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1.
The results of simultaneous high-resolution radio observations of the BL Lac object 1749+701 at 5, 8.4, 15, and 22 GHz are presented. The source has a rich, extended structure displaying a number of interesting features: a strongly bent jet, the presence of transverse and longitudinal magnetic field in different regions of the extended structure, and a very non-uniform rotation-measure distribution on parsec scales, in spite of the fact that the integrated rotation measure is modest. Gradients of the rotation measure across the jet are detected, suggesting the presence of a toroidal magnetic-field component. The rotation measure is higher in the core region, apparently due to an enhanced thermal-electron density and magnetic-field strength. A narrow feature is detected in the rotation-measure distribution, whose sign is opposite to that in the surrounding regions of the radio jet, possibly testifying to the presence of a sharp bend in the jet. Images were constructed using weighting in the uv plane, in order to reveal weak polarization in the extended jet structure. 相似文献
2.
S. A. Tyul’bashev 《Astronomy Reports》2005,49(12):967-972
We present the results of a study of the sources PKS 0405-385, B0917+624, PKS 1257-326, and J1819+3845, which display variability on time scales from 1–7 h (at 5 GHz). Estimates of the physical parameters (magnetic-field intensity, density of relativistic particles, energies of the magnetic field and relativistic particles) are given for B0917+624 and J1819+3845. It is shown that these sources are not in a state of energy equipartition. A number of indirect arguments indicate that the shortest flares in sources with long-time-scale variability have the same parameters as flares in the studied sources. 相似文献
3.
Maps of the radio source 3C 120 obtained from VLBA+ observations at 8.4 GHz at five epochs in January–September 2002 are presented. The images were reconstructed using the maximum entropy method and the Pulkovo VLBImager software package for VLBI mapping. Apparent superluminal motions of the brightest jet knots have been estimated. The speeds of jet knots decreases with distance from the core, changing from (5.40±0.48)c to (2.00±0.48)c over 10 mas (where c is the speed of light) for a Hubble constant of 65 km s?1 Mpc?1. This can be explained by interaction of the jet with the medium through which it propagates. 相似文献
4.
The variability of the blazar S5 1803+784 (J1800+7828) on a timescale of a month is analyzed using daily RATAN-600 observations in 2009 (a total of 154 observations) at five frequences from 2.3 to 21.7 GHz. Cyclic variability of the flux density was detected at 7.7, 11.1, and 21.7 GHz on a timescale of 34–35 days, with modulation indices of 2.1, 3.6, and 6.6%, respectively. Characteristic time scales are derived from the light curves and the structure and autocorrelation functions. The spectrum of the variable component is rising, with spectral index α ≈ 1.3. The delays of the light-curve maxima between 21.7–11.1 and 11.1–7.7 GHz are three to four days. The integrated spectra for different light-curve phases indicate that the maximum shifts toward lower frequencies as the flux density passes through the maximum. Our results suggest that the variability can be explained mainly by non-stationary processes in the radio source itself, due to the propagation of shocks in the jet. 相似文献
5.
A. G. Gorshkov A. V. Ipatov V. K. Konnikova V. V. Mardyshkin M. G. Mingaliev M. A. Kharinov 《Astronomy Reports》2014,58(10):716-724
Results of the observations of the blazar J1159+2914 (S1156+295) in 2010–2013 are reported. The observations were carried out on the RATAN-600 radio telescope (Special Astrophysical Observatory, Russian Academy of Sciences) at 4.85, 7.7, 11.1, and 21.7 GHz and the 32-m Zelenchuk and Badary radio telescopes of the Quasar-KVO Complex (Institute of Applied Astronomy, Russian Academy of Sciences) at 4.85 and 8.57 GHz. A flare peaked in August 2010, after which the flux density decreased monotonically at all studied frequencies. Variability on a timescale of 7 days was detected at 7.7 and 11.1 GHz near the flare maximum. The delay in the maximum at 7.7 GHz relative to the maximum at 11.1 GHz was 1.5 d, implying a Lorentz factor γ = 55 and angle of the jet to the line of sight θ ≈ 2° since mid-2011. Searches for intraday variability (IDV) were undertaken by the 32-m telescopes, mostly since mid-2011. Intraday variability was confidently detected only at the Badary station on November 10–11, 2012 at 4.85 GHz: the IDV timescale was τ acf = 6 h, the modulation index was m = 1.4%, and the flux density of the variable component was S var = 126 mJy. 相似文献
6.
Simultaneous observations on the RATAN-600 radio telescope at 0.97, 2.3, 3.9, 7.7, 11.1, and 21.7 GHz during the period from January 3 to February 25, 1998, revealed variability of 0524+034 on time scales not exceeding 10 days. The variations are correlated at all frequencies where the parameters of the variability could be determined, including in the optically thick part of the spectrum. The mean spectrum of the variable component was derived and is in agreement with the spectrum of a homogeneous, spherically symmetrical source. In the optically thin part of the spectrum, the spectral index of the variable component is α=?0.2, reflecting the initial energy distribution of the relativistic electrons. It is argued that the variable emission is associated with the acceleration of electrons and amplification of the magnetic field and that adiabatic expansion can be neglected. It is proposed that the observed variability is due to illumination of inhomogeneities in the jet by a shock front passing through them and that the light curve reflects the distribution and characteristic sizes of these inhomogeneities (0.14–0.5 pc for angles to the line of sight not exceeding 10°, Lorentz factor γ=10, and adopted redshift z=0.5). In 0524+034, in addition to the rapidly variable component, there are two slowly varying components, one of which has α=?0.7 in the optically thin part of the spectrum. 相似文献
7.
A. G. Gorshkov A. V. Ipatov I. A. Ipatova V. K. Konnikova V. V. Mardyshkin M. G. Mingaliev M. A. Kharinov 《Astronomy Reports》2018,62(3):183-199
The article presents the results of observations of the blazar 3C 454.3 (J2253+1608), obtained in 2010–2017 on the RATAN-600 radio telescope of the Special Astrophysical Observatory at 4.6, 8.2, 11.2, and 21.7 GHz and on the 32-m Zelenchuk and Badary radio telescopes of the Quasar VLBI Network of the Institute of Applied Astronomy at 4.84 and 8.57 GHz. Long-term variability of the radio emission is studied, as well as variability on time scales of several days and intraday variability (IDV). Two flares were observed in the long-term light curve, in 2010 and in 2015–2017. The flux density at 21.7 GHz increased by a factor of ten during these flares. The delay in the maximum of the first flare at 4.85 GHz relative to the maximum at 21.7 GHz was six months. The time scale for variability on the descending branch of the first flare at 21.7 GHz was τvar = 1.2 yrs, yielding an upper limit on the linear size of the emitting region of 0.4 pc, corresponding to an angular size of 0.06 mas. The brightness temperature during the flare exceeded the Compton limit, implying a Doppler factor δ = 3.5, consistent with the known presence of a relativistic jet oriented close to the line of sight. No significant variability on time scales from several days to several weeks was found in five sets of daily observations carried out over 120 days. IDV was detected at 8.57 GHz on the 32-m telescopes in 30 of 61 successful observing sessions, with the presence of IDV correlated with the maxima of flares. The characteristic time scale for the IDV was from two to ten hours. A number of IDV light curves show the presence of a time delay in the maxima in the light curves for simultaneous observations carried out on the Badary and Zelenchuk antennas, which are widely separated in longitude. This demonstrates that the IDV most like arises in the interstellar medium. 相似文献
8.
A. V. Uryson 《Astronomy Reports》2004,48(2):81-88
Particles can be accelerated to ultrahigh energies E≈1021 eV in moderate Seyfert nuclei. This acceleration occurs in shock fronts in relativistic jets. The maximum energy and chemical composition of the accelerated particles depend on the magnetic field in the jet, which is not well known; fields in the range ～5–1000 G are considered in the model. The highest energies of E≈1021 eV are acquired by Fe nuclei when the field in the jet is B≈16 G. When B～(5–40) G, nuclei with Z<10 are accelerated to E≤1020 eV, while nuclei with Z≥10 acquire energies E≥2×1020 eV. Only particles with Z≥23 acquire energies E≤1020 eV when B～1000 G. Protons are accelerated to E<4×1019 eV, and do not fall into the range of energies of interest for any magnetic field B. The particles lose a negligible amount of their energy in interactions with infrared photons in the accretion disk; losses in the thick gas-dust torus are also negligible if the luminosity of the galaxy is L≤1046 erg/s and the angle between the normal to the galactic plane and the line of sight is sufficiently small, i.e., if the axial ratio of the galactic disk is comparatively high. The particles do not lose energy to curvature radiation if their deviations from the jet axis do not exceed 0.03–0.04 pc at distances from the center of R≈40–50 pc. Synchrotron losses are small, since the magnetic field frozen in the galactic wind at R≤40–50 pc is directed (as in the jet) primarily in the direction of motion. If the model considered is valid, the detected cosmic-ray protons could be either fragments of Seyfert nuclei or be accelerated in other sources. The jet magnetic fields can be estimated both from direct astronomical observations and from the energy spectrum and chemical composition of cosmic rays. 相似文献
9.
A cylindrical magneto-hydrodynamical model for the transverse structures of the nonrelativisitic jets observed from young
stars is proposed. The importance of the temperature terms in the equations describing one-dimensional cylindrical flows is
discussed. It is shown that taking into account heating at an oblique shock at the base of the jet makes it possible to obtain
physical parameters of the jet that are in good agreement with observations. In particular, the jet can be confined by an
external magnetic field of the order of 10−6 G at a distance of 100 AU from the rotational axis. 相似文献
10.
Based on the idea that the X-ray emission of the knots in the kiloparsec-scale jet of 3C 273 located closest to the active
nucleus is due to inverse Compton scattering on the quasar radiation, while the X-ray emission of knots further from the nucleus
is due to inverse Compton scattering on the cosmic microwave background, we find that the angle of the jet to the line of
sight is θ ≈ 30°. The magnetic field and electron density in the knots are estimated. It is concluded that there is a break
in the electron-energy spectrum at a Lorentz factor of г ∼ 106. It is shown that the energy density of the relativistic electrons in the knots appreciably exceeds the energy density in
the magnetic field. 相似文献
11.
Western disturbances seen with AMSU-B and infrared sensors 总被引：2，自引：0，他引：2
Western disturbances (WD) of winter and pre-monsoon seasons are the important sources of rainfall in the Indo-Gangetic plains.
WDs are troughs or circulations in the westerly winds modified by the Himalayas. Operationally, WDs are monitored using infrared
(IR) and water vapour (WV) images. Advanced Microwave Sounding Unit-B (AMSU-B), flying onboard the NOAA satellites, also allows
WDs to be monitored in five microwave frequencies. Two are in water vapour window (89, 150 GHz) and three are absorption channels
(centred at 183.31 GHz). Unlike the top of cloud view in IR or WV, AMSU-B radiances show the effect of moisture and hydrometeors
in different layers.
Two cases of WD (17 April 2001 and 18–19 February 2003) are discussed using the microwave data from AMSU-B and the IR and
WV data from Meteosat-5. The aim here is to demonstrate the skill of AMSU-B in delineating structure of WDs. In particular,
the cold intrusion and the moist conveyor belts are examined. It was found that the multi-channel view of the AMSU-B permits
a better understanding of the moist structures seen in the conveyor belts.
The à trous wavelet transform is used to clearly bring out mesoscale features in WDs. AMSU-B brings out intense convection as a large
depression of BTs (>50K) at 150/176 GHz, cirrus and moist bands at 180/182 GHz. Mesoscale convection lines within WDs that
last short time are shown here for the first time only in the AMSU-B images. Large-scale cirrus features are separated using
the à trous wavelet transform.
Lastly, it is shown that there is a good likeness in the rain contours in the 3-h rain 3B42 (computed from TRMM and other
data) to AMSU-B depressions in BT. Overall, AMSU-B shows better skill in delineating the structure of clouds and rain in WDs. 相似文献
12.
M. S. Butuzova 《Astronomy Reports》2018,62(2):116-122
Periodic variations of the position angle of the inner jet of the blazar S5 0716+71 suggest a helical structure for the jet. The geometrical parameters of a model helical jet are determined. It is shown that, when the trajectories of the jet components are non-ballistic, the angle between their velocity vectors and the line of sight lies in a broader interval than is the case for ballistic motions of the components, in agreement with available estimates. The contradictory results for the apparent speeds of components in the inner and outer jet at epochs 2004 and 2008–2010 can be explained in such a model. The ratio of the apparent speeds in the inner and outer jet are used to derive a lower limit for the physical speed of the components (β > 0.999) and to determine the pitch angle of the helical jet (p = 5.5°). The derived parameters can give rise to the conditions required to observe high speeds (right to 37c) for individual jet components. 相似文献
13.
V. A. Hagen-Thorn V. M. Larionov D. A. Morozova A. A. Arkharov E. I. Hagen-Thorn E. S. Shablovinskaya M. S. Prokop’eva V. A. Yakovleva 《Astronomy Reports》2018,62(2):103-115
The results of optical, radio, and gamma-ray observations of the blazar AO 0235+16 are presented, including photometric (BV RIJHK) and polarimetric (R)monitoring carried out at St. Petersburg State University and the Central (Pulkovo) Astronomical Observatory in 2007–2015, 43 GHz Very Long Baseline Interferometry radio observations processed at Boston University, and a gamma-ray light curve based on observationswith the Fermi space observatory are presented. Two strong outbursts were detected. The relative spectral energy distributions of the variable components responsible for the outbursts are determined; these follow power laws, but with different spectral indices. The degree of polarization was high in both outbursts; only an average relationship between the brightness and polarization can be found. There was no time lag between the variations in the optical and gamma-ray, suggesting that the sources of the radiation in the optical and gamma-ray are located in the same region of the jet. 相似文献
14.
Results of observations of the five candidate GPS sources J0626+8202, J0726+7911, J1044+8054, J1823+7938, and J1935+8130 are
presented. GPS sources are extragalactic sources whose spectral peaks are near several GHz. These objects were observed on
the RATAN-600 radio telescope from 1999 through 2010 at 1.1, 2.3, 4.8, 7.7, 11.2, and 21.7 GHz. These radio sources were selected
from a complete sample (S
v
≥ 200 mJy at 1.4 GHz) in the vicinity of the North Celestial Pole (+75° ≤ δ ≤ +88°); four are considered as GPS candidates for the first time here. Their spectral properties, variability and morphology
are analyzed, and confirms that these can be classified as GPS sources. These four to five GPS sources probably comprise a
complete sample of this class of object in this region of the celestial sphere. 相似文献
15.
Results of studies of motions in a filament during its slow ascent and eruption based on spectral observations obtained at the Sayan Solar Observatory are presented. SDO/HMI data on the longitudinal magnetic field and SDO/AIA images in the EUV are also considered. Short-period (∼5 min) vertical oscillations of the filament as a whole were detected during its ascent. An acceleration of the rise of the filament was accompanied by the rupture of an orthogonal loop above the filament, which was observed in 193 A EUV images obtained with SDO/AIA over a long time preceding the event. Two hours before the partial eruption of the filament, SDO/HMI data indicate an increase in the magnetic flux by 2 × 1019 Mx at the footpoints of the loop. The emission from the loop rupture piont propagated toward the east and west along a neutral line, and brightenings were observed at the boundaries of the filament channel. Emission loops were visible in all SDO/AIA channels, testifying to strong heating of the filament plasma. During the rapid phase of the eruption, the filament moved with an acceleration ∼21 m/s2. Hα images show the filament splitting into fragments parallel to its axis during the eruption. The results of these studies of the eruption of the filament are in agreement with other results in the literature, and are supplemented by new observational facts. Vertical oscillations (∼5 min) of the filament as a whole are observed before the ascent phase. During the ascent phase, an interaction of the filament with a higher-lying coronal loop is observed.
相似文献16.
We present an analysis of multifrequency light curves of the sources 2223-052 (3C 446), 2230+114 (CTA 102), and 2251+158 (3C 454.3), which had shown evidence of quasiperiodic activity. The analysis made use of data from the University of Michigan Radio Astronomy Observatory (USA) at 4.8, 8, and 14.5 GHz, as well as the Metsahovi Radio Astronomy Observatory (Finland) at 22 and 37 GHz. Application of two different methods (the discrete autocorrelation function and the method of Jurkevich) both revealed evidence for periodicity in the flux variations of these sources at essentially all frequencies. The periods derived for at least two of the sources—2223-052 and 2251+158—are in good agreement with the time interval between the appearance of successive VLBI components. The derived periods for 2251+158 (P = 12.4 yr and 2223-052 (P = 5.8 yr) coincide with the periods found earlier by other authors based on optical light curves. 相似文献
17.
An expression for the intensity of synchrotron emission from a radio source (in the optically thin regime) in terms of the energy densities in the magnetic field and particles is obtained, based on a definition of a relativistic electron related to its rest energy. A relationship is obtained between the energy densities in particles Ee and the magnetic field EH for a physical system containing a magnetic field and relativistic electrons in a minimum-energy state. A method for estimating the Doppler factors of the relativistic electrons has been developed. This method does not requires that all radio sources have the same radiation energies (brightness temperatures): it is sufficient that the energies of the magnetic fields and relativistic particles in the source be approximately equal. The method yields Doppler-factor estimates with reasonably good accuracy, even when there are modest deviations from energy equipartition in the radio source,making it applicable to many radio sources. The method is used to estimate the Doppler factor of the radio jet in CTA 21.
相似文献18.
Modulations of the microwave emission of the Sun at 11.7 GHz have been studied using more than 40 events observed in 2001
at the Mets?hovi Radio Observatory. In nearly all the observed events, low-frequency modulations with periods of 3–90 min
were detected. As a rule, simultaneous modulation of the emission at several frequencies was observed. One possible origin
of such modulations with periods 5–10 min is parametric resonance arising in coronal magnetic loops as a result of interactions
with the 5-min photospheric oscillations, while the long-period modulations could be a manifestation of sunspot oscillations.
Torsional (ϑ-mode) and radial (r-mode) oscillations have such periods. The frequency of occurrence of oscillations with the determined periods is considered,
and a lower limit for the brightness temperature of the oscillations is estimated. 相似文献
19.
M. S. Butuzova 《Astronomy Reports》2016,60(3):313-321
The X-ray emission of the kiloparsec-scale jets of core-dominant quasars is usually interpreted as inverse Compton scattering on the cosmic microwave background (CMB) emission (Sample I). By analogy with the situation on parsec scales, ultrarelativistic motion along a jet oriented at a small angle to the line of sight is usually invoked to explain the X-ray emission while also satisfying the condition of equipartition between the energies associated with the relativistic particles and the magnetic field on kiloparsec scales. This leads to an increase in the energy flux of the CMB radiation in the rest frame of the kiloparsec-scale jets. Consequently, the intensity of the CMB radiation is enhanced to the level required for detectable X-ray emission. This suggests that kiloparsec jets of quasars with similar extents and radio flux densities that are not detected in the X-ray (Sample II) could have subrelativistic speeds and larger angles to the line of sight, due to deceleration and bending of the jet between parsec and kiloparsec scales. This suggests the possible presence of differences in the distributions of the difference between the position angle for the parsec-scale and kiloparsec-scale jets for these two groups of quasars; this is not confirmed by a statistical analysis of the data for Samples I and II. It is deduced that most of the sources considered exhibit bending of their jets by less than about 1.5 times the angle of the parsec-scale jet to the line of sight. This suggests that the X-ray emission is generated by other mechanisms that there is no equipartition. 相似文献
20.
卫星遥感在西藏安多幅1∶25万区域第四纪地质调查中的应用 总被引：7，自引：3，他引：4
对西藏安多县1∶25万图幅的ETM+图像进行几何精校正和镶嵌后,选取ETM+7、ETM+4、ETM+3波段进行假彩色合成并与全色波段融合,获得研究区1∶25万ETM+影像图;根据不同地质体的影像特征并结合野外踏勘,建立了遥感解译标志;对沉积物、地貌、水系及新构造等进行了初步目视解译,编制了1∶25万第四纪遥感解译图;结合野外地质调查,对研究区的第四纪沉积物的成因类型和分布范围、地貌特征及分区、新构造运动等方面进行了研究。区内分布最广的是晚更新世的冰水、冰碛物及冲洪积物;区内不仅存在晚更新世冰蚀谷,而且发育规模较大的中更新世古冰蚀谷;通过线性影像、水系及洪积扇的偏转等特征,对区内新构造进行了识别及活动性质的初步判断。此研究不但较好地体现了遥感技术在高原区域第四纪地质调查中应用的优点,而且为青藏高原隆升及其环境变迁的研究提供了参考资料。 相似文献