Long-term optical and radio monitoring of the quasars S5 0716+714 and 4C 38.41 on various time scales

We present the results of long-term radio and optical monitoring of two radio-loud quasars. The aim of the work was to study the objects?? variability on various time scales and search for correlations between the radio and optical emission. The monitoring was performed in 2002?C2010. The radio observations were carried out using the 22-m telescope of the Crimean AstrophysicalObservatory, 26-m telescope of the University of Michigan Radio Astronomy Observatory, and 14-m telescope of the Metsahovi Radio Observatory at 4.8, 8.0, 14.5, 22.2, and 36.8 GHz. The optical observations were obtained in the B, V,R bands using the Zeiss-1000 telescope of the Special Astrophysical Observatory with a CCD photometer. Light curves of the quasars 4C 38.41 (1633+382) and S5 0716+714 are presented. Radio flares of 4C 38.41 with amplitudes of 0.5?C1.0 Jy at 4.8 and 8 GHz and 1?C3 Jy at 22.2 and 36.8 GHz were detected on time scales of about 100 days. The amplitude of the optical brightness variations varied between 0.5 ^m and 1.5 ^m over about 200 days. The amplitudes of the flux variations for S5 0716+714 for the period of two months were 0.5?C1.6 Jy at centimeter and 1?C7 Jy at millimeter wavelengths. The amplitudes of flares in the optical reached 2 ^m in the B and V filters and 2.5 ^m in the R filter, on time scales of 200 days. The color indices of these objects did not change during the period covered by observations, i.e., the objects did not become bluer when they brightened. The detected delays between the variations atmillimeter and centimeter wavelengths are several days, which is within the interval between observations during the long-term monitoring. The absence of a distinct correlation between the optical and radio brightness variations was probably due to the presence of substantial time delays between the phenomena occurring in these different wavelength ranges.     

A multi-frequency study of brightness variations of the blazar 0716+714

Based on long-term monitoring at five radio frequencies between 4.8 and 37 GHz performed at the Radio Astronomy Laboratory of the Crimean Astrophysical Observatory, the University of Michigan Radio Astronomy Observatory, and the Metsähovi Radio Observatory, we have analyzed two flare events in the blazar S5 0716+714 during the last five years. The time separation between the flares is in agreement with data derived earlier from a spectral analysis of flux variations at the above frequencies, which revealed a periodic component with a period of about four years in the variations. We consider the dynamics of strong flares in 2003 and 2007 and determine the delays between the development of the event at various radio frequencies. Our data can be used to draw conclusions about the kinematic and dynamical properties of the source.     

Multi-frequency studies of the non-stationary radiation of the blazar 3C 454.3

Long-term monitoring data at five radio frequencies from 4.8 to 37 GHz obtained at the Crimean Astrophysical Observatory, Metsahovi Radio Observatory of Aalto University, and the University of Michigan Radio Astronomy Observatory are used to analyze variations of the flux of the Active Galactic Nucleus (AGN) 3C 454.3. The dynamical characteristics of the three latest powerful flares from 2004 to 2010 are analyzed in detail. Observations in the gamma-ray (0.1–300 GeV), X-ray (2–10 kev, 15–50 keV), and optical are also used. Delays in the development of flares at different frequencies are derived. An empirical frequency dependence for the delays of flares from the gamma-ray to the radio is determined, which can be fit using a logarithmic low and remains the same from flare to flare. The physical characteristics of the central region of the AGN 3C 454.3 are used to estimate the size of its Strömgren sphere, taking into account the relevant mechanisms for heating and cooling the medium, as well as the adopted laws for the variation of the density and temperature with distance from the source of ionization. A model for the location of the radiation regions in the jet at various frequency ranges during the development of flares is proposed.     

The variability of a 3C 454.3 blazar over a 40-year period

Variations in the radio flux of 3C 454.3 on various time scales from decades to a year are analyzed using long-term monitoring data at five frequencies from 4.8 to 36.8 GHz obtained at the University of Michigan Radio Astronomy Observatory and the Crimean Astrophysical Observatory. A spectral analysis of the light curves at the various frequencies reveals the presence of five periodic components. The long-and short-period components of the variability are compared using models for the precessional and orbital periods for motion in the system. The parameters for the supposed binary black-hole system are determined: the dimensions of the orbit and masses of the central black holes. The dynamics of the powerful flare in 2005–2006 are examined, and the time delays for its development from the optical to the radio and between radio frequencies are determined. The different frequency spectra of different individual flares can be explained in a model with a moving, expanding cloud that is first optically thick, then becomes optically thin at successively lower frequencies as it expands.     

Non-stationary emission of the blazar S4 0954+658 over a wide range of wavelength

Data from long-term multi-frequency monitoring are used to analyze variations in the flux density of the active galactic nucleus S4 0954+658. These data were obtained at the CrimeanAstrophysical Observatory, the Metsähovi Radio Observatory of Aalto University, the University of Michigan Radio Astronomy Observatory, the Cavendish Laboratory of Cambridge University, the Special Astrophysical Observatory, and the National Institute of Astrophysics, Optics, and Electronics; 0.1–300-GeV data from the Fermi space gamma-ray observatory were also used. Radio data at 4.8, 8, 14.5, 15, 22.2, and 36.8 GHz are considered together with optical and near-infrared data in the R, J, H, and K filters.     

Variations of the Blazar AO 0235+164 in 2006–2015

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.     

Observation of the powerful solar flare of October 27, 2002 on the far side of the sun

Observations of the hard X-ray and radio event of October 27, 2002 are analyzed. This flare was observed from near-Martian orbit by the HEND instrument developed at the Space Research Institute of the Russian Academy of Sciences and installed on the Mars Odyssey satellite. Although this powerful flare was observed far over the eastern solar limb, the extended source associated with the flare was detected by RHESSI at energies up to about 60 keV. The eruptive event was observed in the radio at the Nobeyama Radio Observatory. The properties of the X-ray radiation are used to calculate the spectrum of the accelerated electrons responsible for the observed radiation, assuming that the target is thick for a Martian observer and thin for a terrestrial observer. The results are compared with the results of radio observations. The conditions for electron propagation in the corona are discussed.     

Radio and optical spectra of objects from two complete samples of radio sources

We present optical identifications and radio spectra for ten radio sources from two flux-density-complete samples. Radio variability characteristics are presented for four objects. The observations were obtained on the RATAN-600 radio telescope at 0.97–21.7 GHz and the 2.1 m telescope of the Haro Observatory in Cananea, Mexico at 4200–9000 Å. Among the ten objects studied, three are quasars, four are BL Lac objects, two are radio galaxies, and one is a Sy 1 galaxy. Two of the sources identified with BL Lac objects, 0509+0541 and 0527+0331, show rapid variability on time scales of 7–50 days.     

H<Subscript>2</Subscript>O maser emission in the direction of Sagittarius B2: Results of monitoring for 1982–1992

The results of monitoring the water-vapor maser at λ=1.35 cm in Sgr B2 are presented. The observations were carried out on the 22-m radio telescope of the Pushchino Radio Astronomy Observatory (Russia) in 1982–1992. A strong flare of the maser radiation associated with Sgr B2(N) was detected in this period. The absolute strength of this flare is comparable to the megamaser emission observed in Orion in 1979–1987. The flare is probably due to a strengthening of the flow of material from the rotating accretion disk, in which are embedded the three ultracompact HII regions K1, K2, and K3. A subsequent excitation of emission features at increasingly higher radial velocities was observed, associated with a gradient of V_LSR along the direction of the outflow. The large width of the lines (>0.86 km/s) could reflect a complex structure for the maser spots, such as a chain or filamentary structure, as has been observed in Orion and S140.     

Rapid variability of the radio flux density of the blazar J0721+7120 (S5 0716+714) in 2010

Results of a study of the variability of the blazar J0721+7120 carried out on the RATAN-600 based on daily observations from March 5, 2010 to April 30, 2010 at five frequencies from 2.3 to 21.7 GHz are reported. In the same time interval, 13 observing sessions at 37 GHz were carried out on the 14-m radio telescope of the Mets?hovi Radio Astronomy Observatory of the Aalto University School of Technology (Finland). From March 19, 2010 to October 20, 2010, 16 daily sessions at 6.2 cm and five sessions at 3.5 cm were conducted on the 32-m radio telescope of the Zelenchukskaya Observatory (Quasar-KVO complex of the Institute of Applied Astronomy, Russian Academy of Sciences). A powerful flare was detected during the observations, with a time scale of approximately 20 days, derived from an analysis of the light curves and the structure and autocorrelation functions. The flare spectrum has been determined. In five sessions on the 32-m Zelenchukskaya telescope at 6.2 cm, intraday variability with time scales 8-16 h was detected; in four sessions, trends with time scales longer than a day were observed. In three sessions at 3.5 cm, intraday variability with a time scale of approximately 5 h was detected.     

Flares of H2O maser emission from SGR B2 in 2005–2012

We present observations of H₂O maser emission from the complex region of active star formation Sgr B2 performed in 2005–2012. The observations were carried out with the 22-m radio telescope of the Pushchino Radio Astronomy Observatory. Seven flares with flux densities higher than 1000 Jy were detected. The flares occurred in all three main sites of star formation in Sgr B2, N,M, and S. The highest peak flux densities were 3200 Jy (60.9 km/s), 2350 Jy (69.4 km/s), and 7300 Jy (69.3 km/s) in N, M, and S, respectively. This last flare was the strongest during our monitoring campaign from 1982 to 2012, both in S and in the entire Sgr B2 complex. Possible associations of the flares were determined. High-velocity, short-lived emission was detected at 124–128 km/s. Emission at 127 km/s with a flux density of 23 Jy is associated with region M. Emission at 80.6 and 84.6 km/s, at radial velocities higher than those observed previously, was detected in region S.     

Fast brightness variations of blazars in the radio and optical

We present coordinated synchronous observations of Active Galactic Nuclei in the radio and optical, aimed at searching for fast (intraday) flux variations and possible correlations in the flux variations in different wavebands. Our observations were performed with the 22-m radio telescope of the Crimean Astrophysical Observatory at 22.2 and 36.8 GHz and the Zeiss-1000 reflector of the Special Astrophysical Observatory in the R filter, using a CCD photometer. We performed five observing runs of 7–10 nights each in 2004–2006. We obtained radio and optical light curves for the variable extragalactic radio sources DA 55, 1633+382, 2134+004, 2145+067, and 2251+158. We detected short-duration flares of DA 55 and 2134+004 in the R band with variations of 0.2 ^m within about 15 minutes. The other sources did not show any considerable flux variations. The radio flux variations of DA 55 and 2134+004 reached 1.5 Jy in about 15 minutes, and those of 2145+067 reached 2 Jy in 2 hours. We observed chaotic flux variations in 2251+158, by 2–2.5 Jy in half an hour. We detected no correlation between the radiation in the optical and radio.     

Radio emission from two anomalous X-ray pulsars

Observations of the anomalous X-ray pulsar (AXP) 1E 2259+586 and the AXP candidate 1RXS J1308.6+212708 at 111, 87, and 61 MHz are reported. The observations were carried out on two high-sensitivity radio telescopes of the Pushchino Radio Astronomy Observatory. Mean pulse profiles are presented, and the dispersion measures, distances, spectral indices, and integrated radio luminosities of both objects are estimated. Comparison with X-ray data shows large differences in the mean pulse widths and luminosities. The detection of radio emission from these two AXPs, together with other data, suggests the need to revise the radio-emission mechanisms in the magnetar model or the magnetar model itself.     

Some results of 22-year monitoring (1982–2003) of Sagittarius B2 in the 1.35-cm line

A catalog of λ=1.35 cm water-vapor maser spectra in Sgr B2 obtained in 1992–2003 is presented; this supplements our results for earlier observations in 1982–1992. Sgr B2 was monitored using the 22 m radio telescope of the Pushchino Radio Astronomy Observatory. The whole monitoring dataset for 1982–2003 has been analyzed. The emission received is a superposition of radiation from various parts of the entire Sgr B2 region, but the main contribution is made by two sources: Sgr B2(M) and Sgr B2(N). The monitoring did not reveal any long-term component of the integrated maser flux variations with a period shorter than 20 years. The flare component of the flux variability and a short-period component with a mean period of two years have been found. The latter are correlated with variations of the velocity centroid, supporting the reality of the short-period variations. It is likely that all the various types of variations are inherent to both Sgr B2(M) and Sgr B2(N), and represent a superposition of the variations occurring in each of these sources. There is an alternation of maxima of the emission from Sgr B2(M) and Sgr B2(N).     

Correlations between the development of a flare in the Blazar 3C 454.3 in the radio and optical

Radio and optical data are used to analyze the development of the flare in the blazar 3C 454.3 observed in 2004–2007. A detailed correspondance between the optical and radio flares is established, with a time delay that depends on the observing frequency. The variation of the delay of the radio flare relative to the optical flare is opposite to the dispersion delay expected for the propagation of radiation in the interstellar medium, testifying to an intrinsic origin for the observed outburst. Small-scale flux variations on time intervals of 5–10 days in the millimeter and optical are also correlated, with a time delay of about ten months. This may provide evidence for a single source generating the radiation at all wavelengths. Rapid flux fluctuations in the radio and optical that are correlated with the indicated time delays could be associated with inhomogeneities in the accretion disk. Detailed studies of the flux variations of Active Galactic Nuclei (AGN) can be used to analyze the structure of the accretion disk. A model for the energy release in AGN that is not associated purely with accretion onto supermassive black holes is proposed. As is the case for other active members of the AGN family, estimates of the lifetime of the binary black-hole system in 3C 454.3 suggest that this object is in a stage of its evolution that is fairly close to the coalescence of its black holes. The energy that is released as the companion of the central black hole loses orbital angular momentum is sufficient to explain the observed AGN phenomena. The source of primary energy release could be heating of the gas behind shock fronts that arise due to the friction between the companion black hole and the ambient gaseous medium. The orbit of the companion could be located at the periphery of the accretion disk of the central body at its apocenter and plunge more deeply into the accretion disk at its pericenter, inducing flares at all wavelengths. Energy-release parameters such as the temperature and density of the heated gas are estimated for 3C 454.3. The model considered assumes omnidirectional radiation of the medium in the presence of a magnetic field. The radiation corresponding to the minimum flux level (base level) could represent omnidirectional radiation due to the orbit of the moving companion. The fraction of the energy that is transferred to directed jets is small, comprising 1–2% of the total energy released due to the loss of orbital angular momentum by the companion.     

New observations of anomalous X-ray pulsars at low frequencies

We report the results of new observations of three anomalous X-ray pulsars: 1E 2259+586, 4U 0142+61, and XTE J1810-197. The observations were carried out on high-sensitivity radio telescopes of the Pushchino Radio Astronomy Observatory: the Large Phased Array at 111MHz and the DKR-1000 at 62 MHz. New, digital, multi-channel receivers designed for pulsar observations were used. Pulse profiles and dynamical spectra for the three pulsars are presented. The mean flux density for XTE J1810-197 is estimated to be ∼160 mJy at 62 MHz. An estimated spectral index for this pulsar is also presented.     

Results of long-term monitoring of 3C 273 over a wide range of wavelengths

The results of long-term monitoring of the quasar 3C 273 at wavelengths from radio to gamma rays between 1963 and 2011 are presented. The variations of the source flux density are studied using harmonic and wavelet analysis techniques. The values and frequency-time localizations of harmonic components in the flux-density variations are determined. The eight-year radio-variability period reported earlier had become gradually reduced and attenuated by 2000. The optical light curve has a component with a quasi-period of approximately 13 years. Cyclic variations whose periodicity gradually increased from approximately one to two years were observed in the X-ray between 1996 and 2006. The relative time delays between the light curves at different radio frequences are determined. The frequency dependence of time delays is approximated by the power law, ΔT(ν) ∝ ν ^?1/k with k = 1.4 ± 0.1, which can be used to infer the corresponding core shift and estimate the core-region magnetic field as B _{1 pc} = 0.5 ± 0.1 G. This approach is preferable to other methods, since it does not require multi-frequency VLBI observations and is a simple and effective tool for studying Active Galactic Nuclei.     

Radio emission of RRAT pulsars at 111 MHz

Observations of the RRAT pulsars J0627+16, J0628+09, J1819?1458, J1826?1419, J1839?01, J1840?1419, J1846?0257, J1848?12, J1850+15, J1854+0306, J1919+06, J1913+1330, J1919+17, J1946+24, and J2033+00 observed earlier on the 64-m Parkes telescope (Australia) and the 300-m Arecibo radio telescope (Puerto Rico) at 1400 MHz were conducted at 111 MHz on the LSA radio telescope of the Pushchino Radio Astronomy observatory in 2010–2012. A characteristic feature of these pulsars is their sporadic radio emission during rare active epochs and the absence of radio emission during long time intervals. No appreciable flare activity of these pulsars was detected in the Pushchino observations. However, processing the observations using the Fast Folding Algorithm taking into account known information about the pulsar dispersion measures and periods shows that, even during quiescent intervals, the majority of the studied pulsars generate weak radio pulses with a period corresponding to that of the radio emission of the sporadic pulses observed at active epochs. The flux of this radio emission does not exceed 100 mJy at the pulse peak, even at the low frequency of 111 MHz. This considerably hinders detection of the radio emission of RRAT pulsars at high frequencies, since the radio fluxes of RRAT pulsars decreases with increasing frequency.     

Spectral studies with the Special Astrophysical Observatory 6 m and RATAN-600 telescopes

We present optical identifications, classifications, and radio spectra for 19 radio sources from a complete sample in flux density with declinations 10°–12°30′ (J2000) obtained with the 6-m optical telescope (4000–9000 Å) and RATAN-600 radio telescope (0.97–21.7 GHz) of the Special Astrophysical Observatory. Twelve objects with redshifts from 0.573 to 2.694 have been classiffied as quasars, and two objects with featureless spectra as BL Lac objects. Four objects are emission-line radio galaxies with redshifts from 0.204 to 0.311 (one also displaying absorption lines), and one object is an absorption-line galaxy with a redshift of 0.214. Radio flux densities have been obtained at six frequencies for all the sources except for two extended objects. The radio spectra of five of the sources can be separated into extended and compact components. Three objects display substantial rapid (on time scales from several days to several weeks) and long-term variability of their flux densities.