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

Diego F. TorresDiego F. Torres

dtorres@igpp.ucllnl.orgdtorres@igpp.ucllnl.org

Lawrence Livermore Lab.California, 94550, USA www.angelfire.com/id/dtorres

SummarySummary

Plausible sources? Plausible sources?

Comments on basic observational features of the CR Comments on basic observational features of the CR spectrum.spectrum.

Connection with gamma-ray sources?Connection with gamma-ray sources?

Some choicesSome choices– From the extragalactic menu:From the extragalactic menu:

AGNs & RadiogalaxiesAGNs & Radiogalaxies Starbursts, LIRGs, ULIRGsStarbursts, LIRGs, ULIRGs

– From the galactic menu: From the galactic menu: The Cygnus region, a TeV photon and UHECR source?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 = Ze B r2 /c

where is the pulsar angular velocity, B the surface magnetic field and r the neutron star radius. Typical potential drops are ~1018 V.

GZK or not?GZK or not?

(Previous talk)

Slanted showers indicate low presence of Slanted showers indicate low presence of photonsphotons

Very difficult to distinguish between p and Very difficult to distinguish between p and nucleinuclei

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.

Observational panorama: compositionObservational panorama: composition

Arrival directions & clusteringArrival directions & clustering

H.E.S.S.17 h datatight cutsno backgr.subtraction

TeV J2032+4131 at HEGRA: Final resultsTeV 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

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.

Galactic neutrons of 1018 eV?

Lower energy analysis: no evidence of anisotropy

1017.9—1018.3 eV: AGASA shows a 4 effect from the Galactic plane (Cygnus + Center). Other experiments seems to point in the same direction.

Apparently Galactic Excesses (especially Cygnus)…

The only cross-confirmedresult for CRs?

For the UHECRs: two-coordinates analysis show no effect for correlations in scales larger than 10 degrees, above 3. There might be anisotropies, but the signal is at too low a level to detect it.

The lonely neutrinos.

Clustering is essential for Clustering is essential for astrophysics 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.

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.

Unified models Unified models

of AGNsof AGNs

Active Galactic Nuclei: Basic Active Galactic Nuclei: Basic phenomenologyphenomenology

Radio to -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 Flares so fast argue against an isotropic origin of the high-energy isotropic origin of the high-energy radiationradiation

Optical depth to gamma-gammaOptical depth to gamma-gamma

For a photon energy of 1 MeV, and a luminosity of 10For a photon energy of 1 MeV, and a luminosity of 104848 erg erg ss-1-1, the optical depth is t > 200 / (t, the optical depth is t > 200 / (tvv/1 day)/1 day)

Elliot Shapiro relation for a spherical accretion: the source Elliot Shapiro relation for a spherical accretion: the source luminosity is limited by Eddington’s and the size of the luminosity is limited by Eddington’s and the size of the source has to be larger than the Schwarzschild radiussource has to be larger than the Schwarzschild radius

(Indication for beamed emission: Distance is not a problem)(Indication for beamed emission: Distance is not a problem)

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

If the emission is beamed -> special relativistic effectsIf the emission is beamed -> special relativistic effects

Active Galactic Nuclei as CR Active Galactic Nuclei as CR emitters: understanding emitters: understanding -ray -ray

emission is keyemission is key Radio to UV -> Synchrotron radiation of Radio to UV -> Synchrotron radiation of

relativistic electronsrelativistic electrons MeV-GeV component-> Inverse Compton MeV-GeV component-> Inverse Compton

scattering of low energy photonsscattering of low energy photons

Bottcher

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: Active Galactic Nuclei:

Theories with hadronic dominanceTheories with hadronic dominance

Observed Observed -ray emission is -ray emission is initiated by accelerated initiated by accelerated protons interacting with protons interacting with ambient gas or lower ambient gas or lower frequency radiation.frequency radiation.

In PIC models: photomeson In PIC models: photomeson developments of pair developments of pair cascades in the jet.cascades in the jet.

Efficiency increase with Efficiency increase with proton energy, usually proton energy, usually requiring E>10requiring E>101919 eV. eV.

Even when energetics is Even when energetics is OK, GZK maybe there.OK, GZK maybe there.

Buckley

Looking from the side: RadiogalaxiesLooking 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 sourcesRadiogalaxies 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

Rachen, Biermann, et al.

Balance between acceleration and losses.

FeaturesFeatures

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 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.

22ndnd step: re-acceleration in the super-wind region step: re-acceleration in the super-wind regionRomero et al. 1999, Anchordoqui et al. 2003

Nearest neighborsNearest neighbors

M82 NGC 253

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

NGC 253

M82

CR arrival direction

If Fe

If Ne

Anchordoqui, Reucroft, Torres, astro-ph/0209546

ASS + extragal.deflection

5 years, 25 events in PAO

Extreme starbursts also nearby: Merging of gas-rich galaxies, LIRGs and ULIRGs

[review on LIRGs and ULIRGs: Sanders and Mirabel, ARA&A, 1996]

Only one ULIRG within the 100 Mpc sphere [Arp 220]

Tens of LIRGs (with infrared luminosities >1011 LSUN).

High energy detectability (e.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

Some powerful local LIRGs: Some powerful local LIRGs: all likely all likely -ray sources, some UHECR -ray sources, some UHECR sourcessources

Arp 220: 72 Mpc, largestStar formation and SN explosion rates known in the universe.

Torres et al. astro-ph/0411429, 0407240, 0405302

Not covered in this talkNot covered in this talk

Magnetohydronamic acceleration of iron nuclei in pulsars; magnetarsagnetars

Other large scale structure (shocks)Other large scale structure (shocks)

Quasar RemnantsQuasar Remnants

Gamma-ray bursts (a session on them later this week)Gamma-ray bursts (a session on them later this week)

Single source modelsSingle source models

Further analysis and about another 10 possible candidates in:

SummarySummary

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 Gorbunov et al. claim correlation (2002) of UHECRs with EGRET blazars (2002) of UHECRs with EGRET blazars by doubling the size of egret by doubling the size of egret detections.detections.

Exercise care: large uncertainties Exercise care: large uncertainties with EGRET=random association with with EGRET=random association with blazars. 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 -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.

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

Extreme starbursts also nearby: Merging of gas-rich galaxies, LIRGs and ULIRGs

Barnes and Hernquist 1996

CreditsCredits

SSC or Self-Synchrotron Compton process: e.g. SSC or Self-Synchrotron Compton process: e.g. Marscher & Gear 1985, Maraschi et al. 1992, Bloom et al. Marscher & Gear 1985, Maraschi et al. 1992, Bloom et al. 19961996

ECD or External Comptonization of Direct disk ECD or External Comptonization of Direct disk radiation process: e.g. radiation process: e.g. Dermer et al. 1992, Dermer & Dermer et al. 1992, Dermer & Schlickeiser 1993Schlickeiser 1993

ECC or External Comptonization of radiation from ECC or External Comptonization of radiation from Clouds:Clouds: e.g. e.g. Sikora et al. 1994, Dermer et al. 1997, Sikora et al. 1994, Dermer et al. 1997, Blandford and Levinson 1995Blandford and Levinson 1995

RS or Reflected Synchrotron mechanism:RS or Reflected Synchrotron mechanism: e.g. e.g. Ghisellini Ghisellini & Madau 1996, Bottcher & Bednarek 1998, Bednarek 1998& Madau 1996, Bottcher & Bednarek 1998, Bednarek 1998

Not exhaustive

In actionIn action

The low-frequency radio emission is expected to be produced by less compact regions.

Most FSRQs are successfully modelled with dominant EC models.

FSRQ 3C 279 Viewing Period P5B: Jan-Feb. 1996Hartman et al. 1999

Acc. Disk

Sync.

SSC.

ECD

ECC

In actionIn action

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

BL Lac Mrk421

BL LACs -> FSRQs

Increasing importance of the external radiation field Ghisellini, Fossati, Celloti, et al.

Theories with hadronic dominance: Theories with hadronic dominance:

CollisionsCollisions

-rays from pp from the collision of jets with gas clouds-rays from pp from the collision of jets with gas clouds

Due to the enhanced density in the BLR clouds, pp interactions can Due to the enhanced density in the BLR clouds, pp interactions can dominate the pdominate the p process process [in the case of PIC models where photopion interactions dominates the [in the case of PIC models where photopion interactions dominates the initiation of the cascade] initiation of the cascade]

Another possible target for the jet could be the wind of an OB star Another possible target for the jet could be the wind of an OB star moving through the jet.moving through the jet.

Protons responsible only for the injection of electrons, which in turn Protons responsible only for the injection of electrons, which in turn produce the observed produce the observed ray emission by SSC mechanism (Kazanas & ray emission by SSC mechanism (Kazanas & Mastiachidis 1999). Large proton densities.Mastiachidis 1999). Large proton densities.

CreditsCredits

PIC or proton induced cascade model: e.g.,PIC or proton induced cascade model: e.g., Mannheim Mannheim & Biermann 1992, Mannheim 1993 & 1996& Biermann 1992, Mannheim 1993 & 1996

Sync. Radiation of protons and modelling of TeV Sync. Radiation of protons and modelling of TeV blazars: e.g.blazars: e.g. Aharonian 2000, Mucke & Protheroe 2000, Aharonian 2000, Mucke & Protheroe 2000, Protheroe & Mucke 2000Protheroe & Mucke 2000

Collisional models with gas: e.g. Collisional models with gas: e.g. Beall & Bednarek 1999, Beall & Bednarek 1999, Purmohammad & Samimi 2001Purmohammad & Samimi 2001

Collisional models with star winds: e.g. Collisional models with star winds: e.g. Bednarek & Bednarek & Protheroe 1997Protheroe 1997

Not exhaustive

GZKGZKAttenuation 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.

MW

CR Enhancement required for detectability/LAT

Detectability of LIRGsDetectability of LIRGs

Gamma-ray detectability is favored in Gamma-ray detectability is favored in starburst galaxies (Akyuz, Aharonian, starburst galaxies (Akyuz, Aharonian, Volk, Fichtel, etc)Volk, Fichtel, etc)– Large Large MM, with high average gas , with high average gas

density, and enhanced cosmic ray density, and enhanced cosmic ray densitydensity

Recent Recent HCN-lineHCN-line survey of Gao & survey of Gao & Solomon (2004) of IR and CO-bright Solomon (2004) of IR and CO-bright galaxies, and nearby spirals galaxies, and nearby spirals – Allows estimate of SFR (from HCN Allows estimate of SFR (from HCN

luminosity) and minimum required luminosity) and minimum required kk for detection by LAT and IACTs (from for detection by LAT and IACTs (from HCN + CO intensities and distance)HCN + CO intensities and distance)

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

Not covered in this talkNot covered in this talk

Magnetohydronamic acceleration of iron nuclei in pulsars; magnetarsagnetars

Gamma-ray bursts (a session on them later this week)Gamma-ray bursts (a session on them later this week)

Single source modelsSingle source models