Transcript Astrophysical origins of ultra

Astrophysical
origins of high energy cosmic
rays
(Some of the possible)
Diego F. Torres
[email protected]
Lawrence Livermore Lab.
California, 94550, USA
www.angelfire.com/id/dtorres
Summary
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Plausible sources?
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Comments on basic observational features of the CR
spectrum.
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Connection with gamma-ray sources?
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Some choices
– From the extragalactic menu:
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AGNs & Radiogalaxies
Starbursts, LIRGs, ULIRGs
– From the galactic menu:
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The Cygnus region, a TeV photon and UHECR source?
Hillas’ plot
Fermi aceleration
To accelerate a particle
efficiently it must cross
the shocks several times.
A general estimate of the
maximal energy that can
be achieved is given by
the requirement:
Rg=E/(Z e B)~R
where
Rg
is
the
gyroradius and R is the
size of the accelerating
region. This can be
written as:
R~110 Z-1E20/B-6 kpc
Hillas’ plot
One shot acceleration
The upper limit on the
energy
of
one-shot
acceleration is similar to
the shock acceleration
case. For instance, the
maximum energy that
can be obtained from a
pulsar is
E = W Ze B r2 /c
where W is the pulsar
angular velocity, B the
surface magnetic field
and r the neutron star
radius. Typical potential
drops are ~1018 V.
(Previous talk)
GZK or not?
Slanted showers indicate low presence of photons
Very difficult to distinguish between p and nuclei
Observational panorama: composition
Within statistical errors and systematic uncertainties introduced by hadronic
interaction models, the data seem to indicate that iron is the dominant
component of CRs between 1017 and 1019 eV.
Arrival directions & clustering
H.E.S.S.
17 h data
tight cuts
no backgr.
subtraction
Aharonian et al. 2005, A&A, astro-ph/0501667
TeV J2032+4131 at HEGRA: Final results
Confirmation of an extended, steady, hard, source above 1 TeV.
No counterpart yet found.
Anchordoqui et al. astro-ph/0311002
TeV J2032+4131 at HEGRA – Excess at AGASA?
Galactic neutrons of 1018 eV?
Neutrons appear by
photodisintegration of Fe
nuclei on site at the source.
High energy n produce the
AGASA excess. Lower energy
neutrons decay in flight.
Hard to detect in ICECUBE, but
oscillate to muon neutrinos.
Anti-neutrinos take only 1/103
of the n energy
4 events/yr, above 90% CL.
Apparently Galactic Excesses
(especially Cygnus)…
The only cross-confirmed
result for CRs?
Lower energy analysis: no
evidence of anisotropy
1017.9—1018.3
eV:
AGASA
shows a 4s effect from the
Galactic plane (Cygnus +
Center). Other experiments
seems to point in the same
direction.
For the UHECRs: twocoordinates analysis show no
effect for correlations in
scales
larger
than
10
degrees, above 3s. There
might be anisotropies, but
the signal is at too low a
level to detect it.
The lonely neutrinos.
Clustering is essential for astrophysics
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AGASA finds 5 doublets and 1 triplet among the 58 events (paired at less than
2.5o) reported with mean energy above 1019.6 eV. The probability of chance
coincidence under an isotropic distribution is 1%. Similar to the result using the
world sample (Uchichori et al. 1999, Anchordoqui DFT et al. 2000)
Tinyakov, Thachev et al.: The angular two-point correlation function of a
combined data sample of AGASA (E > 4.8 × 1019 eV) and Yakutsk (E > 2.4 ×
1019 eV), the probability of chance clustering is reported to be as small as 4 ×
10−6. Discussion on penalties, on sample selection, on search bin.
But:
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The recent analysis reported by the HiRes Collaboration showed that a: “search
based on data recorded between 1999 December and 2004 January, with a total
of 271 events above 1019 eV shows no small-scale anisotropy.”
AGASA events after the claim not consistent with previous clustering
Case not closed. Wait for future data. Exercise care: e.g., incompleteness of
catalogs in counterpart searches, e.g. over-tested samples.
Unified models
of AGNs
Active Galactic Nuclei: Basic phenomenology
Radio
to
g-ray
energy
distribution of 3C 279 in low and
high state measured in January
and February, 1996. Wehrle et
al. (1998).
General features are a) strong
flux variability, b) spectral
variability, especially when
flaring,
and
c)
the
dominance of the gammaray emission over all other
wavelengths.
Flares so fast argue against an isotropic
origin of the high-energy radiation
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Optical depth to gamma-gamma
For a photon energy of 1 MeV, and a luminosity of 1048 erg s-1,
the optical depth is t > 200 / (tv/1 day)
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Elliot Shapiro relation for a spherical accretion: the source
luminosity is limited by Eddington’s and the size of the source
has to be larger than the Schwarzschild radius
(Indication for beamed emission: Distance is not a problem)
Flares so fast imply a beamed,
small source of gamma-rays
If the emission is beamed -> special relativistic effects
Active Galactic Nuclei as CR emitters:
understanding g-ray emission is key
Radio to UV -> Synchrotron radiation of
relativistic electrons
 MeV-GeV component-> Inverse Compton
scattering of low energy photons
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Possible photons targets:
Bottcher
•Synchrotron photons produced
in the jet: SSC
•UV-Soft and X-ray continuum
from the disk: ECD
•UV-Soft X-ray continuum after
reprocessing at the BLR: ECC
•Synchrotron radiation reflected
at the BLR: RS
Active Galactic Nuclei:
Theories with hadronic dominance
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Observed g-ray emission is
initiated by accelerated protons
interacting with ambient gas or
lower frequency radiation.
In PIC models: photomeson
developments of pair cascades
in the jet.
Efficiency increase with proton
energy, usually requiring
E>1019 eV.
Even when energetics is OK,
GZK maybe there.
Buckley
Looking from the side: Radiogalaxies
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FR-II galaxies are the largest
known dissipative objects
(non-thermal sources) in the
Universe. Localized regions of
intense synchrotron emission,
known as ‘hot-spots’, are
observed within their lobes.
These regions are presumably
produced when the bulk kinetic
energy of the jets ejected by a
central active nucleus
(supermassive black hole +
accretion disc) is reconverted
into relativistic particles and
turbulent fields at a ‘working
surface’ in the head of the jets
Rachen, Biermann, et al.
Radiogalaxies as CR sources
the speed vh with which the head of a jet advances into the intergalactic medium of
particle density ne can be obtained by balancing the momentum flux in the jet against
the momentum flux of the surrounding medium. Measured in the frame comoving
with the advancing head,
In the jet
Balance between acceleration and losses.
Features
Cen A: 3.4 Mpc
M87: 16 Mpc
Directionality should be persistent in the Auger data under the assumption that the mag. field is
not too large so as to add substantially to the travel time.
Possible neutron signal which decay in flight close to the Earth preserving directionality and
producing an spike in the direction of the source (part. Cen A)
Starbursts galaxies (or regions of galaxies):
undergoing large scale star formation
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They have strong infrared emission originating in the high levels of
interstellar extinction, and considerable radio emission produced by recent
SNRs.
Starburst regions are located close to the galaxy centers, in the central
kpc. From such an active region, a galactic-scale superwind is driven by the
collective effect of supernovae and particular massive star winds.
The enhanced supernova explosion rate creates a cavity of hot gas (108 K)
whose cooling time is much greater than the expansion timescale. Since
the wind is sufficiently powerful, it can blow out the interstellar medium of
the galaxy, preventing it from remaining trapped as a hot bubble.
1st step: convective blow-out of a nucleus previously accelerated in a SNR
As the cavity expands, a strong shock front is formed on the contact
surface with the cool interstellar medium. The shock velocity can reach few
1000 km/s and ions like iron nuclei can be efficiently accelerated in this
scenario, up to ultrahigh energies, by Fermi’s mechanism.
2nd step: re-acceleration in the super-wind region
Romero et al. 1999, Anchordoqui et al. 2003
Nearest neighbors
M82
NGC 253
Testing the starburst possibility:
number of events close to the sources
ASS + extragal.
deflection
M82
If Fe
CR arrival
direction
If Ne
5 years, 25 events in PAO
NGC 253
Anchordoqui, Reucroft, Torres, astro-ph/0209546
Extreme starbursts also nearby:
Merging of gas-rich galaxies, LIRGs and ULIRGs
Only one ULIRG within the 100
Mpc sphere [Arp 220]
Tens of LIRGs (with infrared
luminosities >1011 LSUN).
High energy detectability (e.g.
g-rays)
depends
on
the
combined effect of distance and
starburst activity.
Arp 299 (VV 118), one of the the
brightest infrared source within 70
Mpc and a system of colliding
galaxies showing intense starburst,
appeared in the list of candidates for
the AGASA triplet
[review on LIRGs and ULIRGs: Sanders and Mirabel, ARA&A, 1996]
Some powerful local LIRGs:
all likely g-ray sources, some UHECR sources
Arp 220: 72 Mpc, largest
Star formation and SN
explosion rates known in
the universe.
Torres et al. astro-ph/0411429, 0407240, 0405302
Not covered in this talk
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Magnetohydronamic acceleration of iron nuclei in pulsars;
magnetars
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Other large scale structure (shocks)
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Quasar Remnants
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Gamma-ray bursts (a session on them later this week)
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Single source models
Further analysis and
about another 10 possible candidates in:
Summary
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With data now at hand, not only there are several interesting,
plausible theoretical models within the standard astrophysical
agenda to explain the CRs detected so far, but there could
indeed be too many.
Perhaps yet unexpected degeneracy problems will appear even
with the forthcoming data of the Pierre Auger Observatory, a
topic which till now has not been a subject of debate. (Source +
Magnetic field degeneracy)
Occam’s razor suggests we completely discard any possible
astrophysical interpretation before embarking in recognizing
new particles, new interactions, or in general, new physics
beyond the standard model.
AGASA experiment uncertainty is rather over estimated in the correlation
analysis with point sources. The selected angular bin size is perhaps
motivated by their earlier autocorrelation analysis (Tinyakov & Tkachev
2001.a), in which the clustering bin size is defined as the uncertainties in
the arrival direction of each cosmic ray added in quadrature, e = 21/2 x
error ~2.5 deg (as in Uchihori et al.)
To test an alignment between BL LACs and UHECRs, a more reasonable
choice for e is to consider just the uncertainty in the CR arrival direction.
There is only 1 positional coincidence between the AGASA sample and
the 22 selected BL Lacs within an angular bin size of 1.8 deg.
! Strong changes in results due to bin sizes ! Not a good signal.
Correlations with EGRET sources
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Gorbunov et al. claim correlation (2002)
of UHECRs with EGRET blazars by
doubling the size of egret detections.
Exercise care: large uncertainties with
EGRET=random association with
blazars.
The expected distribution of radio-loud
quasars (louder than 0.5 Jy at 5 GHz) to
occur by random chance as a function
of the distance from the centre of the
EGRET field. Points represent the
number of g-ray detections for which
the counterparts are beyond the 95%
confidence contour. The dotted curve
are the boundaries of the 68%
confidence band for the hypothesis that
the radio sources are randomly
distributed.
Torres 2004, Torres et al. 2003.
Extreme starbursts also nearby: Merging of gas-rich
galaxies, LIRGs and ULIRGs
Left: Time-evolution of a galactic
encounter, viewed along the
orbital axis. Here dark halo
matter is shown in red, bulge
stars are yellow, disk stars in
blue, and the gas in green.
Right: showing only gas in
both galaxies
Barnes and Hernquist 1996
Credits
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SSC or Self-Synchrotron Compton process: e.g. Marscher &
Gear 1985, Maraschi et al. 1992, Bloom et al. 1996
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ECD or External Comptonization of Direct disk radiation
process: e.g. Dermer et al. 1992, Dermer & Schlickeiser 1993
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ECC or External Comptonization of radiation from Clouds:
e.g. Sikora et al. 1994, Dermer et al. 1997, Blandford and Levinson
1995
RS or Reflected Synchrotron mechanism: e.g. Ghisellini &
Madau 1996, Bottcher & Bednarek 1998, Bednarek 1998
Not exhaustive
In action
The low-frequency radio
emission is expected to
be produced by less
compact regions.
FSRQ 3C 279
Viewing Period P5B: Jan-Feb. 1996
Hartman et al. 1999
Most FSRQs are
successfully modelled
with dominant EC
models.
SSC.
Sync.
Acc. Disk
ECD
ECC
In action
BL Lac Mrk421
Most BL Lacs are
successfully modelled
with pure or dominant
SSC models.
BL LACs ->
FSRQs
Ghisellini, Fossati, Celloti, et al.
Theories with hadronic dominance: Collisions
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g-rays from pp from the collision of jets with gas clouds
Due to the enhanced density in the BLR clouds, pp interactions can dominate
the pg process
[in the case of PIC models where photopion interactions dominates the initiation
of the cascade]
Another possible target for the jet could be the wind of an OB star moving
through the jet.
Protons responsible only for the injection of electrons, which in turn produce the
observed g-ray emission by SSC mechanism (Kazanas & Mastiachidis 1999).
Large proton densities.
Credits
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PIC or proton induced cascade model: e.g., Mannheim &
Biermann 1992, Mannheim 1993 & 1996
Sync. Radiation of protons and modelling of TeV blazars: e.g.
Aharonian 2000, Mucke & Protheroe 2000, Protheroe & Mucke 2000
Collisional models with gas: e.g. Beall & Bednarek 1999,
Purmohammad & Samimi 2001
Collisional models with star winds: e.g. Bednarek & Protheroe
1997
Not exhaustive
GZK
Attenuation length of γ ’s, p’s and
56Fe’s in various background
radiations as a function of
energy. The 3 lowest and leftmost thin solid curves refer to
gamma rays, showing the
attenuation by IR, CMB, and
radio backgrounds. The upper,
right-most thick solid curves refer
to propagation of protons in the
CMB, showing separately the
effect of pair production and
photopion
production.
The
dashed–dotted line indicates the
adiabatic fractional energy loss at
the present cosmological epoch.
The dashed curve illustrates the
attenuation of iron nuclei.
Detectability of LIRGs
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Gamma-ray detectability is favored in
starburst galaxies (Akyuz, Aharonian,
Volk, Fichtel, etc)
– Large M, with high average gas
density, and enhanced cosmic ray
density
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Recent HCN-line survey of Gao &
Solomon (2004) of IR and CO-bright
galaxies, and nearby spirals
– Allows estimate of SFR (from HCN
luminosity) and minimum required k
for detection by LAT and IACTs
(from HCN + CO intensities and
distance)
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Several nearby starburst galaxies and a
number of LIRGs and ULIRGs are
plausible candidates for detection
MW
CR Enhancement required for detectability/LAT
Not covered in this talk
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Magnetohydronamic acceleration of iron nuclei in pulsars;
magnetars
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Gamma-ray bursts (a session on them later this week)
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Single source models