ABSTRACT
The deepest all-sky survey available in the γ-ray band – the last release of the Fermi-LAT catalogue (4FGL-DR3) based on the data accumulated in 12 years contains more than 6600 sources. The ...largest population among the sources is blazar subclass – 3743, 60.1 per cent of which are classified as BL Lacertae objects (BL Lacs) or Flat Spectrum Radio Quasars (FSRQs), while the rest are listed as blazar candidates of uncertain type (BCU) as their firm optical classification is lacking. The goal of this study is to classify BCUs using different machine learning algorithms, which are trained on the spectral and temporal properties of already classified BL Lacs and FSRQs. Artificial Neural Networks, XGBoost, and LightGBM algorithms are employed to construct predictive models for BCU classification. Using 18 input parameters of 2219 BL Lacs and FSRQs, we train (80 per cent of the sample) and test (20 per cent) these algorithms and find that LightGBM model, state-of-the-art classification algorithm based on gradient boosting decision trees, provides the highest performance. Based on our best model, we classify 825 BCUs as BL Lac candidates and 405 as FSRQ candidates, however, 190 remain without a clear prediction, but the percentage of BCUs in 4FGL is reduced to 5.1 per cent. The γ-ray photon index, synchrotron peak frequency, and high-energy peak frequency of a large sample are used to investigate the relationship between FSRQs and BL Lacs (LBLs, IBLs, and HBLs).
Friendships and other rewarding affilliative bonds are associated with the actions of the nonapeptide hormone oxytocin (OT) in humans and many social mammals. We investigated whether OT itself is ...rewarding, and if that reward is dependent upon the presence of conspecifics. We evaluated the reinforcing effects of OT infusion in female mice on social (conditioned social preference; CSP) and nonsocial tests (conditioned place preference; CPP). Ovariectomised females received oestradiol implants and i.c.v. cannulas. During a pre‐test, they were introduced to a three‐chamber apparatus for 10 min. Social and place apparatus were identical, except that each end‐chamber contained a novel stimulus female for CSP, whereas they were distinguished by visual and tactile cues for CPP. For CSP, test females received OT (0, 100, 200 or 100 ng) and were paired for 30 min with one stimulus female. On alternating days, they received saline vehicle and were paired with the opposite female, for a total of four pairings each. The final conditioned preference test was identical to the pre‐test. OT induced CSP. Test mice that received 100 ng of OT increased their preference score from −67.4 ± 22.1 s in pre‐test to +55.7 ± 35.1 s during the conditioned preference test (P < 0.05). It was observed that 200 ng OT induced an increase in preference score from −162.7 ± 47.3 to +74.3 ± 23.7 s (P < 0.001). There was no effect of 0 or 1000 ng of OT on CSP. An additional group of mice was tested for CPP at 200 ng of OT. Testing and pairings were identical to CSP. OT induced a small but significant CPP. Mice increased their preference score from −222.4 ± 38.0 to −126.0 ± 58.7 s (P < 0.05). OT had no effect on anxiety or odour recognition, as assessed by elevated plus maze and olfactory habituation/dishabituation tests, respectively. In conclusion, OT, similar to other motivating stimuli (drugs, food), not only is rewarding when tested under solitary conditions, but also is reinforcing in a social setting.
Multiwavelength study of high-redshift blazars Sahakyan, N; Israyelyan, D; Harutyunyan, G ...
Monthly Notices of the Royal Astronomical Society,
10/2020, Letnik:
498, Številka:
2
Journal Article
Recenzirano
Odprti dostop
ABSTRACT
High-redshift blazars are among the most powerful objects in the Universe. The spectral and temporal properties of 33 distant blazars (z > 2.5) detected in the high-energy γ-ray band are ...investigated by analysing the Fermi-LAT and Swift Ultraviolet and Optical Telescope/X-ray Telescope (UVOT/XRT) data. The considered sources have soft time-averaged γ-ray spectra (Γγ ≥ 2.2) whereas those that have been observed in the X-ray band have hard X-ray spectra (ΓX = 1.01−1.86). The γ-ray flux of high-redshift blazars ranges from 4.84 × 10−10 to 1.50 × 10−7 photon cm−2 s−1 and the luminosity is within (0.10−5.54) × 1048 erg s−1 which during the γ-ray flares increases up to (0.1−1) × 1050 erg s−1. In the X-ray band, only the emission of PKS 0438−43, B2 0743+25, and TXS 0222+185 is found to vary in different Swift XRT observations whereas in the γ-ray band, the emission is variable for fourteen sources: the flux of B3 1343+451 and PKS 0537−286 changes in sub-day scales, that of PKS 0347−211 and PKS 0451−28 in day scales, while the γ-ray variability of the others is in week or month scales. The properties of distant blazar jets are derived by modelling the multiwavelength spectral energy distributions within a one-zone leptonic scenario assuming that the X-ray and γ-ray emissions are produced from inverse Compton scattering of synchrotron and dusty torus photons. From the fitting, the emission region size is found to be ≤0.05 pc and the magnetic field and the Doppler factor are correspondingly within 0.10−1.74 G and 10.0−27.4. By modelling the optical–UV excess, we found that the central black hole masses and accretion disc luminosities are within Ld ≃ (1.09−10.94) × 1046 erg s−1 and (1.69−5.35) × 109 M⊙, respectively.
Abstract Modeling the multiwavelength spectral energy distributions (SEDs) of blazars provides key insights into the underlying physical processes responsible for the emission. While SED modeling ...with self-consistent models is computationally demanding, it is essential for a comprehensive understanding of these astrophysical objects. We introduce a novel, efficient method for modeling the SEDs of blazars by the mean of a convolutional neural network (CNN). In this paper, we trained the CNN on a leptonic model that incorporates synchrotron and inverse Compton emissions, as well as self-consistent electron cooling and pair creation–annihilation processes. The CNN is capable of reproducing the radiative signatures of blazars with high accuracy. This approach significantly reduces the computational time, thereby enabling real-time fitting to multiwavelength data sets. As a demonstration, we used the trained CNN with MultiNest to fit the broadband SEDs of Mrk 421 and 1ES 1959+650, successfully obtaining their parameter posterior distributions. This novel framework for fitting the SEDs of blazars will be further extended to incorporate more sophisticated models based on external Compton and hadronic scenarios, allowing for multimessenger constraints in the analysis. The models will be made publicly available via a web interface at the Markarian Multiwavelength Data Center to facilitate self-consistent modeling of multimessenger data from blazar observations.
ABSTRACT
We present long-term multiwavelength observations of blazar CTA 102 ($z$ = 1.037). Detailed temporal and spectral analyses of γ-ray, X-ray, and UV/optical data observed by Fermi-LAT, Swift ...XRT, NuSTAR, and Swift-UVOT over a period of 14 yr, between 2008 August and 2022 March, were performed. We found strong variability of source emission in all the considered bands; especially in the γ-ray band it exhibited extreme outbursts when the flux crossed the level of 10−5 photon cm−2 s−1. Using the Bayesian Blocks algorithm, we split the adaptively binned γ-ray light curve into 347 intervals of quiescent and flaring episodes and for each period built corresponding multiwavelength spectral energy distributions (SEDs), using the available data. Among the considered SEDs, 117 high-quality (quasi) contemporaneous SEDs, which have sufficient multiwavelength data, were modelled using jetset framework within a one-zone leptonic synchrotron and inverse-Compton emission scenario assuming the emitting region is within the broad-line region and considering internal and external seed photons for the inverse-Compton upscattering. As a result of modelling, the characteristics of the relativistic electron distribution in the jet as well as jet properties are retrieved and their variation in time is investigated. The applied model can adequately explain the assembled SEDs and the modelling shows that the data in the bright flaring periods can be reproduced for high Doppler boosting and magnetic field. The obtained results are discussed in the context of particle cooling in the emitting region.
Abstract In the context of modeling spectral energy distributions (SEDs) for blazars, we extend the method that uses a convolutional neural network (CNN) to include external inverse Compton ...processes. The model assumes that relativistic electrons within the emitting region can interact with and up-scatter external photons originating from the accretion disk, the broad-line region, and the torus, to produce the observed high-energy emission. We trained the CNN on a numerical model that accounts for the injection of electrons, their self-consistent cooling, and pair creation-annihilation processes, considering both internal and all external photon fields. Despite the larger number of parameters compared to the synchrotron self-Compton model and the greater diversity in spectral shapes, the CNN enables an accurate computation of the SED for a specified set of parameters. The performance of the CNN is demonstrated by fitting the SED of two flat-spectrum radio quasars, namely 3C 454.3 and CTA 102, and obtaining their parameter posterior distributions. For the first source, the available data in the low-energy band allowed us to constrain the minimum Lorentz factor of the electrons, γ min , while for the second source, due to the lack of these data, γ min = 10 2 was set. We used the obtained parameters to investigate the energetics of the system. The model developed here, along with one from Bégué et al., enables self-consistent, in-depth modeling of blazar broadband emissions within a leptonic scenario.
The problem of a transition from a system of two-dimensional equations of the micropolar (moment) theory of elasticity in a thin curved region to a one-dimensional system of equations of deformation ...of a micropolar elastic thin beam with a circular axis (a curved beam with a median surface in the form of a circular arc is meant) is discussed. In carrying out this transition, so-called Timoshenko hypotheses generalized to the micropolar case are used. Based on them, an applied model is constructed that describes the stress–strained state during bending of a micropolar (with independent fields of displacements and rotations) elastic thin beam with a circular axis. It is shown that the model includes the law of conservation of energy, energy theorems, and variational principles. All the main functionals of the constructed model are derived from the functional of the two-dimensional micropolar theory of elasticity that contains only the first-order derivatives of displacements and rotations. To solve boundary problems of statics and dynamics on the basis of an applied bending model of a micropolar elastic thin beam with a circular axis, an appropriate variant of the finite element method (FEM) is being developed. The basic concepts and stages of implementation of the modified FEM are formulated: discretization, selection of the main nodal unknowns, approximation of the desired solution, and construction of the basic FEM equations. Examples of finite element solutions of static deformation problems and problems of natural vibrations of beams with a circular axis in the framework of both the micropolar and classical elasticity theories are given. A comparative analysis of the solutions has been performed, as a result of which some effective properties of beams with a circular axis are established when considering their deformations according to the micropolar theory of elasticity.
B3 1343 + 451 is a distant ( z = 2.534 ) and bright flat-spectrum radio quasar observed in the γ -ray band. The results from the multiwavelength observations of B3 1343 + 451 with Fermi-LAT and Swift ...are reported. In the γ -ray band, strong flares were observed on 05 December 2011 and on 13 December 2009 when the flux increased up to (8.78 ± 0.83)·10
-7
photon cm
-2
s
-1
. The hardest photon index Γ = 1.73 ± 0.24 has been observed on MJD 58089 which is not common for flat-spectrum radio quasars. The analysis of Swift XRT data shows that in 2014 the X-ray flux of the source increased ~2 times as compared to 2009, but in both periods the X-ray emission is characterized by a hard photon index of Γ
X-ray
= 1.2–1.3. During the γ -ray flares, the shortest flux halving timescale was ~2.34 days, implying the emission had been produced in a very compact region, R ≤ δ ct /(1 + z) = 3.43·10
16
cm (when δ = 20 ). The spectral energy distribution of B3 1343 + 451 is modeled during the quiescent and flaring periods assuming a compact emitting region outside the BLR. It is found that the flares can be explained by only changing the bulk Lorentz factor of the emitting region without significant modification of the emitting electron parameters and luminosity of the jet.
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