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arXiv · 1007.0448

A Spectropolarimetric Test of the Structure of the Intrinsic Absorbers in the Quasar HS1603+3820

T. Misawa·K. S. Kawabata·M. Eracleous·J. C. Charlton·N. Kashikawa
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Abstract

We report the results of a spectropolarimetric observation of the C IV mini-BAL in the quasar HS1603+3820. The observations were carried out with the FOCAS instrument on the Subaru telescope and yielded an extremely high polarization sensitivity of 0.1%, at a resolving power of 1500. HS1603+3820 has been the target of a high-resolution spectroscopic monitoring campaign for more than four years, aimed at studying its highly variable C IV mini-BAL profile. Using the monitoring observations, in an earlier paper we were able to narrow down the causes of the variability to the following two scenarios: (1) scattering material of variable optical depth redirecting photons around the absorber, and (2) a variable, highly-ionized screen between the continuum source and the absorber which modulates the UV continuum incident on the absorber. The observations presented here provide a crucial test of the scattering scenario and lead us to disfavor it because (a) the polarization level is very small (p~0.6%) throughout the spectrum, and (b) the polarization level does not increase across the mini-BAL trough. Thus, the variable screen scenario emerges as our favored explanation of the C IV mini-BAL variability. Our conclusion is bolstered by recent X-ray observations of nearby mini-BAL quasars, which show a rapidly variable soft X-ray continuum that appears to be the result of transmission through an ionized absorber of variable ionization parameter and optical depth.

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T. Misawa, K. S. Kawabata, M. Eracleous, J. C. Charlton, N. Kashikawa. 2010-07-02. A Spectropolarimetric Test of the Structure of the Intrinsic Absorbers in the Quasar HS1603+3820. https://doi.org/10.1088/0004-637x/719/2/1890

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