(Some of the possible) Astrophysical origins of high energy cosmic rays Diego F. Torres Lawrence Livermore Lab. California, 94550, USA

Summary Plausible sources? Plausible sources? Comments on basic observational features of the CR spectrum. Comments on basic observational features of the CR spectrum. Connection with gamma-ray sources? Connection with gamma-ray sources? Some choices Some choices –From the extragalactic menu: AGNs & Radiogalaxies AGNs & Radiogalaxies Starbursts, LIRGs, ULIRGs Starbursts, LIRGs, ULIRGs –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: R g =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 -1 E 20 /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 r 2 /c where  is the pulsar angular velocity, B the surface magnetic field and r the neutron star radius. Typical potential drops are ~10 18 V.

GZK or not? (Previous talk)

Slanted showers indicate low presence of photons

Very difficult to distinguish between p and nuclei

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 and eV. Observational panorama: composition

Arrival directions & clustering

H.E.S.S. 17 h data tight cuts no backgr. subtraction

TeV J at HEGRA: Final results Aharonian et al. 2005, A&A, astro-ph/ Confirmation of an extended, steady, hard, source above 1 TeV. No counterpart yet found.

TeV J at HEGRA – Excess at AGASA? Anchordoqui et al. astro-ph/ 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 1/10 3 of the n energy 4 events/yr, above 90% CL. Galactic neutrons of eV?

Lower energy analysis: no evidence of anisotropy — 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-confirmed result 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 astrophysics AGASA finds 5 doublets and 1 triplet among the 58 events (paired at less than 2.5 o ) reported with mean energy above 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 × eV) and Yakutsk (E > 2.4 × 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 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  -ray energy distribution of 3C 279 in low and high state measured in January and February, 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 Optical depth to gamma-gamma Optical depth to gamma-gamma For a photon energy of 1 MeV, and a luminosity of erg s -1, the optical depth is t > 200 / (t v /1 day) For a photon energy of 1 MeV, and a luminosity of erg s -1, the optical depth is t > 200 / (t v /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 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  -ray emission is key Radio to UV -> Synchrotron radiation of Radio to UV -> Synchrotron radiation of relativistic electrons MeV-GeV component-> Inverse Compton MeV-GeV component-> Inverse Compton scattering 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: Theories with hadronic dominance Observed  -ray emission is initiated by accelerated protons interacting with ambient gas or lower frequency radiation. Observed  -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. In PIC models: photomeson developments of pair cascades in the jet. Efficiency increase with proton energy, usually requiring E>10 19 eV. Efficiency increase with proton energy, usually requiring E>10 19 eV. Even when energetics is OK, GZK maybe there. Even when energetics is OK, GZK maybe there. Buckley

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 the speed v h with which the head of a jet advances into the intergalactic medium of particle density n e 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.

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 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 (10 8 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. 1 st 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. 2 nd 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 NGC 253 M82 CR arrival direction If Fe If Ne Anchordoqui, Reucroft, Torres, astro-ph/ 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 >10 11 L SUN ). 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: all likely  -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/ , ,

Not covered in this talk agnetars Magnetohydronamic acceleration of iron nuclei in pulsars; magnetars Other large scale structure (shocks) Other large scale structure (shocks) Quasar Remnants Quasar Remnants Gamma-ray bursts (a session on them later this week) Gamma-ray bursts (a session on them later this week) Single source models Single source models Further analysis and about another 10 possible candidates in:

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) 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 = 2 1/2 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 Gorbunov et al. claim correlation (2002) of UHECRs with EGRET blazars by doubling the size of egret detections. 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. 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  -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

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

Credits SSC or Self-Synchrotron Compton process: e.g. Marscher & Gear 1985, Maraschi et al. 1992, Bloom et al SSC or Self-Synchrotron Compton process: e.g. Marscher & Gear 1985, Maraschi et al. 1992, Bloom et al ECD or External Comptonization of Direct disk radiation process: e.g. Dermer et al. 1992, Dermer & Schlickeiser 1993 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 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 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. Most FSRQs are successfully modelled with dominant EC models. FSRQ 3C 279 Viewing Period P5B: Jan-Feb Hartman et al Acc. Disk Sync. SSC. ECD ECC

In 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: Collisions  -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 dominate the p  process Due to the enhanced density in the BLR clouds, pp interactions can dominate the p  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. 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  ray emission by SSC mechanism (Kazanas & Mastiachidis 1999). Large proton densities. Protons responsible only for the injection of electrons, which in turn produce the observed  ray emission by SSC mechanism (Kazanas & Mastiachidis 1999). Large proton densities.

Credits PIC or proton induced cascade model: e.g., Mannheim & Biermann 1992, Mannheim 1993 & 1996 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 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 gas: e.g. Beall & Bednarek 1999, Purmohammad & Samimi 2001 Collisional models with star winds: e.g. Bednarek & Protheroe 1997 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 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 LIRGs Gamma-ray detectability is favored in starburst galaxies (Akyuz, Aharonian, Volk, Fichtel, etc) 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 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 Several nearby starburst galaxies and a number of LIRGs and ULIRGs are plausible candidates for detection

Not covered in this talk agnetars Magnetohydronamic acceleration of iron nuclei in pulsars; magnetars Gamma-ray bursts (a session on them later this week) Gamma-ray bursts (a session on them later this week) Single source models Single source models