Fundamental Issues in High Energy Astrophysics Roger Blandford KIPAC Stanford

5 v 07INPAC2 The Electromagnetic Spectrum r mm smm irouvx  100neV 100TeV mec2mec2 m p c 2 High Energy Astrophysics MeV GeV TeV

5 v 07INPAC3 Other spectra Electromagnetic Cosmology Gravitational Radiation Dark Matter Neutrinos eV eV Hubble Planck Cosmic Rays

5 v 07INPAC4 Radio Astronomy VLA 100 mas VLBA arc sec Green Bank Telescope 10 arc sec 0.1 arc sec Radio telescopes are extremely sensitive and can resolve fine detail Cygnus A

5 v 07INPAC5 Mm waves ALMA (Chile) Owen’s Valley Radio source associated with the first “Quasar” discovered that appears to expand “faster than light”!

5 v 07INPAC6 Far Infrared Radiation Infrared radiation comes from dusty, star forming regions It is possible to distinguish infrared colors just like optical colors Spitzer

5 v 07INPAC7 It is possible to remove the blurring of the atmosphere Near Infrared Emission Keck

5 v 07INPAC8 Optical Emission Centaurus A Hubble Space Telescope orbits above the Earth’s atmosphere and can resolve 0.1”

5 v 07INPAC9 Ultra Violet Radiation Ultraviolet telescopes trace hot stars and measure colors too. GALEX M51

5 v 07INPAC10 X-rays X-ray telescopes observe hot gas and high energy particles Pictor A Chandra XMM-Newton Perseus

5 v 07INPAC11 MeV  -rays INTEGRAL Gamma rays are created by nuclear processes and particles moving with “relativistic” speed

5 v 07INPAC12 GeV  -rays Compton GLAST GeV  -rays are created mainly by relativistic electrons and protons Dec AGILE launched!

5 v 07INPAC13 TeV  -rays Observed by the optical light they produce HESS (Namibia)

5 v 07INPAC14 Radio Continuum (408 MHz) Atomic Hydrogen Radio Continuum (2.4–2.7 GHz) Molecular Hydrogen (CO) Infrared Mid-infrared Near-infrared Optical Soft X-ray Gamma ray Hard X-ray The Milky Way

5 v 07INPAC15 Cosmic Rays Fastest cosmic rays have energy of a well-hit baseball ACE SN1006

5 v 07INPAC16 Very High Energy Neutrinos Nothing yet!

5 v 07INPAC17 Gravitational Radiation LIGO Merging neutron stars, black holes LISA High frequencyLow frequency

5 v 07INPAC18 The Multiwavelength Challenge

5 v 07INPAC19 Fundamental Issues What Powers High Energy Sources? –Does standard (experimentally verified) physics suffice? –As a practical matter have to understand secondary problems Energy transport Emission mechanisms Particle acceleration What can High Energy Astrophysics tell us about Particle Physics Beyond the Standard Model? –Neutrinos, dark energy, dark matter, >TeV collisions… Is Classical GR Correct? –Minimally coupled Einstein-Maxwell Equations?

5 v 07INPAC20 Nonthermal Power Magnetic Flares –Sun –SGR Unipolar Induction –PWN –AGN –GRBs –XRBs

5 v 07INPAC21 Stars Sun –Flares –Solar minimum->maximum –Observe neutrons –Radiation hazard Minutes!

5 v 07INPAC22 Magnetar (Soft Gamma Ray Repeater) SGR Giant burst, Dec Source in our Galaxy; ~10 40 J 300  s rise time; 7s period in tail Relativistically expanding, anisotropic, radio remnant

5 v 07INPAC23 B M  Rules of thumb: –  B R 2 ; V ~   ; –I~ V / Z 0 ; P ~ V I PWN AGN GRB B 100 MT 1 T 1 TT 10 Hz 10  Hz 1 kHz R 10 km 10 Tm 10 km V 3 PV 300 EV 30 ZV I 300 TA 3 EA 300 EA P 100 XW 1 TXW 10 PXW Unipolar Induction UHECR!

5 v 07INPAC24 Consequences of large EMFs Particle energy density / EM energy density – > r L /L, m e c 2 /eV Electric field => rapid breakdown –accelerate electrons –scatter photon –produce electron-positron pair Vacuum is an excellent conductor thanks to QED –B 2 -E 2 >0 Very hard to produce entropy –Not a criticism of neutrino models!

5 v 07INPAC25 The ElectromagneticView Pulsar powers nebula ~ W Mechanical energy => electromagnetic energy at the pulsar (10km) Jets are Ohmic dissipation of current flowing through the nebula (10 12 km) Accelerate electrons Jets are highly unstable X X. O O O O.

5 v 07INPAC26 Black Holes Spin

5 v 07INPAC27 Electromagnetic Jet Model Black Hole plus magnetised disk act as unipolar inductor creating ~ V, A -> W Where does current complete? –Close to hole => emission due to internal shocks in a fluid –In radio source => emission due to ohmic dissipation of current Large electrical resistance E x B J

5 v 07INPAC28 Gamma Ray Bursts Long bursts –t s ~3-100 s E ~ erg (beaming) –~1d -1yr afterglows –Associated with SNIc; BH/NS formation –Achromatic breaks => jets? –Gamma ray escape =>  > 300? Short bursts –t s ~ s –Coalescing neutron stars

5 v 07INPAC29 Active Galactic Nuclei  ~ 3-30 Are these fluid jets?

5 v 07INPAC30 Pulsar Physics Detection –100s pulsars? –50 RQ pulsars? –10 MSP –RRATS –Blind searches How do pulsars shine? –Polar cap vs slot gaps vs outer gaps –Locate gamma ray and radio emission –Does gamma ray power ~ V? Force free models –Compute pulse profiles for different emission sites and fit to radio, gamma ray observations –Is the rotating vector model really supported by observations? Orthogonal polarization! Harding Johnston Ransom Spitkovsky

5 v 07INPAC31 Particle Acceleration 100 yr question of acceleration of cosmic rays –GeV-TeV –PeV –EeV Relativistic outflows dissipate into high energy electrons with high efficiency –PWN, AGN, GRB, XRB –Volumetric?

5 v 07INPAC32 Proton spectrum GeV TeV PeV EeV ZeV ~MWB Energy Density E ~ 50 J c -1fm s -1 c -1km H 0 Iron?? Can one mechanism Accelerate up to the knee?

5 v 07INPAC33 Nonthermal electron acceleration Diffusive Shock Acceleration –Transmit CR protons with P CR ~E 2 N(E)~ E -.2 ~0.1  u 2 –P e ~ 0.03 P p –Accounts for GCR after including propagation –Observed in IPM –Generic - eg clusters of galaxies Radio observations of SNR –Relativistic electron spectrum –Tycho, Cas A…. X-ray observations of SNR –2-100 keV –100TeV electrons –>100  G fields Thermal, Extended Non-thermal, sharp Bamba SN1006 Cas ATycho

5 v 07INPAC34 PeV CR => >100  G field 10’ Nonthermal Proton Acceleration? RX J –AD385, R ~ 10pc, u~3000 km s-1 –  ~ g cm -3 ; P - ~ dyne cm -2 ; –P + ~ dyne cm -2 ; M ~ 150 ~O.1 PeV  -rays –Inverse Compton by electrons? –Pion decay from protons? –Accelerate ~0.3 PeV protons? –Explain knee in GCR spectrum L x /L  ~ 3 => hadronic emission? –=>P + (100TeV) ~ dyne cm -2 –=>P + (GeV) ~ dyne cm -2 ~0 1 P + – P + (e) ~ 3 x dyne cm -2 Particle transport –r L ~ 4 x E GeV B  G -1 Z -1 cm – <u R/c Aharonian et al GeV TeV PeV

5 v 07INPAC35 Diffusive Shock Acceleration Non-relativistic shock front –Protons scattered by magnetic inhomogeneities on either side of a velocity discontinuity –Describe using distribution function f(p,x) uu / r B u B L

5 v 07INPAC36 Transmitted Distribution Function =>N(E)~E -2 for strong shock with r=4 Consistent with Galactic cosmic ray spectrum allowing for energy-dependent propagation

5 v 07INPAC37 Too good to be true! Diffusion: CR create their own magnetic irregularities ahead of shock through instability if >a –Instability likely to become nonlinear - Bohm limit –What happens in practice? –Parallel vs perpendicular diffusion? Cosmic rays are not test particles –Include in Rankine-Hugoniot conditions –u=u(x) –Include magnetic stress too? Acceleration controlled by injection –Cosmic rays are part of the shock What happens when v ~ u? –Relativistic shocks How do you accelerate ~PeV cosmic rays? –E < euBR ~ TeV for  G magnetic field

5 v 07INPAC38 Particle Transport Alfven waves scatter cosmic rays – ~ (B/  B) 2 r L Bohm? –D ~ c /3 Parallel vs perpendicular –L ~ D/u > 100r L ~ 100 E PeV B  G -1 Z -1 pc R SNR < 10pc –Highest energy cosmic rays stream furthest ahead of shock L ~ E ? –Wave Turbulence spectrum 3, 4 Wave processes. Transit time damping? Nonlinear P(E) /  u 2 GeVTeV PeV 0.1 Shock X E P(E) /  u 2 GeV TeV PeV Cosmic ray pressure dominates magnetic and gas pressure far ahead of the shock. Furthermore the pressure drives instability and magnetic field growth leading to efficient particle acceleration

5 v 07INPAC39 Particle acceleration in relativistic outflows may not be due to shaocks Inter-knot X-ray emission in M87 Magnetic shocks are weak Stochastic acceleration (by em wave) is efficient

5 v 07INPAC40 UHE Cosmic Rays GZK cutoff? –Distant or local Clusters –CR astronomy or physics Composition –Protons in EeV range? L>r L /  ;  =u/c –BL>E 21 G pc=>I>3 x E 21 A! –Lateral diffusion P>P EM ~B 2 L 2  c/4  3 x E 21 2  -1 W –Powerful extragalactic radio sources,  ~1 Relativistic motion eg gamma ray bursts –P EM ~  2 (E/e  ) 2 /Z 0 ~ (E/e) 2 /Z 0 Radiative losses; remote acceleration site –P mw < (L/1pc)W Adiabatic losses –E ~   Leat unpromising astronomical sources –Dormant AGN –GRBs

5 v 07INPAC41 Summary Great opportunities in High Energy Astrophysics Opening up astronomical energy frontiers in electromagnetic, neutrino, cosmic ray, gravitational radiation channels –Plausible sources in all of these bands but no guarantees No compelling evidence yet that “new” physics needed for any high energy astronomical sources –cf cosmology where dark matter and energy were discovered –cf stellar physics where neutrino masses were “discovered” –Worth keeping in mind Auger, GLAST, AGILE, HESS, VERITAS, MAGIC, IceCube, LIGO… can all make major discoveries