Cosmic Rays: Open Problems
and
Perspectives for the future
Paolo Lipari MAPS Perugia 20th october 2009 COSMIC RAYS
A (nearly) one century old problem....
Victor Hess before the balloon flight of 1912
Discovery of Cosmic Rays Beginning of High Energy Astrophysics Review article in 1931 of Karl Darrow (Millikan collaborator). ``Data and nature of Cosmic Rays''
Physicists with their frail machines have gone to high mountain ponds in the Sierras and in the Andes, to the distant wildernesses about the Earth Magnetic poles; they have scooped out cavities in Alpine glaciers, they have lifted hundredweights of lead to the tops of peaks above the snow line, they have cruised the arctic and the tropical oceans, they have descended into tunnels and deep mines, they have ascended into the sky in airplanes and balloons .... Leading theory for CR in 1931:
Georges-Henry Lemaitre
New York Times article:
Prof. Albert Einstein has given his scientifc blessing to the ingenious theory proposed by Abbe' Georges Lemaitre that cosmic rays are birth cries of the universe and the radiations from the superradioactive primeval matter that existed when the universe was young. COMPTON (1933) Cosmic Rays are CHARGED
LATITUDE EFFECT GEOMAGNETIC EFFECTS
Latitude efect → Charged particles East-West efect → Positively charged particles An understanding of the Origin of Cosmic Ray is still incomplete. Most fundamental problems are still open. Which are the sources ? What are the production mechanisms ? ..... An understanding of the Origin of Cosmic Ray is still incomplete. Most fundamental problems are still open. Which are the sources ? What are the production mechanisms ? .....
… but...
The perspectives to arrive soon to clear Answers to (many) of these fundamental questions are (in my opinion) excellent.
CR measurements (ground, space) Gamma Astronomy + multi=wavelength observations [neutrino astronomy] Cosmic Rays Spectrum Features: 1. Knee [1a. 2nd Knee] 2. Ankle 3. High Energy bending
Remarkably smooth (nearly featureless) Energy Spectrum. UHECR Flux * E3 representation.
Knee 2nd Knee “suppression”
Ankle UHECR Flux * E3 representation.
HIRES
Tibet ARRAY Data points depend on the interaction model used for modeling the showers AUGER QGSJET-1 QGSJET-2 SIBYLL We do not have a convincing, unique explanation for ANY of the main features observed in the CR spectrum: (knee, 2nd knee, ankle, high energy suppression).
[Diferent explanations for the (astro)physics that produces these features have been advanced (with diferent degrees of plausibility)]
Clarifcation of these issues is a main goal for future studies Proton, electron, positron, antiproton Spectra
Diferent spectra For diferent Particle types High Energy Astrophysical Source:
Object (or an “event”) that produces (and for some time contains) relativistic particles
p
e±
Escaping particles: CR High Energy Astrophysical Source:
Object (or an “event”) that produces (and for some time contains) relativistic particles
Unavoidable p Photon emission !
e±
Escaping particles: CR “Hadronic Emission”
“Leptonic Emission” “The HIGH ENERGY UNIVERSE”
WHERE are high energy particles produced? which sources (source classes)
WHICH physical mechanism produce them? [Fermi mechanism ? Pulsars? ...]
HOW do they get from the production point to the observation point [Magnetic feld, energy loss, ....] GAMMA ASTRONOMY [multi-wavelength photon observations]
Several diferent type of astrophysical objects emit high energy photons (GeV, TeV).
Therefore contain populations of high energy relativistic charged particles. [And therefore can accelerate them with “non-thermal mechanisms”]
Are these relativistic particles electrons/positrons or protons and Nuclei? “Leptonic versus Hadronic radiation mechanism”
Which (if any) of these high energy sources produce the particles we observe at the Earth ? GAMMA ASTRONOMY [multi-wavelength photon observations]
Several diferent type of astrophysical objects emit high energy photons (GeV, TeV).
Therefore contain populations of high energy relativistic charged particles. [And therefore can accelerate them with “non-thermal mechanisms”]
Are these relativistic particles electrons/positrons or protons and Nuclei? “Leptonic versus Hadronic radiation mechanism”
Which (if any) of these high energy sources produce the particles we observe at the Earth
(Neutrino Astronomy ?!) Agile Fermi
Hess Magic GALACTIC
EXTRAGALACTIC
Cosmic Rays We live in a “bubble” flled with Cosmic Rays.
A “magnetic bottle” where the CR density is enhanced by magnetic trapping.
B
Extra-galactic space is flled by a much more tenuous gas of cosmic rays injected during the entire history of the Universe. This “extragalactic population” emerges only at sufciently high energy. Galactic Sources Injection Q(E,x) Containement D(E/Z, x) Difusion Escape Galactic Sources Injection Q(E,x) Lifetime Containement Of a particle D(E/Z, x) Difusion Escape Galactic Sources Injection Q(E,x) Lifetime Containement Of a particle D(E/Z, x) Difusion
(high energy) Extra-galactic CR crossing the Galaxy. Piece of extragalactic space “MilkyWay-like sources”
Milky Way
Galaxy Piece of extragalactic space: Non MilkyWay-like sources
AGN
Milky Way
Galaxy
Measurement of the CR density
SMC
Dominant contribution to the GeV photon emission: CR density in the Large and Small Magellanic Clouds much smaller than in our Milky Way
Eγ > 100 MeV Fermi all sky Map Galactic and Extra-Galactic components One general way to state the problem of the cosmic ray fuxes:
For each particle type: p, e-, e+, He, Li, Be, B, … , Fe, ....
Compute this integral: Source of CR particles with energy E 0 at time t (in the past) 0 at position r 0
(Measurable) Density of CR particles With energy E, at the present time “Propagation “here” (r ) obs Probability”
Propagation as difusion
Sources “Primary Particles” Directly produced in astrophysical Objects (like SNR, GRB).
For primary particles (protons, electrons): Ensemble of “quasi-instantaneous” [SNR, Pulsars] point sources? Universal Shape of The Spectrum ?
Time-averaged, Space-smoothed source: Stationary. Space dependence, refects Galaxy structure “Secondary Particles:”
Continuous (time, space) Injection In the volume Of the Galaxy Source spectrum of secondary has a the shape determined by the primary spectrum. (and known physics).
Source of Relativistic particles From Dark Matter annihilation:
Annihilation DM density “Branching Cross section Ratios” in Diferent Annihilation channels
MILKY WAY sun Fundamental propagation equation:
Source Difusion Energy Loss
...
additional terms:
interaction decay convection reacceleration Fundamental propagation equation:
Source Difusion Energy Loss Fundamental propagation equation:
0
Source Difusion Energy Loss
Stationary Solution Escape as “absorbing boundary condition” The difusion coefcient become infnity at the boundary
Galaxy as a cylinder PROTON SPECTRUM
Injection Spectrum
Escape [difusion description]
Interaction [small efect]
Energy Loss [negligible] Toy Model: “Spherical Galaxy” :
Exact solution :
“Concentrical spheres Galaxy”
Two models Same CR injection
Larger/smaller halo Galaxy modeled “Slab Galaxy” as an infnite “slab” 1-D problem
Creation of particles
difusion with escape “normal” difusion”
Time and space origin of the protons (in the “slab galaxy” toy model)
Homogeneous Stationary injection
Dashed line: exponential of same average Stationary sources (no time dependence)
Isotropic Difusion description Good approximation:
Factorization of the energy dependence: For the source. For the difusion coefcient
Cosmic Ray Nuclear Composition Cosmic Ray Nuclear Composition
Overabundance of Li, Be, B
Sub-iron elements
Spallation efect:
Column density Confnement time Injection of Secondary Nuclei: A = Primary Nucleus (C, N, O) A' = “Secondary Nucleus” (Li, Be, B)
E = Energy per nucleon: Injection of Secondary Nuclei: A = Primary Nucleus (C, N, O) A' = “Secondary Nucleus” (Li, Be, B)
E = Energy per nucleon:
Diferent Spectrum! Primary Nucleus
Secondary Nucleus
Primary/Secondary Primary Nucleus
Secondary Nucleus
Primary/Secondary From CREAM
tau(E) ~ E-0.6 What are the SOURCES of COSMIC RAYS? ENERGETICS Where can one fnd the power to create the cosmic rays ?
Non-thermal DYNAMICS Non-equilibrium How is the energy transformed “Violent” into ultra-relativistic particles phenomena Power Provided by SN is sufcient with a conversion efciency of 15-20 % in relativistic particles POWERING THE GALACTIC COSMIC RAYS CAS A (1667) SuperNovae types
Chandra X-Ray images
SN1006 Tycho Cas A FERMI acceleration mechanism
Collision with Moving Plasma Clouds in the Galaxy Unshocked material at rest
Shock Piston Front 2
The Energy Spectrum of Particle accelerated near Shock Waves has a UNIVERSAL FORM
In agreement with observations.
SuperNova Discovered in 1996 by the Roentgen Satellite RX J1713.7-3946 (Rosat)
Foreground star
Point Source (Neutron Star) 1st observation of RX J1713.7-3946 AD 393
A guest star appeared within the asterism Wei during 2nd lunar month of the 18th year of the Tai-Yuan reign period (february 27-march 28 AD 393), and disappeared during the 9th lunar month (october 22 - november 19) HESS Telescope Observations with TeV photons
Comparison with ROSAT observation ENERGY Spectrum Hess estimate
Essentially compatible with the Ortodoxy (10% conversion of SN kinetic energy into relativisic particles) G23.3-0.3 VELA JUNIOR
W41 Have we proved that SNR are the source of the bulk of the Galactic Cosmic Rays ?
Important “Hints” But conclusion Still Controversial.
Need additional Data. Cherenkov telescopes, FERMI (Glast)
NEED ADDITIONAL SOURCES
at high Energy GAMMA RAY BURSTS (GRB's)
Proposed source Of the CR
Γ > 100
GRB : associated with a subset of SN Stellar Gravitational Collapse Geometry of the emission of the two jets
Intense radiation feld Of the companon star Absorbs TeV photons [?] Electron SPECTRUM
Injection Spectrum
Escape [difusion description]
Interaction [small efect]
Energy Loss [Synchrotron, Inverse Compton] Proton and electron energy spectra
E-2.70
E-3.04
Efect of energy Losses on the spectrum
Energy Loss (variation) Propagation equation for electrons
Energy Loss Source Difusion
Boundary Condition
protons
electrons
Secondary nuclei
Pair production Which are the SOURCES of the CR electrons ? Are they the same as the proton sources?
Is the Shape of electron Source Spectrum the same as for protons ?
Relative Normalization ? Which are the SOURCES of the CR electrons ? Are they the same as the proton sources?
Probably yes !
Is the Shape of electron Source Spectrum the same as for protons ? Probably yes !
Relative Normalization ? Only partially understood Which are the SOURCES of the CR electrons ? Are they the same as the proton sources?
Probably yes !
Is the Shape of electron Source Spectrum the same as for protons ? Probably yes !
Relative Normalization ? Only partially understood
CO-ACCELERATION (electrons, p, nuclei) problem Injection is a power law in MOMENTUM
Normalization Condition for the same source:
Protons and Electrons from SAME dominant source The PAMELA “Positron Excess” High energy: ratio e+/e- grow with E !!
Very unexpected result for the “astrophysical background” FERMI: electron + positron fux FERMI: electron + positron fux
“Excess” [??] of electrons + positrons
.... Possible... but certainly not necessary FERMI: electron + positron fux Proton and electron + Positron energy spectra
Use: e+/e- ratio from Pamela ft of e=(e++e-) data to estimate e+ fux
E-2.70
E-3.04
Proton and electron + Positron energy spectra
Use: e+/e- ratio from Pamela ft of e=(e++e-) data to estimate e+ fux
New component “emerging” at high energy ?? ATIC Balloon experiment (electron + positron)
HESS Cherenkov Telescope
POSITRON EXCESS possible explanations:
“Near Sources”
Dark Matter
“NEW Sources” New Astrophysical Source (Pulsars)
New mechanism in standard sources Cascade pair injection P.Blasi astro-ph/0903.2794
New mechanism in “standard Supernova acceleration” scenario
INJECTION of e+e- pairs from accelerated particles at the source
Crucial problems: Normalization Spectrum
Detailed calculation PULSARS
CRAB Nebula CRAB Nebula
Red Radio Green Optical Blue X-rays Fermi Pulsar detection Hooper, Blasi, Serpico 2008
Energy is available
Dynamics of particle production? Hooper, Blasi, Serpico 2008 Contribution from all Pulsars Hooper, Blasi, Serpico 2008 Contribution from single close Pulsar
“Low energy problem” [solar modulation]
“High energy problem” at the center of intense interest Solar Modulations BESS proton fux measurements Sunspot number
Neutron Monitor Counts
Time of BESS fights: Moving magnetic scattering centers
Reasonably good approximation:
The efect of the solar wind is equivalent to a POTENTIAL Ε = E - Z ∆ V with particles losing an energy f i ∆ E = Z V Time Variations of Cosmic Rays Induced by variations in intensity of the solar wind
Commonly used approximation for the description of the modulation is the FORCE FIELD approximation. The efect of the wind is equivalent to a potential
A single parameter controls the variation of the spectra E = E - |Z| V (t) earth inter stellar solar wind
Φ (E,t) = (p /p )2 Φ [E + V(t)] earth earth i.s. inter stellar Charge Dependent Solar Modulation The Highest Energy
Cosmic Rays AUGER detector in ARGENTINA 1.5 Km
The Fly's Eye Detector concept The Fly's Eye Detector concept FLUORESCENCE DETECTION In principle little model dependence for shower energy determination
Observed Emitted Shower Light Photons Size
Geometry Fluorescence Atmospheric Yields Absorption Absorption corrected
In principle only weak dependence in the Energy determination AUGER detector 3000 Km2 (Argentina)
Hybrid system
The “GZK” controversy
and the
“END of the Cosmic Ray Spectrum”
Discovery of the Cosmic Background Radiation (1965: Penzias, Wilson)
COBE: nearly perfect Black Body 2.74 K After a few months: (1966) understanding of the consequences Of CMBR for CR.
Greisen Zatsepin, Kuzmin
Intergalactic space full of soft photons (410 cm-3) Becomes not transparent for high energy protons.
[neutrino production] Additional (less efective) Energy loss mechanism For protons: Energy Loss for Nuclei: Photo-disintegration. Suppression Volcano Ranch Efect not [John Linsley PRL 10 (1963).] Seen.... ??! Haverah Park
AGASA Suppression Volcano Ranch Efect not (John Linsley PRL 10 (1963). Seen.... ??!
Haverah Park Top Down Models [Decay of Super massive Particles AGASA M ~1024 eV ] GUT
Great excitement ! Violations of Lorentz Invariance Several hundred speculative theoretical works... Suppression Volcano Ranch Efect not (John Linsley PRL 10 (1963). Seen.... ??! Haverah Park
AGASA Clarifcation: (2008, 2009) Great excitement ! HIRES
Several hundred speculative theoretical works... AUGER Claim of Evidence for the Existence of the GZK suppression by the HiRes Collaboration:
HiRes I , HiRes II , Agasa Energy Spectra Exposure ~ 17000 km2-yr Zenith angle ≤ 600
A “bending” in the UHECR spectrum is now convincingly observed by the HIRES and AUGER collaborations.
Its structure is CONSISTENT with the “GZK” bending for a spectrum of protons.
Its nature is not yet frmly established.
Other explanations are also possible:
Photo-disintegration of nuclei
“End of Acceleration”
The “Scientifc Landscape” is deeply modifed.
The study of UHECR is now predominantly an essential branch of High Energy Astrophysics.
Speculations and searches for “ New Physics” efects in UHECR can (and will) continue.
Some interesting ideas have been put forward and their test and study remain valid goals.
(Violation of LORENTZ INVARIANCE). “TOP DOWN” Models. Highest energy cosmic rays must be extra-galactic
Magnetic Field of the Milky Way Dimension of the milky way to small for confnement. Galactic and Extra-Galactic components
Extragalactic Cosmic Rays
Visible tail Crossing at the “2nd Knee” Proton Energy Evolution with Redshift ) V e (
y g r e n E
Redshift (z) “Horizon” (in time) for protons ) x a m z (
n o z i r o H
t f i h s d e R
Energy (eV) Power law injection of particles
Resulting spectrum at the present epoch is deformed
Adimensional Shape Factor
Only Redshift losses: Constant Shape factor (Berezinski “Modifcation factor”) for diferent power law indices. (No cosmic evolution) The “Olbers (Kepler) Paradox”
Why is night sky dark ?
Eternal, infnite Euclidean Universe
Infnite fux
Solution : Finite time for the universe Redshift efects.
“horizon” Homogeneous distribution of sources Diferent Injection spectra Possible efects of evolution Power Law Injection (No Cosmic Evolution)
2.7
α = 2.5
2.3 2.0 Power Law Injection (No Cosmic Evolution)
Remarkable “coincidence” (?!)
2.7
α = 2.5
2.3 2.0
Berezinski et al “DIP Model” Combine galactic and extragalactic part
“second knee”
Hence no Gal. outfow detected
EG
G
from Michael Hillas “Average Power Density” needed to produce the Extra-Galactic Cosmic Rays
Present CR Accumulation of cosmic rays emitted Energy density During the history of the universe Cosmic Ray Energy Density
Much larger Energy in Extragalactic Cosmic Ray.
More Power Needed
Available Energy Sources in the Universe ACTIVE GALACTIC NUCLEI
Optical
Radio 3C219 JETS
Invisible Counter JET
JET M87
Opening of
Cosmic Ray Astronomy [?] From: Medina Tanco Distance of source
Coherence Length of Magnetic Field Galaxies with Redshift z < 0.018 AUGER RESULT CR come from 3.1 degrees from the sources 20/27 coincident with near AGN Estimate of the Extragalactic Magnetic Field Galaxies with Redshift z < 0.018 AGN in same Volume Auger Events
CENTAURUS A
(with very high probability)
First object imaged with Cosmic Rays
Radio Image 408 MHz Chandra X-ray image
Spectral Energy Distribution of CEN A Several puzzles:
Non confrmation by HIRES
New (just released) AUGER data
18/27 events in correlation in frst data set 8/31 in new data set Cosmic Ray Composition
and
Hadronic interactions Fluorescence Light Composition SHAPE of the Shower Measurements Longitudinal Development dependences:
Composition Hadronic Interaction Modeling
and the Composition of Cosmic Rays Xmax
Proton Showers Logarithmic growth
of average Xmax with energy
Mass dependence
From Cosmic Ray Data Hadronic Interactions
C.R. DATA
Astrophysical Hadronic Information Interactions
“Astrophysical Cosmic magnetic spectrometer. Composition Methods” Features in the spectrum
Auger Results
July 2009
composition
Fluctuations On X max
Composition Becoming Heavy !! COMPOSITION: (becoming heavier with E)
AGN correlation (small Z particles: p, He)
Conficting Results From HIRES Contradiction ?? detector Elongation rate corrected for detector acceptance and comparison with previous results
HIRES Xmax analysis Comparison of data and p-QGSJET02 fuctuation widths Use 2-sigma truncated gaussian width to ft Xmax distr. Detector resolution is NOT deconvoluted!
HIRES Fluctuations analysis No conclusion... but fnal comment....
....Many problems remain open...
… but are fnally beginning to understand the mechanisms that produce the highest energy particles in the Universe
MULTI-MESSENGER ASTRONOMY Is a new way to observe the Universe With remarkable potential for new discoveries and a deeper understanding of Nature I think it is a good time today to be a young scientist In the feld of high energy astrophysics.
[… if research is supported as it should …!]
New results and new understanding will soon arrive
Have a good workshop !