Theoretical aspects of VHE  -ray astronomy: Exploring Nature’s Extreme Accelerators

  • Published on

  • View

  • Download

Embed Size (px)


APP UK 2008 meeting, Oxford, June 20, 2008. Theoretical aspects of VHE -ray astronomy: Exploring Natures Extreme Accelerators. Felix Aharonian Dublin Institute for Advanced Studies, Dublin Max-Planck-Institut f. Kernphysik, Heidelberg. Astroparticle Physics. - PowerPoint PPT Presentation


<ul><li><p>Theoretical aspects of VHE -ray astronomy: Exploring Natures Extreme AcceleratorsFelix AharonianDublin Institute for Advanced Studies, DublinMax-Planck-Institut f. Kernphysik, Heidelberg</p><p>APP UK 2008 meeting, Oxford, June 20, 2008</p></li><li><p>Astroparticle Physics a modern interdisciplinary research field at the interface of astronomy, physics and cosmology </p><p>one of the major objectives: study of nonthermal phenomena in their most energetic and extreme forms in the Universe (the High Energy Astrophysics branch of Astroparticle Physics) all topics of this research area are related, in one way or another, to exploration of Natures perfectly designed machines Extreme Particle Accelerators </p></li><li><p> Extreme Accelerators [TeVatrons, PeVatrons, EeVatrons] machines where acceleration proceeds with efficiency close to 100% efficiency ? (i) fraction of available energy converted to nonthermal particles in PWNe and perhaps also in SNRs, can be as large as 50 % (ii) maximum (theoretically) possible energy achieved by individual particles acceleration rate close to the maximum (theoretically) possible rate * sometimes efficiency can exceed 100% (!) e.g. at CR acceleration in SNRs in Bohm diffusion regime with amplification of B-field by CRs (Emax= ~ B (v/c)2 ) this effect provides the extension of the spectrum of Galactic CRs to at least 1 PeV</p><p> &gt; 100% efficiency because of nonlinear effects: acceleration of particles creates better conditions for their further acceleration </p></li><li><p>Extragalactic?T. GaisserSNRs ?</p><p>up to 1015-16 (knee) - Galactic </p><p> SNRs: Emax ~ vshock Z x B x Rshock for a standard SNR: Ep,max ~ 100 TeV solution? amplification of B-field by CRs 1016 eV to 1018 eV: </p><p> a few special sources? Reacceleration?</p><p> above 1018 eV (ankle) - Extragalactic</p><p> 1020 eV particles? : two options top-down (non- acceleration) origin or Extreme AcceleratorsCosmic Rays from 109 to 1020 eV</p></li><li><p>Particles in CRs with energy 1020 eV difficult to understand unless we assume extreme accelerators</p><p> the Hillas condition - l &gt; RL - an obvious but not sufficient condition </p><p>(i) maximum acceleration rate allowed by classical electrodynamics t-1=qBc ( x (v/c)2 in shock acceleration scenarios) with ~ 1 (ii) B-field cannot be arbitrarily increased - the synchrotron and curvature radiation losses become a serious limiting factor, unless we assume perfect linear accelerators </p><p> only a few options survive from the original Hillas (l-B) plot: &gt;109 Mo BH magnetospheres, small and large-scale AGN jets, GRBs </p></li><li><p>acceleration sites of 1020 eV CRs ?FA, Belyanin et al. 2002, Phys Rev D, 66, id. 023005confinementconfinementenergy lossesenergy losses signatures of extreme accelerators?</p><p> synchrotron self-regulated cutoff: neutrinos (through converter mechanism)production of neutrons (through p interactions) which travel without losses and at large distan- ces convert again to protons =&gt; 2 energy gain ! Derishev, FA et al. 2003, Phys Rev D 68 043003 observable off-axis radiation radiation pattern can be much broader than 1/ Derishev, FA et al. 2007, ApJ, 655, 980 FA 2000, New astronomy, 5, 377 </p></li><li><p>VHE gamma-ray and neutrino astronomies: two key research areas of High Energy Astrophysics/Astroparticle Physics</p><p>VHE- and - astronomies address diversity of topics related to the nonthermal Universe: acceleration, propagation and radiation of ultrarelativistic protons/nuclei and electrons </p><p> generally under extreme physical conditions in environments characterized with huge gravitational, magnetic and electric elds, highly excited media, shock waves </p><p> and very often associated with relativistic bulk motions linked, in particular, to jets in black holes (AGN, Microquasars, GRBs) and cold ultrarelativistic pulsar winds </p></li><li><p> over last several years HESS has revolutionized the field before astronomy with several sources and advanced branch of Particle Astrophysics now a new astronomical discipline with all characteristic astronomical key words: energy spectra, images, lightcurves, surveys...</p><p> VHE gamma-ray astronomy - a success story major factors which make possible this success ? </p><p> effective acceleration of Tev/PeV particles almost everywhere in Universe the potental of the detection technique (stereoscopic IACT arrays) </p></li><li><p> good performance =&gt; high quality data =&gt; solid basis for theoretical studies 28th July 2006TeV image and energy spectrum of a SNRenrgy dependent image of a pulsar wind nebulavariability of TeV flux of a blazar on minute timescales huge detection area+effective rejection of different backgrounds good angular (a few arcminutes) and energy (15 %) resolutionsbroad energy interval - from 100 (10) GeV to 100 (1000) TeV nice sensitivity (minimum detectable flux): 10-13 (10-14) erg/cm2 s</p><p> multi-functional tools: spectrometry temporal studies morphology </p><p> extended sources: from SNRs to Clusters of Galaxies</p><p> transient phenomena QSOs, AGN, GRBs, ...</p><p> Galactic Astronomy | Extragalactic Astronomy | Observational Cosmology</p><p>RXJ 1713.7-3946PSR 1826-1334PKS 2155-309</p></li><li><p> VHE gamma-ray observations: Universe is full of extreme accelerators on all astronomical scales Extended Galactic Objects Shell Type SNRs Giant Molecular Clouds Star formation regions Pulsar Wind Nebulae </p><p> Compact Galactic Sources Binary pulsar PRB 1259-63 LS5039, LSI 61 303 microquasars? Cyg X-1 ! - a BH candidate Galactic Center Extragalactic objects M87 - a radiogalaxy TeV Blazars with redshift from 0.03 to 0.18 and a large number of yet unidentified TeV sources VHE gamma-ray source populationsTeV gamma-ray source populations</p></li><li><p> highlight topics particle acceleration by strong shocks in SNR physics and astrophysics of relativistic outflows (jets and winds) probing processes close to the event horizon of black holescosmological issues - Dark Matter, Extragalactic Background Light (EBL) ..</p></li><li><p>Potential Gamma Ray SourcesMajor Scientific Topics G-CRs Relativistic Outflows Compact Objects Cosmology ISM SNRsSFRsPulsars Binaries Galactic SourcesExtragalactic SourcesGRBsAGN GLXCLUST IGMGMCsMagnetosphereMicroquasars Cold WindPulsar Nebula Binary PulsarsRadiogalaxies Blazars Normal StarburstEXG-CRsEBLGeVGeVGeVGeVGeVGeV</p></li><li><p> unique carriers of astrophysical and cosmological information about non-thermal phenomena in many galactic and extragalactic sources why TeV neutrinos ? like gamma-rays, are effectively produced, but only in hadronic interactions (important - provides unambiguous unformation) </p><p> unlike gamma-rays do not interact with matter, radiation and B-fields </p><p> (1) energy spectra and fluxes without internal/external absorption (2) hidden accelerators ! but unlike gamma-rays, cannot be effectively detected even 1km3 volume class detectors have limited performance: minimum detectable flux approximately equivalent to 1 Crab gamma-ray flux TeV neutrinos -- a complementary channel </p></li><li><p>detection rate of neutrinos with KM3NeT R.White</p></li><li><p>sensitivity of km3 volume neutrino detectors</p><p>1 Crab after several years of observations effective energy range around 10 TeV</p><p> so far only four galactic gamma-ray sources are detected with a TeV gamma-ray flux at the level of 1 Crab </p><p>10 Crab for less than 1 month (background free); effective energy range 1-10 TeV</p><p> blazars? quite possible if TeV gamma-rays are of hadronic origin burst-like events: fluence: t x FE &gt; 10-5 erg/cm2 GRBs, SGRs/Magnetars, SN events, ets. </p></li><li><p> some remarks concerning the neutrino/gamma ratio: typically &gt; 1, but </p><p> synchrotron radiation of protons - pure electromagnetic process interaction of hadrons without production of neutrinos </p><p> generally in hadronic neutrinos and gamma-rays are produced with same rates, but in high density environments (n &gt; 1018 cm-3 and/or B&gt;106 G) production of TeV neutrinos is suppressed because charged mesons are cooled before they decay</p><p> on the other hand, in compact objects muons and charged pions can be accelerated and thus significantly increase the energy and the flux of neutrinos, e.g. from GRBs</p></li><li><p>synchrotron radiation of secondary electrons from Bethe-Heitler and photomeson production at interaction of CRs with 2.7K MBR in a medium with B=1 G (e.g. Galaxy Clusters) what should we do if hadronic gamma-rays and neutrinos appear at wrong energies ?photomesonelectronsBethe-HeitlerelectronsKelner and FA, 2008, Phys Rev D detect radiation of secondary electrons !E* = 3x1020 eV</p></li><li><p>probing hadrons with secondary X-rays with sub-arcmin resolution! Simbol-Xnew technology focusing telescopes NuSTAR (USA), Simbol-X (France-Italy), NeXT (Japan) will provide X-ray imaging and spectroscopy in the 0.5-100 keV band with angular resolution 10-20 arcsec and sensitivity as good as 10-14 erg/cm2s! complementary to gamma-ray and neutrino telescopes </p><p>advantage - (a) better performance, deeper probes (b) compensates lack of neutrinos and gamma-rays at right energies</p><p>disadvantage - ambiguity of origin of X-rays </p></li><li><p> exploring Natures Extreme Particle Accelerators with neutrinos, gamma-rays, and hard X-rays </p></li><li><p> Microquasars ?Pulsars/Plerions ?SNRs ? Galactic Center ?. . .Gaisser 2001OB, W-R Stars ? * the source population responsible for the bulk of GCRs are PeVatrons ?Galactic TeVatrons and PeVatrons - particle acceleratorsresponsible for cosmic rays up to the knee around 1 PeV </p></li><li><p>Visibility of SNRs in high energy gamma-rays</p><p>Fg(&gt;E)=10-11 A (E/1TeV)-1 ph/cm2s</p><p>A=(Wcr/1050erg)(n/1cm-3 )(d/1kpc) -2 for CR spectrum with =2if electron spectrum &gt;&gt; 10 TeV synchrotron X-rays and IC TeV gs</p><p> main target photon field 2.7 K: Fg,IC/Fx,sinch=0.1 (B/10mG)-2 Detectability ? compromise between angle q (r/d) and flux Fg (1/d2) typically A: 0.1-0.01 q: 0.1o - 1o 1000 yr old SNRs (in Sedov phase) po component dominates if A &gt; 0.1 (Sx/10 mJ)(B/10 mG ) -2 TeV g-rays detectable if A &gt; 0.1nucleonic component of CRs - visible through TeV (and GeV) gamma-rays !Inverse Comptonp0 decay (A=1)</p></li><li><p>TeV -rays and shell type morphology: acceleration of p or e in the shell toenergies exceeding 100TeV2003-2005 datacan be explained by -rays from pp -&gt;o -&gt;2 but IC canot be immediately excluded RXJ1713.7-4639and with just right energetics</p><p> Wp=1050 (n/1cm-3)-1 erg/cm3</p></li><li><p> leptonic versus hadronicIC origin ? very small B-field, B &lt; 10 mG, and very large E, Emax &gt; 100 TeV </p><p>two assumptions hardly can co-exists within standard DSA models, bad fit of gamma-ray spectrum below a few TeV, nevertheless arguments against hadronic models:</p><p>nice X-TeV correlaton well, in fact this is more natural for hadronic rather than leptonic models </p><p>relatively weak radio emission problems are exaggerated </p><p>lack of thermal X-ray emission =&gt; very low density plasma or low Te ? we do not (yet) know the mechanism(s) of electron heating in supernova remnants so comparison with other SNRs is not justified at all</p></li><li><p>Suzaku measurements =&gt; electron spectrum 10 to 100 TeV</p></li><li><p>Variability of X-rays on year timescales - witnessing particle acceleration in real time flux increase - particle accelerationflux decrease - synchrotron cooling *)both require B-field of order 1 mG in hot spots and, most likely, 100G outside</p><p>Uchiyama, FA, Tanaka, Maeda, Takahashi, Nature 2007*) explanation by variation of B-field doest work as demonstrated for Cas A (Uciyama&amp;FA, 2008) strong support of the idea of amplification of B-field by in strong nonlinear shocks through non-resonant streaming instability of charged energetic particles (T. Bell; see also recent detailed theoretical treatment of the problem by Zirakashvili et al. 2007) </p></li><li><p>acceleration in Bohm diffusion regime Strong support for Bohm diffusion - from the synchrotron cutoffgiven the upper limit on the shock speed of order of 4000 km/s ! with h=0.67 +/- 0.02keVenergy spectrum of synchrotron radiation of electrons in the framework of DSA (Zirakashvili&amp;FA 2007) B=100 G + Bohm diffusion - acceleration of particles to 1 PeV(Tanaka et al. 2008)</p></li><li><p>protons:dN/dE=K E-a exp[-(E/Ecut)b]</p><p>-rays:dN/dE v E-G exp[-(E/E0)bg]</p><p>=a+da, da 0.1, bg=b/2, E0 = Ecut/20 Wp(&gt;1 TeV) ~ 0.5x1050 (n/1cm-3)-1 (d/1kpc)2RXJ 1713.7-3946neutrinos: marginally detectable by KM3NeT</p></li><li><p>Probing PeV protons with X-rays SNRs shocks can accelerate CRs to 100 mG is possible through plasma waves generated by CRs </p><p> &gt;1015 eV protons result in &gt;1014 eV gamma-rays and electrons prompt synchrotron X-rays </p><p> t(e) = 1.5 (e/1keV) -1/2 (B/1mG) -3/2 yr </p></li><li><p>three channels of information about cosmic PeVatrons:</p><p>10-1000 TeV gamma-rays 10-1000 TeV neutrinos 10 -100 keV hard X-rays g-rays: difficult, but possible with future 10km2 area multi-TeV IACT arrays</p><p> neutrinos: marginally detectable by IceCube, Km3NeT - dont expect spectrometry, morphology; uniqueness - unambiguous signatute! prompt synchrotron X-rays: smooth spectrum...</p></li></ul>