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COSMIC RAY ORIGINS Stella Bradbury, University of Leeds, U.K.  -ray sources the cosmic ray connection detection technique galactic and extragalactic.

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Presentation on theme: "COSMIC RAY ORIGINS Stella Bradbury, University of Leeds, U.K.  -ray sources the cosmic ray connection detection technique galactic and extragalactic."— Presentation transcript:

1 COSMIC RAY ORIGINS Stella Bradbury, University of Leeds, U.K.  -ray sources the cosmic ray connection detection technique galactic and extragalactic accelerators future instruments and new targets Ultra High Energies

2 On 7th August 1912, Victor Hess demonstrated that the flux of “ionising radiation” increased above 2 km altitude Cosmic Rays ?

3 collection area of satellite detector ~ 0.8 m 2 collection area of Cherenkov Telescope ~ 40,000 m 2 typically number of  -rays per m 2 above energy E  E -1.5 < 0.1 % of the “cosmic rays” are actually  -rays

4 cosmic ray nuclei should produce  -rays  in collisions with interstellar material  diffuse  -ray  background along galactic plane? high energy  -rays indicate extreme environments and particle acceleration processes  -rays which are not deflected by galactic magnetic fields may point to localized cosmic sources  -ray astronomy

5 < 50 GeV e - e + pairs produced in satellite volume and trapped > 250 GeV sample the Cherenkov light pool at ground  calorimetric measurement ~ 0.01% of primary energy  Cherenkov light TECHNIQUE

6 Background Rejection  -ray generates “airshower” through e + e - pair production & bremsstrahlung cosmic ray and air nuclei collide   0      +  simulations rely on extrapolation from accelerator data) Simulated Cherenkov lateral distribution at ground:  -ray proton

7 Imaging Atmospheric Cherenkov Telescopes Energy threshold depends on Cherenkov light collection efficiency location - altitude and background light level trigger efficiency for  -rays

8 a single 12.5 mm Ø photomultiplier pixel of the Whipple Telescope camera subtends 0.12º width of a typical  -ray Cherenkov image is 0.3º use cluster trigger  -ray ? nucleon?local muon ?

9 humidity unexpected loads! temperature cycle lightning Nature’s Challenges field stars, night sky light moving targets!

10 attractiveness to rats - similar to co-ax Analogue Optical Fibre Signal Transmission 120 prototype channels based on VCSELs in the Whipple Telescope camera 150 MHz bandwidth low pulse-dispersion allows a short ADC gate  less background light included lightweight - 50 kg for a 1000 pixel camera vs. 400 kg for co-axial cable

11 EGRET 100 MeV - 30 GeV The Compton Gamma Ray Observatory spark chamber time of flight scintillators NaI calorimeter

12 Solar flare evidence for p + collisions    decay   -rays of mean E  ~  m  c 2 ~ 67 MeV excess  -rays < 100 MeV require e - bremsstrahlung   -ray sources Likely  -ray production mechanisms : p + + p +  p + + p + +  + +  - +  0 then  0    thermal photon  p +  X then  0    e - bremsstrahlung or synchrotron   below a few 100 MeV inverse Compton scattering of thermal photons   by relativistic e - EGRET solar flare spectrum :

13 Diffuse background due to p + CR + H nuclei   0   observed but where do we get the p + CR from?

14 The Crab Nebula, standard candle of TeV astronomy. 1965: TeV  -rays from Crab Nebula predicted 1989: 9  detection above 700 GeV published from 82 hours of data Chandra X-ray image TeV  -rays - point source VLT optical image The Crab pulsar wind shock injects relativistic particles into its surrounding supernova remnant.

15 Spectral energy distribution   -ray production mechanism? TeV spectrum consistent with e - synchrotron self-Compton emission  magnetic field ~16 nT within 0.4 pc of the pulsar.

16 Where do cosmic ray nucleons come from? Shell-type supernova remnants? outer layers of dead star bounce off collapsing core (in which e - + p +  n + e ) huge release of energy + O, N… Fe present shock front propagates, sweeping up gas from interstellar medium compressed B fields act as scattering centres for relativistic charged particles particles gain momentum as they cross the shock front repeatedly 1st order Fermi acceleration

17 Chandra X-ray image of Cas A Detection of TeV  -rays from Cassiopeia A by HEGRA can still be explained as e - inverse Compton without e.g. a  o decay component Still no conclusive evidence for acceleration of relativistic nuclei

18 Giant molecular clouds could act as a target for p + CR + H      +  if bathed in uniform cosmic rays or as a cosmic beam dump for a neighboring particle accelerator such as a black hole binary: Cosmic ray production must be high in starburst galaxies where there is a high supernova rate and strong stellar winds?

19 Of 271 discrete sources detected by EGRET above 100 MeV 170 remain unidentified 67 are active galactic nuclei (AGN)

20 photon flux forward beamed and Doppler shifted  -ray emission region must be > a light day from AGN core to escape absorption via pair production - probably moving along jet rapid optical variability and lack of thermal emission lines in EGRET’s AGN suggest we are looking almost straight down the jet ~ 1 % of galaxies have a bright central nucleus that outshines the billions of stars around it Radio and X-ray observations reveal relativistic jets presumed to be powered by a central supermassive black hole Active Galactic Nuclei

21 optical depth for  TeV +  UV/optical  e ± must be less than 1  limits ratio of rest frame luminosity to size of emission region a Doppler beaming factor of   9 was derived from flare on right Rapid TeV  -ray flares  emission region only ~ size of solar system! Whipple Telescope - Mkn 421

22  -ray Production Mechanism? synchrotron self-Compton e - +  synch  e - +  -ray external inverse Compton e - +  external  e - +  -ray photo-meson production p + +   0,  ±   -rays, e ±, n, Assume emission region is associated with shock accelerated particles, then pick any combination of :

23 Markarian 501 April ‘97 Multiwavelength Observations might expect simultaneous TeV  -ray and X-ray flares if due to the same e - population (self-Compton) increase in e - density  increase in ratio of self-Compton to synchrotron emission? in external IC model  -ray & optical flares could come from different sites  time lag? proton induced cascade  outbursts?  4.2  2.6  1.7  1.1

24 Markarian 501 Spectral Energy Distribution Power in X-rays &  -rays very similar - both much greater in 1997 Synchrotron peak shifted from 1 keV to 100 keV during outburst

25 TeV  -ray Energy Spectra of Mkn 421 & Mkn 501 There are only 6 established TeV  -ray emitting AGN; the most recent flared to a detectable level on 17/05/02 Mkn 421 Mkn 501 Common feature is a cut-off at E 0 ~ TeV. Is this intrinsic to such objects - limit of accelerator?

26 Extragalactic Infrared Background : may cut-off  -ray flux from distant AGN as   -ray +  IR  e - + e + ( cross-section peaks at   -ray  target ~ 2 (m e c 2 ) 2 )

27 TeV  -ray detection of AGN 600 million light years away  limits on IR background density 10  more restrictive than direct satellite measurement in  m range plagued by foreground starlight Possible IR contributors: early star formation Very Massive Objects (dark matter candidates) heavy  light +   IR for 0.05 eV < m  < 1 eV  -ray Horizon

28 In the Vela 5 nuclear test detection satellites discovered  -ray bursts. A whole new class of objects? 20 keV - 1 MeV VLT optical afterglow of GRB at redshift 4.5  light years distant (epoch of galaxy formation?)

29 A hypernova ? Merging neutron stars ? Cosmological distances  require an astronomical energy source! Invoke shocks in beamed jets!

30 Swift NASA Gamma Ray Bursts mission hard X-ray, UV & optical instruments launch autumn 2003 INTEGRAL ESA mission for spectroscopy & imaging at 15 keV - 10 MeV launch 17th October 2002 AGILE Italian Space Agency mission optimised for fast timing & simultaneous coverage at 10 keV - 40 keV & 30 MeV - 30 GeV launch beginning of 2004 Future Instruments

31 GLAST launch due September 2006 lifetime > 5 years Energy range 20 MeV GeV Gamma Cygni

32 CELESTE, Solar II & GRAAL use the same principle. Lowering the energy threshold of ground-based  -ray detection Solar arrays: very large mirror area but small field of view. STACEE ( ) 50 GeV GeV > 2000 m 2 of heliostats reflect Cherenkov light via a secondary mirror onto a photomultiplier camera in the tower.

33 The MAGIC Telescope on La Palma Imaging telescope with a single 17m diameter dish. Energy threshold < 15 GeV with future hybrid photodetectors or APDs operational late 2002 ?

34 VERITAS array of 12m telescopes in Arizona: 1st telescope on-line by end of 2006 uses stereoscopic technique - viewing Cherenkov flash from different angles to improve background rejection

35 energy threshold ~100 GeV first telescope now in place at the Gamsberg H.E.S.S. - an array of 4 (  16 ?) 12 m diameter telescopes

36 Flux sensitivity: bridging the gap between ground-based instruments and satellite data Mkn 421

37  -rays from Cold Dark Matter? CDM candidate neutralinos may be collected at the galactic centre accelerator experiments restrict particle mass to 30 GeV - 3 TeV an annihilation line may be observable with GLAST or next generation Atmospheric Cherenkov Observatories Simulated GLAST detection above diffuse background   

38 UN-conventional TARGETS neutralino search    or  q q  e.g.  decays primordial black holes - TeV photons emitted during final s of evaporation ? quantum gravity  E dependent time dispersion of AGN flares ?? Bose Einstein condensates e.g. coherent bunch of 100 GeV photons could mimic an airshower due to a single 1TeV photon EGRET unidentified sources - position location to 0.02  should reduce number of possible counterparts by  10 TeV all-sky surveys cosmic ray composition studies - Cherenkov light emitted before primary interaction  Z 2, independent of energy, arrives 3-6 ns after main image


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