Two flares with one shock: the interesting case of 3C 454.3

The quasar 3C 454.3 is a blazar known for its rapid and violent outbursts seen across the electromagnetic spectrum. Using γ-ray, X-ray, multiband optical, and very-long-baseline interferometric data we investigate the nature of two such events that occurred in 2013 and 2014 accompanied by strong variations in optical polarization, including a ~230° electric vector position angle (EVPA) rotation. Our results suggest that a single disturbance was responsible for both flaring events. We interpret the disturbance as a shock propagating down the jet. Under this interpretation the 2013 flare originated most likely due to changes in the viewing angle caused by perhaps a bent or helical trajectory of the shock upstream of the radio core. The 2014 flare and optical polarization behavior are the result of the shock exiting the 43 GHz radio core, suggesting that shock crossings are one of the possible mechanisms for EVPA rotations.Accepted manuscrip

Emission-line Variability during a Nonthermal Outburst in the Gamma-Ray Bright Quasar 1156+295

This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted reuse, distribution, and reproduction in any medium, provided the original work is properly cited.We present multi-epoch optical spectra of the γ-ray bright blazar 1156+295 (4C +29.45, Ton 599) obtained with the 4.3 m Lowell Discovery Telescope. During a multiwavelength outburst in late 2017, when the γ-ray flux increased to 2.5 × 10−6 phot cm−2 s−1 and the quasar was first detected at energies ≥100 GeV, the flux of the Mg ii λ2798 emission line changed, as did that of the Fe emission complex at shorter wavelengths. These emission-line fluxes increased along with the highly polarized optical continuum flux, which is presumably synchrotron radiation from the relativistic jet, with a relative time delay of ≲2 weeks. This implies that the line-emitting clouds lie near the jet, which points almost directly toward the line of sight. The emission-line radiation from such clouds, which are located outside the canonical accretion-disk related broad-line region, may be a primary source of seed photons that are up-scattered to γ-ray energies by relativistic electrons in the jet. © 2022. The Author(s). Published by the American Astronomical Society.This research was supported in part by NASA Fermi guest investigator program grants 80NSSC19K1504 and 80NSSC20K1565. We thank A. Tchekhovskoy for discussion of possible origins of the variable line-emitting clouds. These results made use of the Lowell Discovery Telescope (LDT) at Lowell Observatory. Lowell Observatory is a private, non-profit institution dedicated to astrophysical research and public appreciation of astronomy, and operates the LDT in partnership with Boston University, the University of Maryland, the University of Toledo, Northern Arizona University and Yale University. This study was based in part on observations conducted using the 1.8 m Perkins Telescope Observatory (PTO) in Arizona, which is owned and operated by Boston University. I.A. acknowledges financial support from the Spanish "Ministerio de Ciencia e Innovación" (MCINN) through the "Center of Excellence Severo Ochoa" award for the Instituto de Astrofísica de Andalucía-CSIC (SEV-2017-0709). Acquisition and reduction of the MAPCAT data were supported in part by MICINN through grants AYA2016-80889-P and PID2019-107847RB-C44. The MAPCAT observations were carried out at the German-Spanish Calar Alto Observatory, which is jointly operated by Junta de Andalucía and Consejo Superior de Investigaciones Científicas. Data from the Steward Observatory spectropolarimetric monitoring project were used; this program was supported by Fermi Guest Investigator grants NNX08AW56G, NNX09AU10G, NNX12AO93G, and NNX15AU81G. C.C. acknowledges support from the European Research Council (ERC) under the European Union Horizon 2020 research and innovation program under the grant agreement No. 771282.Peer reviewe

Multiwavelength behaviour of the blazar 3C 279: Decade-long study from γ -ray to radio

We report the results of decade-long (2008-2018) γ -ray to 1 GHz radio monitoring of the blazar 3C 279, including GASP/WEBT, Fermi and Swift data, as well as polarimetric and spectroscopic data. The X-ray and γ -ray light curves correlate well, with no delay ≳ 3 h, implying general cospatiality of the emission regions. The γ -ray-optical flux-flux relation changes with activity state, ranging from a linear to amore complex dependence. The behaviour of the Stokes parameters at optical and radio wavelengths, including 43 GHz Very Long Baseline Array images, supports either a predominantly helical magnetic field or motion of the radiating plasma along a spiral path. Apparent speeds of emission knots range from 10 to 37c, with the highest values requiring bulk Lorentz factors close to those needed to explain γ -ray variability on very short time-scales. The MgII emission line flux in the 'blue' and 'red' wings correlates with the optical synchrotron continuum flux density, possibly providing a variable source of seed photons for inverse Compton scattering. In the radio bands, we find progressive delays of the most prominent light-curve maxima with decreasing frequency, as expected from the frequency dependence of the τ= 1 surface of synchrotron self-absorption. The global maximum in the 86 GHz light curve becomes less prominent at lower frequencies, while a local maximum, appearing in 2014, strengthens toward decreasing frequencies, becoming pronounced at ∼5 GHz. These tendencies suggest different Doppler boosting of stratified radio-emitting zones in the jet. © 2020 The Author(s).We thank the referee for attentive reading and comments that helped to improve presentation of the manuscript. The data collected by the WEBT collaboration are stored in the WEBT archive at the Osservatorio Astrofisico di Torino -INAF (ht tp://www.oato.inaf.it/blazars/webt/); for questions regarding their availability, please contact the WEBT President Massimo Villata([email protected]).TheSt.Petersburg University team acknowledges support from Russian Science Foundation grant 17-12-01029. The research at BU was supported in part by National Science Foundation grant AST-1615796 and NASA Fermi Guest Investigator grants 80NSSC17K0649, 80NSSC19K1504, and 80NSSC19K1505. The PRISM camera at Lowell Observatory was developed by K. Janes et al. at BU and Lowell Observatory, with funding from the NSF, BU, and Lowell Observatory. The emission-line observations made use of the DCT at Lowell Observatory, supported by Discovery Communications, Inc., BU, the University of Maryland, the University of Toledo, and Northern Arizona University. The VLBA is an instrument of the National Radio Astronomy Observatory. The National Radio Astronomy Observatory is a facility of the US NSF, operated under cooperative agreement by Associated Universities, Inc. This research has used data from the UMRAO which was supported by the University of Michigan; research at this facility was supported by NASA under awards NNX09AU16G, NNX10AP16G, NNX11AO13G, and NNX13AP18G, and by the NSF under award AST-0607523. The Steward Observatory spectropolarimetric monitoring project was supported by NASA Fermi Guest Investigator grants NNX08AW56G, NNX09AU10G, NNX12AO93G, and NNX15AU81G. The Torino group acknowledges financial contribution from agreement ASI-INAF n.2017-14-H.0 and from contract PRIN-SKA-CTA-INAF 2016. I.A. acknowledges support by a Ramon y Cajal grant (RYC-2013-14511) of the 'Ministerio de Ciencia, Innovacion, y Universidades (MICIU)' of Spain and from MCIU through the 'Center of Excellence Severo Ochoa' award for the Instituto de Astrofisica de Andalucia-CSIC (SEV-20170709). Acquisition and reduction of the POLAMI and MAPCAT data were supported by MICIU through grant AYA2016-80889-P. The POLAMI observations were carried out at the IRAM 30-m Telescope, supported by INSU/CNRS (France), MPG (Germany) and IGN (Spain). The MAPCAT observations were carried out at theGerman-Spanish Calar Alto Observatory, jointly operated by the Max-Plank-Institut fur Astronomie and the Instituto de Astrofisica de Andalucia-CSIC. The study is based partly on data obtained with the STELLA robotic telescopes in Tenerife, an AIP facility jointly operated by AIP and IAC. The OVRO 40-m monitoring program is supported in part by NASA grants NNX08AW31G, NNX11A043G, and NNX14AQ89G, and NSF grants AST-0808050 and AST-1109911. TH was supported by the Academy of Finland projects 317383 and 320085. AZT-24 observations were made within an agreement between Pulkovo, Rome and Teramo observatories. The Submillimeter Array is a joint project between the Smithsonian Astrophysical Observatory and the Academia Sinica Institute of Astronomy and Astrophysics and is funded by the Smithsonian Institution and the Academia Sinica. The Abastumani team acknowledges financial support by the Shota Rustaveli National Science Foundation under contract FR/217950/16. r This research was partially supported by the Bulgarian National Science Fund of the Ministry of Education and Science under grants DN 081/2016, DN 18-13/2017, KP-06-H28/3 (2018), and KP-06-PN38/1 (2019), Bulgarian National Science Programme 'Young Scientists and Postdoctoral Students 2019', Bulgarian National Science Fund under grant DN18-10/2017 and National RI Roadmap Projects DO1-157/28.08.2018 and DO1-153/28.08.2018 of the Ministry of Education and Science of the Republic of Bulgaria. GD and OV gratefully acknowledge observing grant support from the Institute of Astronomy and Rozhen National Astronomical Observatory via bilateral joint research project `Study of ICRF radio-sources and fast variable astronomical objects' (head -G. Damljanovic). This work was partly supported by the National Science Fund of the Ministry of Education and Science of Bulgaria under grant DN 08-20/2016, and by project RD-08-37/2019 of the University of Shumen. This work is a part of projects nos 176011, 176004, and 176021, supported by theMinistry of Education, Science and Technological Development of the Republic of Serbia. MGM acknowledges support through the Russian Government Program of Competitive Growth of Kazan Federal University. The Astronomical Observatory of the Autonomous Region of the Aosta Valley (OAVdA) is managed by the Fondazione Clement Fillietroz-ONLUS, which is supported by the Regional Government of the Aosta Valley, the Town Municipality of Nus and the 'Unite des Communes vald 'otainesMont-Emilius'. The research at the OAVdA was partially funded by several `Research and Education' annual grants from Fondazione CRT. This article is partly based on observations made with the IAC80 and TCS telescopes operated by the Instituto de Astrofisica de Canarias in the Spanish Observatorio del Teide on the island of Tenerife. A part of the observations were carried out using theRATAN-600 scientific equipment (SAO of the Russian Academy of Sciences)

Detection of the blazar S4 0954+65 at very-high-energy with the MAGIC telescopes during an exceptionally high optical state

The very high energy (VHE ¿ 100 GeV) -ray MAGIC observations of the blazar S4 0954+65, were triggered by an exceptionally high flux state of emission in the optical. This blazar has a disputed redshift of z = 0.368 or z ¿ 0.45 and an uncertain classification among blazar subclasses. The exceptional source state described here makes for an excellent opportunity to understand physical processes in the jet of S4 0954+65 and thus contribute to its classification. Methods. We investigated the multiwavelength (MWL) light curve and spectral energy distribution (SED) of the S4 0954+65 blazar during an enhanced state in February 2015 and have put it in context with possible emission scenarios. We collected photometric data in radio, optical, X-ray, and ¿-ray. We studied both the optical polarization and the inner parsec-scale jet behavior with 43 GHz data. Results. Observations with the MAGIC telescopes led to the first detection of S4 0954+65 at VHE. Simultaneous data with Fermi-LAT at high energy ¿-ray(HE, 100 MeV < E < 100 GeV) also show a period of increased activity. Imaging at 43 GHz reveals the emergence of a new feature in the radio jet in coincidence with the VHE flare. Simultaneous monitoring of the optical polarization angle reveals a rotation of approximately 100. Conclusions. The high emission state during the flare allows us to compile the simultaneous broadband SED and to characterize it in the scope of blazar jet emission models. The broadband spectrum can be modeled with an emission mechanism commonly invoked for flat spectrum radio quasars (FSRQs), that is, inverse Compton scattering on an external soft photon field from the dust torus, also known as external Compton. The light curve and SED phenomenology is consistent with an interpretation of a blob propagating through a helical structured magnetic field and eventually crossing a standing shock in the jet, a scenario typically applied to FSRQs and low-frequency peaked BL Lac objects (LBL). © ESO 2018.The financial support of the German BMBF and MPG, the Italian INFN and INAF, the Swiss National Fund SNF, the ERDF under the Spanish MINECO (FPA2015-69818-P, FPA2012-36668, FPA2015-68378-P, FPA2015-69210-C6-2-R, FPA2015-69210-C6-4-R, FPA2015-69210-C6-6-R, AYA2015-71042-P, AYA2016-76012-C3-1-P, ESP2015-71662-C2-2-P, CSD2009-00064), and the Japanese JSPS and MEXT is gratefully acknowledged. This work was also supported by the Spanish Centro de Excelencia “Severo Ochoa” SEV-2012-0234 and SEV-2015-0548, and Unidad de Excelencia “María de Maeztu” MDM-2014-0369, by the Croatian Science Foundation (HrZZ) Project IP-2016-06-9782 and the University of Rijeka Project 13.12.1.3.02, by the DFG Collaborative Research Centers SFB823/C4 and SFB876/C3, the Polish National Research Centre grant UMO-2016/22/M/ST9/00382 and by the Brazilian MCTIC, CNPq, and FAPERJ. IA acknowledges support by a Ramón y Cajal grant of the Ministerio de Economía, Industria y Competitividad (MINECO) of Spain. The research at the IAA–CSIC was supported in part by the MINECO through grants AYA2016–80889–P, AYA2013–40825–P, and AYA2010–14844, and by the regional government of Andalucía through grant P09–FQM–4784.Peer Reviewe

Multiwavelength variability of BL Lacertae measured with high time resolution

In an effort to locate the sites of emission at different frequencies and physical processes causing variability in blazar jets, we have obtained high time-resolution observations of BL Lacertae over a wide wavelength range: with the Transiting Exoplanet Survey Satellite (TESS) at 6000–10000 Å with 2 minute cadence; with the Neil Gehrels Swift satellite at optical, UV, and X-ray bands; with the Nuclear Spectroscopic Telescope Array at hard X-ray bands; with the Fermi Large Area Telescope at γ-ray energies; and with the Whole Earth Blazar Telescope for measurement of the optical flux density and polarization. All light curves are correlated, with similar structure on timescales from hours to days. The shortest timescale of variability at optical frequencies observed with TESS is ~0.5 hr. The most common timescale is 13 ± 1 hr, comparable with the minimum timescale of X-ray variability, 14.5 hr. The multiwavelength variability properties cannot be explained by a change solely in the Doppler factor of the emitting plasma. The polarization behavior implies that there are both ordered and turbulent components to the magnetic field in the jet. Correlation analysis indicates that the X-ray variations lag behind the γ-ray and optical light curves by up to ~0.4 day. The timescales of variability, cross-frequency lags, and polarization properties can be explained by turbulent plasma that is energized by a shock in the jet and subsequently loses energy to synchrotron and inverse Compton radiation in a magnetic field of strength ~3 G.Accepted manuscrip

Multiwavelength behaviour of the blazar 3C 279: decade-long study from γ-ray to radio

We report the results of decade-long (2008–2018) γ-ray to 1 GHz radio monitoring of the blazar 3C 279, including GASP/WEBT, Fermi and Swift data, as well as polarimetric and spectroscopic data. The X-ray and γ-ray light curves correlate well, with no delay ≳ 3 h, implying general cospatiality of the emission regions. The γ-ray–optical flux–flux relation changes with activity state, ranging from a linear to a more complex dependence. The behaviour of the Stokes parameters at optical and radio wavelengths, including 43 GHz Very Long Baseline Array images, supports either a predominantly helical magnetic field or motion of the radiating plasma along a spiral path. Apparent speeds of emission knots range from 10 to 37c, with the highest values requiring bulk Lorentz factors close to those needed to explain γ-ray variability on very short time-scales. The Mg ii emission line flux in the ‘blue’ and ‘red’ wings correlates with the optical synchrotron continuum flux density, possibly providing a variable source of seed photons for inverse Compton scattering. In the radio bands, we find progressive delays of the most prominent light-curve maxima with decreasing frequency, as expected from the frequency dependence of the τ = 1 surface of synchrotron self-absorption. The global maximum in the 86 GHz light curve becomes less prominent at lower frequencies, while a local maximum, appearing in 2014, strengthens toward decreasing frequencies, becoming pronounced at ∼5 GHz. These tendencies suggest different Doppler boosting of stratified radio-emitting zones in the jet.First author draf

The complex variability of blazars: time-scales and periodicity analysis in S4 0954+65

Among active galactic nuclei, blazars show extreme variability properties. We here investigate the case of the BL Lac object S4 0954+65 with data acquired in 2019–2020 by the Transiting Exoplanet Survey Satellite (TESS) and by the Whole Earth Blazar Telescope (WEBT) Collaboration. The 2-min cadence optical light curves provided by TESS during three observing sectors of nearly 1 month each allow us to study the fast variability in great detail. We identify several characteristic short-term time-scales, ranging from a few hours to a few days. However, these are not persistent, as they differ in the various TESS sectors. The long-term photometric and polarimetric optical and radio monitoring undertaken by the WEBT brings significant additional information, revealing that (i) in the optical, long-term flux changes are almost achromatic, while the short-term ones are strongly chromatic; (ii) the radio flux variations at 37 GHz follow those in the optical with a delay of about 3 weeks; (iii) the range of variation of the polarization degree and angle is much larger in the optical than in the radio band, but the mean polarization angles are similar; (iv) the optical long-term variability is characterized by a quasi-periodicity of about 1 month. We explain the source behaviour in terms of a rotating inhomogeneous helical jet, whose pitch angle can change in time.Accepted manuscrip

Молодежь в политической и социокультурной жизни Африки

Представляемая работа является первым за последние 25 лет монографическим изданием, посвященным проблемам африканской молодежи и ее роли в становлении и развитии молодых государств. Особое внимание уделяется вопросам социализации и формирования идентичности как в традиционном, так и в современном обществах, спецификt молодежных политических движений и молодежной политике государственных структур. Затрагиваются вопросы демографического фактора и влияния средств массовой информации на решении проблемы занятости