1201.2150 (Ivan Agudo et al.)

3C 286: a bright, compact, stable, and highly polarized calibrator for millimeter-wavelength observations    [PDF]

Ivan Agudo, Clemens Thum, Helmut Wiesemeyer, Sol N. Molina, Carolina Casadio, Jose L. Gomez, Dimitrios Emmanoulopoulos

Context. A number of millimeter and submillimeter facilities with linear polarization observing capabilities have started operating during last years. These facilities, as well as other previous millimeter telescopes and interferometers, require bright and stable linear polarization calibrators to calibrate new instruments and to monitor their instrumental polarization. The current limited number of adequate calibrators implies difficulties in the acquisition of these calibration observations. Aims. Looking for additional linear polarization calibrators in the millimeter spectral range, in mid-2006 we started monitoring 3C 286, a standard and highly stable polarization calibrator for radio observations. Methods. Here we present the 3 and 1mm monitoring observations obtained between September 2006 and October 2011 with the XPOL polarimeter on the IRAM 30m Millimeter Telescope. Results. Our observations show that 3C 286 is a bright source of constant total flux with 3mm flux density S_3mm = (0.90 \pm 0.02) Jy. The 3mm linear polarization degree (p_3mm = [13.6\pm 0.3]%) and polarization angle (chi_3mm = [37.5\pm 0.8] deg, expressed in the equatorial coordinate system) are also constant during the time span of our observations. Although with poorer time sampling and data quality, our 1mm observations of 3C 286 are also consistent with a constant 1mm source with flux density S_1mm = (0.29 \pm 0.03) Jy. Indeed, our statistical analysis demonstrate that the linear polarization degree and polarization angle of 3C 286 at 1mm (p_1mm = [16.1\pm1.6]%, and chi_1mm = [33.0 \pm 6.8] deg., respectively) are also constant. Conclusions. This, together with the previously known compact structure of 3C 286 -extended by \sim 3.5" in the sky- allow us to propose 3C 286 as a new calibrator for both single dish and interferometric polarization observations at 3mm, and possibly at shorter wavelengths.

View original: http://arxiv.org/abs/1201.2150