Active Galactic Nuclei Sources Research Articles

X-ray occultations in active galactic nuclei: Physical properties of eclipsing clouds as part of the broad-line region cloud ensemble

Context. Short-term X-ray variability in active galactic nuclei (AGNs) can be explained as being due to varying X-ray absorption induced by the temporary occultation of the primary X-ray source, when moving absorbing clouds cross the line of sight to the X-ray source itself. Earlier work suggests that these absorbing clouds have physical properties similar to those of broad-line region (BLR) emitting clouds and are located in the same spatial region. Aims. We intend to extract physical information on each individual absorber associated with any given occultation event detected in our sample and to analyse general properties of the cloud ensemble whose components can produce X-ray eclipses. Methods. From the analysis of previously detected occultation events, two ‘observables’ characterising each single occultation event can be derived: the peak fractional hardness ratio variation (ΔHR/HR) and the duration of the event normalised by a characteristic eclipse timescale evaluated for each AGN source. To determine the eclipsing cloud properties, we devised a procedure a) based on simplifying assumptions on the geometry of both the X-ray source and the cloud-like gas condensations, and on the cloud X-ray absorbing properties in the energy range of interest (2–10 keV), and b) relying on a set of simulated instrumental responses from both XMM and Suzaku relevant instruments to different incoming X-ray spectra, absorbed with varying absorber column density and maximum covering factor during the occultation. Thus, we derived information on the individual cloud producing any given occultation event, determining the cloud radius normalised to that of the X-ray source, the spatial location of the cloud, and an estimate of the cloud gas number density for reasonable values of the equivalent absorber column density. Results. The physical properties of eclipsing clouds that we obtained are consistent with those of BLR clouds. We can exclude the dominance, in the ensemble cloud size distribution, of clouds larger than about 10–12 times the Schwarzschild radius characterising each AGN, and we do not find any significant dependence of the cloud physical size on the distance from the central black hole, in agreement with the results of our previous work. As for the number density of these gas condensations, with our procedure we obtained values within a range of ∼109 − 1011 cm−3, which is consistent with the estimates derived from broad emission line analysis.

Deciphering the imprint of active galactic nucleus feedback in Seyfert galaxies. Nuclear-scale molecular gas deficits

We study the distribution of cold molecular gas in the circumunuclear disks (CND; $r pc) of a sample of 64 nearby L $=7-45 Mpc) disk galaxies ---including 45 active galactic nuclei (AGN) and 19 nonAGN--- for which high-spatial-resolution (median value $ pc) multiline CO interferometer observations have been obtained at millimeter wavelengths with the Atacama Large Millimeter Array (ALMA) and/or Plateau de Bure Interferometer (PdBI). We decipher whether or not the concentration and normalized radial distribution of cold molecular gas change as a function of X-ray luminosity in the 2--10 keV range X $) in order to analyze the imprint left by AGN feedback. We also look for similar trends in the concentration and normalized radial distribution of the hot molecular gas and in the hot-to-cold-molecular gas mass ratio in a subset of 35 galaxies using near-infrared (NIR) integral field spectroscopy data obtained for the H$_2$ 1-0 S(1) line. We find a significant turnover in the distribution of the cold molecular gas concentration as a function of X-ray luminosity with a breakpoint that divides the sample into two branches: (1) the `AGN build-up branch'' ($L_ X pm0.3 $erg s$^ $) and (2) the ``AGN feedback branch'' ($L_ X pm0.3 $erg s$^ $) . Lower-luminosity AGN and nonAGN of the AGN build-up branch show high cold molecular gas concentrations and centrally peaked radial profiles on nuclear ($r pc) scales. Higher-luminosity AGN of the AGN feedback branch show a sharp decrease in the concentration of molecular gas and flat or inverted radial profiles. The cold molecular gas concentration index ($CCI$) --- defined as the ratio of surface densities at $r pc ($ gas $) and $r pc $( gas $), namely $CCI gas gas $)--- spans a 0.63 dex range, equivalent to a factor simeq 4-5, between the galaxies lying at the high end of the AGN build-up branch and the galaxies showing the most extreme nuclear-scale molecular gas deficits in the AGN feedback branch. The concentration and radial distributions of the hot molecular gas in our sample follow qualitatively similar but less extreme trends as a function of X-ray luminosity. As a result, we find higher values of hot-to-cold molecular gas mass ratios on nuclear scales in the highest luminosity AGN sources of the AGN feedback branch. These observations confirm ---with a three times larger sample--- previous evidence found in the context of the Galaxy Activity Torus and Outflow Survey (GATOS) that the imprint of AGN feedback on the CND-scale distribution of molecular gas is more extreme in higher luminosity Seyfert galaxies of the local Universe.

A Self-consistent Treatment of the Line-driving Radiation Force for Active Galactic Nuclei Outflows: New Prescriptions for Simulations

Flows driven by photons have been studied for almost a century, and a quantitative description of the radiative forces on atoms and ions is important for understanding a wide variety of systems with outflows and accretion disks, such as active galactic nuclei (AGN). Quantifying the associated forces is crucial to determining how these outflows enable interactive mechanisms within these environments, such as AGN feedback. The total number of spectral lines in any given ion of the outflow material must be tabulated in order to give a complete characterization of this force. Here, we provide calculations of the dimensionless line force multiplier for AGN environments. For a wide array of representative AGN sources, we explicitly calculate the photoionization balance at the proposed wind-launching region above the accretion disk, compute the strength of the line-driving force on the gas, and revisit and formalize the role of the commonly used ionization parameter ξ in ultimately determining the line-driving force. We perform these computations and analyses for a variety of AGN central source properties, such as black hole mass, initial wind velocity, and number density. We find that, while useful, the ionization parameter provides an incomplete description of the overall ionization state of the outflow material. We use these findings to provide an updated method for calculating the strength of the radiative line-driving using both the X-ray spectral index Γ X and the ionization parameter.

The XXL survey

We model the evolution of active galactic nuclei (AGN) by constructing their radio LFs. We used a set of surveys of varying area and depth, namely, the deep COSMOS survey of 1916 AGN sources; the wide, shallow 3CRR, 7C, and 6CE surveys, together containing 356 AGN; and the intermediate XXL-North and South fields consisting of 899 and 1484 sources, respectively. We also used the CENSORS, BRL, Wall & Peacock, and Config surveys, respectively consisting of 150, 178, 233, and 230 sources. Together, these surveys account for 5446 AGN sources and constrained the LFs at high redshift and over a wide range of luminosities (up to z ≈ 3 and log(L/W Hz−1)∈[22, 29]). We concentrated on parametric methods within the Bayesian framework, which allowed us to perform model selection between a set of different models. By comparing the marginalised likelihoods and both the Akaike information criterion and the Bayesian information criterion, we show that the luminosity-dependent density evolution (LDDE) model fits the data best, with evidence ratios varying from “strong” (> 10) to “decisive” (> 100), according to the Jeffreys’ interpretation. The best-fitting model gives insight into the physical picture of AGN evolution, where AGN evolve differently as a function of their radio luminosity. We determined the number density, luminosity density, and kinetic luminosity density as a function of redshift, and we observed a flattening of these functions at higher redshifts, which is not present in simpler models. We explain these trends by our use of the LDDE model. Finally, we divided our sample into subsets according to the stellar mass of the host galaxies in order to investigate a possible bimodality in evolution. We found a difference in LF shape and evolution between these subsets. All together, these findings point to a physical picture where the evolution and density of AGN cannot be explained well by simple models but require more complex models either via AGN sub-populations, where the total AGN sample is divided into sub-samples according to various properties, such as optical properties and stellar mass, or via luminosity-dependent functions.

Benchmarks and explanations for deep learning estimates of X-ray galaxy cluster masses

ABSTRACTWe evaluate the effectiveness of deep learning (DL) models for reconstructing the masses of galaxy clusters using X-ray photometry data from next-generation surveys. We establish these constraints using a catalogue of realistic mock eROSITA X-ray observations which use hydrodynamical simulations to model realistic cluster morphology, background emission, telescope response, and active galactic nucleus (AGN) sources. Using bolometric X-ray photon maps as input, DL models achieve a predictive mass scatter of $\sigma _{\ln M_\mathrm{500c}} = 17.8~{{\ \rm per\ cent}}$, a factor of two improvements on scalar observables such as richness Ngal, 1D velocity dispersion σv,1D, and photon count Nphot as well as a 32 per cent improvement upon idealized, volume-integrated measurements of the bolometric X-ray luminosity LX. We then show that extending this model to handle multichannel X-ray photon maps, separated in low, medium, and high energy bands, further reduces the mass scatter to 16.2 per cent. We also tested a multimodal DL model incorporating both dynamical and X-ray cluster probes and achieved marginal gains at a mass scatter of 15.9 per cent. Finally, we conduct a quantitative interpretability study of our DL models and find that they greatly down-weight the importance of pixels in the centres of clusters and at the location of AGN sources, validating previous claims of DL modelling improvements and suggesting practical and theoretical benefits for using DL in X-ray mass inference.

AGNs in the CALIFA survey: X-ray detection of nuclear sources

ABSTRACT A complete demographic of active galactic nuclei (AGNs) is essential to understand the evolution of the Universe. Optical surveys estimate the population of AGNs in the local Universe to be of ∼ 4 per cent. However, these results could be biased towards bright sources, not affected by the host galaxy attenuation. An alternative method for detecting these objects is through the X-ray emission. In this work, we aim to complement the AGN population of the optical CALIFA survey (941 sources), by using X-ray data from Chandra, which provides the best spatial resolution to date, essential to isolate the nuclear emission from the host galaxy. We study a total of 138 sources with available data. We find 34 new bona fide AGNs and 23 AGN candidates, which could increase the AGN population to 7–10 per cent among the CALIFA survey. X-rays are particularly useful for low-luminosity AGNs since they are excluded by the criterion of large equivalent width of the $\rm {H\alpha }$ emission line when applied to optical selections. Indeed, placing such a restrictive criteria might cause a loss of up to 70 per cent of AGN sources. X-ray detected sources are preferentially located in the right side of the [${\mathrm{O}}\, {\small {\rm III}}$ ]/Hβ versus [${\mathrm{N}}\, {\small {\rm II}}$ ]/Hα diagram, suggesting that this diagram might be the most reliable at classifying AGN sources. Our results support the idea that multiwavelength studies are the best way to obtain a complete AGN population.

Multiply charged naphthalene and its C10H8 isomers: bonding, spectroscopy, and implications in AGN environments

ABSTRACT Naphthalene (C10H8) is the simplest polycyclic aromatic hydrocarbon (PAH) and an important component in a series of astrochemical reactions involving hydrocarbons. Its molecular charge state affects the stability of its isomeric structures, which is specially relevant in ionized astrophysical environments. We thus perform an extensive computational search for low-energy molecular structures of neutral, singly, and multiply charged naphthalene and its isomers with charge states +q = 0–4 and investigate their geometric properties and bonding situations. We find that isomerization reactions should be frequent for higher charged states and that open chains dominate their low-energy structures. We compute both the scaled-harmonic and anharmonic infrared (IR) spectra of selected low-energy species and provide the calculated scaling factors for the naphthalene neutral, cation, and dication global minima. All simulated spectra reproduce satisfactorily the experimental data and, thus, are adequate for aiding observations. Moreover, the potential presence of these species in the emission spectra of the circumnuclear regions of active galactic nuclei (AGNs), with high energetic X-ray photon fluxes, is explored using the experimental value of the naphthalene photodissociation cross-section, σph − d, to determine its half-life, t1/2, at a photon energy of 2.5 keV in a set of relevant sources. Finally, we show that the computed IR bands of the triply and quadruply charged species are able to reproduce some features of the selected AGN sources.

Radio continuum properties of OH megamaser galaxies

ABSTRACT We present a study of the radio continuum properties of two luminous/ultraluminous infrared galaxy samples: the OH megamaser (OHM) sample (74 objects) and the control sample (128 objects) without detected maser emission. We carried out pilot observations for 140 objects with the radio telescope RATAN-600 at 1.2, 2.3, 4.7, 8.2, 11.2, and 22.3 GHz in 2019–2021. The OHM sample has two times more flat-spectrum sources (32 per cent) than the control sample. Steep radio spectra prevail in both samples. The median spectral index at 4.7 GHz α4.7 = −0.59 for the OHM sample, and α4.7 = −0.71 for the non-OHM galaxies. We confirm a tight correlation of the far-infrared (FIR) and radio luminosities for the OHM sample. We found correlations between isotropic OH line luminosity LOH and the spectral index α4.7 (ρ = 0.26, p-val. = 0.04) and between LOH and radio luminosity P1.4 (ρ = 0.35, p-val. = 0.005). Reviewing subsamples of masers powered by active galactic nuclei (AGNs) and star formation revealed insignificant differences for their FIR and radio properties. None the less, AGN-powered galaxies exhibit larger scatter in a range of parameters and their standard deviations. The similarities in the radio and FIR properties in the two samples are presumably caused by the presence of a significant amount of AGN sources in both samples (47 and 30 per cent in the OHM and control samples) and/or possibly by the presence of undetected OH emission sources in the control sample.

A New Sample of Gamma-Ray Emitting Jetted Active Galactic Nuclei—Preliminary Results

We are compiling a new list of gamma-ray jetted active galactic nuclei (AGN), starting from the fourth catalog of point sources of the Fermi Large Area Telescope (LAT). Our aim is to prepare a list of jetted AGN with known redshifts and classifications to be used to calibrate jet power. We searched in the available literature for all the published optical spectra and multiwavelength studies useful to characterize the sources. We found new, missed, or even forgotten information leading to a substantial change in the redshift values and classification of many sources. We present here the preliminary results of this analysis and some statistics based on the gamma-ray sources with right ascension within the interval 0h--12h (J2000). Although flat-spectrum radio quasars and BL Lac objects are still the dominant populations, there is a significant increase in the number of other objects, such as misaligned AGN, narrow-line Seyfert 1 galaxies, and Seyfert galaxies. We also introduced two new classes of objects: changing-look AGN and ambiguous sources. About one third of the sources remain unclassified.

Galaxy Mergers up to z < 2.5. II. AGN Incidence in Merging Galaxies at Separations of 3–15 kpc

Abstract We present a study of the incidence of active galactic nucleus (AGN) in a sample of major merging systems at 0.3 < z < 2.5. Galaxies in this merger sample have projected separations between 3 and 15 kpc and are selected from the CANDELS/3D-Hubble Space Telescope catalogs using a peak-finding algorithm. AGNs in mergers and non-mergers are identified on the basis of their X-ray emission, optical lines, mid-infrared colors, and radio emission. Among galaxies with adequate measurements to find potential AGNs, we find a similar fraction of AGNs in mergers (16.4 %) compared to the fraction found in non-merging galaxies (15.4% ± 0.6%). In mergers, this fraction is obtained by assuming that, in unresolved observations, only one of the merging galaxies is the AGN source (16 merging systems have at least one AGN galaxy). The similarity between the fractions is possibly due to the higher availability of cold gas at high redshifts, where the excess of nuclear activity as a result of merging is less important than at lower redshifts. Star-forming galaxies have a higher incidence of AGNs than quiescent galaxies. In particular, starbursts in mergers are the most common sites of AGN activity, since they present higher AGN fractions and black hole accretion rates. We find no clear correlation between the black hole accretion rate and the galaxy properties (i.e., star formation rate, stellar mass) in mergers and non-mergers. However, mergers seem to have a higher correlation with star formation than non-mergers, which possibly indicates that the merging process is starting to influence the star formation and AGN activity even at this pre-coalescence stage.

The origin of the power–law form of the extragalactic gamma–ray flux

The Fermi–LAT telescope has measured the extragalactic gamma–ray background (EGB) generated by the ensemble of all extragalactic sources. The energy distribution of the EGB is well described as a power–law with a spectral index approximately equal to 2.3, and an exponential cutoff, that is consistent with being the effect of absorption of high energy photons assuming an emission that is an unbroken power–law spectrum. The observations of the Fermi telescope have also resolved the EGB, determining that most of it is formed by the sum of the contributions of Active Galactic Nuclei (AGN) of the blazar class. The spectra of the individual AGN sources have a broad range of spectral shapes, and the brightest and most precisely measured sources have curved spectra that can be fitted with the “log–parabola” (or log–normal) form. This suggests that the power law form of the extragalactic gamma–ray flux emerges as a property of the ensemble of all sources, and not as a universal shape generated by each individual source. This result is consistent with the idea that particle acceleration in blazars can be considered as a “critical phenomenon”. A curved log–parabola (log–normal) form is also required to fit the spectra of many Galactic gamma–ray sources, including the emission from the brightest supernova remnants (SNR), and an intriguing possibility is that also the Galactic cosmic rays are injected in interstellar space by their sources not with a single universal power–law spectrum, as predicted by the commonly accepted models, but instead with a broad range of spectral shapes.

ConvoSource: Radio-Astronomical Source-Finding with Convolutional Neural Networks

Finding and classifying astronomical sources is key in the scientific exploitation of radio surveys. Source-finding usually involves identifying the parts of an image belonging to an astronomical source, against some estimated background. This can be problematic in the radio regime, owing to the presence of correlated noise, which can interfere with the signal from the source. In the current work, we present ConvoSource, a novel method based on a deep learning technique, to identify the positions of radio sources, and compare the results to a Gaussian-fitting method. Since the deep learning approach allows the generation of more training images, it should perform well in the source-finding task. We test the source-finding methods on artificial data created for the data challenge of the Square Kilometer Array (SKA). We investigate sources that are divided into three classes: star forming galaxies (SFGs) and two classes of active galactic nuclei (AGN). The artificial data are given at two different frequencies (560 MHz and 1400 MHz), three total integration times (8 h, 100 h, 1000 h), and three signal-to-noise ratios (SNRs) of 1, 2, and 5. At lower SNRs, ConvoSource tends to outperform a Gaussian-fitting approach in the recovery of SFGs and all sources, although at the lowest SNR of one, the better performance is likely due to chance matches. The Gaussian-fitting method performs better in the recovery of the AGN-type sources at lower SNRs. At a higher SNR, ConvoSource performs better on average in the recovery of AGN sources, whereas the Gaussian-fitting method performs better in the recovery of SFGs and all sources. ConvoSource usually performs better at shorter total integration times and detects more true positives and misses fewer sources compared to the Gaussian-fitting method; however, it detects more false positives.

Destruction and multiple ionization of PAHs by X-rays in circumnuclear regions of AGNs

ABSTRACT The infrared signatures of polycyclic aromatic hydrocarbons (PAHs) are observed in a variety of astrophysical objects, including the circumnuclear medium of active galactic nuclei (AGNs). These are sources of highly energetic photons (0.2–10 keV), exposing the PAHs to a harsh environment. In this work, we examined experimentally the photoionization and photostability of naphthalene (C10H8), anthracene (C14H10), 2-methyl-anthracene (C14H9CH3), and pyrene (C16H10) upon interaction with photons of 275, 310, and 2500 eV. The measurements were performed at the Brazilian Synchrotron Light Laboratory using time-of-flight mass-spectrometry. We determined the absolute photoionization and photodissociation cross-sections as a function of the incident photon energy; the production rates of singly, doubly, and triply charged ions; and the molecular half-lives in regions surrounding AGNs. Even considering moderate X-ray optical depth values (τ = 4.45) due to attenuation by the dusty torus, the half-lives are not long enough to account for PAH detection. Our results suggest that a more sophisticated interplay between PAHs and dust grains should be present in order to circumvent molecular destruction. We could not see any significant difference in the half-life values by increasing the size of the PAH carbon backbone, NC, from 10 to 16. However, we show that the multiple photoionization rates are significantly greater than the single ones, irrespective of the AGN source. We suggest that an enrichment of multiply charged ions caused by X-rays can occur in AGNs.

Constraints on Lorentz invariance and CPT violation using optical photometry and polarimetry of active galaxies BL Lacertae and S5 B0716+714

Various quantum gravity approaches that extend beyond the standard model predict Lorentz Invariance and Charge-Parity-Time Violation at energies approaching the Planck scale. These models frequently predict a wavelength dependent speed of light, which would result in time delays between promptly emitted photons at different energies, as well as a wavelength-dependent rotation of the plane of linear polarization for photons resulting from vacuum birefringence. Here, we describe a pilot program with an automated system of small telescopes that can simultaneously conduct high cadence optical photometry and polarimetry of Active Galactic Nuclei (AGN) in multiple passbands. We use these observations as a proof-of-principle to demonstrate how such data can be used to test various Lorentz Violation models, including special cases of the Standard Model Extension (SME). In our initial campaign with this system, the Array Photo Polarimeter, we observed two AGN sources, including BL Lacertae at redshift z = 0.069, and S5 B0716+714 at z = 0.31. We demonstrate that optical polarimetry with a broadband Luminance filter combined with simultaneous $I_c$-band observations yields SME parameter constraints that are up to ~10 and ~30 times more sensitive than with a standard $I_c$-band filter, for SME models with mass dimension d = 5 and d = 6, respectively. Using only a small system of telescopes with an effective 0.45-m aperture, we further demonstrate d = 5 constraints for individual lines of sight that are within a factor of ~1-10 in sensitivity to comparable constraints from optical polarimetry with a 3.6-m telescope. Such an approach could significantly improve existing SME constraints via a polarimetric all-sky survey of AGN with multiple 1-meter class telescopes.

Observing—and Imaging—Active Galactic Nuclei with the Event Horizon Telescope

Originally developed to image the shadow region of the central black hole in Sagittarius A* and in the nearby galaxy M87, the Event Horizon Telescope (EHT) provides deep, very high angular resolution data on other active galactic nucleus (AGN) sources too. The challenges of working with EHT data have spurred the development of new image reconstruction algorithms. This work briefly reviews the status of the EHT and its utility for observing AGN sources, with emphasis on novel imaging techniques that offer the promise of better reconstructions at 1.3 mm and other wavelengths.

Outflows driven by quasars in high-redshift galaxies with radiation hydrodynamics

The quasar mode of Active Galactic Nuclei (AGN) in the high-redshift Universe is routinely observed in gas-rich galaxies together with large-scale AGN-driven winds. It is crucial to understand how photons emitted by the central AGN source couple to the ambient interstellar-medium to trigger large-scale outflows. By means of radiation-hydrodynamical simulations of idealised galactic discs, we study the coupling of photons with the multiphase galactic gas, and how it varies with gas cloud sizes, and the radiation bands included in the simulations, which are ultraviolet (UV), optical, and infrared (IR). We show how a quasar with a luminosity of $10^{46}$ erg/s can drive large-scale winds with velocities of $10^2-10^3$ km/s and mass outflow rates around $10^3$ M$_\odot$/yr for times of order a few million years. Infrared radiation is necessary to efficiently transfer momentum to the gas via multi-scattering on dust in dense clouds. However, IR multi-scattering, despite being extremely important at early times, quickly declines as the central gas cloud expands and breaks up, allowing the radiation to escape through low gas density channels. The typical number of multi-scattering events for an IR photon is only about a quarter of the mean optical depth from the center of the cloud. Our models account for the observed outflow rates of $\sim$500-1000 M$_\odot$/yr and high velocities of $\sim 10^3$ km/s, favouring winds that are energy-driven via extremely fast nuclear outflows, interpreted here as being IR-radiatively-driven winds.

Luminosity of ultrahigh energy cosmic rays and bounds on magnetic luminosity of radio-loud active galactic nuclei

We investigate the production of magnetic flux from rotating black holes in active galactic nuclei (AGNs) and compare it with the upper limit of ultrahigh energy cosmic ray (UHECR) luminosities, calculated from observed integral flux of GeV-TeV gamma rays for nine UHECR AGN sources. We find that, for the expected range of black hole rotations (0.44<a<0.80), the corresponding bounds of theoretical magnetic luminosities from AGNs coincides with the calculated UHECR luminosity. We argue that such result possibly can contribute to constrain AGN magnetic and dynamic properties as phenomenological tools to explain the requisite conditions to proper accelerate the highest energy cosmic rays.

High-energy neutrino fluxes from AGN populations inferred from X-ray surveys

High-energy neutrinos and photons are complementary messengers, probing violent astrophysical processes and structural evolution of the Universe. X-ray and neutrino observations jointly constrain conditions in active galactic nuclei (AGN) jets: their baryonic and leptonic contents, and particle production efficiency. Testing two standard neutrino production models for local source Cen A (Koers & Tinyakov and Becker & Biermann), we calculate the high-energy neutrino spectra of single AGN sources and derive the flux of high-energy neutrinos expected for the current epoch. Assuming that accretion determines both X-rays and particle creation, our parametric scaling relations predict neutrino yield in various AGN classes. We derive redshift-dependent number densities of each class, from Chandra and Swift/BAT X-ray luminosity functions (Silverman et al. and Ajello et al.). We integrate the neutrino spectrum expected from the cumulative history of AGN (correcting for cosmological and source effects, e.g. jet orientation and beaming). Both emission scenarios yield neutrino fluxes well above limits set by IceCube(by ∼4–10 6 × at 1 PeV, depending on the assumed jet models for neutrino production). This implies that: (i) Cen A might not be a typical neutrino source as commonly assumed; (ii) both neutrino production models overestimate the efficiency; (iii) neutrino luminosity scales with accretion power differently among AGN classes and hence does not follow X-ray luminosity universally; (iv) some AGN are neutrino-quiet (e.g. below a power threshold for neutrino production); (v) neutrino and X-ray emission have different duty cycles (e.g. jets alternate between baryonic and leptonic flows); or (vi) some combination of the above.

The Cosmic Ray’s Chaotic Motion in the Galaxy

The time series data of ASS (air shower size) obtained by Nishimura-Kamata-Greisen formula are analyzed by the correlation dimension analysis to pick up the chaotic time series events. The arrival directions of the events in the chaotic time series are confirmed to have the anisotropy around 5, 15 and 20 h of R.A. (right ascension). In these directions, there are SNR (supernova remnants), AGN (active galactic nuclei) or TeV (tera electron volts) gamma ray sources. However, they are not expected to be the candidate of the chaotic cosmic rays which have the primary energy between 10 13 eV and 10 16 eV, because the proton cosmic rays should migrate with Larmor rotation at radius 0.3 pc (parsec) and the TeV gamma rays seem not to be emitted so often. Recently, Machida et al. reported the numerical results indicated that the magnetic fields were amplified on the azimuthal direction by the magneto rotational instability. The 20 h R.A is the azimuthal direction, while 5 and 15 h R.A. are around the direction perpendicular to the azimuthal direction. This amplified magnetic field could be the origin of the chaotic cosmic rays. The possible correlation between cosmic ray protons and the dark-matter is guessed also.

Active Galactic Nuclei: Jets as the Source of Hadrons and Neutrinos

Active galactic nuclei are extragalactic sources, and their relativistic hot-plasma jets are believed to be the main candidates of the cosmic-ray origin, above the so-called knee region of the cosmic-ray spectrum. Relativistic shocks, either single or multiple, have been observed or been theorized to be forming within relativistic jet channels in almost all active galactic nuclei sources. The acceleration of non-thermal particles (e.g. electrons, protons) via the shock Fermi acceleration mechanism, is believed to be mainly responsible for the power-law energy distribution of the observed cosmic-rays, which in very high energies can consequently radiate high energy gamma-rays and neutrinos, through related radiation channels. Here, we will focus on the primary particle (hadronic) shock acceleration mechanism, and we will present a comparative simulation study of the properties of single and multiple relativistic shocks, which occur in AGN jets. We will show that the role of relativistic (quasi-parallel either quasi-perpendicular) shocks, is quite important since it can dramatically alter the primary CR spectral indices and acceleration eciencies. These properties being carried onto gamma-ray and neutrino radiation characteristics, makes the combination of them a quite appealing theme for relativistic plasma and shock acceleration physics, as well as observational cosmic-ray, gamma-ray and neutrino astronomy.