Multifrequency study of the gamma-ray flaring BL Lacertae object PKS 2233-148 in 2009-2012

We study the jet physics of the BL Lacertae object PKS 2233-148, making use of the synergy of observational data sets in the radio and gamma-ray energy domains. The four-epoch multifrequency (4-43 GHz) very-long-baseline array (VLBA) observations focused on the parsec-scale jet were triggered by a flare in gamma-rays registered by Fermi-LAT on 2010 April 23. We also used 15-GHz data from the OVRO 40-m telescope and MOJAVE VLBA monitoring programs. The jet shape of the source is found to be conical on scales probed by the VLBA observations, setting a lower limit of about 0.1 on its unknown redshift. Nuclear opacity is dominated by synchrotron self-absorption, with a wavelength-dependent core shift of r(core) ([mas]) approximate to 0.1 lambda[cm] mas co-aligned with the innermost jet direction. The turnover frequency of the synchrotron spectrum of the very-long-baseline interferometry core shifts towards lower frequencies as the flare propagates down the jet, and the speed of this propagation is significantly higher, about 1.2 mas yr(-1), than results from traditional kinematics based on tracking bright jet features. We have found indications that the gamma-ray production zone in the source is located at large distances, 10-20 pc, from a central engine, and could be associated with the stationary jet features. These findings favour synchrotron self-Compton, possibly in combination with external Compton scattering by infrared seed photons from a slow sheath of the jet, as the dominant high-energy emission mechanism of the source

Color characteristics of the blazar S5 0716+714 under geometrical origin of the long-term variability

Оптическое излучение блазара S5 0716+714 формируется в его ультрарелятивистском джете в компактной области, расположенной вблизи истинного начала струи. Предполагая, что переменность образуется только за счет изменения коэффициента релятивистского усиления излучения (допплер-фактора) для некоторой части излучающей области и что спектр излучающей области, характеризуемый степенным законом на наблюдаемых частотах, имеет завал на более низких частотах, вызванный синхротронным самопоглощением, мы анализируем архивные данные Крымской астрофизической обсерватории по B-, V-, R-, I-фотометрии блазара S5 0716+714 с 2002 по 2019 г. Получено объяснение наблюдаемому изменению показателя цвета при переменности блазара S5 0716+714 без изменений физических параметров источника.The optical radiation of the blazar S5 0716+714 is formed within its ultrarelativistic jet in a compact region located near the true origin of the jet. Assuming that the variability is formed only by changing the relativistic radiation amplification coefficient (Doppler factor) for some part of the emitting region and that the spectrum of the emitting region, characterized by a power law at the observed frequencies, has a turn-over at lower frequencies, caused by synchrotron self-absorption, we analyze the archival data of the Crimean Astrophysical Observatory of B-, V-, R-, I-photometry of the blazar S5 0716+714 from 2002 to 2019. An explanation for the observed change in the color index during the blazar S5 0716+714 variability without changes in the physical parameters of the source was obtained.Работа выполнена при частичной поддержке РНФ (грант 19-72-00105)

Inverse Compton scattering of radiation of the central source as a mechanism for the formation of X-Ray radiation from kiloparsec jets of quasars

Уже около двадцати лет для интерпретации рентгеновского излучения килопарсековых джетов квазаров широко используется обратное комптоновское рассеяние реликтового излучения. Однако недавний анализ данных наблюдений космического телескопа Fermi-LAT показал неприменимость указанного предположения для джетов нескольких квазаров. Мы рассматриваем обратное комптоновское рассеяние фотонов центрального источника как возможный механизм образованияентгеновского излучения килопарсековых джетов для нескольких квазаров: PKS 0637–752, 3C 273, PKS 1510–089 и PKS 1045–188. Получены оценки угла с лучом зрения и скорости килопарсековых джетов. Предсказываемый поток излучения в гамма-диапазоне для всех объектов оказался ниже верхнего ограничения на поток от килопарсекового джета, полученного из данных наблюдений Fermi-LAT. Показано, что наше предположение о механизме образования рентгеновского излучения килопарсековых джетов согласуется со всеми имеющимися к настоящему времени данными многоволновых наблюдений.For the interpretation of X-ray radiation from kiloparsec jets of quasars, the inverse Compton scattering of the cosmic microwave background has been widely used for almost 20 years. A recent analysis of the Fermi-LAT observational data showed that this assumption is inapplicable for jets of several quasars. In this paper, we consider the inverse Compton scattering of photons from a central source as a possible mechanism for the formation of X-ray radiation from kiloparsec jets of the quasars PKS 0637–752, 3C 273, PKS 1510–089, and PKS 1045–188. Estimates of the angle between the line of sight and the velocity of kiloparsec jets are obtained. The predicted gamma-ray flux for all objects turned out to be below the upper limit on the flux from a kiloparsec jet obtained from the Fermi-LAT data. It is shown that our assumption about the mechanism of X-ray radiation from kiloparsec jets is consistent with all data of multiwavelength observations available to date

New Insights into the mineralogy of the Atlantis II deep metalliferous sediments, Red Sea

The Atlantis II Deep of the Red Sea hosts the largest known hydrothermal ore deposit on the ocean floor and the only modern analog of brine pool-type metal deposition. The deposit consists mainly of chemical-clastic sediments with input from basin-scale hydrothermal and detrital sources. A characteristic feature is the millimeter-scale layering of the sediments, which bears a strong resemblance to banded iron formation (BIF). Quantitative assessment of the mineralogy based on relogging of archived cores, detailed petrography, and sequential leaching experiments shows that Fe-(oxy)hydroxides, hydrothermal carbonates, sulfides, and authigenic clays are the main “ore” minerals. Mn-oxides were mainly deposited when the brine pool was more oxidized than it is today, but detailed logging shows that Fe-deposition and Mn-deposition also alternated at the scale of individual laminae, reflecting short-term fluctuations in the Lower Brine. Previous studies underestimated the importance of nonsulfide metal-bearing components, which formed by metal adsorption onto poorly crystalline Si-Fe-OOH particles. During diagenesis, the crystallinity of all phases increased, and the fine layering of the sediment was enhanced. Within a few meters of burial (corresponding to a few thousand years of deposition), biogenic (Ca)-carbonate was dissolved, manganosiderite formed, and metals originally in poorly crystalline phases or in pore water were incorporated into diagenetic sulfides, clays, and Fe-oxides. Permeable layers with abundant radiolarian tests were the focus for late-stage hydrothermal alteration and replacement, including deposition of amorphous silica and enrichment in elements such as Ba and Au

Blazar spectral variability as explained by a twisted inhomogeneous jet

Blazars are active galactic nuclei, which are powerful sources of radiation whose central engine is located in the core of the host galaxy. Blazar emission is dominated by non-thermal radiation from a jet that moves relativistically towards us, and therefore undergoes Doppler beaming1. This beaming causes flux enhancement and contraction of the variability timescales, so that most blazars appear as luminous sources characterized by noticeable and fast changes in brightness at all frequencies. The mechanism that produces this unpredictable variability is under debate, but proposed mechanisms include injection, acceleration and cooling of particles2, with possible intervention of shock waves3,4 or turbulence5. Changes in the viewing angle of the observed emitting knots or jet regions have also been suggested as an explanation of flaring events6,7,8,9,10 and can also explain specific properties of blazar emission, such as intra-day variability11, quasi-periodicity12,13 and the delay of radio flux variations relative to optical changes14. Such a geometric interpretation, however, is not universally accepted because alternative explanations based on changes in physical conditions—such as the size and speed of the emitting zone, the magnetic field, the number of emitting particles and their energy distribution—can explain snapshots of the spectral behaviour of blazars in many cases15,16. Here we report the results of optical-to-radio-wavelength monitoring of the blazar CTA 102 and show that the observed long-term trends of the flux and spectral variability are best explained by an inhomogeneous, curved jet that undergoes changes in orientation over time. We propose that magnetohydrodynamic instabilities17 or rotation of the twisted jet6 cause different jet regions to change their orientation and hence their relative Doppler factors. In particular, the extreme optical outburst of 2016–2017 (brightness increase of six magnitudes) occurred when the corresponding emitting region had a small viewing angle. The agreement between observations and theoretical predictions can be seen as further validation of the relativistic beaming theory

Blazar spectral variability as explained by a twisted inhomogeneous jet

© 2017 Macmillan Publishers Limited, part of Springer Nature. All rights reserved. Blazars are active galactic nuclei, which are powerful sources of radiation whose central engine is located in the core of the host galaxy. Blazar emission is dominated by non-thermal radiation from a jet that moves relativistically towards us, and therefore undergoes Doppler beaming. This beaming causes flux enhancement and contraction of the variability timescales, so that most blazars appear as luminous sources characterized by noticeable and fast changes in brightness at all frequencies. The mechanism that produces this unpredictable variability is under debate, but proposed mechanisms include injection, acceleration and cooling of particles, with possible intervention of shock waves or turbulence. Changes in the viewing angle of the observed emitting knots or jet regions have also been suggested as an explanation of flaring events and can also explain specific properties of blazar emission, such as intra-day variability, quasi-periodicity and the delay of radio flux variations relative to optical changes. Such a geometric interpretation, however, is not universally accepted because alternative explanations based on changes in physical conditions - such as the size and speed of the emitting zone, the magnetic field, the number of emitting particles and their energy distribution - can explain snapshots of the spectral behaviour of blazars in many cases. Here we report the results of optical-to-radio-wavelength monitoring of the blazar CTA 102 and show that the observed long-term trends of the flux and spectral variability are best explained by an inhomogeneous, curved jet that undergoes changes in orientation over time. We propose that magnetohydrodynamic instabilities or rotation of the twisted jet cause different jet regions to change their orientation and hence their relative Doppler factors. In particular, the extreme optical outburst of 2016-2017 (brightness increase of six magnitudes) occurred when the corresponding emitting region had a small viewing angle. The agreement between observations and theoretical predictions can be seen as further validation of the relativistic beaming theory

Investigating the multiwavelength behaviour of the flat spectrum radio quasar CTA 102 during 2013-2017

We present a multiwavelength study of the flat-spectrum radio quasar CTA 102 during 2013-2017. We use radio-to-optical data obtained by the Whole Earth Blazar Telescope, 15 GHz data from the Owens Valley Radio Observatory, 91 and 103 GHz data from the Atacama Large Millimeter Array, near-infrared data from the Rapid Eye Monitor telescope, as well as data from the Swift (optical-UV and X-rays) and Fermi (gamma-rays) satellites to study flux and spectral variability and the correlation between flux changes at different wavelengths. Unprecedented gamma-ray flaring activity was observed during 2016 November-2017 February, with four major outbursts. A peak flux of (2158 +/- 63) x 10(-8) ph cm(-2) s(-1), corresponding to a luminosity of (2.2 +/- 0.1) x10(50) erg s(-1), was reached on 2016 December 28. These four gamma-ray outbursts have corresponding events in the near-infrared, optical, and UV bands, with the peaks observed at the same time. A general agreement between X-ray and gamma-ray activity is found. The gamma-ray flux variations show a general, strong correlation with the optical ones with no time lag between the two bands and a comparable variability amplitude. This gamma-ray/optical relationship is in agreement with the geometrical model that has successfully explained the low-energy flux and spectral behaviour, suggesting that the long-term flux variations are mainly due to changes in the Doppler factor produced by variations of the viewing angle of the emitting regions. The difference in behaviour between radio and higher energy emission would be ascribed to different viewing angles of the jet regions producing their emission