No abstract

We present results from a large 86 GHz global VLBI survey of compact radio sources. The main goal of the survey is to increase by factors of 3-5 the total number of objects accessible for future 3-mm VLBI imaging. The survey observations reach the baseline sensitivity of 0.1 Jy and image sensitivity of better than 10 mJy/beam. The total of 127 compact radio sources have been observed. The observations have yielded images for 109 sources, extending the database of the sources imaged at 86 GHz with VLBI observation by a factor of 5, and only 6 sources have not been detected. The remaining 12 objects have been detected but could not be imaged due to insufficient closure phase information. Radio galaxies are less compact than quasars and BL Lacs on submilliarcsecond scale. Flux densities and sizes of core and jet components of all imaged sources have been estimated using Gaussian model fitting. From these measurements, brightness temperatures have been calculated, taking into account resolution limits of the data. The cores of 70% of the imaged sources are resolved. The core brightness temperatures of the sources peak at ∼ 10 11 K and only 1% have brightness temperatures higher than 10 12 K. Cores of Intraday Variable (IDV) sources are smaller in angular size than non-IDV sources, and so yield higher brightness temperatures.Every source in the sample was observed for 3-4 scans of 7-minute duration (snapshot mode). Although the uv-coverage of such an experiment limits the dynamic range and structural sensitivity of images, the large number of the participating antennas gives a sufficient uv-coverage of the sources at low and high declinations ( Figure 2). The data were recorded either with 128-MHz or 64-MHz bandwidth using the MkIV VLBI system with 1-and 2-bit sampling adopted at different epochs.The observations were made in lefthand circular polarization (LCP). Three to four scans per hour were recorded, using the time between the scans for antenna focusing, pointing and calibration. The data were correlated using the MkIV correlator of the Max-Planck-Institut für Radioastronomie (MPIfR) in Bonn (Alef & Müskens 2001). Data ProcessingIn this section, we describe the post-correlation processing of the 3 mm-VLBI survey datasets. Fringes were searched in two steps using HOPS (Haystack Observatory Postprocessing System) and AIPS (The NRAO Astronomical Image Processing System). In the first step, the HOPS task fourfit was used to precisely determine phase-residuals. The first fourfit was run with a wide search window (e.g. a width of 1 µsec for singleband delay, 2 µsec for multiband delay and 500 psec sec −1 for delay rate) centered at zero in delay. Since the fourfit produces baseline-based fringe solutions, the mean and standard deviation of the detected fringe solutions on each baseline were estimated and served as the offset and width of the search window for the second fourfit. The detected fringe solutions from the second run were used to interpolate the offset of the singleband delay for nondetected scans. In the f...

We present COSAS (CO Survey of late AGB Stars), a project to map and analyze the 12 CO J = 1−0 and J = 2−1 line emission in a representative sample of circumstellar envelopes around AGB and post-AGB stars. The survey was undertaken with the aim of investigating small-and large-scale morphological and kinematical properties of the molecular environment surrounding stars in the late AGB and early post-AGB phases. For this, COSAS combines the high sensitivity and spatial resolving power of the IRAM Plateau de Bure interferometer with the better capability of the IRAM 30 m telescope to map extended emission. The global sample encompasses 45 stars selected to span a range in chemical type, variability type, evolutionary state, and initial mass. COSAS provides means to quantify variations in the mass-loss rates, assess morphological and kinematical features, and to investigate the appearance of fast aspherical winds in the early post-AGB phase. This paper, which is the first of a series of COSAS papers, presents the results from the analyses of a first sample of 16 selected sources. The envelopes around late AGB stars are found to be mostly spherical, often mingled with features such as concentric arcs (R Cas and TX Cam), a broken spiral density pattern (TX Cam), molecular patches testifying to aspherical mass-loss (WX Psc, IK Tau, V Cyg, and S Cep), and also with well-defined axisymmetric morphologies and kinematical patterns (X Her and RX Boo). The sources span a wide range of angular sizes, from relatively compact (CRL 2362, OH 104.9+2.4 and CRL 2477) to very large (χ Cyg and TX Cam) envelopes, sometimes partially obscured by self-absorption features, which particularly for IK Tau and χ Cyg testifies to the emergence of aspherical winds in the innermost circumstellar regions. Strong axial structures with more or less complex morphologies are detected in four early post-AGB stars (IRAS 20028+3910, IRAS 23321+6545, IRAS 19475+3119 and IRAS 21282+5050) of the sub-sample.

Aims. The BL Lac object S5 0716+71 was observed in a global multi-frequency campaign to search for rapid and correlated flux density variability and signatures of an inverse-Compton (IC) catastrophe during the states of extreme apparent brightness temperatures. Methods. The observing campaign involved simultaneous ground-based monitoring at radio to IR/optical wavelengths and was centered around a 500-ks pointing with the INTEGRAL satellite (November 10−17, 2003). Here, we present the combined analysis and results of the radio observations, covering the cm-to sub-mm bands. This facilitates a detailed study of the variability characteristics of an inter-to intra-day variable IDV source from cm-to the short mm-bands. We further aim to constrain the variability brightness temperatures (T B ) and Doppler factors (δ) comparing the radio-bands with the hard X-ray emission, as seen by INTEGRAL at 3−200 keV. Results. 0716+714 was in an exceptionally high state and different (slower) phase of short-term variability, when compared to the past, most likely due to a pronounced outburst shortly before the campaign. The flux density variability in the cm-to mm-bands is dominated by a ∼4 day time scale amplitude increase of up to ∼35%, systematically more pronounced towards shorter wavelengths. The cross-correlation analysis reveals systematic time-lags with the higher frequencies varying earlier, similar to canonical variability on longer time-scales. The increase of the variability amplitudes with frequency contradicts expectations from standard interstellar scintillation (ISS) and suggests a source-intrinsic origin for the observed inter-day variability. We find an inverted synchrotron spectrum peaking near 90 GHz, with the peak flux increasing during the first 4 days. The lower limits to T B derived from the inter-day variations exceed the 10 12 K IC-limit by up to 3−4 orders of magnitude. Assuming relativistic boosting, our different estimates of δ yield robust and self-consistent lower limits of δ ≥ 5−33 -in good agreement with δ VLBI obtained from VLBI studies and the IC-Doppler factors δ IC > 14−16 obtained from the INTEGRAL data. Conclusions. The non-detection of S5 0716+714 with INTEGRAL in this campaign excludes an excessively high X-ray flux associated with a simultaneous IC catastrophe. Since a strong contribution from ISS can be excluded, we conclude that relativistic Doppler boosting naturally explains the apparent violation of the theoretical limits. All derived Doppler factors are internally consistent, agree with the results from different observations and can be explained within the framework of standard synchrotron-self-Compton (SSC) jet models of AGN.

No abstract