H. G. Song

The IDV source J 1128+5925, a new candidate for annual modulation?

Context. Short time-scale radio variations of compact extragalactic radio sources, known as IntraDay Variability (IDV), can be explained in at least some sources by a source-extrinsic effect, in which the variations are interpreted as scintillation of radio waves caused by the turbulent interstellar medium of the Milky Way. One of the most convincing observational arguments in favour of propagation-induced variability is the so-called “annual modulation” of the characteristic variability time-scale, which is due to the orbital motion of the Earth. So far there are only two sources known which show such a well-defined seasonal cycle, a few more sources with fewer data can be regarded as possible candidates for this effect. However, source-intrinsic effects, such as structural variations, can also cause the observed changes of the variability time-scale. Data for the new, recently discovered, and highly variable IDV source J 1128+5925 are presented. Aims. We study the frequency and time dependence of the IDV in this compact quasar. We measure the characteristic variability time-scale of the IDV throughout the year, and analyze whether the observed changes in the variability time-scale are consistent with annual modulation. Assuming a radio wave propagation effect as origin, we are able to constrain some physical properties (such as distance, scattering-strength, and possible anisotropy) of the “plasma” screen, which may cause the scintillation. Methods. We monitored the flux density variability of J 1128+5925 with dense time sampling between 2.7 and 10.45 GHz. We observed with the 100 m Effelsberg radio telescope of the Max-Planck-Institut fur Radioastronomie (MPIfR) at 2.70 GHz, 4.85 GHz, and 10.45 GHz, as well as with the 25 m Urumqi radio telescope (China) at 4.85 GHz. From ten observing sessions, each of which lasted several days during the period between 2004–2006, we determine the variability characteristics and time-scales which we investigate in view of possible scintillation and annual modulation. Results. The observed pronounced changes of the variability time-scale of J 1128+5925 are modelled with an anisotropic annual modulation model. The observed frequency dependence of the variation is in good agreement with the prediction from interstellar scintillation. Adopting a simple model for the annual modulation model and also using the frequency dependence of the IDV, we derive a lower limit to the distance the scattering screen and an upper limit for the scintillating source size. The latter is found to be consistent with the measured core size from Very Long Baseline Interferometry (VLBI).

Intra-day variability observations of S5 0716+714 over 4.5 years at 4.8 GHz

Aims. We aim to search for evidence of annual modulation in the time scales of the BL Lac object S5 0716+714.

The radio lightcurve of SN 2008iz in M82 revealed by Urumqi observations

We report on a set of 5 GHz Urumqi observations of the galaxy M82, made between August 2005 and May 2009. From the resulting flux densities, we detect a strong flare, starting in March or April and peaking in June 2008. We identify this flare with supernova SN 2008iz. The time sampling of the radio light curve allows us to obtain information on the precursor mass-loss rate, the strength of the magnetic field in the radiating region, the explosion date, and the deceleration of the expanding shock. We also check the possible contribution of synchrotron self absorption to the radio light curve and compare our model with other observations of the supernova at 22 GHz.

A seasonal cycle and an abrupt change in the variability characteristics of the intraday variable source S4 0954+65

The BLLac object S4 0954+65 is one of the main targets of the Urumqi monitoring program targeting intraday variable (IDV) sources. Between August 2005 and December 2009, the source was included in 41 observing sessions, carried out at a frequency of 4.8 GHz. The time analysis of the collected light curves, performed by applying both a structure function analysis and a specifically developed wavelet-based algorithm, discovered an annual cycle in the variability timescales, suggesting that there is a fundamental contribution by interstellar scintillation to the IDV pattern of the source. The combined use of the two analysis methods also revealed that there was a dramatic change in the variability characteristics of the source between February and March 2008, at the starting time of a strong outburst phase. The analysis results suggest that the flaring state of the source coincides with the appearance of multiple timescales in its light curves, indicating that changes in the structure of the relativistically moving emitting region may strongly influence the variability observed on IDV timescales.

Radio observations of the first three-months of Fermi AGN at 4.8 GHz

mathsfsl{Aims~and~Methods}

Very Long Baseline Array observations of the intraday variable source J1128+592

. We present the results of VLBI observations of nineteen GHz-peaked-spectrum (GPS) radio sources at 1.6xa0GHz. Of them, 15 sources are selected from the Parkes half-jansky (PHJ) sample (Snellen etxa0al. 2002, MNRAS, 337, 981), and 4 others are from our previous observation list. We aimed at imaging the structure of GPS sources, searching for compact symmetric objects (CSOs) and studying the absorption for the convex radio spectra of GPS sources.u2029

Intra-day variability observations and the VLBI structure analysis of quasar S4 0917+624

mathsfsl{Results}

On the influence of the Sun on the rapid variability of compact extragalactic sources

. We obtained total-intensity 1.6xa0GHz VLBI images of 17xa0sources for the first time. Of them, 80% show a mini-double-lobe radio structure, indicating that they are CSOs or candidates, and their host AGNs could be edge-on to us. This result suggests that there is a high incidence of mini double-lobe sources (orxa0CSOs) in the PHJ sample. The sources J0323+0534, J1135-0021, J1352+0232, J2058+0540, J2123-0112, and J2325-0344 are classified as CSOs with measured redshift, showing double-lobe structure with sizes of <1xa0kpc. Three sources J1057+0012, J1600-0037, and J1753+2750 are considered as core-jet sources according to their morphologies and flux variability.

High resolution studies of the IDV quasar J1128+592

Using the Urumqi 25 m radio telescope, sources from the first t hree months of the Fermi-large area telescope detected active galactic nuclei (AGN) catalog with a declination of > 0 ◦ were observed in 2009 at 4.8 GHz. The radio flux density ap- peared to correlate with the -ray intensity. Intra-day variability (IDV) observations were performed in March, April and May 2009 for 42 selected -ray bright blazars, and ∼60% of them showed evidence of flux variability at 4.8 GHz duri ng the IDV observations. The IDV detection rate was higher than that in previous flat-spectrum AGN samples. IDV appeared more often in the very long baseline interferometry-core dominant blazars, and the non-IDV blazars showed relatively steeper spectral in- dices than the IDV blazars. Pronounced inter-month variability was also found in two BL Lac objects: J0112+2244 and J0238+1636.