultrarelativistic electrons and hadrons • Non-thermal windows • Radio (low energy electrons) • Hard X-ray • g-ray • Detectors? Energy Flux (F) 0 decay Synchrotron Emission Optical, UV, Soft X-ray – Heavily absorbed Inverse Compton Scattering Radio Infra-red X-rays g-rays Energy

  4. Tracers • X-rays • Soft X-rays still dominated by thermal emission • 2-10 keV band excellent resolution, very sensitive instruments • – but – Synchrotron emission gives information only on energetic electrons ( ×B2 ) • Hard X-ray detectors not yet as sensitive • GeV g-rays? • Hard to launch large detectors, poor angular resolution (< a few GeV) • TeV Neutrinos? • Small effective collection area, atmospheric background • TeV g-rays? • Large detection areas, better angular resolution

  5. Particle Shower ~ 10 km ~ 120 m Air Cherenkov Technique Primary g-ray • Pair production • g →e+ e- • Bremsstrahlung • e- + (g) → e- + g • Cascade develops

  6. Particle Shower ~ 10 km ~ 120 m ~ 100 m Air Cherenkov Technique Primary g-ray • Pair production • g →e+ e- • Bremsstrahlung • e- + (g) → e- + g • Cascade develops • Charged relativistic particles emit Cherenkovlight • 1° angle at 10 km height → 100 m radius ‘light-pool’ • ~10 ns light ‘flash’

  7. Detecting Very High Energy Gamma-Rays with Cherenkov Light Particle Shower ~ 10 km Focal Plane Image Analysis gives  Shower Energy  Background rejection  Shower Direction ~ 120 m ~ 100 m Air Cherenkov Technique Primary g-ray Air-shower...

  8. Detecting Very High Energy Gamma-Rays with Cherenkov Light Particle Shower ~ 10 km Focal Plane Image Analysis gives  Shower Energy  Background rejection  Shower Direction Stereoscopic views  Improved angular resolution and background rejection ~ 120 m ~ 100 m Air Cherenkov Technique Primary g-ray Air-shower...

  9. Particle Shower Water Tank Photosensors Total amount of Cherenkov light produced (approx) Shower Energy Arrival times at photosensors (approx) Shower Direction Distribution of particles on ground  (some) background rejection ~ 120 m Water Cherenkov Technique Primary g-ray • + ~100% duty cycle • + Wide FoV - Background  Sensitivity - Angular resolution - Energy resolution

  10. IACT Systems • 3 Major systems, all have • ~100 GeV energy threshold • ~0.1° angular resolution • ~4° Field of View • 1% Crab flux (~ 3 ×10-13 erg/cm2/s ) sensitivity

  11. MILAGRO MAGIC VERITAS HESS Major VHE Instruments TIBET ARGO-YBJ MILAGRO STACEE TACTIC PACT UK + Ireland

  12. e.g. HESS • Four 13m diameter telescopes in the Khomas highlands of Namibia (southern Africa) • Latitude 23° south → galactic sources • 100 GeV – 100 TeV, 15% energy resolution • 5’ angular resolution, 5° field of view • 150 hours/year open to external observation proposals • completed early 2004

  13. e.g. HESS • VERITAS • Very similar system in Arizona, completed early 2007 • Four 13m diameter telescopes in the Khomas highlands of Namibia (southern Africa) • Latitude 23° south → galactic sources • 100 GeV – 100 TeV, 15% energy resolution • 5’ angular resolution, 5° field of view • 150 hours/year open to external observation proposals

  14. Under Construction • MAGIC-II • A second 17 m  tel. • HESS-II • A new 30 m  tel. • Aiming at lower energies and better sensitivity

  15. Milagro Performance: Sensitivity Funk, Reimer, Torres, Hinton 2007 (VERITAS)+

  16. Performance: Angular Resolution • Can reach 2 orders of magnitude better resolution than at 1 GeV • for much less money! • Resolution  Science • source IDs, resolved systems… Funk, Reimer, Torres, Hinton 2007 1’ Simulation: 36x 18m telescopes

  17. Source number versus time • Adapted from T. Kifune by R. White

  18. The TeV Sky in 2007

  19. TeV Source Populations • Extragalactic • Active galactic nuclei 20 ( point-like emission, variability seen in all strong sources) • Galactic • Supernova remnants ~10 • Pulsar wind nebulae ~20 • Unidentified galactic plane sources ~20 ( all typically extended on 0.1-1 degree scales ) + • Gamma-ray binaries 3 (4) ( all showing variable/periodic emission)

  20. HESS Galactic Plane Survey Significance of -ray excess ~6° +65° Galactic Centre 2004-07, 40 sources, scale saturated at 20 σ - 85°

  21. Milagro Northern Sky Survey • 7 year exposure • ~20 TeV median energy • 0.5° angular resolution • ~0.5 Crab sensitivity • 3 significant new sources (all on galactic plane) Abdo et al ICRC 2007

  22. HESS ICRC 2007 Milagro Northern Sky Survey • 7 year exposure • ~20 TeV median energy • 0.5° angular resolution • ~0.5 Crab sensitivity • 3 significant new sources (all on galactic plane) Abdo et al ICRC 2007

  23. Milagro Northern Sky Survey • 7 year exposure • ~20 TeV median energy • 0.5° angular resolution • ~0.5 Crab sensitivity • 3 significant new sources (all on galactic plane) Abdo et al ICRC 2007

  24. Supernova remnants • Best candidates for acceleration of the bulk of the galactic cosmic rays • Well established mechanism (diffusive shock acceleration) • Energetics are OK (10% kinetic energy into cosmic-rays) • Evidence for ultrarelativisitic electrons in young SNR • X-ray synchrotron emission: x2 x2 x2

  25. TeV Shells e.g. RX J1713.7-3946 • Purely non-thermal X-ray source • 1000 year old, Distance ~ 1 kpc, dense environment? • First TeV gamma-ray SNR (and first image, Nature 432, 75) • Closely correlated keV/TeV morphology… Moon For Scale HESS – TeV -ray ROSAT – X-ray ASCA contours

  26. Energy Spectrum • Close correlation with X-rays [+electrons] • Spectral shape [+protons] • IC interpretation implies (too) low B-field [+protons] • No correlation with molecular material [+electrons] • Not yet clear… • Need data at lower energies to be sure, e.g. GLAST protons electrons

  27. VERITAS 2007 SNR/cloud interactions? • Correlations with available target material • IC 443 and W 28, Old (>104 yr) SNRs near mol. Clouds • Both have associated GeV sources HESS / NANTEN 2007 pp →π0→ ?

  28. Pulsar Wind Nebulae High ISM density Reverse shock crushes PWN • Relativistic e-/e+ plasma wind driven by pulsar - confined by SNR of pulsar progenitor • Efficient conversion of rotation power into relativistic particles • Associated with young pulsars - high ‘spin-down power’ • Expansion in non-uniform medium may lead to complex morphol. Low ISM density G21.5-0.9 Chandra / H.Matheson & S.Safi-Harb Blondin et al. ApJ 563 (2001) 806

  29. The PWN Population • Many known X-ray PWN now identified as TeV emitters and almost all of the highest spin-down power radio pulsars have associated TeV emission • Efficient particle accelerators • May be easier to detect in TeV than keV ? • Integration over pulsar lifetime for TeV electrons (less cooling) • TeV instruments sensitive to more extended objects • no confusion with thermal emission • Many of our unidentified sources may be PWN

  30. Search for TeV PWN HESS -ray PWN can be large, asymmetric and offset from the pulsar Need to assess chance coincidence HESS scan analysis shows that 70% of Edot/d2 > 1035 erg/s/kpc2 are TeV sources Implied efficiency Spin-down → TeV ~ 1% Random Catalogues

  31. HESS J1825-137 HESS • PSR J1826-1334 • 31036 erg/s spin-down power, ~2104 years old • 5’ X-ray PWN • G 18.0-0.7 (Gaensler et al 2002) • 1° TeV -ray source • HESS J1825-137 (Aharonian et al 2005) • Energy dependent morphology • A first at TeV energies • Cooling of electrons away from pulsar? (tcool 1/E) [ 2 keV synchrotron emission comes from 200 TeV electrons (if B  10 G)…, -rays come from lower energy electrons ]

  32. Gamma-ray binaries • Three (4) systems, two basic scenarios • PSR B1259-63 / SS 2883, LSI +61 303, LS 5039 + (Cyg X-1) Mirabel 2007

  33. Gamma-ray binaries VERITAS - LS I +61 303 • High mass companions • O and B stars • PSR B1259-63 = NS • LS 5039/LS I +61 303 • Nature of compact object not clear • Both appear to have relativistic radio jets • Gamma-ray spectral modulation (LS 5039), gg absorption, variation of acceleration with phase ?? HESS - LS 5039

  34. Gamma-ray binaries VERITAS - LS I +61 303 • High mass companions • O and B stars • PSR B1259-63 = NS • LS 5039/LS I +61 303 • Nature of compact object not clear • Both appear to have relativistic radio jets • Gamma-ray spectral modulation (LS 5039), gg absorption, variation of acceleration with phase ?? HESS - LS 5039

  35. H.E.S.S. / VLA XMM Funk, Hinton et al 2007 Unidentified Sources • Some sources have been (rather rapidly) identified through multiwavelength work • e.g HESS J1813-178 new radio SNR and new X-ray PWN • Some objects with compelling association but … • E.g. Sgr A*, Stellar cluster Westerlund 2 • Several rather extended objects where ID is difficult • Need more MWL work, and perhaps more sensitive TeV instruments (substructure, spectral clues, E-dep. morph. …)

  36. HESS Sgr A SNR/PWN G 0.9+0.1 Sgr A The Galactic Centre • TeV source in Sgr A discovered using Whipple 10m • Confirmed by CANGAROO, HESS + MAGIC • Gravitational centre of our galaxy – dark matter annihilation? • Deep HESS observations • Precise (10”) localisation of source • Spectrum measured over two decades in energy • Discovery of diffuse emission in the central 200 pc

  37. Contours - VLA radio H.E.S.S. 2005 Sgr A East Pulsar? - G359.95-0.04 Sgr A* 100'' Sagittarius A • Supernova remnant Sgr A East • Pulsar wind nebula G359.95-0.04 • Supermassive Black Hole Sgr A* • Dark matter cusp?

  38. Contours - VLA radio H.E.S.S. 2005 preliminary HESS 2007 stat. +sys. G359.95 G359.95 Sgr A East Pulsar? - G359.95-0.04 Sag A* Sgr A* 100'' 10'' 10'' Chandra – X-ray Sagittarius A Supernova remnant Sgr A East Pulsar wind nebula G359.95-0.04 Supermassive Black Hole Sgr A* Dark matter cusp?

  39. Diffuse Emission Point-source subtracted HESS 1 degree pp →π0→ ? CS Line Emission (dense clouds) smoothed to match H.E.S.S. PSF

  40. PSF Radio TeV emission from Westerlund 2? • Extended TeV source coincident with the massive stellar cluster Westerlund 2 discovered using HESS in 2006 • Collective effect of stellar winds?

  41. PSF Radio TeV emission from Westerlund 2? • Extended TeV source coincident with the massive stellar cluster Westerlund 2 discovered using HESS in 2006 • Collective effect of stellar winds?

  42. Extragalactic Sources • All 20 known extragalactic VHE gamma-ray sources are active galactic nuclei • All but one (M 87) are blazars • Particle acceleration in relativistic jets • Beaming allows us to see distant objects… but, • The gamma-ray horizon is limited by absorption via pair-production on the extragalactic background light (EBL) • Lower gamma-ray energies → more distant objects • The spectral shapes of VHE sources can be used to place limits on the EBL – important cosmologically

  43. TeV Blazars keV TeV • Relativistic AGN jet aligned within a few deg. of the line-of-sight • Highly variable broad-band emission • typically correlated TeV/keV emission IC Sync. Mrk 421 Whipple 10m tel. Synchrotron Self Compton Fits

  44. TeV Blazar Flares Mrk 501 (MAGIC),PKS 2155-304 (HESS) ×10-9 • 2-3 minute variability timescales • Very constraining for models, implies Г> 50 • can be used to probe Quantum Gravity HESS 28th July 2006 Crab Nebula Flux >2 order of magnitude flare, July 2006 MAGIC 30th June 2005 Crab Nebula Flux Quiescent Flux e.g. Begelmann, Fabian, Rees 2007 e.g. Albert et al 2007

  45. TeV Blazars and the EBL • New HESS and MAGIC AGN Approx. `Gamma-ray horizon’ gVHEgEBL e+e- x x x EBL RGB J0152+017 1ES 1011+496 20 known TeV AGN 3C 279 (z=0.54)  Absorption signature

  46. EBL constraints Direct limits Combined limits from all VHE blazars Galaxy Counts Mazin+Raue 2007

  47. M 87 HESS source pos. • Famous nearby radio galaxy • 16 Mpc, Jet angle ~30° • HESS 2 day variability • Emission region < 5 d RS • Multi-year observations from HEGRA, HESS, VERITAS • Long timescale variability • Emission site? • Knot HST1? • Very close to SMBH?

  48. M 87 - Variability Colin et al 2007

  49. M 87 – X-ray connection • 2-10 keV emission (core dominated?) correlates well with TeV emission on long (6 month) timescales

  50. GeV - TeV -Ray Projects Phase 2 Phase 1 Phase 2 Phase 1 Move to permanent site Design Study Construction We may be entering the golden age of (>GeV) gamma-ray astronomy

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