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Why Gamma Ray Astronomy at energies above 10 TeV ?

Why Gamma Ray Astronomy at energies above 10 TeV ?. F.A. Aharonian DIAS(Dublin)/MPIK(Heidelberg). Adelaide, Dec 6, 2006. Gamma-Ray Astronomy. branch of high energy astrophysics for study of the sky in MeV, GeV, TeV (and more energetic) photons

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Why Gamma Ray Astronomy at energies above 10 TeV ?

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  1. Why Gamma Ray Astronomy at energies above 10 TeV ? F.A. Aharonian DIAS(Dublin)/MPIK(Heidelberg) Adelaide, Dec 6, 2006

  2. Gamma-Ray Astronomy branch of high energy astrophysics for study of the sky in MeV, GeV, TeV (and more energetic) photons provides crucial window in the spectrum of cosmic E-M radiation for exploration of nonthermal phenomena in the Universe in their most extreme and violent forms “the last windowin the spectrum of cosmic E-M radiation to be oppened...´´(a popular phrase since 1950s) is already (partly) opened

  3. the last E-M window ...15+ decades: LE or MeV : 0.1 -100 MeV(0.1 -10+ 10 -100) HE or GeV : 0.1 -100 GeV(0.1 -10 + 10 -100 ) VHE or TeV : 0.1 -100 TeV(0.1 -10+ 10 -100) UHE or PeV :0.1 -100 PeV EHE or EeV :0.1 -100 EeV(TDs ?) the window is opened in MeV, GeV, and TeV bands: LE,HE – domain of space-based astronomy VHE, .... - domain of ground-based astronomy ‘‘Atmospheric Cherenkov Technique“ covers (potentially) 10 GeV to 1 PeV

  4. Status of the field 1989:first reliable detection of a TeV g-ray signal (Whipple) 1990s: several exciting discoveries (HEGRA, Whipple, CAT, CANGAROO), but not yet a breakthrough; gamma-ray astronomy recognized as (perhaps) most advanced area of Astroparticle Physics, but not yet a nominal astronomical discipline 2000s: HESSrevolutionized the field – g-ray astronomy emerged as a truly observational (astronomical discipline) with viable detection technique – stereoscopic IACT arrays high quality spectrometric, morphological and temporal studies of more than 40 sources representing several galactic and extragalactic source populations

  5. Expectations from the foreseeable future • GLASTlarge source statistics ! “Era of gamma-ray astronomy with thausand sources“ (0.1-10 GeV) also:a few objects and G- & EXG- backgrounds in 10-100 GeV range • HESS/VERITAS/MAGIC-2large photon statistics ! high qualitymorphological and spectrometricstudies in 0.1-10 TeV range of up to 100 (or so) sources in both hemisphere based on on data sets consisting of more than 1,000 gamma-ray photons also:exploration of limited number of objects in > 10TeV domain • HAWK (?) firsteffective all sky surveyat TeV energies

  6. next generation of multi-telescope arrays - 2010+ main objectives ? – to be formulated yet … although the ultimate goal is clear: (1) sensitivity – improvement by an order of magnitude  down to 1 mCrab (at 1TeV) (2) energy range 10 GeV – 100 TeV (3) angular resolution 1 arcmin or so it is believed that both the improvement of the flux sensitivity in the “classical” 0.1-10 TeV interval and reduction of the energy threshold down to 10 GeV should lead to a discovery of hundreds or, hopefully, thousands of sources. effective ways of realization of this ultimate goal on realistic timescales ? different options and opinions under discussion … new activity beyond HESS/MAGIC/VERITAS

  7. three possible developments(my opinion) • 30 GeV to 30 TeV range with emphasis on 100 GeV to 10 TeV realization: 15m diameter class multi (two dozens or more) telescope array located at 3.5-4 km a.s.l. mountain levels (super HESS) • 3-300 GeV range with emphasis on E < 30 GeV realization: a telescope system consisting of several 25+ m diameter telescopes located at 5+ km a.s.l. altitudes and equipped with high quantum efficiency 50%+ multipixel cameras (concept 5@5) • 3 TeV to 300 TeV with emphasis on E > 10 TeV realization: a telescope array consisting of 10 to 30 m2 area and large, 6 deg to 8 deg FoV telescopes located at 250m to 500m distances from each other to cover up to 10km2 at 10 TeV

  8. a nasty question do we really need > 10 TeV region ? given that only the nearby Cosmos (< 100 Mpc or so) is visible at these energies, and that realistically one expects only limited number of sources above 10 TeV my answer:number of sources is not a key issue; physics/astrophysics is a more important issue...

  9. TeV astronomy - a viable discipline in its own right Generally, TeV emission is considered as extension of the GeV region... however visibility of sources inGeV gamma-raysdoes not yet imply visibility in TeV gamma-rays, and vice versa Reasons ?Efficiency of acceleration mechanisms, spectral cutoffs due to internal and external absorption, particle diffusion... ... TeV astronomy is not merely an extension of MeV/GeV astronomy but a viable discipline in its own right with several major objectives > 10 TeV astronomy is an extension of TeV astronomy; and many key scientific ssues are contained in this part of the spectrum

  10. HESS detected > 10 TeV gamma-rays from all of these classes TeV g-ray Source Populations Extended Galactic Objects • Shell Type SNRs • Giant Molecular Clouds (star formation regions) • Pulsar Wind Nebulae (Plerions) Compact Galactic Sources • Binary pulsar PRB 1259-63 • LS5039, LSI +61 303 – microquasars (?) Galactic Center Extragalactic objects • M87 - a radiogalaxy • TeV Blazars – with redshift from 0.03 to 0.18 • and large number of yet unidentified TeV sources …

  11. Origin of Galactic Cosmic Rays and SNRs a mystery since the discovery in 1912 by V.Hess … but now we are quite close (hopefully) to the solution of the (galactic) component below the energy 1PeV (1015eV) standard theory of particle acceleration by SNR shocks: Emax = 100 TeV or so (Lagage-Cesarsky (1974) limit) but what about the knee around 1 PeV ? one needs a strongamplification of the B-field; recent recent developments of theory (e.g. Bell and Lucek 2001)  it is possible ! what gamma-ray observations tell us ?

  12. RXJ1713: > 40 TeV g-rays and shell type morphology: first model-indepen dent evidence of acceleration of particles (e and/or p) to > 100 TeV hadronic orgin? – most likely, but unfortunately we cannot make rubust (unambiguous) statements almost constant photon index ! can be explained by g-rays from pp->po ->2g forapw2 and Eo w100 TeV 2003-2005 data cannot be explained by IC because of KN effect

  13. spectrum of protons ? IC vs po IC vs po Wp = 1050 (n/1cm-3)-1 erg ; n close to 1 cm-3 ?preferable – can explain the production rate of GCRs by SNRs Eo significantly smaller than 1PeV ?, yes, although that could be connected with fast fast escape of protons from accelerator, so RXJ 1713still could be treated as aPeVatron one needs flux measurement below 100 GeV and well above 10 TeV

  14. searching for galactic PeVatrons ... TeV gamma–rays from Cas A and RX1713.7-3946, Vela Jr – a proof that SNRs are responsible for the bulk of GCRs ?–not yet the hunt for galactic PeVatrons continues unbiased approach – deep survey of the Galactic Plane – not to miss any recent (or currently active) acceleration site: SNRs, Pulsars/Plerions, Microquasars... not only from accelerators, but also from nearby dense regions

  15. Gamm-rays/X-rays from dense regions surrounding accelerators the existence of a powerful accelerator by itself is not sufficenrt for gamma radiation; an additional component – a dense gas target - is required gamma-rays from surrounding regions add much to our knowledge about highest energy protons which quickly escape the accelerator and therefotr do not signifi- cantly contribute to gamma-ray production inside the proton accelerator-PeVatron

  16. older source – steeper gamma-ray spectrum

  17. Giant Molecular Clouds (GMCs) as tracers of Galactic Coismic Rays GMCs - 103 to 105 solar masses clouds physically connected withstar formation regions - the likely sites of CR accelerators (with or without SNRs) - perfect objects to play the role of targets ! While travelling from the accelerator to the cloud the spectrum of CRs is a strong function of timet,distance to the sourceR,and the (energy- dependent) Diffusion CoefficientD(E) depending ont, R, D(E)onemay expect any proton, and therefore gamma-ray spectrum – very hard, very soft, without TeV tail, without GeV counterpart ...

  18. Propagation Effects on the spectrum of Gamma Rays emissivities and fluxes (M5/d2kpc ) of gamma rays from a cloud at different times and dis- tances from an impulsive accelerater with W=1050 erg [ D(E)=1026 (E/10GeV)0.5 cm2/s ]

  19. Relativistic outflows as extreme accelerators distinct feature of relativistic outflows: effective particle acceleration at different stages of their development close to the central engine during propagation on large scales, at the jet (wind) termination the theory of relativistic jets – very complex and not (yet) fully understood – all aspects (MHD, electrodynamics, shock waves, particle acceleration) contain many problems and uncertainties maximim (theoretically possible) acceleration rate:hqBc or minimum acceleration time:tmin=hRL/c RL [cm] =3 x109 ETeV BG-1 cm– Larmor radius

  20. fromtacc=tsynch : tacc=hRL/c  hnmax= (9/4)af-1 mc2w 150 h-1 MeV for electrons * w300 h-1 GeV for protons small h – signature of extreme accelerators ? h close to 1 – extreme accelerators high energy gamma-rays best cariers of information about extreme accelerators relativistic outflows – high energy gamma-ray emitters (“on“ and “off“ axis) _______________________________ * SNRs – sources of GCRs are not extreme accelerators: particle acceleration in young SNRs through DSA  hw 10(c/v)2 w105 (in the Bohm regime)  hn0w 1 keV

  21. Crab Nebula – a perfect PeVatron of electrons (and protons ?) 1-10MeV standard MHD theory (Kennel&Coroniti) cold ultrarelativistc pulsar wind terminates by reverse shock resulting in acceleration of multi-TeV electrons synchrotron radiation => nonthermal optical/X-ray nebula Inverse Compton => high energy gamma-ray nebula MAGIC (?) . 100TeV EGRET HEGRA Crab Nebula – a powerful We=1/5 Lrot w 1038 erg/s and extreme accelerator: Ee >> 100 TeV Emax=60 (B/1G) -1/2h-1/2 TeV and hncut w 150 h-1 MeV • Cutoff at hncut =10-20 MeV ? h w10 - acceleration at 10 % of the max. rate • g-rays: Eg> 50 TeV (HEGRA, HESS) => Ee > 200 TeV B-field w 100 mG=>h w10 - independent and more robust estimate

  22. Synch. cutoff at 10 MeVand IC - up to 100 TeV ? EGRET contribution of hadronic component of g-rays ? not necessary, but cannot be excluded (provided higher acceleration rate in the past), • Energy-dependent size 0.1 -10 TeV (MAGIC –II,VERITAS,HESS) • Energy spectrum 100 MeV to 100 GeV (GLAST) • Detection of a sharp cutoff around 100 TeV (HESS ?) • Detection of g-ray line signatures (at Eg= me c2 x G) of the unshocked wind (?) • > 1 TeV neutrinos (marginally) detectable (Ice Cube) HEGRA important tests

  23. TeV gamm-rays from other Plerions ? Crab Nebula is a very effective accelerator but not an effective IC g-ray emitter We see TeV gamma-rays from the Crab Nebula because of very large spin-down flux but gamma-ray flux << “spin-down flux“ because of large magnetic field but the strength of B-field also depends on less powerful pulsar weaker magnetic field higher gamma-ray efficiency detectable gamma-ray fluxes from other plerions HESS confirms this prediction ! ( ? ) – several famous PWN already detected - MSH 15-52, PSR 1825, Vela X, ... * Plerions – Pulsar Driven Nebulae

  24. HESS J1825 (PSR J1826-1334) TeV image • the g-ray luminosity is comparable to the TeV • luminosity of the Crab Nebula, while the spin- • down luminosity is two orders of magnitude less ! • implications ? • magnetic field of order of 10mG. • (b) spin-down luminosity in the past - higher red – below 0.8 TeV yellow – 0.8-2.5 TeV blue – above 2.5 TeV noticeable softening of g-ray spectrum away from position of the pulsar PSRJ 1926-1334: evidence for IC origin of g-rays! S.Funk

  25. MSH 15-52 dN/dE  E-G G = 2.270.030.15 2/n = 13.3/12 Flux > 280 GeV 15% Crab Nebula • the energy spectrum - a perfect hard power-law with photon index G=2.2-2.3 • over 2 decades ! • cannot be easily explained by IC… • (unless intense IR sources around) • hadronic (po-decay) origin of g-rays ? since 2.7 K MBR is the main target field, TeV images reflect spatial distributions of electrons Ne(E,x,y); coupled with synchrotron X-rays, TeV images allow measurements of B(x,y)

  26. HESS J0835-456 (Vela X) – do we see the Compton peak ? the image of TeV electrons ! (?) photon index 1.45 with exponential cutoff at 13.8 TeV spectral index ae= 2 with a break around 70 TeV total energy We=2x1045 erg !!! • questions: • B-field – as weak as 2 mG ? • energy in ultrarelativistic electrons only 2x1045 erg ? • integrated energy over 11kyr: >2.5x1048 erg – in which form the “dark energy“ is released? adiabatic losses?, ‘inisible‘ low energy electrons? or in ultrarelativistic protons?

  27. pulsar wind consisting of protons and nuclei ... Horns et al. 2006 dNp/dE=AE2 exp[-(E/80TeV)2] Wp = 1.3 x 1049 (n/0.6cm-3) erg total spin down energy released over the last 11kyr: 5 x1048 – 5 x1051 erg depending on the braking index (time-history of Lrot) B=10 mG , We=1045 (B/10mG)-2 erg for B=100 mG – half of X-ray flux can be explained by secondary electrons fluxes of TeV neutrinos are detectable by KM3NeT !

  28. TeV Gamma Rays From LS5039 and LSI+61 303 HESS, 2005 MAGIC, 2006 microqusars or binary pulsars? independent of the answer – particle acceleration is linked to (sub) relativistic outflows See talk by J. Paredes

  29. Molecular Clouds in the Galactic Center Region diffuse emission along the plane! HESS J1745-303 HESS collaboration: Nature Feb 9, 2006

  30. Diffuse emission from the GC ridge no indication of a cutoff below 10 TeV ! Photon index 2.3 Harder CR spectrum Compared to local CRs Higher CR density above 10 TeV Source of CRs - Sgr A* ? very important – detection of E > 10 TeV gamma-rays, hard X-rays, neutrinos (?)

  31. Extragalactic Sources of > 10 TeV gamma-rays? • neraby BL Lac Objects • Clusters of Galaxies • Nearby radio galaxies • nearby starburst galaxies • Microblazars within 1 Mpc • ...

  32. Intergalactic Absorption

  33. time average spectra of Mkn 421 and Mkn 501 Gamma-rays detected beyond 10 TeV! Unprecedented photon statistics Mkn 421 – 60,000 TeV photons detected in 2001 Mkn 501 – 40,000 TeV photons detected in 1997 spectra: canonical power-law with exponential cutoff Cutoff = 6.2 TeV and 3.8 TeV for Mkn 501 and Mkn 421 TeV

  34. Multi-TeV gamma-rays expected from Clusters of Galaxies core – 1 deg accretion shocks 3 deg diameteer Coma cluster of galaxies

  35. M 87 –evidence for production of TeV g-rays close to BH • Distance: ~16 Mpc • central BH: 3109 MO • Jet angle: ~30° not a blazar! • discovery (>4s) of TeV g-rays by HEGRA (1998) confirmed by HESS (2003)

  36. X-ray (Chandra) nucleus knot A HST-1 M87: light curve and variabiliy X-ray emission: • knot HST-1[Harris et al. (2005),ApJ, 640, 211] • nucleus(D.Harris private communication) I>730 GeV [cm-2 s-1] short-term variability within 2005 (>4s) constrains size of emission region (R ~ 5x1015dj cm)

  37. energy spectra – no indication of a cutoff below 10 TeV energy spectra for 2004 (~5s) and 2005 (~10s) Differential spectra well described by power-laws: F13 = 10-13 cm-2 s-1 TeV-1 2004 vs. 2005:Photon indices compatible, but different flux levels

  38. Probing DEBRA at MIR /FIR with Eg > 10 TeV g-rays from nearby extragalactic sources (d < 100 Mpc)

  39. Conclusions • >10 TeV gamma-rays are expected and/or detected from all potential Galactic TeV source populations – SNRs, PWNe, mQSOs, GMCs/SFR, ISM,... as well as from nearby (within 100-200 Mpc) Extragalactic source populations: BL Lac objects, Radiogalaxies, Clusters of Galaxies, Starburst Galaxies, etc. • >10 TeV gamma-rays provide key information about physics and astrophysics of Cosmic TeVatrons and PeVatrons • we need dedicated detectors for studies of multi-TeV sources with detection area 10km2and energy flux sensitivity better than 10-13 erg/cm2s @10 TeV • arrays of relatively modest IACTs optimized for the energy region from 1 TeV to 100 TeV have significant discovery potential and should be treated as an important and complementary approach to the ongoing efforts for im- provement of the performance at sub-100 GeV energies (HESS phase-2, MAGIC VERITAS,CANGAROO) – before arrival of the (next generation) major ground based detectors – Very Large Arrays of Very Large Cherenkov Telescopes

  40. Extragalactic Sources Galactic Sources GeV GeV GeV GeV GeV GeV GRBs AGN GLX CLUST IGM ISM SFRs SNRs Pulsars Binaries Potntial Gamma Ray Sources Blazars Normal Starburst Radiogalaxies GMCs Cold Wind Microquasars Magnetosphere Binary Pulsars Pulsar Nebula EBL Major Scientific Areas GCRs Compact Objects EXGCRs Relativistic Outflows Cosmology

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