We report the first results of a search for 6.7 GHz methanol masers in the direction of 1399 IRAS objects north of declination −20 • with the flux densities greater than 100 Jy at 60 µm and the flux density ratio F 60 /F 25 > 1. Observations were made with the sensitivity of 1.7 Jy and the velocity resolution of 0.04 km s −1 using the 32-m Toruń radio telescope. Maser emission was found in 182 sources, including 70 new detections. 32 new sources were identified with objects of radio emission associated with star-forming regions. Comparison of the present data set with other observations suggests that about 65% of methanol masers exhibit moderate or strong variations on timescales of about 4 and 8 years.

We present first results on polarization swings in optical emission of blazars obtained by RoboPol, a monitoring programme of an unbiased sample of gamma-ray bright blazars specially designed for effective detection of such events. A possible connection of polarization swing events with periods of high activity in gamma rays is investigated using the data set obtained during the first season of operation. It was found that the brightest gamma-ray flares tend to be located closer in time to rotation events, which may be an indication of two separate mechanisms responsible for the rotations. Blazars with detected rotations during non-rotating periods have significantly larger amplitude and faster variations of polarization angle than blazars without rotations. Our simulations show that the full set of observed rotations is not a likely outcome (probability ≤ 1.5 × 10 −2 ) of a random walk of the polarization vector simulated by a multicell model. Furthermore, it is highly unlikely (∼ 5 × 10 −5 ) that none of our rotations is physically connected with an increase in gamma-ray activity.

Abstract. We present two-epoch, multifrequency complete modeling of Mrk 501 broad band emission from the radio frequencies up to the very high gamma ray regime as observed during April 1997 outburst. To reproduce the X-ray and the gamma-ray radiation we assume an homogeneous Synchrotron-Self-Compton (SSC) model and approximate the electrons energy distribution by a broken power-law function with a sharp cut-off at high energy. We assume also spherical geometry of the emitting region (a blob) and uniform magnetic field. For this scenario we derive constrains on physical parameters obtained from the observable quantities and can reproduce very well the observed Very High Energy (VHE) spectra. We find that the two different high energy states cannot be explained by varying the particle energy distribution only. To obtain good spectral fits we have to change additionally one of the global parameters which describe the emitting blob: the magnetic field intensity (B), the radius (R b ) or the Doppler factor (δ b ). We use a model of an inhomogeneous conical jet to explain radiation from the low radio frequencies up to the ultraviolet. A part of the physical parameters of this jet can be constrained from our fits of the high energy emission. The remaining parameters are estimated independently from other observations. We assume that the blob is placed somewhere inside the jet, relatively close to the central engine. Within this "blobin-jet" scenario we analyze the effect of External Inverse-Compton (EIC) scattering of low energy synchrotron photons from the jet and thermal radiation surrounding the central engine. We show that EIC scattering can also very well explain VHE emission of Mrk 501 when external radiation is dominated by photons from the jet itself, which is an interesting alternative of the "blob-in-jet" scenario. Additional inverse-Compton scattering of relatively weak thermal external radiation cannot explain alone the spectra but can significantly modify them, especially in the sub-TeV range, in comparison to spectral shape generated only with SSC model. We also analyze the absorption effect due to pair-production inside the source, which appears almost negligible. The same effect in the Intergalactic Infrared Background (IIB) may introduce significant changes to the observed VHE spectra. In the infrared and optical parts of the spectrum, the contribution of the host galaxy is well reproduced by an elliptical galaxy evolution model. Three miniflares of Mrk 501 occurred in ten days between 7 and 16 April 1997 at the X-ray and gamma-ray frequencies. They can be well reproduced by simple variation of the break in the electron energy distribution function on time scale of a few hours, superposed to variation of the blob radius and of the particle density on time scale of about two days.

Abstract. We report the results of an unbiased survey for 6.7 GHz methanol maser emission of a ∼21 deg 2 strip of the Galactic plane carried out with the 32 m Toruń radio telescope. An area at 20• ≤ l ≤ 40• , |b| ≤ 0.• 52 was surveyed in an equilateral triangular grid with a sensitivity limit of about 1.6 Jy. We detected a total of 100 sources, 26 of which are new detections. All the new sources are of moderate intensity and their peak flux densities have median value of 6.5 Jy, i.e. about half that of previously known sources in the sample. About 80% of maser sources have IR counterpart candidates within a 1 radius but not all the IRAS counterparts of methanol masers have colours typical of ultracompact HII regions. An excess of masers unassociated with IR sources occurs at 30• because of incompleteness of IR catalogues due to strong confusion near the tangential region of the spiral arm. Our unbiased survey doubled the number of detections as compared to IRAS-based observations. Within the positional uncertainty of 1 about one third of the methanol sources have radio continuum counterparts at 5 GHz of a flux density greater than 2.5-10 mJy. The distribution of methanol sources appears to be consistent with a clustered mode of formation of massive stars.

We present average R-band optopolarimetric data, as well as variability parameters, from the first and second RoboPol observing season. We investigate whether gammaray-loud and gamma-ray-quiet blazars exhibit systematic differences in their optical polarization properties. We find that gamma-ray-loud blazars have a systematically higher polarization fraction (0.092) than gamma-ray-quiet blazars (0.031), with the hypothesis of the two samples being drawn from the same distribution of polarization fractions being rejected at the 3σ level. We have not found any evidence that this discrepancy is related to differences in the redshift distribution, rest-frame R-band luminosity density, or the source classification. The median polarization fraction versus synchrotron-peak-frequency plot shows an envelope implying that high synchrotronpeaked sources have a smaller range of median polarization fractions concentrated around lower values. Our gamma-ray-quiet sources show similar median polarization fractions although they are all low synchrotron-peaked. We also find that the randomness of the polarization angle depends on the synchrotron peak frequency. For high synchrotron-peaked sources it tends to concentrate around preferred directions while for low synchrotron-peaked sources it is more variable and less likely to have a preferred direction. We propose a scenario which mediates efficient particle acceleration in shocks and increases the helical B-field component immediately downstream of the shock.