(Some of the possible) Astrophysical origins of high energy cosmic rays

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(Some of the possible) Astrophysical origins of
high energy cosmic rays

• Diego F. Torres
• dtorres_at_igpp.ucllnl.org

www.angelfire.com/id/dtorres
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Summary

• Plausible sources?
• Comments on basic observational features of the
  CR spectrum.
• Connection with gamma-ray sources?
• Some choices
• From the extragalactic menu
• AGNs Radiogalaxies
• Starbursts, LIRGs, ULIRGs
• From the galactic menu
• The Cygnus region, a TeV photon and UHECR source?

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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 RgE/(Z e B)R where Rg is the
gyroradius and R is the size of the accelerating
region. This can be written as R110 Z-1E20/B-6
kpc
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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.
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GZK or not?
(Previous talk)
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Slanted showers indicate low presence of photons
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Very difficult to distinguish between p and nuclei
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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.
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Arrival directions clustering
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TeV J20324131 at HEGRA Final results
Aharonian et al. 2005, AA, astro-ph/0501667
Confirmation of an extended, steady, hard, source
above 1 TeV. No counterpart yet found.
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TeV J20324131 at HEGRA Excess at AGASA?
Anchordoqui et al. astro-ph/0311002
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.
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Apparently Galactic Excesses (especially
Cygnus) The only cross-confirmed result for
CRs?
Lower energy analysis no evidence of
anisotropy 1017.91018.3 eV AGASA shows a 4s
effect from the Galactic plane (Cygnus Center).
Other experiments seems to point in the same
direction.
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For the UHECRs two-coordinates 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.
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Clustering is essential for astrophysics

• 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 gt 4.8 1019 eV) and Yakutsk (E gt 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
• 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.

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Unified models of AGNs
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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 gamma-ray emission
over all other wavelengths.
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Flares so fast argue against an isotropic origin
of the high-energy radiation

• 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 gt 200 / (tv/1 day)
• Elliot Shapiro relation for a spherical
  accretion the source luminosity is limited by
  Eddingtons and the size of the source has to be
  larger than the Schwarzschild radius
• (Indication for beamed emission Distance is not
  a problem)

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Flares so fast imply a beamed, small source of
gamma-rays

• If the emission is beamed -gt special relativistic
  effects

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Active Galactic Nuclei as CR emitters
understanding g-ray emission is key

• Radio to UV -gt Synchrotron radiation of
• relativistic electrons
• MeV-GeV component-gt Inverse Compton
• scattering of low energy photons

• Possible photons targets
• 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

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Active Galactic Nuclei Theories with hadronic
dominance

• 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 Egt1019 eV.
• Even when energetics is OK, GZK maybe there.

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Looking from the side Radiogalaxies

• 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

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Radiogalaxies as CR sources
Rachen, Biermann, et al.
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.
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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)
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Starbursts galaxies (or regions of galaxies)
undergoing large scale star formation

• 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 Fermis mechanism.
• 2nd step re-acceleration in the super-wind region

Romero et al. 1999, Anchordoqui et al. 2003
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Nearest neighbors
M82 NGC 253
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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
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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
gt1011 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,
ARAA, 1996
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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
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Not covered in this talk

• Magnetohydronamic acceleration of iron nuclei in
  pulsars magnetars
• Other large scale structure (shocks)
• Quasar Remnants
• Gamma-ray bursts (a session on them later this
  week)
• Single source models

Further analysis and about another 10 possible
candidates in
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Summary

• 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)
• Occams 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.

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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.
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Correlations with EGRET sources

• Gorbunov et al. claim correlation (2002) of
  UHECRs with EGRET blazars by doubling the size of
  egret detections.
• Exercise care large uncertainties with
  EGRETrandom 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.
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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
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Credits

• SSC or Self-Synchrotron Compton process e.g.
  Marscher Gear 1985, Maraschi et al. 1992, Bloom
  et al. 1996
• ECD or External Comptonization of Direct disk
  radiation process e.g. Dermer et al. 1992,
  Dermer Schlickeiser 1993
• 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
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In action
The low-frequency radio emission is expected to
be produced by less compact regions. Most FSRQs
are successfully modelled with dominant EC
models.
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In action
BL Lac Mrk421
Most BL Lacs are successfully modelled with pure
or dominant SSC models.
BL LACs -gt FSRQs
Ghisellini, Fossati, Celloti, et al.
Increasing importance of the external radiation
field
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Theories with hadronic dominance Collisions

• 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.

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Credits

• 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
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GZK
Attenuation length of ? s, ps and 56Fes in
various background radiations as a function of
energy. The 3 lowest and left-most 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 dasheddotted line
indicates the adiabatic fractional energy loss at
the present cosmological epoch. The dashed curve
illustrates the attenuation of iron nuclei.
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Detectability of LIRGs

• 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
• 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)
• Several nearby starburst galaxies and a number of
  LIRGs and ULIRGs are plausible candidates for
  detection

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Not covered in this talk

• Magnetohydronamic acceleration of iron nuclei in
  pulsars magnetars
• Gamma-ray bursts (a session on them later this
  week)
• Single source models