Effective spectral index properties for Fermi blazars

Blazars are a special subclass of active galactic nuclei with extreme observation properties. This subclass can be divided into two further subclasses of flat spectrum radio quasars(FSRQs) and BL Lacertae objects(BL Lacs) according to their emission line features. To compare the spectral properties of FSRQs and BL Lacs, the 1.4 GHz radio, optical R-band, 1 keV X-ray, and 1 GeVy-ray flux densities for 1108 Fermi blazars are calculated to discuss the properties of the six effective spectral indices of radio to optical(α_(RO)), radio to X-ray(α_(RX)), radio to y ray(α_(Ry)), optical to X-ray(α_(OX)), optical to y ray(α_(Oy)), and X-ray to y ray(α_(Xy)).The main results are as follows: For the averaged effective spectral indices, α_(OX_ α_(Oy) α_(Xy) α_(Ry) α_(RX) α_(RO) for samples of whole blazars and BL Lacs; α_(Xy)≈α_(Ry)≈α_(RX) for FSRQs and low-frequency-peaked BL Lacs(LBLs); and α_(OX)≈α_(Oy)≈α_(Xy) for high-synchrotron-frequency-peaked BL Lacs(HBLs). The distributions of the effective spectral indices involving optical emission(α_(RO), α_(OX), and α_(Oy)) for LBLs are different from those for FSRQs, but if the effective spectral index does not involve optical emission(α_(RX), α_(Ry), and α_(Xy)), the distributions for LBLs and FSRQs almost come from the same parent population. X-ray emissions from blazars include both synchrotron and inverse Compton (IC) components; the IC component for FSRQs and LBLs accounts for a larger proportion than that for HBLs; and the radiation mechanism for LBLs is similar to that for FSRQs, but the radiation mechanism for HBLs is different from that for both FSRQs and LBLs in X-ray bands. The tendency of α_(Ry) decreasing from LBLs to HBLs suggests that the synchrotron self-Compton model explains the main process for highly energetic y rays in BL Lacs.     

Active galactic nuclei at gamma-ray energies

Active Galactic Nuclei can be copious extragalactic emitters of MeV–GeV–TeV γ rays, a phenomenon linked to the presence of relativistic jets powered by a super-massive black hole in the center of the host galaxy. Most of γ-ray emitting active galactic nuclei, with more than 1500 known at GeV energies, and more than 60 at TeV energies, are called “blazars”. The standard blazar paradigm features a jet of relativistic magnetized plasma ejected from the neighborhood of a spinning and accreting super-massive black hole, close to the observer direction. Two classes of blazars are distinguished from observations: the flat-spectrum radio-quasar class (FSRQ) is characterized by strong external radiation fields, emission of broad optical lines, and dust tori. The BL Lac class (from the name of one of its members, BL Lacertae) corresponds to weaker advection-dominated flows with γ-ray spectra dominated by the inverse Compton effect on synchrotron photons. This paradigm has been very successful for modeling the broadband spectral energy distributions of blazars. However, many fundamental issues remain, including the role of hadronic processes and the rapid variability of a few FSRQs and several BL Lac objects whose synchrotron spectrum peaks at UV or X-ray frequencies. A class of γ-ray-emitting radio galaxies, which are thought to be the misaligned counterparts of blazars, has emerged from the results of the Fermi-Large Area Telescope and of ground-based Cherenkov telescopes. Soft γ-ray emission has been detected from a few nearby Seyfert galaxies, though it is not clear whether those γ rays originate from the nucleus. Blazars and their misaligned counterparts make up most of the ≳100 MeV extragalactic γ-ray background (EGB), and are suspected of being the sources of ultra-high energy cosmic rays. The future “Cherenkov Telescope Array”, in synergy with the Fermi-Large Area Telescope and a wide range of telescopes in space and on the ground, will write the next chapter of blazar physics.     

Tachyonic γ-ray spectra of active galactic nuclei: Evidence for intrinsic spectral curvature

Tachyonic spectral densities of ultra-relativistic electron populations are fitted to the γ-ray spectra of two TeV blazars, the BL Lacertae objects 1ES 0229+200 and 1ES 0347-121. The spectral maps are compared to Galactic TeV sources, the γ-ray binary LS 5039 and the supernova remnant W28. In contrast to TeV photons, the extragalactic tachyon flux is not attenuated by interaction with the cosmic background light; there is no absorption of tachyonic γ-rays via pair creation, as tachyons do not interact with infrared background photons. The curvature of the observed γ-ray spectra is intrinsic, caused by the Boltzmann factor of the electron densities, and reproduced by a tachyonic cascade fit. In particular, the curvature in the spectral map of the Galactic microquasar is more pronounced than of the two extragalactic γ-ray sources. Estimates of the thermodynamic parameters of the thermal or, in the case of supernova remnant W28, shock-heated nonthermal electron plasma generating the tachyon flux are obtained from the spectral fits.     

Radio core dominance of Fermi/LAT-detected AGNs

We present a sample of 4388 AGNs with available radio core-dominance parameters—defined as the ratio of the core flux densities to the extended ones, R = S_core/S_ext.—which includes 630 Fermi-detected AGNs from the fourth source catalog(4FGL) of the Fermi Large Area Telescope(Fermi/LAT);the rest are non-Fermi-detected AGNs. In our sample, 584 blazars are Fermi-detected and 1310 are not. The sample also contains other subclasses, such as Seyferts, Fanaroff-Riley I/II galaxies, and normal galaxies.We investigate various properties of the Fermi-detected and non-Fermi-detected AGNs by using core-dominance parameters,capitalizing on a previous study which showed that R is a good indicator of beaming. We then calculate radio spectral indices for the whole sample, and adopt γ-ray-photon indices for the Fermi AGNs from the 4FGL catalog to discuss the properties of different subclasses. We obtain a relation between the core-dominance parameters and the radio spectral indices for both Fermi and non-Fermi sources, assuming a two-component model in the radio band. Our previous study ruled out the assumption that the core-dominance parameters and radio spectral indices are quite different for different AGN subclasses. This holds not only for Fermi sources but also for non-Fermi sources. In particular, R is, on average, greater for the former AGNs than for the latter.In this study, we enlarge our sample with available values of R to 4388 AGNs, and the obtained conclusions are consistent with our previous study. We assume that the same two-component model holds for the γ-ray band as for the radio band, and therefore,adopt the same relation between the core-dominance parameters and the γ-ray-photon indices for Fermi AGNs. Our fitting results indicate that the γ-ray emissions of Fermi blazars originate mainly from the jet, and therefore, we conclude that the Fermi blazars are beamed.     

Competition between few nucleon emission andγ-ray deexcitation for the reaction systems65Cu+87Rb and40Ar+110Pd

Bothγ-ray and neutron emission have been studied for the reaction systems⁶⁵Cu(237MeV) +⁸⁷Rb→¹⁵²Dy^* and⁴⁰Ar(158MeV)+¹¹⁰Pd→¹⁵⁰Gd^*. By using a sum spectrometer in coincidence with neutron counters, Ge(Li) or Nal detectors, we have measured the totalγ-ray energy and the average totalγ-multiplicity distributions as well as the neutron spectra for various exit channels. These measurements provide strong evidence for thermal equilibrium in reactions involving a small number of emitted neutrons (i.e.⁸⁷Rb(⁶⁵Cu,n or 2n)) at rather high excitation energy (～54MeV). This statistical emission of only a few neutrons is controlled by very strong y-ray competition: theγ-entry line is found not to be parallel to the yrast line. Instead the energy gap is about 8MeV for J～27? and rises to at least 13MeV for J～36?. There are some indications that the main part of the energy from this gap is removed by statisticalγ-ray cascades. The main features of the experimental data for both entrance channels are well reproduced by statistical model calculations with proper attention to the yrast line position and an adjustement of the dipoleγ-ray normalization coefficient. It is conceivable that the y-ray enhancement that we introduce may be related to a lack of knowledge of the absolute level densities at high energy and spin, or possibly to the presence of new or additional degrees of freedom that may enter into the competition between neutron andγ-ray emission.     

Photon initiated reactions in the resonance region

A consistent picture of two body photon initiated reactions is achieved by implementing a resonance model in the s-channel compatible with duality and gauge invariance. Large real parts generated by contact terms to achieve gauge invariance appear in a well defined pattern. Their size explains hitherto puzzling reactions like γN → ?N, γN → ?^? and γN → ω^?, near their thresholds.     

ω Meson photoproduction from deuterium at 3.9 GeV photon energy

Measurements are presented of the cross sections for ω meson photoproduction from deuterium at an average photon energy of 3.9 GeV. The cross section for the coherent process γd → dω is found to be 1.4 ± 0.5 μb and that for the incoherent process γd → npω is 3.3 ± 0.7 μb. The forward differential cross section for γd → dω is estimated to be (dσ/dt)_t=0 = 54 ± 20 μb/GeV². This result indicates that the value of the A₂ exchange amplitude in ω photoproduction from hydrogen is less than that predicted from the measurements of the difference between the total hadron photoproduction cross sections from neutrons and protons. We note that the world data tend to show that the A₂ exchange amplitude is more consistent with zero than with the value needed to explain these differences. Measurements are also presented of the ratio of the coupling constants of the photon to the ? and ω mesons which tend to favour the vector dominance model proposed by Das, Mathur and Okubo with exact SU(3) symmetry at infinite energies.     

Long-term observations of the Cyg X-3 and λCygni SNR at ultrahigh energies by SHALON mirror Cherenkov telescopes

The Cygnus X region contains a number of powerful sources of radio and X-ray radiation which are also considered as potential sources of high and ultrahigh-energy radiation. One of such sources is the massive binary system Cyg X-3 systematically observed by the SHALON telescope from 1995 to the present. The results of Cyg X-3 observations are presented by γ-ray spectra and images at energies of 800 GeV-85 TeV. In the field of the SHALON telescope, an ultrahigh-energy γ-ray source was detected, whose position is ～2° from Cyg X-3; its coordinates coincide with coordinates of the known source of radio and X-ray radiation, i.e., the γCygni SNR supernova remnant. The γCygni SNR spectra, spectral energy distribution, and image according to the SHALON telescope data are presented in the energy range of 800 GeV-50 TeV.     

Conformal approach to fluctuations in hadroproduction

We study two-photon final-states atep-colliders. In particular, we investigate the process γ+p →γ+γ+X at HERA and LEP/LHC energies with the intention of determining its measurability at these accelerators. We find that the transverse momentum distribution will be measured top _T=25 GeV/c at HERA andp _T=50 GeV/c at LEP/LHC. We find that the cross section of this process is too small for it to be a sensitive, direct probe of the gluon content of the proton and the photon. However, we find that it will supplement deep inelastic structure function investigations of the quark distributions within the proton and photon. Further, we predict that at very low transverse momenta, this process will allow the measurement of the box diagramg+g→γ+γ.     

Large-pT direct photon production and opposite-side photon-hadron correlations in QCD

Direct photon production in p-p, π-p and $\text{p}\text{-}\text{p}$ collisions at large transverse momenta (p_T) is studied in QCD and compared with existing data. Apart from the quark-gluon and quark-antiquark contributions, corrections due to bremsstrahlung of photons (q+q→q+q+γ) and to partons' intrinsic transverse momenta are taken into account. It is shown that p+p→γ+X provides one of the best determinations of the gluon distribution in the proton. Hadron production with an opposite-side large-p_T photon trigger is also studied. It is shown that the difference between the momentum sharing (x_e) distributions of π^?+p→γ+π^±+X and π⁺+p →γ+π^±+X (or of $\text{p}\text{+}\text{p}\text{→γ+π}{}^{\mathrm{\pm }}\text{+}\text{X}$ and p+p→γ+π^±+X) provides a good determinati on of the gluon fragmentation to a pion.     

Gamma-ray emission in competition with neutron emission in the beta decay of Br

Evidence is presented for the existence of a γ-ray at 5594.7±0.6 keV following beta decay of ⁸⁷Br. This observation indicates population of neutron unbound levels in ⁸⁷Kr from which photon emission competes successfully with neutron emission.     

Radiative π0 photoproduction on protons in the Δ+ (1232) region

The reaction γp → pπ ⁰γ′ has been measured with the Crystal Ball/TAPS detectors using the energy-tagged photon beam at the electron accelerator facility MAMI-B. Energy and angular differential cross-sections for the emitted photon γ′ and angular differential cross-sections for the π⁰ have been determined with high statistics in the energy range of the Δ⁺ (1232)-resonance. Cross-sections and the ratio of the cross-section to the nonradiative process γp → pπ ⁰ are compared to theoretical reaction models, having the anomalous magnetic moment κ _Δ as free parameter. As the shape of the experimental distributions is not reproduced in detail by the model calculations, currently no extraction of κ _Δ is feasible.     

Superluminal spectral densities of ultra-relativistic electrons in intense electromagnetic wave fields

Superluminal radiation from electrons accelerated in electromagnetic waves is investigated. The radiation field is a Proca field with negative mass-square, minimally coupled to the electron current. The spectrum is continuous in the ultra-relativistic regime, where steepest-descent asymptotics can be used to evaluate the power coefficients. The time averaging of Lissajous orbits in polarized wave fields is discussed, and the tachyonic spectral densities of electrons orbiting in intense laser beams are derived. In the ultra-relativistic limit, realized by high injection energy or high field intensity, the spectral functions are evaluated in closed form in terms of Airy integrals. In contrast to electromagnetic radiation, there is a longitudinal polarization component, and oscillations emerge at high beam intensity in the longitudinal and transversal spectral slopes, generated by the negative mass-square of the tachyonic quanta. The thermal ultra-relativistic electron plasma of two active galactic nuclei is analyzed in this regard, based on TeV spectral maps obtained with imaging air Cherenkov detectors. Specifically, tachyonic cascade fits are performed to γ-ray flares of the TeV blazars RGB J0152+017 and 3C 66A, and the transversal and longitudinal radiation components are disentangled in the spectral maps. The curvature of the spectral slopes is shown to be intrinsic, caused by the Boltzmann factor of the electronic source plasma radiating the tachyonic cascades.     

Photon states and Wigner functions in parametric generation

The problem of preparation of photon states from two correlated modes of subharmonics generated in pulsed regime of optical parametric oscillator is investigated. Because of quantum correlation, detecting of n-photon Fock states in one mode transfers the other mode into also an n-photon state. Conditional Wigner functions are calculated whose negative parts describe the prepared photon states in cases of one-, two-, and three-photon schemes of measurements.     

Positive pion production from polarized protons by linearly polarized photons in the energy range 280–420 MeV

The method is described of measuring the polarization observables Σ, P and T for the reaction γp → nπ⁺ in a double polarization experiment (polarized target + polarized beam). The measured angular distribution of these observables are presented for the photon energy range 280–420 MeV at c.m. pion emission angles between 30° and 150°. The obtained experimental data are included in the energy-independent multipole analysis of the reactions γp → Nπ.     

GAMMA-RAY AND X-RAY EMISSION FROM GAMMA-RAY-LOUD BLAZARS

We present a strong correlation of the gamma-ray (above 100 MeV) mean spectral indices α_γ and X-ray (1 keV) mean spectral indices α_X for 34 gamma-ray-loud blazars (16 BL Lac objects and 18 flat spectrum radio quasars). A strong correlation is also found between the gamma-ray flux densities F_γ and X-ray flux densities F_X in the low state for 47 blazars (17 BL Lac and 30 flat spectrum radio quasars). Possible correlation on the gamma-ray emission mechanism is discussed. We suggest that the main gamma-ray radiation mechanism is probably the synchrotron process. The gamma-ray emission may be somewhat different from that of BL Lac objects and flat spectrum radio quasars.     

Tycho’s supernova remnant as a source of cosmic rays in our galaxy

The Tycho’s supernova remnant was observed using the SHALON atmospheric Cherenkov telescope at the Tien Shan High-Altitude Observatory. This object has long been considered to be a candidate for sources of cosmic ray hadrons in the Northern Hemisphere. In [1, 2], the Tycho’s properties were described using the nonlinear kinetic model of cosmic ray acceleration in supernovae remnants. The expected γ-ray flux from π ⁰-decay extends to energies > 30 eV, whereas the γ-ray photon flux generated by inverse Compton scattering is cut off above several TeV. Therefore, the detection of γ-rays at energies of 10–80 TeV by the SHALON telescope is an indication of their hadron origin. From the SHALON telescope data, additional information on such parameters of the Tycho’s supernova remnant as the distance and interstellar medium density was obtained within the theory [1, 2].     

Photoproduction of neutral pions on deuterium at forward angles in the first resonance region

At the 500 MeV electron synchrotron in Bonn differential cross sections of the reaction γ + d → π⁰ + d were measured in forward pion c.m. angles and photon energies between 340 and 420 MeV.