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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 EnergiesJim HintonUniversity 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 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
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
Particle Shower ~ 10 km ~ 120 m Air Cherenkov Technique Primary g-ray • Pair production • g →e+ e- • Bremsstrahlung • e- + (g) → e- + g • Cascade develops
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’
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...
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...
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
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
MILAGRO MAGIC VERITAS HESS Major VHE Instruments TIBET ARGO-YBJ MILAGRO STACEE TACTIC PACT UK + Ireland
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
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
Under Construction • MAGIC-II • A second 17 m tel. • HESS-II • A new 30 m tel. • Aiming at lower energies and better sensitivity
Milagro Performance: Sensitivity Funk, Reimer, Torres, Hinton 2007 (VERITAS)+
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
Source number versus time • Adapted from T. Kifune by R. White
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)
HESS Galactic Plane Survey Significance of -ray excess ~6° +65° Galactic Centre 2004-07, 40 sources, scale saturated at 20 σ - 85°
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
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
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
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
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
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
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→ ?
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
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
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
HESS J1825-137 HESS • PSR J1826-1334 • 31036 erg/s spin-down power, ~2104 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 ]
Gamma-ray binaries • Three (4) systems, two basic scenarios • PSR B1259-63 / SS 2883, LSI +61 303, LS 5039 + (Cyg X-1) Mirabel 2007
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
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
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. …)
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
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?
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?
Diffuse Emission Point-source subtracted HESS 1 degree pp →π0→ ? CS Line Emission (dense clouds) smoothed to match H.E.S.S. PSF
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?
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?
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
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
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
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
EBL constraints Direct limits Combined limits from all VHE blazars Galaxy Counts Mazin+Raue 2007
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?
M 87 - Variability Colin et al 2007
M 87 – X-ray connection • 2-10 keV emission (core dominated?) correlates well with TeV emission on long (6 month) timescales
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