Breña Baja, Spain
Breña Baja, Spain

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Covino S.,National institute for astrophysics | Baglio M.C.,National institute for astrophysics | Baglio M.C.,University of Insubria | Foschini L.,National institute for astrophysics | And 26 more authors.
Astronomy and Astrophysics | Year: 2015

Context. Blazars are astrophysical sources whose emission is dominated by non-thermal processes, i.e. synchrotron and inverse Compton emission. Although the general picture is rather robust and consistent with observations, many aspects are still unexplored. Aims. Polarimetric monitoring can offer a wealth of information about the physical processes in blazars. Models with largely different physical ingredients can provide almost indistinguishable predictions for the total flux, but usually are characterized by different polarization properties. We explore the possibility to derive structural information about the emitting regions of blazars by means of a joint analysis of rapid variability of the total and polarized flux at optical wavelengths. Methods. Short timescale (from tens of seconds to a couple of minutes) optical linear polarimetry and photometry for two blazars, BL Lacertae and PKS 1424+240, was carried out with the PAOLO polarimeter at the 3.6 m Telescopio Nazionale Galileo. Several hours of almost continuous observations were obtained for both sources. Results. Our intense monitoring allowed us to draw different scenarios for BL Lacertae and PKS1424+240, with the former characterized by intense variability and the latter practically constant in total flux. Essentially the same behavior is observed for the polarized flux and the position angle. The variability time-scales turned out to be as short as a few minutes, although involving only a few percent variation of the flux. The polarization variability time-scale is generally consistent with the total flux variability. Total and polarized flux appear to be essentially uncorrelated. However, even during our relatively short monitoring, different regimes can be singled out. Conclusions. No simple scenario is able to satisfactorily model the very rich phenomenology exhibited in our data. Detailed numerical simulations show that the emitting region should be characterized by some symmetry, and the inclusion of turbulence for the magnetic field may constitute the missing ingredient for a more complete interpretation of the data. © ESO, 2015.

Covino S.,National institute for astrophysics | Molinari E.,INAF Fund. Galileo Galilei | Molinari E.,Istituto di Astrofisica Spaziale e Fisica Cosmica | Bruno P.,National institute for astrophysics | And 12 more authors.
Astronomische Nachrichten | Year: 2014

We describe a new polarimetric facility available at the Istituto Nazionale di AstroFisica / Telescopio Nazionale Galileo at La Palma, Canary islands. This facility, PAOLO (Polarimetric Add-On for the LRS Optics), is located at a Nasmyth focus of an alt-az telescope and requires a specific modeling in order to remove the time- and pointing position-dependent instrumental polarization. We also describe the opto-mechanical structure of the instrument and its calibration and present early examples of applications. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Leone F.,University of Catania | Leone F.,National institute for astrophysics | Cecconi M.,INAF Fund. Galileo Galilei | Cosentino R.,INAF Fund. Galileo Galilei | And 10 more authors.
Proceedings of SPIE - The International Society for Optical Engineering | Year: 2014

Usually observational astronomy is based on direction and intensity of radiation considered as a function of wavelength and time. Despite the polarisation degree of radiation provides information about asymmetry, anisotropy and magnetic fields within the radiative source or in the medium along the line of sight, it is commonly ignored. Because of the importance of high resolution spectropolarimetry to study a large series of phenomena related to the interaction of radiation with matter, as in stellar atmospheres or more generally stellar envelopes, we designed and built a dual beam polarimeter for HARPS-N that is in operation at the Telescopio Nazionale Galileo. Since the polarisation degree is measured from the combination of a series of measurements and accuracy is limited by the instrumental stability, just the great stability (0.6 m/s) and spectral resolution (R=115000) of the HARPS-N spectrograph should result in an accuracy in the measurements of Stokes parameters as small as 0.01%. Here we report on the design, realization, assembling, aligning and testing of the polarimetric unit whose first light is planned in August 2014. © 2014 SPIE.

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