TY - JOUR

T1 - Optical polarization variations in the blazar PKS 1749+096

AU - Uemura, Makoto

AU - Itoh, Ryosuke

AU - Liodakis, Ioannis

AU - Blinov, Dmitry

AU - Nakayama, Masanori

AU - Xu, Longyin

AU - Sawada, Naoko

AU - Wu, Hsiang-Yun

AU - Fujishiro, Issei

PY - 2017/12

Y1 - 2017/12

N2 - We report on the variation in the optical polarization of the blazar PKS 1749+096 observed in 2008-2015. The degree of polarization (PD) tends to increase in short flares, having a time-scale of a few days. The object favors a polarization angle (PA) of 40 degrees-50 degrees at the flare maxima, which is close to the position angle of the jet (20 degrees-40 degrees). Three clear polarization rotations were detected in the negative PA direction associated with flares. In addition, a rapid and large decrease in the PA was observed in the other two flares, while another two flares showed no large PA variation. The light-curve maxima of the flares possibly tended to lag behind the PD maxima and color-index minima. The PA became -50 degrees to -20 degrees in the decay phase of active states, which is almost perpendicular to the jet position angle. We propose a scenario to explain these observational features, where transverse shocks propagate along curved trajectories. The favored PA at the flaremaxima suggests that the observed variations were governed by the variations in the Doppler factor, delta. Based on this scenario, the minimum viewing angle of the source, theta(min) = 4 degrees.8-6 degrees.6, and the location of the source, Delta r greater than or similar to 0.1 pc, from the central black hole were estimated. In addition, the acceleration of electrons by the shock and synchrotron cooling would have a time-scale similar to that of the change in delta. The combined effect of the variation in delta and acceleration/ cooling of electrons is probably responsible for the observed diversity of the polarization variations in the flares.

AB - We report on the variation in the optical polarization of the blazar PKS 1749+096 observed in 2008-2015. The degree of polarization (PD) tends to increase in short flares, having a time-scale of a few days. The object favors a polarization angle (PA) of 40 degrees-50 degrees at the flare maxima, which is close to the position angle of the jet (20 degrees-40 degrees). Three clear polarization rotations were detected in the negative PA direction associated with flares. In addition, a rapid and large decrease in the PA was observed in the other two flares, while another two flares showed no large PA variation. The light-curve maxima of the flares possibly tended to lag behind the PD maxima and color-index minima. The PA became -50 degrees to -20 degrees in the decay phase of active states, which is almost perpendicular to the jet position angle. We propose a scenario to explain these observational features, where transverse shocks propagate along curved trajectories. The favored PA at the flaremaxima suggests that the observed variations were governed by the variations in the Doppler factor, delta. Based on this scenario, the minimum viewing angle of the source, theta(min) = 4 degrees.8-6 degrees.6, and the location of the source, Delta r greater than or similar to 0.1 pc, from the central black hole were estimated. In addition, the acceleration of electrons by the shock and synchrotron cooling would have a time-scale similar to that of the change in delta. The combined effect of the variation in delta and acceleration/ cooling of electrons is probably responsible for the observed diversity of the polarization variations in the flares.

KW - BL Lacertae objects: individual (PKS 1749+096)

KW - galaxies: active

KW - galaxies: jets

KW - polarization

KW - BL-LAC OBJECTS

KW - LACERTAE OBJECTS

KW - RADIO OUTBURSTS

KW - DOPPLER FACTORS

KW - BRIGHT BLAZARS

KW - INNER JET

KW - VARIABILITY

KW - ROBOPOL

KW - ROTATIONS

KW - FLARE

U2 - 10.1093/pasj/psx111

DO - 10.1093/pasj/psx111

M3 - статья

VL - 69

JO - Publication of the Astronomical Society of Japan

JF - Publication of the Astronomical Society of Japan

SN - 0004-6264

IS - 6

M1 - 96

ER -