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We describe the POLAMI (Polarimetric Monitoring of AGN at Millimetre Wavelengths) programme for the monitoring of all four Stokes parameters of a sample of bright radio-loud active galactic nuclei with the IRAM30-m telescope at 3.5 and 1.3 mm. The programme started in 2006 October and accumulated, until 2014 August, 2300 observations at 3.5 mm, achieving a median time sampling interval of 22 d for the sample of 37 sources. This first paper explains the source selection, mostly blazars, the observing strategy and data calibration and gives the details of the instrumental polarization corrections. The sensitivity (1σ) reached at 3.5mm is 0.5 per cent (linear polarization degree), 4.°7 (polarization angle), and 0.23 per cent (circular polarization), while the corresponding values at 1.3mm are 1.7 per cent, 9.°9 and 0.72 per cent, respectively. The data quality is demonstrated by the time sequences of our calibrators Mars and Uranus. For the quasar 3C 286, widely used as a linear polarization calibrator, we give improved estimates of its linear polarization, and show for the first time occasional detections of its weak circular polarization, which suggests a small level of variability of the source at millimeter wavelengths. [ABSTRACT FROM AUTHOR]

We analyse the circular polarization data accumulated in the first 7 years of the Polarimetric Monitoring of Active Galactic Nuclei at MillimetreWavelengths (POLAMI) project introduced in an accompanying paper. In the 3-mm wavelength band, we acquired more than 2600 observations, and all but one of our 37 sample sources were detected, most of them several times. For most sources, the observed distribution of the degree of circular polarization is broader than that of unpolarized calibrators, indicating that weak (≲0.5 per cent) circular polarization is present most of the time. Our detection rate and the maximum degree of polarization found, 2.0 per cent, are comparable to previous surveys, all made at much longer wavelengths. We argue that the process generating circular polarization must not be strongly wavelength dependent, and we propose that the widespread presence of circular polarization in our short wavelength sample dominated by blazars is mostly due to Faraday conversion of the linearly polarized synchrotron radiation in the helical magnetic field of the jet. Circular polarization is variable, most notably on time-scales comparable to or shorter than our median sampling interval of ≲1 month. Longer time-scales of about 1 yr are occasionally detected, but severely limited by the weakness of the signal. At variance with some longer wavelength investigations we find that the sign of circular polarization changes in most sources, while only seven sources, including three already known, have a strong preference for one sign. The degrees of circular and linear polarization do not show any systematic correlation. We do find however one particular event where the two polarization degrees vary in synchronism during a time span of 0.9 yr. This paper also describes a novel method for calibrating the sign of circular polarization observations. [ABSTRACT FROM AUTHOR]

We report on the first results of the POLAMI (Polarimetric Monitoring of AGNs with Millimetre Wavelengths) programme, a simultaneous 3.5 and 1.3mm full-Stokes-polarization monitoring of a sample of 36 of the brightest active galactic nuclei in the northern sky with the IRAM 30m telescope. Through a systematic statistical study of data taken from 2006 October (from 2009 December for the case of the 1.3mm observations) to 2014 August, we characterize the variability of the total flux density and linear polarization. We find that all sources in the sample are highly variable in total flux density at both 3.5 and 1.3 mm, as well as in spectral index, which (except in particularly prominent flares) is found to be optically thin between these two wavelengths. The total flux-density variability at 1.3mm is found, in general, to be faster, and to have larger fractional amplitude and flatter power-spectral-density slopes than at 3.5 mm. The polarization degree is on average larger at 1.3mm than at 3.5 mm, by a factor of 2.6. The variability of linear polarization degree is faster and has higher fractional amplitude than for total flux density, with the typical time-scales during prominent polarization peaks being significantly faster at 1.3mm than at 3.5 mm. The polarization angle at both 3.5 and 1.3mm is highly variable. Most of the sources show one or two excursions of >18° on time-scales from a few weeks to about a year during the course of our observations. The 3.5 and 1.3mm polarization angle evolution follows each other rather well, although the 1.3mm data show a clear preference to more prominent variability on the short time-scales, i.e. weeks. The data are compatible with multizone models of conical jets involving smaller emission regions for the shortest-wavelength emitting sites. Such smaller emitting regions should also be more efficient in energising particle populations, as implied by the coherent evolution of the spectral index and the total flux density during flaring activity of strong enough sources. The data also favour the integrated emission at 1.3mm to have better ordered magnetic fields than the one at 3.5 mm. [ABSTRACT FROM AUTHOR]

The source NRAO?150 is a very prominent millimeter to radio emitting quasar at redshift z = 1.52 for which previous millimeter VLBI observations revealed a fast counterclockwise rotation of the innermost regions of the jet. Here we present new polarimetric multi-epoch VLBI-imaging observations of NRAO?150 performed at 8, 15, 22, 43, and 86?GHz with the Very Long Baseline Array (VLBA), and the Global Millimeter VLBI Array (GMVA) between 2006 and 2010. All new and previous observational evidence - i.e., spectral index maps, multi-epoch image cross-correlation, and low level of linear polarization degree in optically thin regions - are consistent with an interpretation of the source behavior where the jet is seen at an extremely small angle to the line of sight, and the high frequency emitting regions in NRAO?150 rotate at high speeds on the plane of the sky with respect to a reference point that does not need to be related to any particularly prominent jet feature. The observed polarization angle distribution at 22, 43, and 86?GHz during observing epochs with high polarization degree suggests that we have detected the toroidal component of the magnetic field threading the innermost jet plasma regions. This is also consistent with the lower degree of polarization detected at progressively poorer angular resolutions, where the integrated polarization intensity produced by the toroidal field is explained by polarization cancellation inside the observing beam. All this evidence is fully consistent with a kinematic scenario where the main kinematic and polarization properties of the 43?GHz emitting structure of NRAO?150 are explained by the internal rotation of such emission regions around the jet axis when the jet is seen almost face on. A simplified model developed to fit helical trajectories to the observed kinematics of the 43?GHz features fully supports this hypothesis. This explains the kinematics of the innermost regions of the jet in NRAO?150 in terms of internal jet rotation. [ABSTRACT FROM AUTHOR]

We present the results from an ultra-high-resolution 7 mm Very Long Baseline Array study of the relativistic jet in the BL Lacertae object OJ287 from 1995 to 2011 containing 136 total intensity images. Analysis of the image sequence reveals a sharp jet-position-angle swing by >100° during [2004,2006], as viewed in the plane of the sky, which we interpret as the crossing of the jet from one side of the line of sight to the other during a softer- and longer-term swing of the inner jet. Modulating such long-term swing, our images also show for the first time a prominent erratic wobbling behavior of the innermost ~0.4 mas of the jet with fluctuations in position angle of up to ~40° over timescales ~2 yr. This is accompanied by highly superluminal motions along non-radial trajectories, which reflect the remarkable non-ballistic nature of the jet plasma on these scales. The erratic nature and short timescales of the observed behavior rule out scenarios such as binary black hole systems, accretion disk precession, and interaction with the ambient medium as possible origins of the phenomenon on the scales probed by our observations, although such processes may cause longer-term modulation of the jet direction. We propose that variable asymmetric injection of the jet flow, perhaps related to turbulence in the accretion disk, coupled with hydrodynamic instabilities leads to the non-ballistic dynamics that causes the observed non-periodic changes in the direction of the inner jet. [ABSTRACT FROM AUTHOR]

We present the multiwavelength flaring activity of the blazar AO 0235 + 164 during its recent active period from 2013 to 2019. From a discrete correlation function analysis, we find a significant (⁠|$\gt 95~{{\ \rm per\ cent}}$|⁠) correlation between radio and gamma-ray light curves with flares at longer wavelengths following flares at shorter wavelengths. We identify a new jet component in 43 GHz Very Long Baseline Array data that was ejected from the radio core on MJD |$57246^{+26}_{-30}$| (2015 August 12), during the peak of the 2015 radio flare. From the analysis of the jet component, we derived a Doppler factor of δvar = 28.5 ± 8.4, a bulk Lorentz factor of |$\Gamma =16.8^{+3.6}_{-3.1}$|⁠ , and an intrinsic viewing angle of |$\theta _{\rm v}=1.42^{+1.07}_{-0.52}\textrm {~degrees}$|⁠. Investigation of the quasi-simultaneous radio data revealed a partially absorbed spectrum with the turnover frequency varying in the range of 10−70 GHz and the peak flux density varying in the range of 0.7−4 Jy. We find the synchrotron self-absorption magnetic field strength to be |$B_{\rm SSA}=15.3^{+12.6}_{-14.0}\textrm {~mG}$| at the peak of the 2015 radio flare, which is comparable to the equipartition magnetic field strength of |$B_{\rm EQ}=43.6^{+10.6}_{-10.4}\textrm {~mG}$| calculated for the same epoch. Additional analysis of the radio emission region in the relativistic jet of AO 0235 + 164 suggests that it did not significantly deviate from equipartition during its recent flaring activity. [ABSTRACT FROM AUTHOR]

The blazar 1156+295 was active at γ-ray energies, exhibiting three prominent flares during the year 2010. Here, we present results using the combination of broad-band (X-ray through mm single-dish) monitoring data and radio-band imaging data at 43 GHz on the connection of γ-ray events to the ejections of superluminal components and other changes in the jet of 1156+295. The kinematics of the jet over the interval 2007.0-2012.5 using 43 GHz Very Long Baseline Array observations reveal the presence of four moving and one stationary component in the inner region of the blazar jet. The propagation of the third and fourth components in the jet corresponds closely in time to the active phase of the source in γ-rays. We briefly discuss the implications of the structural changes in the jet for the mechanism of γ-ray production during bright flares. To localize the γ-ray emission site in the blazar, we performed the correlation analysis between the 43 GHz radio core and the γ-ray light curve. The time lag obtained from the correlation constrains the γ-ray emitting region in the parsec-scale jet. [ABSTRACT FROM AUTHOR]

We analyze the multi-frequency behavior of the quasar 3C 454.3 during three prominent γ -ray outbursts: 2009 Autumn, 2010 Spring, and 2010 Autumn. The data reveal a repeating pattern, including a triple flare structure, in the properties of each γ -ray outburst, which implies similar mechanism(s) and location for all three events. The multi-frequency behavior indicates that the lower frequency events are co-spatial with the γ -ray outbursts, although the γ -ray emission varies on the shortest timescales. We determine that the variability from UV to IR wavelengths during an outburst results from a single synchrotron component whose properties do not change significantly over the different outbursts. Despite a general increase in the degree of optical linear polarization during an outburst, the polarization drops significantly at the peak of the γ -ray event, which suggests that both shocks and turbulent processes are involved. We detect two disturbances (knots) with superluminal apparent speeds in the parsec-scale jet associated with the outbursts in 2009 Autumn and 2010 Autumn. The kinematic properties of the knots can explain the difference in amplitudes of the γ -ray events, while their millimeterwave polarization is related to the optical polarization during the outbursts. We interpret the multi-frequency behavior within models involving either a system of standing conical shocks or magnetic reconnection events located in the parsec-scale millimeter-wave core of the jet. We argue that γ -ray outbursts with variability timescales as short as ∼3 hr can occur on parsec scales if flares take place in localized regions such as turbulent cells. [ABSTRACT FROM AUTHOR]