Astroparticle physics with high-energy photons I – The physics Alessandro de Angelis Lisboa 2003...
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Transcript of Astroparticle physics with high-energy photons I – The physics Alessandro de Angelis Lisboa 2003...
Astroparticle physicswith high-energy photons
I – The physics
Alessandro de AngelisLisboa 2003
http://wwwinfo.cern.ch/~deangeli
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The starting point Physics constructs models explaining Nature (or better
our observations of Nature, or better observations of our interactions with Nature)
We know Nature mostly through our eyes, which are sensitive to a narrow band of wavelengths centered on the emission wavelength of the Sun
3
We see only partly what surrounds us
We see only a narrow band of colors, from red to purple in the rainbow
Also the colors we don’t see have names familiar to us: we listen to the radio, we heat food in the microwave, we take pictures of our bones through X-rays…
5
The universe we don’t see
When we take a picture we capture light(a telescope image comes as well from visible light)
In the same way we can map into false colors the image from a “X-ray telescope”
Elaborating the information is crucial
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We know there is something important we don’t see
Gravity:G M(r) / r2 = v2 / renclosed mass: M(r) = v2 r / G
velocity vradius r
Luminous stars only small fraction of mass of galaxy
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The high-energy spectrum
E > 30 keV ( ~ 0.4 A, ~ 7 109 GHz)
Although arbitrary, this limit reflects astrophysical and experimental facts:
Thermal emission -> nonthermal emission Problems to concentrate photons (-> telescopes
radically different from larger wavelengths) Large background from cosmic particles
10
The subject of these lectures…(definition of terms)
Detection of high-energy photons from space High-E X: probably the most interesting part of the spectrum for
astroparticle
What are X and gamma rays ? Arbitrary !
(Weekles 1988)
X 1 keV-1 MeVX/low E 1 MeV-10 MeV
medium 10-30 MeVHE 30 MeV-30 GeVVHE 30 GeV-30 TeVUHE 30 TeV-30 PeVEHE above 30 PeVNo upper limit, apart from low flux (at 30 PeV, we expect ~ 1 /km2/day)
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Outline of these lectures
0) Introduction & definition of terms
1) Motivations for the study high-energy photons
2) Historical milestones
3) X/ detection and some of the present & past detectors
4) Future detectors
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1) Motivations for the study of X/
Probe the most energetic phenomena occurring in nature
Nonthermal
Nuclear de-excitation/disintegration
Electron interactions w/ matter, magnetic & photon fields
Matter/antimatter ann.
Decay of unstable
particles
Clear signatures
from new physics
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Motivations (cont’d)
Penetrating
No deflection from magnetic fields, point ~ to the sources
Magnetic field in the galaxy: ~ 1GR (pc) = 0.01p (TeV) / B (G)=> for p of 300 PeV @ GC the directional information is lost
Large mean free path
Regions otherwise opaque can be transparent to X/
Good detection efficiency
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Astronomy Scales
4.5 pc 450 kpc 150 Mpc
Nearest Stars Nearest Galaxies Nearest Galaxy Clusters
1 pc= 3 light years
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‘GZK cutoff’ HE cosmic rays
HE gamma rays
Mrk 501 120Mpc
Mrk 421 120Mpc
Sources uniform in universe
100 Mpc
10 Mpc
e+ e
p N
Interaction with background ( infrared and 2.7K CMBR)
Milky Way
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PHYSICS GOALS
AGNsAGNs SNRsSNRs
-ray Backg.-ray Backg.Cold Cold Dark Dark MatterMatter
PulsarsPulsars GRBsGRBs
Photon Photon propagation- propagation- Invariance of Invariance of
cc
AnomalouAnomalous eventss events
New VHM New VHM particlesparticles
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Energetic protons and electrons in the vicinity of astrophysical objects might produce gammas
Synchrotron radiation by electrons in magnetic fields could be boosted to TeV energies by inverse Compton scattering
If acceleration mechanisms involve hadronic interactions, there are many 0 -> (& the give a clear signature)
Acceleration mechanisms and the origin of cosmic rays
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Active galaxies
Many sources, mostly classified according to observational criteria
Unified AGN model (Begelman et al. 1984): 10% of the accreted mass is transformed into radiation
Different models predict different spectra
But warning : ~300 sources @ the GeV scale, only 15 @ the TeV
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Pulsars
Rapidly rotating neutron stars with
T between ~1ms and ~1s Strong magnetic fields (~100 MT) Mass ~ 3 solar masses R ~ 10 Km (densest stable object
known)
For the pulsars emitting TeV gammas, such an emission is unpulsed
Crab pulsar
X-ray image (Chandra)
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-ray bursts (History, I)
An intriguing puzzle of today’s astronomy… A brief history
Beginning of the ‘60s: Soviets are ahead in the space war
1959: USSR sends a satellite to impact on the moon
1961: USSR sends in space the 27-years old Yuri Gagarin
1963: the US Air Force launches the 2 Vela satellites to spy if the Soviets are doing nuclear tests in space or on the moon
Equipped with NaI (Tl) scintillators
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-ray bursts (History, II)
1967 : an anomalous emission of X and rays is observed. For a few seconds, it outshines all the sources in the Universe put together. Then it disappears completely. Another in 1969...
After careful studies (!), origination from Soviet experiments is ruled out
The bursts don’t come from the vicinity of the Earth
1973 (!) : The observation is reported to the world
Now we have seen hundreds of gamma ray bursts...
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-ray bursts: why they are important
They might represent objects near the edge of the observable Universe
The energy could be 1015 times larger than the energy from a supernova
E ~ 1045 J They could be a new
observational tool for cosmologist
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-ray bursts: what we knowand what we’d like to know
They come from every direction in the sky
Mostly extragalactic
Frequently no optical emission (BeppoSAX 1997)
Far away from the galaxy A puzzle…
Time duration is wildly variable Afterglows after > 1h…
Several mechanisms proposed, enormous energies: a great chance that they’re so far...
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A recent consensus
Many sources can be related to SN remnants
Mechanism accounting for repeated shocks (Dar, De Rujula)
Matter of precise poninting:Work for GLAST
Synergy with gravitational wave detectors Work for LIGO
But: Maybe different kinds of bursts…
28
Probability of bursts
Present estimate: 1 GRB/100My/Milky Way Galaxy=> Already ~ 100 GRB in our
galaxy
Energy ~ 1045 J
According to Dar, it is not unlikely that a GRB has already interacted with the atmosphere…
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Diffuse background radiation
Is it really diffuse (<- produced at a very early epoch) or a flux from unresolved sources ?
Angular resolution is the key
30
Physics in extreme conditions: photon propagation
Due to -> e+e-, CMB and visible light absorb at the PeV and at the TeV
At the GKZ cutoff (1020 eV) the Universe regains transparency to
The transparency of the Universe gives insights on the infrared/ optical diffuse background
Quantum gravity (Amelino-Camelia et al., Ellis et al.)
V = c (1 - E/EQG)
Effects on GRB could be O(100 ms)
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=> Intergalactic absorption
Photons interact with the IR background => relationship source distance / maximum observed photon energy
Measurement from the distortion of AGN spectra Data in the range 50 GeV - 300 GeV would be crucial
And an important byproduct:
the best constraints on Lorentz violation, photon oscillations etc.
32
Particle physics at high energies
Today’s accelerator physics limited & many early discoveries in particle physics came from the study of cosmic rays
Motivation for particle physicists to join
33
Energy of accelerated particles
Dia
met
er o
f co
llid
er
Cyclotron Berkeley 1937
LHC CERN, Geneva, 2007
Active Galactic Nuclei
Binary Systems
SuperNova Remnant
Particle Physics Particle Astrophysics
35
Probing dark matter: WIMPs
Some dark matter candidates (e.g. SUSY particles) would lead to mono-energetic lines through annihilation
X
X
q
qor or Z
36
Anomalous events
Anomalous showers at UHE (> 7 PeV)
from Cygnus X-3 (Samorski & al. 1983): almost no photons… Increasing total photon X-section
due to virtual gluons Increasing neutrino X-section New particles
Anomalous events (highly penetrating hadrons)
Normally killed as “irreproducible results”, but…
37
Study of exotic objects: other phenomena
Top-Down : Decay of massive cosmic strings (1015 GeV, Kolb & Turner 1990)
Unknown transients
Time resolution is the key
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2) Historical milestones
1952 Prediction of He X/ high energy emission (Hayakawa)
1957 Sputnik 1
1958 Inventory of cosmic sites expected to radiate in the X/(Morrison)
1968 (11 years after the Sputnik): X emission of the galaxy
1972 from Crab Nebula
1973 First report on gamma ray bursts
1978 Gamma-ray spectroscopy : e+e- annihilations @ the GC
1983 Nuclear processes at the GC
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X/ Satellites in the ’90s
GRANAT (SIGMA), 1990/97 Accreting black holes Jets
CGRO, 1991/2000 BATSE, thousands of GRB EGRET, hundreds of GRB in the HE region
BEPPO Sax, 1996/2002 SN remnants
41
Gamma satellites
EGRET [+BATSE] Diffuse emissions dominate
the -ray sky. After removing the identified point sources, ~ mass distribution
Moreover, isotropic emission at high latitude going like E-2.07+-0.03
Pulsars, all observed also in the radio (apart from Geminga)
Most point sources unidentified Gamma-Ray Bursts, not
expected in any model. No apparent E cut-off, E as high as 18 GeV
The pulsar spectrum depends on the wavelength => Different energies produced in different regions
43
VHE sources
Observations in the ‘90s confirm earlier detection of VHE emissions from Crab nebula and discover new VHE sources in pulsars (PSR 1706-44, Vela)
No pulsed emission TeV emission from AGN, with flares
Mkr 421 Mkr 501
Models differ in the kind of particles emitted & E spectrum
Synchrotron model => 2 humps, one from synchrotron and one from inverse Compton
Variability over a large range of timescales
Observational holeupper limit from EGRET
44
UHE (and EHE ?)
No sources of UHE (only diffuse emission)
No signal from established VHE sources
No signals from hypothetical new sources (primordial black holes, black holes accreting from a nearby star…)
Although the GRB spectrum from BATSE/EGRET is hard (E-2), no UHE seen (and they would be expected…)
Absorption in the em field ?
Detection problems ?
45
Comment on VHE and UHE gammas
Ground-based astronomy operates in regimes of large background => results are matter of discussions
VHE emissions from Crab and Vela are accepted as genuine No episodic emission widely accepted yet
Many astronomical models of AGN suffer from lack of information in the ~50 GeV region…
Fill the hole
No relevant information for particle physics, yet
Relevant is what should have been observed, but has not TeV gammas from SN shocks should have been seen Correlation between EGRET objects, TeV emissions and SNR ?
48
Summary
High energy photons (often traveling through large distances) are a great probe of physics under extreme conditions
What better than a crash test to break a theory ?
Observation of X/ rays gives an exciting view of the HE universe Many sources, often unknown Diffuse emission Gamma Ray Bursts
No clear sources above ~ 30 TeV Do they exist or is this just a technological limit ?
We are just starting… Next lecture: many new detectors being built or plannedFuture detectors: have observational capabilities to give SURPRISES !