scholarly journals Polarization of changing-look quasars

2019 ◽  
Vol 625 ◽  
pp. A54 ◽  
Author(s):  
D. Hutsemékers ◽  
B. Agís González ◽  
F. Marin ◽  
D. Sluse ◽  
C. Ramos Almeida ◽  
...  

If the disappearance of the broad emission lines observed in changing-look quasars originates from the obscuration of the quasar core by dusty clouds moving in the torus, high linear optical polarization would be expected in those objects. We then measured the rest-frame UV-blue linear polarization of a sample of 13 changing-look quasars, 7 of them being in a type 1.9-2 state. For all quasars but one the polarization degree is lower than 1%. This suggests that the disappearance of the broad emission lines cannot be attributed to dust obscuration, and supports the scenario in which changes of look are caused by a change in the rate of accretion onto the supermassive black hole. Such low polarization degrees also indicate that these quasars are seen under inclinations close to the system axis. One type 1.9-2 quasar in our sample shows a high polarization degree of 6.8%. While this polarization could be ascribed to obscuration by a moving dusty cloud, we argue that this is unlikely given the very long time needed for a cloud from the torus to eclipse the broad emission line region of that object. We propose that the high polarization is due to the echo of a past bright phase seen in polar-scattered light. This interpretation raises the possibility that broad emission lines observed in the polarized light of some type 2 active galactic nuclei can be echoes of past type 1 phases and not evidence of hidden broad emission line regions.

1996 ◽  
Vol 173 ◽  
pp. 241-246
Author(s):  
Geraint F. Lewis ◽  
Mike J. Irwin ◽  
Paul C. Hewett

The degree of microlensing induced amplification is dependent upon the size of a source. As quasar spectra consist of the sum of emission from different regions this scale dependent amplification can produce spectral differences between the images of a macrolensed quasar. This paper presents the first direct spectroscopic evidence for this effect, providing a limit on the scale of the continuum and the broad line emission regions at the center of a source quasar (2237+0305). Lack of centroid and profile differences in the emission lines indicate that substructure in the broad emission line region is > 0.05 parsecs.


2012 ◽  
Vol 372 ◽  
pp. 012069
Author(s):  
Andrea J Ruff ◽  
David J E Floyd ◽  
Kirk T Korista ◽  
Rachel L Webster ◽  
Ryan L Porter ◽  
...  

1997 ◽  
Vol 159 ◽  
pp. 175-178 ◽  
Author(s):  
Brian Espey

AbstractWe present a brief review of emission-line velocity differences, and describe an ongoing project to determine the driving mechanisms responsible. We conclude with a brief outline of the use of velocity differences as probes of the conditions in the nuclear region of AGNs.


2019 ◽  
Vol 629 ◽  
pp. A43 ◽  
Author(s):  
D. Hutsemékers ◽  
L. Braibant ◽  
D. Sluse ◽  
R. Goosmann

The quadruply lensed quasar HE0435−1223 shows a clear microlensing effect that affects differently the blue and red wings of the Hα line profile in its image D. To interpret these observations, and constrain the broad emission line region (BLR) properties, the effect of gravitational microlensing on quasar broad emission line profiles and their underlying continuum has been simulated considering representative BLR models and microlensing magnification maps. The amplification and distortion of the Hα line profile, characterized by a set of four indices, can be reproduced by the simulations. Although the constraints on the BLR models set by the observed single-epoch microlensing signal are not very robust, we found that flattened geometries (Keplerian disk and equatorial wind) can more easily reproduce the observed line profile deformations than a biconical polar wind. With an additional independent constraint on the size of the continuum source, the Keplerian disk model of the Hα BLR is slightly favored.


2015 ◽  
Vol 812 (2) ◽  
pp. 99 ◽  
Author(s):  
Zhenzhen Li ◽  
Hongyan Zhou ◽  
Lei Hao ◽  
Huiyuan Wang ◽  
Tuo Ji ◽  
...  

2012 ◽  
Vol 754 (1) ◽  
pp. 18 ◽  
Author(s):  
Andrea J. Ruff ◽  
David J. E. Floyd ◽  
Rachel L. Webster ◽  
Kirk T. Korista ◽  
Hermine Landt

1997 ◽  
Vol 479 (1) ◽  
pp. 200-221 ◽  
Author(s):  
Mark Bottorff ◽  
Kirk T. Korista ◽  
Isaac Shlosman ◽  
Roger D. Blandford

1996 ◽  
Vol 463 ◽  
pp. 144 ◽  
Author(s):  
Christine Done ◽  
Julian H. Krolik

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