Please use this identifier to cite or link to this item:
Title: SDSS J1138+3517: a quasar showing remarkably variable broad absorption lines
Authors: Wildy, C.
Goad, Michael R.
Allen, J. T.
First Published: 28-Feb-2015
Publisher: Oxford University Press on behalf of the Royal Astronomical Society
Citation: Monthly Notices of the Royal Astronomical Society, 2015
Abstract: We report on the highly variable Si IV and C IV broad absorption lines in SDSS J113831.4+351725.2 across four observational epochs. Using the Si IV doublet components, we find that the blue component is usually saturated and non-black, with the ratio of optical depths between the two components rarely being 2:1. This indicates that these absorbers do not fully cover the line of sight and thus a simple apparent optical depth model is insufficient when measuring the true opacity of the absorbers. Tests with inhomogeneous (power-law) and pure-partial coverage (step-function) models of the absorbing Si IV optical depth predict the most un-blended doublet's component profiles equally well. However, when testing with Gaussian-fitted doublet components to all Si IV absorbers and averaging the total absorption predicted in each doublet, the upper limit of the power-law index is mostly unconstrained. This leads us to favour pure-partial coverage as a more accurate measure of the true optical depth than the inhomogeneous power-law model. The pure-partial coverage model indicates no significant change in covering fraction across the epochs, with changes in the incident ionizing flux on the absorbing gas instead being favoured as the variability mechanism. This is supported by (a) the coordinated behaviour of the absorption troughs, (b) the behaviour of the continuum at the blue end of the spectrum and (c) the consistency of photoionization simulations of ionic column density dependencies on ionization parameter with the observed variations. Evidence from the simulations together with the C IV absorption profile indicates that the absorber lies outside the broad line region, though the precise distance and kinetic luminosity are not well constrained.
DOI Link: 10.1093/mnras/stv142
ISSN: 0035-8711
eISSN: 1365-2966
Version: Publisher Version
Status: Peer-reviewed
Type: Journal Article
Rights: This article has been accepted for publication in Monthly Notices of the Royal Astronomical Society ©: 2015 The Authors. Published by Oxford University Press on behalf of the Royal Astronomical Society. All rights reserved.
Appears in Collections:Published Articles, Dept. of Physics and Astronomy

Files in This Item:
File Description SizeFormat 
MNRAS-2015-Wildy-2397-411.pdfPublished (publisher PDF)724.98 kBAdobe PDFView/Open
1501.04975.pdfPost-review (final submitted)503.1 kBAdobe PDFView/Open

Items in LRA are protected by copyright, with all rights reserved, unless otherwise indicated.