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Register a new userRadio-to-gamma-ray synchrotron and neutrino emission from proton-proton interactions in active galactic nuclei
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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.
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Active galactic nuclei (AGN) with jets seen at small viewing angles are the most luminous and abundant objects in the $gamma$-ray sky. AGN with jets misaligned along the line-of-sight appear fainter in the sky, but are more numerous than the brighter blazars. We calculate the diffuse $gamma$-ray emission due to the population of misaligned AGN (MAGN) unresolved by the Large Area Telescope (LAT) on the {it Fermi} Gamma-ray Space Telescope ({it Fermi}). A correlation between the $gamma$-ray luminosity and the radio-core luminosity is established and demonstrated to be physical by statistical tests, as well as compatible with upper limits based on {it Fermi}-LAT data for a large sample of radio-loud MAGN. We constrain the derived $gamma$-ray luminosity function by means of the source count distribution of the radio galaxies (RGs) detected by the {it Fermi}-LAT. We finally calculate the diffuse $gamma$-ray flux due to the whole MAGN population. Our results demonstrate that the MAGN can contribute from 10% up to nearly the entire measured Isotropic Gamma-Ray Background (IGRB). We evaluate a theoretical uncertainty on the flux of almost an order of magnitude.
To explain X-ray spectra of active galactic nuclei (AGN), non-thermal activity in AGN coronae such as pair cascade models has been extensively discussed in the past literature. Although X-ray and gamma-ray observations in the 1990s disfavored such pair cascade models, recent millimeter-wave observations of nearby Seyferts establish the existence of weak non-thermal coronal activity. Besides, the IceCube collaboration reported NGC 1068, a nearby Seyfert, as the hottest spot in their 10-yr survey. These pieces of evidence are enough to investigate the non-thermal perspective of AGN coronae in depth again. This article summarizes our current observational understandings of AGN coronae and describes how AGN coronae generate high-energy particles. We also provide ways to test the AGN corona model with radio, X-ray, MeV gamma-ray, and high-energy neutrino observations.
We estimate the neutrino emission from the decay chain of the $pi$-meson and $mu$-lepton, produced by proton-proton inelastic scattering in energetic ($E_{rm iso}gtrsim 10^{52}$~erg) long gamma-ray bursts (GRBs), within the type I binary-driven hypernova (BdHN) model. The BdHN I progenitor is textcolor{red}{a} binary system composed of a carbon-oxygen star (CO$_{rm core}$) and a neutron star (NS) companion. The CO$_{rm core}$ explosion as supernova (SN) triggers a massive accretion process onto the NS. For short orbital periods of few minutes, the NS reaches the critical mass, hence forming a black hole (BH). Recent numerical simulations of the above scenario show that the SN ejecta becomes highly asymmetric, creating a textit{cavity} around the newborn BH site, due to the NS accretion and gravitational collapse. Therefore, the electron-positron ($e^{pm}$) plasma created in the BH formation, during its isotropic and self-accelerating expansion, engulfs different amounts of ejecta baryons along different directions, leading to a direction-dependent Lorentz factor. The protons engulfed inside the high-density ($sim 10^{23}$~particle/cm$^3$) ejecta reach energies in the range $1.24lesssim E_plesssim 6.14$ GeV and interact with the unshocked protons in the ejecta. The protons engulfed from the low density region around the BH reach energies $sim 1$ TeV and interact with the low-density ($sim1$~particle/cm$^3$) protons of the interstellar medium (ISM). The above interactions give rise, respectively, to neutrino energies $E_{ u}leq 2$ GeV and $10leq E_{ u}leq 10^3$ GeV, and for both cases we calculate the spectra and luminosity.
We calculate the diffuse $gamma$-ray emission due to the population of misaligned AGN (MAGN) unresolved by the Large Area Telescope (LAT) on the {it Fermi} Gamma-ray Space Telescope ({it Fermi}). A correlation between the $gamma$-ray luminosity and the radio-core luminosity is established and demonstrated to be physical by statistical tests, as well as compatible with upper limits based on {it Fermi}-LAT data for a large sample of radio-loud MAGN. We constrain the derived $gamma$-ray luminosity function by means of the source count distribution of the MAGN detected by the {it Fermi}-LAT. We finally estimate the diffuse $gamma$-ray flux due to the whole MAGN population which ranges from 10% up to nearly the entire measured Isotropic Gamma-Ray Background (IGRB). We evaluate also the room left to galactic DM at high latitudes ($>10^circ$), by taking into account the results on the MAGN together with the other significant galactic and extragalactic $gamma$-rays emitting sources.
For nearly seven decades astronomers have been studying active galaxies, that is to say galaxies with actively accreting central supermassive black holes, AGN. A small fraction of these are characterized by luminous, powerful radio emission: this class is known as radio-loud. A substantial fraction, the so-called radio-quiet AGN population, displays intermediate or weak radio emission. However, an appreciable fraction of strong X-rays emitting AGN are characterized by the absence of radio emission, down to an upper limit of about $10^{-7}$ times the luminosity of the most powerful radio-loud AGN. We wish to address the nature of these - seemingly radio-silent - X-ray-luminous AGN and their host galaxies: is there any radio emission, and if so, where does it originate? Focusing on the GOODS-N field, we examine the nature of these objects employing stacking techniques on ultra-deep radio data obtained with the JVLA. We combine these radio data with Spitzer far-infrared data. We establish the absence, or totally insignificant contribution of jet-driven radio-emission in roughly half of the otherwise normal population of X-ray luminous AGN, which appear to reside in normal star-forming galaxies. We conclude that AGN- or jet-driven radio emission is simply a mechanism that may be at work or may be dormant in galaxies with actively accreting black holes. The latter can be classified as radio-silent AGN.
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