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Lawrence Livermore Lab. California, 94550, USA. (Some of the possible) Astrophysical origins of high energy cosmic rays. Diego F. Torres Summary. Plausible sources? Comments on basic observational features of the CR spectrum.

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some of the possible astrophysical origins of high energy cosmic rays

Lawrence Livermore Lab.

California, 94550, USA

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

Diego F. Torres

  • 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?

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.


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.



17 h data

tight cuts

no backgr.


tev j2032 4131 at hegra final results
TeV J2032+4131 at HEGRA: Final results

Aharonian et al. 2005, A&A, astro-ph/0501667

Confirmation of an extended, steady, hard, source above 1 TeV.

No counterpart yet found.

tev j2032 4131 at hegra excess at agasa
TeV J2032+4131 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.


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: 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.

clustering is essential for astrophysics
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 > 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.


  • 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.
active galactic nuclei basic phenomenology
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.

flares so fast argue against an isotropic origin of the high energy radiation
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 > 200 / (tv/1 day)

  • 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
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


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

  • 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
active galactic nuclei theories with hadronic dominance


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 E>1019 eV.
  • Even when energetics is OK, GZK maybe there.
looking from the side radiogalaxies
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
radiogalaxies as cr sources

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.


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
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 Fermi’s mechanism.

2nd step: re-acceleration in the super-wind region

Romero et al. 1999, Anchordoqui et al. 2003

testing the starburst possibility number of events close to the sources
Testing the starburst possibility: number of events close to the sources

ASS + extragal.



If Fe

CR arrival


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
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
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
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:

  • 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
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 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 ulirgs35
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

  • 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

in action

FSRQ 3C 279

Viewing Period P5B: Jan-Feb. 1996

Hartman et al. 1999




Acc. Disk


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.

in action38
In action

BL Lac Mrk421

Most BL Lacs are successfully modelled with pure or dominant SSC models.


Ghisellini, Fossati, Celloti, et al.

Increasing importance of the external radiation field

theories with hadronic dominance collisions
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.
  • 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


Attenuation length of γ ’s, p’s and 56Fe’s 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 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
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


CR Enhancement required for detectability/LAT

Detectability of LIRGs
not covered in this talk43
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