CCD photo-polarimetry of the blazar AO0235+164: extreme microvariability

CELLONE, S. A.; ROMERO, G. E.; COMBI, J. A.; MARTÍ, J.

La Plata

Congreso; 50 Reunión de la Asociación Argentina de Astronomía; 2007

IAR

We present results from a high-temporal resolution photo-polarimetric campaign on the BL Lac object AO 0235+164, showing significant microvariations in R-band flux, B-R colour index, percent of linear polarization, and its associated position angle. We also detect strong variations in all these parameters at longer (>24 h) time-scales. Total flux was found to correlate neither with colour index nor with linear polarization degree. On the other hand, we detect a trend in the sense that colour index gets redder (i.e., the spectrum gets softer) when the measured polarization is higher. We briefly discuss these results within the context of composite models proposed to explain the optical emission in blazars.