Recent studies on the high-energy photons from gamma-ray bursts~(GRBs) suggested a light speed variation $v(E)=c(1-E/E_{\mathrm{LV}})$ with $E_\mathrm{LV}=3.6\times 10^{17}$ GeV. We check this speed variation from previous observations on light curves of three active galactic nuclei (AGNs), namely Markarian 421 (Mrk 421), Markarian 501 (Mrk 501) and PKS 2155-304. We show that several phenomena related to the light curves of these AGNs can serve as the supports for the light speed variation determined from GRBs.
The underlying hypothesis of this work is that the active galactic nuclei (AGNs) are wormhole mouths rather than supermassive black holes (SMBHs). Under some - quite general - assumptions such wormholes may emit gamma radiation as a result of a collision of accreting flows inside the wormholes. This radiation has a distinctive spectrum much different from those of jets or accretion disks of AGNs. An observation of such radiation would serve as evidence of the existence of wormholes.
Galactic nuclei harbouring a central supermassive black hole (SMBH), possibly surrounded by a dense nuclear cluster (NC), represent extreme environments which house a complex interplay of many physical processes that uniquely affect stellar formation, evolution, and dynamics. The discovery of gravitational waves (GW) emitted by merging black holes (BHs) and neutron stars (NSs), funnelled a huge amount of work focused on understanding how compact object binaries (COBs) can pair-up and merge together. Here, we review from a theoretical standpoint how different mechanisms concur to the formation,…
The Second Catalog of Blazars and other Active Galactic Nuclei detected by the Fermi/LAT (2LAC) includes about 1100 sources, 886 of which comprise the Clean Sample. The general properties of the different populations of sources classified according to the strength of their emission lines (FSRQs, BL Lacs) or the estimated position of the synchrotron peak are reviewed.
Deceleration of relativistic jets from active galactic nuclei (AGNs) detected recently by MOJAVE team is discussed in connection with the interaction of the jet material with the external photon field. Appropriate energy density of the isotropic photon field which is necessary to decelerate jets is determined. It is shown that the disturbances of the electric potential and magnetic surfaces play important role in general dynamics of particle deceleration.
Observations are consistent with a significant fraction of heavy nuclei in the cosmic ray flux above a few times 10^19 eV. Such nuclei can be deflected considerably in the Galactic magnetic field, with important implications for the search of their sources. We perform detailed simulations of heavy nuclei propagation within recent Galactic magnetic field models. While such models are not yet sufficiently constrained to predict deflection maps in detail, we find general features of the distribution of (de-) magnified flux from sources. Since in most theoretical models sources of heavy nuclei are…
We explore possible physical origin of correlation between radio wave and very-high-energy neutrino emission in active galactic nuclei (AGN), suggested by recently reported evidence for correlation between neutrino arrival directions and positions of brightest radio-loud AGN. We show that such correlation is expected if both synchrotron emitting electrons and neutrinos originate from decays of charged pions produced in proton-proton interactions in parsec-scale relativistic jet propagating through circum-nuclear medium of the AGN.
In this work we study how the turbulent component of the Galactic magnetic field (GMF) affects the propagation of ultrahigh energy heavy nuclei. We investigate first how the images of individual sources and of the supergalactic plane depend on the properties of the turbulent GMF. Then we present a quantitative study of the impact of the turbulent field on (de-) magnification of source fluxes, due to magnetic lensing effects. We also show that it is impossible to explain the Pierre Auger data assuming that all ultrahigh energy nuclei are coming from Cen A, even in the most favorable case of a s…
Observations of many dim galactic nuclei in local universe give good estimation of gas density and temperature at Bondi radius. If we assume the black hole accretes at Bondi accretion rate and radiates at efficiency of low-luminosity hot accretion flow, the predicted nuclei luminosity can be significantly higher than observations. Therefore, the real black hole mass accretion rate in these sources may be significantly smaller than the Bondi value. Active galactic nuclei (AGN) feedback may be responsible for decreasing black hole accretion rate to values much smaller than Bondi rate. We perform…
Ultra high energy cosmic ray events presently show a spectrum, which we interpret here as galactic cosmic rays due to a starburst in the radio galaxy Cen A pushed up in energy by the shock of a relativistic jet. The knee feature and the particles with energy immediately higher in galactic cosmic rays then turn into the bulk of ultra high energy cosmic rays. This entails that all ultra high energy cosmic rays are heavy nuclei. This picture is viable if the majority of the observed ultra high energy events come from the radio galaxy Cen A, and are scattered by intergalactic magnetic fields acros…
The Laser Interferometer Gravitational-Wave Observatory, LIGO, found direct evidence for double black hole binaries emitting gravitational waves. Galactic nuclei are expected to harbor the densest population of stellar-mass black holes. A significant fraction ($\sim30\%$) of these black holes can reside in binaries. We examine the fate of the black hole binaries in active galactic nuclei, which get trapped in the inner region of the accretion disk around the central supermassive black hole. We show that binary black holes can migrate into and then rapidly merge within the disk well within a Sa…
In this chapter I will review the status of our phenomenological understanding of the relation between accretion and outflows in accreting black hole systems. This understanding arises primarily from observing the relation between X-ray and longer wavelength (infrared, radio) emission. The view is necessarily a biased one, beginning with observations of X-ray binary systems, and attempting to see if they match with the general observational properties of active galactic nuclei.
The supermassive black holes harboured in active galactic nuclei are at the origin of powerful jets which can emit copious amounts of gamma-rays. The exact interplay between the infalling matter, the black hole and the relativistic outflow is still poorly known, and this parallel session of the 12th Marcel Grossman meeting intended to offer the most up to date status of observational results with the latest generation of ground and space-based instruments, as well as the theoretical developments relevant for the field.
Pierre Auger collaboration have recently put forward the hypothesis that the arrival directions of the highest energy cosmic rays correlate with the subset of local active galactic nuclei (AGN). We perform a blind test of AGN hypothesis using publicly available event sets collected by Yakutsk, AGASA and HiRes experiments. The consistency of the procedure requires the event energies to be normalized towards the common energy scale. The number of correlating events in resulting data-set is 3 of 21 which is consistent with expected random background.
This is a White Paper in support of the mission concept of the Large Observatory for X-ray Timing (LOFT), proposed as a medium-sized ESA mission. We discuss the potential of LOFT for the study of radio-loud Active Galactic Nuclei. For a summary, we refer to the paper.
Jets powered by active galactic nuclei appear impressively stable compared with their terrestrial and laboratory counterparts-they can be traced from their origin to distances exceeding their injection radius by up to a billion times. However, some less energetic jets get disrupted and lose their coherence on the scale of their host galaxy. Quite remarkably, on the same scale, these jets are expected to become confined by the thermal pressure of the intra-galactic gas. Motivated by these observations, we have started a systematic study of active galactic nuclei jets undergoing reconfinement vi…
Recent astronomical observations reveal that Active Galactic Nuclei (AGN) are sources of high-energy radiation. For example, the Fermi-LAT and Hess telescopes have detected gamma-ray emissions from the cores of several types of AGN's. Even more, the Pierre Auger observatory has found a correlation of ultra-high energy cosmic ray events with the position of Active Galactic Nuclei, such as Centaurus A. In this way, according to particle physics, a flux of high-energy neutrinos should be expected from the interactions of cosmic and gamma-rays with the ambient matter and radiation at the source. I…
For active galactic nuclei (AGNs) we study the role of the mechanism of quasi-linear diffusion (QLD) in producing the high energy emission in the MeV-GeV domains strongly connected with the submillimeter/infrared radiation. Considering the kinetic equation governing the stationary regime of the QLD we investigate the feedback of the diffusion on electrons. We show that this process leads to the distribution of particles by the pitch angles, implying that the synchrotron mechanism is no longer prevented by energy losses. Examining a reasonable interval of physical parameters, we show that it is…
The first part of this article is a historical and physical introduction to quasars and their close cousins, called Active Galactic Nuclei (AGN). In the second part, I argue that our progress in understanding them has been unsatisfactory and in fact somewhat illusory since their discovery fifty years ago, and that much of the reason is a pervasive lack of critical thinking in the research community. It would be very surprising if other fields do not suffer similar failings.
This Astro2020 white paper advocates for a multi-messenger approach that combines high-energy neutrino and broad multi-wavelength electromagnetic observations to study AGN during the coming decade. The unique capabilities of these joint observations promise to solve several long-standing issues in our understanding of AGN as powerful cosmic accelerators.
We perform a systematic search of quasi-periodic variabilities in $γ$-ray active galactic nuclei (AGNs) in the third \emph{Fermi} Large Area Telescope source catalog (3FGL). We employe two techniques, Lomb-Scargle Periodogram (LSP) and Weighted Wavelet Z-transform (WWZ), to obtain power spectra of $γ$-ray light curves covering from 2008 August to 2016 December. The results show that besides several objects that have been reported in previous works, an additional source, the FSRQ PKS 0601-70 has a possible quasi-periodic variability of 450 days in its $γ$-ray light curves with the significance …
This Astro2020 white paper summarizes the unknowns of active galactic nuclei (AGN) physics that could be unveiled thanks to a new, space-born, ultraviolet spectropolarimeter. The unique capabilities of high energy polarimetry would help us to understand the precise mechanisms of matter and energy transfer and supermassive black holes growth, together with the impact of AGN feedback on galaxy evolution.
The current very high energy (VHE; E>100GeV) experiments have tremendously increased the number of detected extragalactic sources. We present a synchrotron self-Compton modeling tour of the active galactic nuclei currently established as VHE emitters so far, and investigate possible correlations among the intrinsic and derived parameters.
Galactic nuclei are expected to be one of the main sites for formations of eccentric binary black holes (EBBHs), with an estimated detection rate of $\mathcal{O}(1-100$ yr$^{-1})$ with Advanced LIGO (aLIGO) detectors operating at design sensitivity. The two main formation channels of these binaries are gravitational capture and the secular Kozai-Lidov mechanism, with expectedly commensurable formation rates. We used Monte Carlo simulations to construct the eccentricity distributions of EBBHs formed through these channels in galactic nuclei, at the time their gravitational-wave signals enter th…
It has been recently proposed that the broad line region in active galactic nuclei originates from dusty clouds driven from the accretion disk by radiation pressure, at a distance from the black hole where the disk is cooler than the dust sublimation temperature. We test this scenario by checking the consistency of independent broad line region and accretion disk reverberation measurements, for a sample of 11 well studied active galactic nuclei. We show that independent disk and broad line region reverberation mapping measurements are compatible with a universal disk temperature at the Hβ radi…
The jets of active galactic nuclei can carry a large fraction of the accreted power of the black-hole system into interstellar and even extragalactic space. They radiate profusely from radio to X-ray and gamma-ray frequencies. In the most extreme cases, the outward flow speeds correspond to high Lorentz factors that can reach 40 or more. This chapter displays images at various wavebands as well as light curves and continuum spectra that illustrate the variability with location, time, and frequency of the emission from compact, parsec- and subparsec-scale jets. It presents a physical framework …
Active Galactic Nuclei (AGN) are traditionally divided empirically into two main classes: "radio-loud" and "radio-quiet" sources. These labels, which are more than fifty years old, are obsolete, misleading, and wrong. I argue that AGN should be classified based on a fundamentally physical rather than just an observational difference, namely the presence (or lack) of strong relativistic jets, and that we should use the terms "jetted" and "non-jetted" AGN instead.
We review the current state of understanding how accretion onto a black hole proceeds and what are they key elements needed to form relativistic jets. Since the theoretical progress is severely halted by the lack of deep understanding of the microphysics involved, particularly in the presence of strong magnetic fields, all proposed solutions have a status of models, and their selection has to be based directly on observational constraints.
Active Galactic Nuclei are the dominant sources of gamma rays outside our Galaxy and also candidates for being the source of ultra-high energy cosmic rays. In addition to being emitters of broad-band non-thermal radiation throughout the electromagnetic spectrum, their emission is highly variable on timescales from years to minutes. Hence, high-cadence monitoring observations are needed to understand their emission mechanisms. The Africa Millimetre Telescope is planned to be the first mm-wave radio telescope on the African continent and one of few in the Southern hemisphere. Further to contribu…
This volume presents an overview of selected aspects of physical processes occurring in the inner regions of Active Galactic Nuclei (AGN). The observational evidence suggests that strong gravitational fields play a significant role in governing the energy output of AGN and their influence on the surrounding medium, possibly due to the presence of a supermassive black hole. In order to reduce an unnecessary overlap with numerous reviews on the subject of AGN, here we focus on several selected topics.
To constrain models of the jet-disc connection, we explore Eddington ratios reported in Foschini (2011) and interpret them in relation to the values in Sikora et al. across the active galactic nuclei population from radio loud quasars, their flat spectrum radio quasar subclass, the recently discovered gamma-ray loud narrow-line type 1 Seyfert galaxies, Fanaroff-Riley type I (FRI) radio galaxies and radio quiet quasars of the Palomar Green survey. While appeal to disc truncation in radiatively inefficient flow appears to explain the observed inverse relation between radio loudness and Eddington…
Active galactic nuclei (AGNs) can act as black hole assembly lines, funneling some of the stellar-mass black holes from the vicinity of the galactic center into the inner plane of the AGN disk where the black holes can merge through dynamical friction and gravitational wave emission. Here, we show that stars near the galactic center are also brought into the AGN disk, where they can be tidally disrupted by the stellar-mass black holes in the disk. Such micro-tidal disruption events (micro-TDEs) could be useful probe of stellar interaction with the AGN disk. We find that micro-TDEs in AGNs occu…
Active Galactic Nuclei (AGNs) and their relativistic jets belong to the most promising class of ultra-high-energy cosmic ray (UHECR) accelerators. This compact review summarises basic experimental findings by recent instruments, and discusses possible interpretations and astrophysical constraints on source energetics. Particular attention is given to potential sites and mechanisms of UHECR acceleration in AGNs, including gap-type particle acceleration close to the black hole, as well as first-order Fermi acceleration at trans-relativistic shocks and stochastic shear particle acceleration in la…
We predict the observational signatures of galaxy scale outflows powered by active galactic nuclei (AGN). Most of the emission is produced by the forward shock driven into the ambient interstellar medium (ISM) rather than by the reverse shock. AGN powered galactic winds with energetics suggested by phenomenological feedback arguments should produce spatially extended 1-10 keV X-ray emission of 10^(41-44) erg/s, significantly in excess of the spatially extended X-ray emission associated with normal star forming galaxies. The presence of such emission is a direct test of whether AGN outflows sig…
The perfect case for time-domain investigations are active galactic nuclei (AGNs) since they are luminous objects that show strong variability. Key result from the studies of AGNs variability is the estimated mass of a supermassive black hole (SMBH), which resides in the center of an AGN. Moreover, the spectral variability of AGN can be used to study the structure and physics of the broad line region, which in general can be hardly directly observed. Here we review the current status of AGNs variability investigations in Serbia, in the perspectives of the present and future monitoring campaign…
High-density cusps of compact remnants are expected to form around supermassive black holes (SMBHs) in galactic nuclei via dynamical friction and two-body relaxation. Due to the high density, binaries in orbit around the SMBH can frequently undergo close encounters with compact remnants from the cusp. This can affect the gravitational wave merger rate of compact binaries in galactic nuclei. We investigated this process by means of high accuracy few-body simulations, performed with a novel Monte Carlo approach. We find that, around a SgrA*-like SMBH, three-body encounters increase the number of…
According to the currently favored picture, relativistic jets in active galactic nuclei (AGN) are launched in the vicinity of the black hole by magnetic fields extracting energy from the spinning black hole or the accretion disk. In the past decades, various models from shocks to magnetic reconnection have been proposed as the energy dissipation mechanism in the jets. This paper presents a short review on how linear polarization observations can be used to constrain the magnetic field structure in the jets of AGN, and how the observations can be used to constrain the various emission models.
We briefly review the synergy between X-ray and infrared observations for Active Galactic Nuclei (AGNs) detected in cosmic X-ray surveys, primarily with XMM-Newton, Chandra, and NuSTAR. We focus on two complementary aspects of this X-ray-infrared synergy (1) the identification of the most heavily obscured AGNs and (2) the connection between star formation and AGN activity. We also briefly discuss future prospects for X-ray-infrared studies over the next decade.
Axion-Like Particles (ALPs) are the focus of intense current research. We analyze photon-ALP conversion in the context of relativistic jet models of Active Galactic Nuclei (AGN) for more than 100 sources. Contrary to previous claims, we find that this process cannot occur above 100 GeV regardless of the actual AGN model and the values of ALP parameters. This result rules out a proposed strategy to bypass the cosmic opacity above 100 GeV, as apparently required by observations. We also show that for some AGN an observable effect can show up in the X and soft gamma-ray bands.
Radio-loud sources with blazar-like properties, but having a jet that does not directly point in the direction of the observer are among the most interesting classes of gamma-ray emitters. These sources are known as Misaligned Active Galactic Nuclei (MAGN). Understanding MAGN properties is useful to improve the knowledge of blazar energetics. We searched for new MAGN candidates among the remaining blazars of uncertain type detected by the Fermi Large Area Telescope (LAT) using a methodology based on characterizing their radio morphology. We identified seven new candidates associated with gamma…
Antimatter nuclei in cosmic rays (CRs) are a promising tool for the indirect detection of dark-matter annihilation signatures. However, the search of new-physics signals in CRs relies on our knowledge of the astrophysical antimatter background which, in turns, depends critically on the several fragmentation cross-sections that regulate production and destruction of antiparticles in the interstellar medium. In this work, we have re-evaluated the astrophysical background of CR antiproton, antineutron, and antihelium nuclei in Galactic CRs using improved calculations. The production cross-section…
Cosmic-ray boosted inelastic dark matter from neutrino-emitting active galactic nuclei
Virginia Tech（弗吉尼亚理工大学）；Massachusetts Institute of Technology（麻省理工学院）；Harvard University（哈佛大学）；The Pennsylvania State University（宾夕法尼亚州立大学）；Fermi National Accelerator Laboratory（费米国家加速实验室）；University of Chicago（芝加哥大学）
We provide a new approach to measure power spectra and reconstruct time series in active galactic nuclei (AGNs) based on the fact that the Fourier transform of AGN stochastic variations is a series of complex Gaussian random variables. The approach parameterizes a stochastic series in frequency domain and transforms it back to time domain to fit the observed data. The parameters and their uncertainties are derived in a Bayesian framework, which also allows us to compare the relative merits of different power spectral density models. The well-developed fast Fourier transform algorithm together …
We suggest a mechanism for the amplification of high-velocity water-vapor maser emission features from the central regions of active galactic nuclei. The model of an emitting accretion disk is considered. The high-velocity emission features originate in the right and left wings of the Keplerian disk. The hyperfine splitting of the signal levels leads to an asymmetry in the spectral profile of the water vapor maser line at a frequency of 22.235 GHz. We show that the gain profile asymmetry must lead to an enhanced brightness of the blueshifted high-velocity emission features compared to the reds…
Radiatively inefficient accretion flows (RIAFs) in low-luminosity active galactic nuclei (LLAGNs) have been suggested as cosmic-ray and neutrino sources that may largely contribute to the observed diffuse neutrino intensity. We show that this scenario naturally predicts hadronic multi-TeV gamma-ray excesses around Galactic centers. The protons accelerated in the RIAF in Sagittarius A$^*$ (Sgr A$^*$) escape and interact with dense molecular gas surrounding Sgr A$^*$, which is known as the central molecular zone (CMZ), and produce gamma rays as well as neutrinos. Based on a theoretical model tha…
We study the influence of the centrifugally driven curvature drift instability (CDI) on the dynamics of relativistic electrons in the magnetospheres of active galactic nuclei (AGN). We generalize our previous work by considering relativistic particles with different initial phases. Considering the Euler, continuity, and induction equations, by taking into account the resonant conditions, we derive the growth rate of the CDI. We show that due to the centrifugal effects, the rotational energy is efficiently pumped directly into the drift modes, that leads to the generation of a toroidal componen…
The mixing of photons with axion-like particles (ALPs) in the large-scale magnetic field $B$ changes the polarization angle of a linearly polarized photon beam from active galactic nuclei in radio galaxies as it propagates over cosmological distances. Using available ultraviolet polarization data concerning these sources we derive a new bound on the product of the photon-ALP coupling $g_{aγ}$ times $B$. We find $g_{aγ} B \lesssim 10^{-11}$ GeV$^{-1}$ nG for ultralight ALPs with $m_a \lesssim 10^{-15}$ eV. We compare our new bound with the ones present in the literature and we comment about pos…
We perform Monte Carlo simulations of transrelativistic shear acceleration dedicated to a jet-cocoon system of active galactic nuclei. A certain fraction of galactic cosmic rays in a halo is entrained, and sufficiently high-energy particles can be injected to the reacceleration process and further accelerated up to 100 EeV. We show that the shear reacceleration mechanism leads to a hard spectrum of escaping cosmic rays, $dL_E/dE\propto E^{-1}-E^0$, distinct from a conventional $E^{-2}$ spectrum. The supersolar abundance of ultrahigh-energy nuclei is achieved due to injections at TeV-PeV energi…
The direction of parsec-scale jets in active galactic nuclei (AGNs) is essential information for many astrophysical and astrometric studies, including linear polarization and magnetic field structure, frequency-dependent synchrotron opacity, proper motion, and reference frame alignment. We developed a rigorous, simple, and completely automated method to measure the directions from calibrated interferometric visibility data at frequencies ranging from 1.4 GHz to 86 GHz. We publish the results for 9220 AGNs with the typical accuracy below 10 degrees. An internal check of the method comparing the…
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 t…
The Interferometric Monitoring of Gamma-ray Bright Active galactic nuclei (iMOGABA) program provides not only simultaneous multifrequency observations of bright gamma-ray detected active galactic nuclei (AGN), but also covers the highest Very Large Baseline Interferometry (VLBI) frequencies ever being systematically monitored, up to 129 GHz. However, observation and imaging of weak sources at the highest observed frequencies is very challenging. In the second paper in this series, we evaluate the viability of the frequency phase transfer technique to iMOGABA in order to obtain larger coherence…
