Variations In 3C Research Articles

Multiwavelength analysis of brightness variations of 3C 279: probing the relativistic jet structure and its evolution

Aims. We studied the correlation between brightness and polarization variations in 3C 279 at different wavelengths, over time intervals long enough to cover the time lags due to opacity effects. We used these correlations together with VLBI images to constrain the radio and high energy source position. Methods. We made 7 mm radio continuum and R-band polarimetric observations of 3C 279 between 2009 and 2014. The radio observations were performed at the Itapetinga Radio Observatory, while the polarimetric data were obtained at Pico dos Dias Observatory, both in Brazil. We compared our observations with the γ-ray Fermi/LAT and R-band SMARTS light curves. Results. We found a good correlation between 7 mm and R-band light curves, with a delay of 170 ± 30 days in radio, but no correlation with the γ rays. However, a group of several γ-ray flares in April 2011 could be associated with the start of the 7 mm strong activity observed at the end of 2011. We also detected an increase in R-band polarization degree and rotation of the polarization angle simultaneous with these flares. Contemporaneous VLBI images at the same radio frequency show two new strong components close to the core, ejected in directions very different from that of the jet. Conclusions. The good correlation between radio and R-band variability suggests that their origin is synchrotron radiation. The lack of correlation with γ-rays produced by the Inverse Compton process on some occasions could be due to the lack of low energy photons in the jet direction or to absorption of the high energy photons by the broad line region clouds. The variability of the polarization parameters during flares can be easily explained by the combination of the jet polarization parameters and those of newly formed jet components.

Correlated spectral and temporal changes in 3C 390.3: a new link between AGN and Galactic black hole binaries?

We present the results of a systematic search for evidence of temporal changes (i.e., non-stationarity) associated with spectral variations in 3C 390.3, using data from a two-year intensive RXTE monitoring campaign of this broad-line radio galaxy. In order to exploit the potential information contained in a time series more efficiently, we adopt a multi-technique approach, making use of linear and non-linear techniques. All the methods show suggestive evidence of non-stationarity in the temporal properties of 3C 390.3 between 1999 and 2000, where the characteristic time-scale of variability decreases as the energy spectrum of the source softens. However, only the non-linear, “scaling index method” is able to conclusively show that the temporal characteristics of the source do vary, although the physical interpretation of this result is not clear at the moment. Our results indicate that the variability properties of 3C 390.3 may vary with time, in the same way as they do in Galactic black holes in the hard state, strengthening the analogy between the X-ray variability properties of the two types of object. This is the first time that such a behavior is detected in an AGN X-ray light curve. Further work is needed to investigate whether this is a common behavior in AGN, as it is in the Galactic binaries.

CCD Photometry and Long-Term Optical Variability of 3C 345

This paper presents evidence for long-term optical variability and colour behaviour of the blazar 3C 345 (1641+399, z=0.595). Our results show that the amplitude of the optical variations of 3C 345 has been only about 3 magnitudes from its photometric history; existent significant correlation between brightness and colours is found for 3C 345. Our recent CCD photometry of 3C 345 in May 1996 and May 1997 showed that they are in good agreement with our prediction of the optical variability period of about 10 years (see Zhang et al., 1998; Webb et al., 1988).

Simultaneous X-ray and IR variability in the quasar 3C 273

From a combination of high-quality X-ray observations from the NASA Rossi X-ray Timing Explorer (RXTE) and IR observations from the UK Infrared Telescope (UKIRT) we show that the medium-energy X-ray (3–20 keV) and near-IR fluxes in the quasar 3C 273 are highly correlated. It is widely believed that the X-ray emission in quasars like 3C 273 arises from Compton scattering of low-energy seed photons, and our observations provide the first reliable detection of correlated variations in 3C 273 between the X-ray band and any lower energy band. For a realistic electron distribution we demonstrate that it is probable that each decade of the seed-photon distribution from the mm to IR wavebands contributes roughly equally to the medium-energy X-ray flux. However, the expected mm variations are too small to be detected above the noise, probably explaining the lack of success of previous searches for a correlation between X-ray and mm variations. In addition, we show that the IR leads the X-rays by 0.75±0.25 d. These observations rule out the ‘External Compton’ emission process for the production of the X-rays.

The multifrequency spectral evolution of blazar 3C 345

The blazar 3C 345 underwent a 2.5 mag optical outburst between 1990 November and 1991 May. We have obtained 10 nearly simultaneous multifrequency spectra during the course of the outburst in order to study the multifrequency spectral variations of 3C 345 as a function of time. Although our observations were not sampled frequently enough to completely resolve the variations in every frequency band, the general rise and decline of the outburst were seen in the UV through radio with differing rise times. Simulations of an electron distribution injected into a tangled magnetic field show a relationship between frequency and characteristic timescale that was also observed in the radio variations of 3C 345. The two X-ray observations made during the monitoring period showed no evidence of variability. The multifrequency spectrum was modeled with two major components: a relativistic jet and a relativistic thermal accretion disk. Models calculated for each spectrum indicate that the outburst can be explained in terms of these models by varying the high-energy cutoff of the injected electron distribution in the jet model, while also varying the mass accretion rate in the disk model. There is marginal evidence that the inferred accretion rate varies with the jet luminosity.

Light variations in 3C 273

view Abstract Citations (21) References (17) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Light variations in 3C 273. Moles, Mariano ; Garcia-Pelayo, Jose Manuel ; Masegosa, Josefa ; Garrido, Rafael Abstract UBVRI data for the quasar 3C 273, corresponding to the beginning of 1985, show small amplitude variations in all the colors except in the I band, where a change of 0.19 mag in less than 2 hr has been detected. This kind of behavior, already reported for PKS 2128-123 and for 3C 273 itself, is consistent with the model proposed by Malkan (1985). The available photoelectric UBV data for 3C 273 have been analyzed. No periodicities have been found in any color. The variations in the three bands are well correlated without time lags between them. Publication: The Astronomical Journal Pub Date: November 1986 DOI: 10.1086/114233 Bibcode: 1986AJ.....92.1030M Keywords: Electrophotometry; Light Curve; Quasars; Radio Galaxies; Ubv Spectra; Colorimetry; Covariance; Spectral Bands; Time Lag; Astronomy full text sources ADS | data products SIMBAD (1) NED (1)

Rapid structural variations in 3C 120

VLBI observations of the radio galaxy 3C 120 at 2.8 and 6.0 cm between 1978.24 and 1980.27 are presented. The source consists of a highly variable linear emission region with a relatively stable, compact component at one end, suggestive of a ''core-jet'' morphology. The observations were not frequent enough and did not have sufficient dynamic range to clearly show the evolution of individual components, with the probable exception of one bright component which appeared to separate from the ''core'' at an apparent rate of 3.7 +- 0.8 times the speed of light (H/sub 0/ = 55 km s/sup -1/ Mpc/sup -1/) during 1979.

Superluminal variations in 3C 120, 3C 273, and 3C 345

view Abstract Citations (57) References (13) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Superluminal variations in 3C 120, 3C 273, and 3C 345. Cohen, M. H. ; Pearson, T. J. ; Readhead, A. C. S. ; Seielstad, G. A. ; Simon, R. S. ; Walker, R. C. Abstract The superluminal behavior of 3C 120, 3C 273, and 3C 345 has been reexamined in light of new hybrid maps of these objects. The maps of 3C 273 and 3C 345 are consistent with superluminal expansion. 3C 120 appeared to expand superluminally from 1972.6 to 1974.5, but the evidence has been inconclusive since 1974.5. It is suggested that the jetlike structure of these sources can be explained by a model in which all the components are approaching at a small angle to the line of sight. There is a range of ejection velocities for which components separate superluminally but still maintain comparable intensities. Publication: The Astrophysical Journal Pub Date: July 1979 DOI: 10.1086/157192 Bibcode: 1979ApJ...231..293C Keywords: Astronomical Maps; Astronomical Models; Luminous Intensity; Quasars; Radio Sources (Astronomy); Astronomical Photometry; Centimeter Waves; Interferometry; Microwave Emission; Astronomy; Radio Sources:Variations full text sources ADS | data products NED (3)

Two-Frequency Brightness and Polarization Distributions in 3c 123 and 3c 427.1

view Abstract Citations (15) References (13) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Two-Frequency Brightness and Polarization Distributions in 3c 123 and 3c 427.1 Kronberg, P. P. ; Strom, R. G. Abstract High-resolution observations of the distant radio galaxies 3C 123 and 3C 427.1 made at 8085 MHz and 4995 MHz are compared and examined in some detail. The polarization data indicate that in both sources variations in rotation measure occur amounting to hundreds of radians m -2 Magnetic fields tend to be directed along the axes or "tongues" of the radio components. Some subregions of 3C 123 have a very high degree of linear polarization (> 30%) at 8 0Hz and 2" resolution. The rotation measure variations in 3C 123 can be simply explained as the result of a changing projection of the radio component having a highly aligned longitudinal magnetic field. Depolarization in both objects is the result of internal Faraday dispersion. At the two frequencies we establish low upper limits to radio emission from both of the optical galaxies, and find no evidence for a radio bridge linking the components of 3C 427.1. We do, however, detect weak emission around the brightest component in 3C 123, and we find that the size of the entire source exceeds 300 kpc (H = 75), nearly twice as large as was previously thought. Both objects are among the most luminous of all identified sources in the 3C catalog. Subject headings: galaxies: individual - galaxies: structure - magnetic fields - polarization - radio sources: general Publication: The Astrophysical Journal Pub Date: July 1977 DOI: 10.1086/155373 Bibcode: 1977ApJ...215..438K full text sources ADS |

On the Problem of Explaining Decimeter Flux Variations in 3c 454.3 and Other Extragalactic Sources

On the Problem of Explaining Decimeter Flux Variations in 3c 454.3 and Other Extragalactic Sources

Cyclicity of Optical Variations of 3C 273

WHEELER1 has discussed our method for the analysis of optical variability of 3C 273 but has come to different conclusions. The aim of this letter is to establish the reasons for this difference.

Yearly Variations of 3C 120

THE photographic light curve1 of the Seyfert galaxy 3C 120 shows a large-amplitude (∼1.2 magnitudes) long-term decline in brightness over five consecutive seasons from 1934/35 to 1939/40. Short-term fluctuations of smaller amplitude (∼0.3 to 0.6 magnitudes) with decline times of about 200 days are apparently superimposed on this decline1, and the question immediately arises whether these fluctuations are intrinsic to the source or are due to some yearly observational selection effect. Kinman2 has pointed out the existence of an hour-angle effect for 3C 345 and inspection of the hour angles of the 3C 120 plates reveals that the hour angles are selectively larger at the beginning and end of the season than in the middle. In this report we conclude that the yearly fluctuations in 3C 120 are almost certainly intrinsic to the source.

Optical Variations in 3C 345

Hunter and Lu1 claim that on June 11, 1969 (UT), the quasi-stellar source 3C 345 showed a variation of ≈0.4 blue magnitudes within the span of a few hours. The first ten of their observations on this night (shown in Fig. 3 of their article) have a range of only 0.19 mag, while the inclusion of their eleventh and last observation increases the range to 0.38 mag. If ten observations have a range of 0.19 mag, then the expected r.m.s. deviation of a single observation (σ) is ±0.062 mag and the expected probable error of a single observation is ±0.042 mag (ref. 2, Table 6). Because Hunter arid Lu give probable errors in the range ±0.02 to ±0.055 for their ten observations, it would seem that these ten observations give little or no evidence for any real variation in the object. The reality of the alleged variation therefore depends entirely on the reliability of their last observation on that night.

Additional Data on the Optical Variations in 3c 371 and Other Properties of N-Type Galaxies

Additional Data on the Optical Variations in 3c 371 and Other Properties of N-Type Galaxies

Optical Variations in 3C 446

Cannon and Penston1 have reported observations of the rapid optical fluctuations of the quasi-stellar object 3C 446. These add further to the study of rapid variations discovered in this object by Sandage2 and followed in 1966 by Kinman, Lamla and Wirtanen3. Variations of this kind lead to the conclusion that the region which gives rise to the fluctuation is very small, and in general it is found that for this region R ⩽ c τ, where τ is the period over which a flux change has occurred. A detailed discussion of this result has been given by Terrell4 and others. These limitations lead to very restrictive conditions on the possible models of quasi-stellar objects which arise largely from the high radiation density that must be present in the continuum source. The upper limits to the sizes which have been used range from light months to light days (∼1017 — 1015 cm) and the corresponding lower limits to the energy densities are then in the range 10–105 erg/cm3 if the quasi-stellar objects are at cosmo-logical distances, and 10−3–10 ergs/cm3 if the objects lie at distances ∼ 10 megaparsec (Mpc). If the objects are at cosmological distances, then this radiation field is so intense that it would be self-destructive, whether it arises by the synchrotron process or from the inverse Compton process5,8. The difficulties that are encountered in arriving at satisfactory models, if the quasi-stellar objects are at cosmological distances, have been considered by Hoyle, Burbidge and Sargent5. Attempts to evade or to minimize these difficulties if the objects are at cosmological distances have been made by Rees6, by Woltjer7, and by Hoyle and Burbidge8, and they require that the radiating blobs are moving at relativistic speeds and/or that there is a large degree of directivity in the streams of relativistic electrons. If the quasi-stellar objects are much closer, the radiation density is accordingly reduced and the problems are less severe.

Optical Variation of 3C 446

THE observations of Sandage1 and of Kinman et al.2 have shown that the optical brightness of the quasar 3C 446 is variable. This quasar has been observed as part of a programme of optical monitoring of quasars at the Royal Greenwich Observatory. Our results show a continuation of the earlier behaviour and lead to the speculation that the variation is caused by the occultation of the quasar by absorbing clouds in its vicinity.