The difference of optical polarization properties between XBLs and RBLs

On the basis of the beaming model, we have derived a relation between the observed polarization (P-ob) and Doppler-corrected optical magnitude (m(corr)), log P-ob = 0.4(1 - k)m(corr) + C. We tested the correlation between P-ob and m(corr). The main results are as follows: (1) for both high and low states, there are strong correlations between P-ob and m(corr) for 29 RBLs with well-observed polarization and Doppler factor, where m(corr) = m(ob) + (3 + alpha )log delta /0.4, and delta is the optical Doppler factor; (2) no correlation exists between P-ob and the observed optical magnitude, m(ob), for the 29 RBLs in high state, but there is a close correlation for the 29 RBLs in low state; (3) however, there is an obvious anti-correlation between P-ob and m(corr) for 35 XBLs with good simultaneous observation data. Our results show that (i) a new difference in polarization is found between RBLs and XBLs; (ii) this difference in polarization between RBLs and XBLs seems really to be physical differences.