Eugeniusz Pazderski

RoboPol: optical polarization-plane rotations and flaring activity in blazars

We present measurements of rotations of the optical polarization of blazars during the second year of operation of RoboPol, a monitoring programme of an unbiased sample of gamma-ray bright blazars specially designed for effective detection of such events, and we analyse the large set of rotation events discovered in two years of observation. We investigate patterns of variability in the polarization parameters and total flux density during the rotation events and compare them to the behaviour in a non-rotating state. We have searched for possible correlations between average parameters of the polarization-plane rotations and average parameters of polarization, with the following results: (1) there is no statistical association of the rotations with contemporaneous optical flares; (2) the average fractional polarization during the rotations tends to be lower than that in a non-rotating state; (3) the average fractional polarization during rotations is correlated with the rotation rate of the polarization plane in the jet rest frame; (4) it is likely that distributions of amplitudes and durations of the rotations have physical upper bounds, so arbitrarily long rotations are not realized in nature.

30 GHz flux density measurements of the Caltech-Jodrell flat-spectrum sources with OCRA-p

To measure the 30-GHz flux densities of the 293 sources in the Caltech-Jodrell Bank flat-spectrum (CJF) sample. The measurements are part of an ongoing programme to measure the spectral energy distributions of flat spectrum radio sources and to correlate them with the milliarcsecond structures from VLBI and other measured astrophysical properties.Methods.The 30-GHz data were obtained with a twin-beam differencing radiometer system mounted on the Torun 32-m telescope. The system has an angular resolution of 1.2�.Results.Together with radio spectral data obtained from the literature, the 30-GHz data have enabled us to identify 42 of the CJF sources as Giga-hertz Peaked Spectrum (GPS) sources. Seventeen percent of the sources have rising spectra (

Cavity mode-width spectroscopy with widely tunable ultra narrow laser

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30 GHz observations of sources in the Very Small Array fields

> 0) between 5 and 30 GHz.

One Centimetre Receiver Array-prototype observations of the CRATES sources at 30 GHz

We explore a cavity-enhanced spectroscopic technique based on determination of the absorbtion coefficient from direct measurement of spectral width of the mode of the optical cavity filled with absorbing medium. This technique called here the cavity mode-width spectroscopy (CMWS) is complementary to the cavity ring-down spectroscopy (CRDS). While both these techniques use information on interaction time of the light with the cavity to determine absorption coefficient, the CMWS does not require to measure very fast signals at high absorption conditions. Instead the CMWS method require a very narrow line width laser with precise frequency control. As an example a spectral line shape of P7 Q6 O₂ line from the B-band was measured with use of an ultra narrow laser system based on two phase-locked external cavity diode lasers (ECDL) having tunability of ± 20 GHz at wavelength range of 687 to 693 nm.

RoboPol: connection between optical polarization plane rotations and gamma-ray flares in blazars

Small angular scale (high l) studies of cosmic microwave background (CMB) anisotropies require accurate knowledge of the statistical properties of extragalactic sources at cm-mm wavelengths. We have used a 30 GHz dual-beam receiver (One Centimetre Receiver Array prototype) on the Torun 32-m telescope to measure the flux densities of 121 sources in Very Small Array fields selected at 15 GHz with the Ryle Telescope. We have detected 57 sources above a limiting flux density of 5 mJy, of which 31 sources have a flux density greater than 10 mJy, which is our effective completeness limit. From these measurements we derive a surface density of sources above 10 mJy at 30 GHz of 2.2 ± 0.4 deg -2 . This is consistent with the surface density obtained by Mason et al. who observed a large sample of sources selected at a much lower frequency (1.4 GHz). We have also investigated the dependence of the spectral index distribution on flux density by comparing our results with those for sources above 1 Jy selected from the Wilkinson Microwave Anisotropy Probe 22 GHz catalogue. We conclude that the proportion of steep spectrum sources increases with decreasing flux density, qualitatively consistent with the predictions of de Zotti et al. We find no evidence for an unexpected population of sources above our completeness limit of 10 mJy whose spectra rise towards high frequencies, which would affect our ability to interpret current high-resolution CMB observations at 30 GHz and above.

30 GHz observations of sources in the Very Small Array fields: 30 GHz observations of sources in VSA fields

Knowledge of the population of radio sources in the range �?2-200 GHz is important for understanding their effects on measurements of the cosmic microwave background power spectrum. We report measurements of the 30-GHz flux densities of 605 radio sources from the Combined Radio All-sky Targeted Eight-GHz Survey (CRATES), which have been made with the One Centimetre Receiver Array-prototype (OCRA-p) on the Toru�? 32-m telescope. The flux densities of sources that were also observed by Wilkinson Microwave Anisotropy Probe (WMAP) and previous OCRA surveys are in broad agreement with those reported here, however a number of sources display intrinsic variability. We find a good correlation between the 30 GHz and Fermi gamma-ray flux densities for common sources. We examine the radio spectra of all observed sources and report a number of gigahertz-peaked and inverted spectrum sources. These measurements will be useful for comparison to those from the Low Frequency Instrument of the Planck satellite, which will make some of its most sensitive observations in the region covered here.

Fibre-optic delivery of time and frequency to VLBI station

We use results of our 3 yr polarimetric monitoring programme to investigate the previously suggested connection between rotations of the polarization plane in the optical emission of blazars and their gamma-ray flares in the GeV band. The homogeneous set of 40 rotation events in 24 sources detected by RoboPol is analysed together with the gamma-ray data provided by Fermi-LAT. We confirm that polarization plane rotations are indeed related to the closest gamma-ray flares in blazars and the time lags between these events are consistent with zero. Amplitudes of the rotations are anticorrelated with amplitudes of the gamma-ray flares. This is presumably caused by higher relativistic boosting (higher Doppler factors) in blazars that exhibit smaller amplitude polarization plane rotations. Moreover, the time-scales of rotations and flares are marginally correlated.

New 6‐cm observations of a large sample of radio SNRs

Small angular scale (high l) studies of cosmic microwave background (CMB) anisotropies require accurate knowledge of the statistical properties of extragalactic sources at cm-mm wavelengths. We have used a 30 GHz dual-beam receiver (One Centimetre Receiver Array prototype) on the Torun 32-m telescope to measure the flux densities of 121 sources in Very Small Array fields selected at 15 GHz with the Ryle Telescope. We have detected 57 sources above a limiting flux density of 5 mJy, of which 31 sources have a flux density greater than 10 mJy, which is our effective completeness limit. From these measurements we derive a surface density of sources above 10 mJy at 30 GHz of 2.2 ± 0.4 deg -2 . This is consistent with the surface density obtained by Mason et al. who observed a large sample of sources selected at a much lower frequency (1.4 GHz). We have also investigated the dependence of the spectral index distribution on flux density by comparing our results with those for sources above 1 Jy selected from the Wilkinson Microwave Anisotropy Probe 22 GHz catalogue. We conclude that the proportion of steep spectrum sources increases with decreasing flux density, qualitatively consistent with the predictions of de Zotti et al. We find no evidence for an unexpected population of sources above our completeness limit of 10 mJy whose spectra rise towards high frequencies, which would affect our ability to interpret current high-resolution CMB observations at 30 GHz and above.

6.7 GHz methanol masers at sites of star formation - A blind survey of the Galactic plane between 20°

The quality of Very Long Baseline Interferometry (VLBI) radio observations predominantly relies on precise and ultra-stable time and frequency (T&F) standards, usually hydrogen masers (HM), maintained locally at each VLBI station. Here, we present an operational solution in which the VLBI observations are routinely carried out without use of a local HM, but using remote synchronization via a stabilized, long-distance fibre-optic link. The T&F reference signals, traceable to international atomic timescale (TAI), are delivered to the VLBI station from a dedicated timekeeping laboratory. Moreover, we describe a proof-of-concept experiment where the VLBI station is synchronized to a remote strontium optical lattice clock during the observation.