Hadronuclear interpretation of the possible neutrino emission from PKS B1424-418, GB6 J1040+0617 and PKS 1502+106

In addition to neutrino event IceCube-170922A which is observed to be associated with a γ-ray flare from blazar TXS 0506+056, there are also several neutrino events that may be associated with blazars. Among them, PKS B1424-418, GB6 J1040+0617 and PKS 1502+106 are low synchrotron peaked sources, which are usually believed to have the broad line region in the vicinity of the central black hole. They are considered as counterparts of IceCube event 35, IceCube-141209A and IceCube-190730A, respectively. By considering the proton-proton (pp) interactions between the dense gas clouds in the broad line region and the relativistic protons in the jet, we show that the pp model that is applied in this work can not only reproduce the multi-waveband spectral energy distribution but also suggest a considerable annual neutrino detection rate. We also discuss the emission from the photopion production and Bethe-Heitler pair production with a sub-Eddington jet power that is suggested in our model and find that it has little effect on the spectrum of total emission for all of three sources.

γ-Ray Flux and Spectral Variability of Blazar Ton 599 during Its 2021 Flare

Blazars are known to emit exceptionally variable non-thermal emission over the wide range (from radio to γ-rays) of electromagnetic spectrum. We present here the results of our γ-ray flux and spectral variability study of the blazar Ton 599, which has been recently observed in the γ-ray flaring state. Using 0.1−300 GeV γ-ray data from the Fermi Gamma-ray Space Telescope (hereinafter Fermi), we generated one-day binned light curve of Ton 599 for a period of about one-year from MJD 59,093 to MJD 59,457. During this one year period, the maximum γ-ray flux detected was 2.24 ± 0.25 ×10−6 ph cm−2 s−1 at MJD 59,399.50. We identified three different flux states, namely, epoch A (quiescent), epoch B (pre-flare) and epoch C (main-flare). For each epoch, we calculated the γ-ray flux variability amplitude (Fvar) and found that the source showed largest flux variations in epoch C with Fvar∼ 35%. We modelled the γ-ray spectra for each epoch and found that the Log-parabola model adequately describes the γ-ray spectra for all the three epochs. We estimated the size of the γ-ray emitting region as 1.03 ×1018 cm and determined that the origin of γ-ray radiation, during the main-flare, could be outside of the broad line region.

Optical Singly-Ionized Iron Emission in Radio-Quiet and Relativistically Jetted Active Galactic Nuclei

The issue of the difference between optical and UV properties of radio-quiet and radio-loud (relativistically “jetted”) active galactic nuclei (AGN) is a long standing one, related to the fundamental question of why a minority of powerful AGN possess strong radio emission due to relativistic ejections. This paper examines a particular aspect: the singly-ionized iron emission in the spectral range 4400–5600 Å, where the prominent HI Hβ and [Oiii]λλ4959,5007 lines are also observed. We present a detailed comparison of the relative intensity of Feii multiplets in the spectral types of the quasar main sequence where most jetted sources are found, and afterwards discuss radio-loud narrow-line Seyfert 1 (NLSy1) nuclei with γ-ray detection and with prominent Feii emission. An Feii template based on I Zw 1 provides an accurate representation of the optical Feii emission for RQ and, with some caveats, also for RL sources. CLOUDY photoionization simulations indicate that the observed spectral energy distribution can account for the modest Feii emission observed in composite radio-loud spectra. However, spectral energy differences alone cannot account for the stronger Feii emission observed in radio-quiet sources, for similar physical parameters. As for RL NLSy1s, they do not seem to behave like other RL sources, likely because of their different physical properties, that could be ultimately associated with a higher Eddington ratio. active galactic nuclei; optical spectroscopy; ionized gas; broad line region

Multi-wavelength observations of the Blazar 4C +28.07

The active galactic nucleus 4C +28.07 is a flat spectrum radio quasar, one of the brightest at γ-ray energies. We study its multi-wavelength emission by analysing ∼12.3 years of Fermi-LAT data in the γ-ray band and Swift-XRT/UVOT available data in X-ray and Optical-to-Ultraviolet bands. In the γ-ray band, five flaring periods have been detected, and quasi-simultaneously with these flaring times, the X-ray and UVOT data detected by Swift-XRT/UVOT have also been analysed. In one of the brightest flare periods (Flare 5; observed on Oct 12, 2018) the γ-ray flux reached (6.7 ± 0.81) × 10−6 photon cm−2 s−1 (∼31 × higher than the mean flux over 12.3 years) with detection significance of σ = 6.1. The estimated variability time(∼2 hours) constrains the γ-ray emitting region size to ≤9 × 1014 cm, which is close to the black hole radius. The spectral energy distributions (SEDs) in the γ-ray band for the ∼12.3 years of data show an early cut-off at ∼14 GeV; beyond ∼60 GeV, however, the spectrum hardens and is detected up to ∼316 GeV. Similar spectral behaviour is also noticeable for the SEDs of flares, which can be linked to the photon absorption by the emitting region’s internal and external narrow-band radiation fields. In the quiescent period, the γ-ray emission was described by the Synchrotron-Self-Compton scenario, while the external photons contributions from the Disk and the broad-line region were required to explain the short-term flaring γ-ray emission. Considering the significance of the obtained results from 4C +28.07, we compared the parameters with 3C 279 and M87, to motivate further studies.

Flux profile at focal area of concentrating solar dishes

We analytically, experimentally and computationally explore the solar radiation flux distribution in the interior region of a spherical mirror and compare it to that of a paraboloidal one with the same aperture area. Our investigation has been performed in the framework of geometrical optics. It is shown that despite one can assign a quasi focus, at half the radius, to a spherical mirror, the light concentration occurs as well on an extended line region which starts at half-radius on the optical axis. In contrast to a paraboloidal concentrator, a spherical mirror can concentrate the radiation parallel to its optical axis both in a point-focus and in a line-focus manner. The envelope of the reflected rays is also obtained. It is shown that the flux distribution has an axial symmetry. The radial dependence of the flux on a flat circular receiver is obtained. The flux longitudinal dependence is shown to exhibit three distinctive regions in the interval [0, R] (R is mirror radius). We obtain the radiational (optical) concentration ratio characteristics and find the optimal location of the flat receiver of a given size at which the concentration ratio is maximised. In contrast to a parabolic mirror, it is shown that this location depends on the receiver size. Our findings offers that in spherical mirrors one can alternatively use a line receiver and gains a considerable thermal energy harvest. Our results are supported by Monte Carlo ray tracing performed by Zemax optical software. Experimental validation has been performed in lab with a silver-coated lens as the spherical mirror.

AGN STORM 2. I. First results: A Change in the Weather of Mrk 817

We present the first results from the ongoing, intensive, multiwavelength monitoring program of the luminous Seyfert 1 galaxy Mrk 817. While this active galactic nucleus was, in part, selected for its historically unobscured nature, we discovered that the X-ray spectrum is highly absorbed, and there are new blueshifted, broad, and narrow UV absorption lines, which suggest that a dust-free, ionized obscurer located at the inner broad-line region partially covers the central source. Despite the obscuration, we measure UV and optical continuum reverberation lags consistent with a centrally illuminated Shakura–Sunyaev thin accretion disk, and measure reverberation lags associated with the optical broad-line region, as expected. However, in the first 55 days of the campaign, when the obscuration was becoming most extreme, we observe a de-coupling of the UV continuum and the UV broad emission-line variability. The correlation recovered in the next 42 days of the campaign, as Mrk 817 entered a less obscured state. The short C iv and Lyα lags suggest that the accretion disk extends beyond the UV broad-line region.

Studying the Influence of External Photon Fields on Blazar Spectra Using a One-Zone Hadro-Leptonic Time-Dependent Model

The recent associations of neutrinos with blazars require the efficient interaction of relativistic protons with ambient soft photon fields. However, along side the neutrinos, γ-ray photons are produced, which interact with the same soft photon fields producing electron-positron pairs. The strength of this cascade has significant consequences on the photon spectrum in various energy bands and puts severe constraints on the pion and neutrino production. In this study, we discuss the influence of the external thermal photon fields (accretion disk, broad-line region, and dusty torus) on the proton-photon interactions, employing a newly developed time-dependent one-zone hadro-leptonic code OneHaLe. We present steady-state cases, as well as a time-dependent case, where the emission region moves through the jet. Within the limits of this toy study, the external fields can disrupt the “usual” double-humped blazar spectrum. Similarly, a moving region would cross significant portions of the jet without reaching the previously-found steady states.

Bifurcated Current Sheet Observed on the Boundary of Kelvin-Helmholtz Vortices

On May 5, 2017 MMS observed a bifurcated current sheet at the boundary of Kelvin-Helmholtz vortices (KHVs) developed on the dawnside tailward magnetopause. We use the event to enhance our understanding of the formation and structure of asymmetric current sheets in the presence of density asymmetry, flow shear, and guide field, which have been rarely studied. The entire current layer comprises three separate current sheets, each corresponding to magnetosphere-side sunward separatrix region, central near-X-line region, and magnetosheath-side tailward separatrix region. Two off-center structures are identified as slow-mode discontinuities. All three current sheets have a thickness of ∼0.2 ion inertial length, demonstrating the sub-ion-scale current layer, where electrons mainly carry the current. We find that both the diamagnetic and electron anisotropy currents substantially support the bifurcated currents in the presence of density asymmetry and weak velocity shear. The combined effects of strong guide field, low density asymmetry, and weak flow shear appear to lead to asymmetries in the streamlines and the current-layer structure of the quadrupolar reconnection geometry. We also investigate intense electrostatics waves observed on the magnetosheath side of the KHV boundary. These waves may pre-heat a magnetosheath population that is to participate into the reconnection process, leading to two-step energization of the magnetosheath plasma entering into the magnetosphere via KHV-driven reconnection.

AGN orientation through the spectroscopic correlations and model of dusty cone shell

The differences between Narrow Line Seyfert 1 galaxies (NLS1s) and Broad Line AGNs (BLAGNs) are not completely understood; it is thought that they may have different inclinations and/or physical characteristics. The FWHM(Hβ)–luminosities correlations are found for NLS1s and their origin is the matter of debate. Here we investigated the spectroscopic parameters and their correlations considering a dusty, cone model of AGN. We apply a simple conical dust distribution (spreading out of broad line region, BLR), assuming that the observed surface of the model is in a good correlation with MIR emission. The dusty cone model in combination with a BLR provides the possibility to estimate luminosity dependence on the cone inclination. The FWHM(Hβ)–luminosities correlations obtained from model in comparison with observational data show similarities which may indicate the influence of AGN inclination and structure to this correlation. An alternative explanation for FWHM(Hβ)–luminosities correlations is the selection effect by the black hole mass. These FWHM(Hβ)–luminosities correlations may be related to the starburst in AGNs, as well. The distinction between spectral properties of the NLS1s and BLAGNs could be caused by multiple effects: beside physical differencies between NLS1s and BLAGNs (NLS1s have lighter black hole mass than BLAGNs), inclination of the conical AGN geometry may have important role as well, where NLS1s may be seen in lower inclination angles.