Gravitational microlensing of quasar broad-line regions at large optical depths
Identifieur interne : 001275 ( Istex/Corpus ); précédent : 001274; suivant : 001276Gravitational microlensing of quasar broad-line regions at large optical depths
Auteurs : Geraint F. Lewis ; R. A. IbataSource :
- Monthly Notices of the Royal Astronomical Society [ 0035-8711 ] ; 2004-02-11.
English descriptors
Abstract
Recent estimates of the scale of structures at the heart of quasars suggest that the regions responsible for the broad-line emission are smaller than previously thought. With this revision of scale, the broad-line region is amenable to the influence of gravitational microlensing. This study investigates the influence on microlensing at high optical depth on a number of current models of the broad-line region (BLR). It is found that the BLR can be significantly magnified by the action of microlensing, although the degree of magnification is dependent upon the spatial and kinematic structure of the BLR. Furthermore, while there is a correlation between the microlensing fluctuations of the continuum source and the BLR, there is substantial scatter about this relation, revealing that broad-band photometric monitoring is not necessarily a guide to microlensing of the BLR. The results of this study demonstrate that the spatial and kinematic structure within the BLR may be determined via spectroscopic monitoring of microlensed quasars.
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DOI: 10.1111/j.1365-2966.2004.07349.x
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ISTEX:640DEAF2BD289F2CE173958D49A6B22D6A65E819Le document en format XML
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Lewis</name><affiliation><mods:affiliation>Institute of Astronomy, School of Physics, University of Sydney, NSW 2006, Australia</mods:affiliation></affiliation><affiliation><mods:affiliation>E-mail: gfl@physics.usyd.edu.au</mods:affiliation></affiliation><affiliation><mods:affiliation>E-mail: gfl@physics.usyd.edu.au</mods:affiliation></affiliation><affiliation><mods:affiliation>E-mail: gfl@physics.usyd.edu.au</mods:affiliation></affiliation></author><author><name sortKey="Ibata, R A" sort="Ibata, R A" uniqKey="Ibata R" first="R. A." last="Ibata">R. A. Ibata</name><affiliation><mods:affiliation>Observatoire de Strasbourg, 11, rue de l'Université, F-67000, Strasbourg, France</mods:affiliation></affiliation><affiliation><mods:affiliation>E-mail: gfl@physics.usyd.edu.au</mods:affiliation></affiliation><affiliation><mods:affiliation>E-mail: gfl@physics.usyd.edu.au</mods:affiliation></affiliation><affiliation><mods:affiliation>E-mail: gfl@physics.usyd.edu.au</mods:affiliation></affiliation></author></analytic><monogr></monogr><series><title level="j">Monthly Notices of the Royal Astronomical Society</title><title level="j" type="abbrev">Mon. Not. R. Astron. 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With this revision of scale, the broad-line region is amenable to the influence of gravitational microlensing. This study investigates the influence on microlensing at high optical depth on a number of current models of the broad-line region (BLR). It is found that the BLR can be significantly magnified by the action of microlensing, although the degree of magnification is dependent upon the spatial and kinematic structure of the BLR. Furthermore, while there is a correlation between the microlensing fluctuations of the continuum source and the BLR, there is substantial scatter about this relation, revealing that broad-band photometric monitoring is not necessarily a guide to microlensing of the BLR. The results of this study demonstrate that the spatial and kinematic structure within the BLR may be determined via spectroscopic monitoring of microlensed quasars.</div></front></TEI><istex><corpusName>oup</corpusName><author><json:item><name>Geraint F. Lewis</name><affiliations><json:string>Institute of Astronomy, School of Physics, University of Sydney, NSW 2006, Australia</json:string><json:string>E-mail: gfl@physics.usyd.edu.au</json:string><json:string>E-mail: gfl@physics.usyd.edu.au</json:string><json:string>E-mail: gfl@physics.usyd.edu.au</json:string></affiliations></json:item><json:item><name>R. A. Ibata</name><affiliations><json:string>Observatoire de Strasbourg, 11, rue de l'Université, F-67000, Strasbourg, France</json:string><json:string>E-mail: gfl@physics.usyd.edu.au</json:string><json:string>E-mail: gfl@physics.usyd.edu.au</json:string><json:string>E-mail: gfl@physics.usyd.edu.au</json:string></affiliations></json:item></author><subject><json:item><value>gravitational lensing</value></json:item><json:item><value>quasars: emission lines</value></json:item><json:item><value>quasars: individual: Q2237+0305</value></json:item></subject><arkIstex>ark:/67375/HXZ-92T7XMMM-Z</arkIstex><language><json:string>unknown</json:string></language><originalGenre><json:string>research-article</json:string></originalGenre><abstract>Recent estimates of the scale of structures at the heart of quasars suggest that the regions responsible for the broad-line emission are smaller than previously thought. With this revision of scale, the broad-line region is amenable to the influence of gravitational microlensing. This study investigates the influence on microlensing at high optical depth on a number of current models of the broad-line region (BLR). It is found that the BLR can be significantly magnified by the action of microlensing, although the degree of magnification is dependent upon the spatial and kinematic structure of the BLR. Furthermore, while there is a correlation between the microlensing fluctuations of the continuum source and the BLR, there is substantial scatter about this relation, revealing that broad-band photometric monitoring is not necessarily a guide to microlensing of the BLR. The results of this study demonstrate that the spatial and kinematic structure within the BLR may be determined via spectroscopic monitoring of microlensed quasars.</abstract><qualityIndicators><refBibsNative>true</refBibsNative><abstractWordCount>158</abstractWordCount><abstractCharCount>1044</abstractCharCount><keywordCount>3</keywordCount><score>8.896</score><pdfWordCount>5253</pdfWordCount><pdfCharCount>29779</pdfCharCount><pdfVersion>1.4</pdfVersion><pdfPageCount>10</pdfPageCount><pdfPageSize>595.276 x 782.362 pts</pdfPageSize></qualityIndicators><title>Gravitational microlensing of quasar broad-line regions at large optical depths</title><genre><json:string>research-article</json:string></genre><host><title>Monthly Notices of the Royal Astronomical Society</title><language><json:string>unknown</json:string></language><issn><json:string>0035-8711</json:string></issn><eissn><json:string>1365-2966</json:string></eissn><publisherId><json:string>mnras</json:string></publisherId><volume>348</volume><issue>1</issue><pages><first>24</first><last>33</last></pages><genre><json:string>journal</json:string></genre></host><namedEntities><unitex><date><json:string>2237</json:string><json:string>2004</json:string></date><geogName></geogName><orgName><json:string>Swinburne University</json:string></orgName><orgName_funder></orgName_funder><orgName_provider></orgName_provider><persName><json:string>J. 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(2002)</json:string><json:string>Wandel, Peterson & Malkan 1999</json:string><json:string>Wambsganss 1992</json:string><json:string>Kaspi et al. 2000</json:string><json:string>Schmidt et al. 1998</json:string><json:string>Kayser, Refsdal & Stabell 1986</json:string><json:string>Wandel et al. 1999</json:string><json:string>Rees, Netzer & Ferland 1989</json:string><json:string>Belle & Lewis 2000</json:string><json:string>Peterson et al. 1985</json:string><json:string>Wambsganss & Paczynski 1991</json:string><json:string>Wyithe et al. 2000</json:string><json:string>Jaroszynski, Wambsganss & Paczynski 1992</json:string><json:string>Filippenko 1989</json:string><json:string>Wambsganss, Paczynski & Katz 1990</json:string><json:string>Irwin et al. 1989</json:string><json:string>Yonehara 1999</json:string><json:string>Lewis et al. 1998</json:string></ref_bibl><bibl></bibl></unitex></namedEntities><ark><json:string>ark:/67375/HXZ-92T7XMMM-Z</json:string></ark><categories><wos><json:string>science</json:string><json:string>astronomy & astrophysics</json:string></wos><scienceMetrix><json:string>natural sciences</json:string><json:string>physics & astronomy</json:string><json:string>astronomy & astrophysics</json:string></scienceMetrix><scopus><json:string>1 - Physical Sciences</json:string><json:string>2 - Earth and Planetary Sciences</json:string><json:string>3 - Space and Planetary Science</json:string><json:string>1 - Physical Sciences</json:string><json:string>2 - Physics and Astronomy</json:string><json:string>3 - Astronomy and Astrophysics</json:string></scopus><inist><json:string>sciences appliquees, technologies et medecines</json:string><json:string>sciences biologiques et medicales</json:string><json:string>sciences biologiques fondamentales et appliquees. psychologie</json:string><json:string>immunologie fondamentale</json:string></inist></categories><publicationDate>2004</publicationDate><copyrightDate>2004</copyrightDate><doi><json:string>10.1111/j.1365-2966.2004.07349.x</json:string></doi><id>640DEAF2BD289F2CE173958D49A6B22D6A65E819</id><score>1</score><fulltext><json:item><extension>pdf</extension><original>true</original><mimetype>application/pdf</mimetype><uri>https://api.istex.fr/document/640DEAF2BD289F2CE173958D49A6B22D6A65E819/fulltext/pdf</uri></json:item><json:item><extension>zip</extension><original>false</original><mimetype>application/zip</mimetype><uri>https://api.istex.fr/document/640DEAF2BD289F2CE173958D49A6B22D6A65E819/fulltext/zip</uri></json:item><istex:fulltextTEI uri="https://api.istex.fr/document/640DEAF2BD289F2CE173958D49A6B22D6A65E819/fulltext/tei"><teiHeader><fileDesc><titleStmt><title level="a">Gravitational microlensing of quasar broad-line regions at large optical depths</title></titleStmt><publicationStmt><authority>ISTEX</authority><publisher scheme="https://publisher-list.data.istex.fr">Blackwell Science Ltd</publisher><pubPlace>Oxford, UK</pubPlace><availability><licence><p>© 2004 RAS</p></licence><p scheme="https://loaded-corpus.data.istex.fr/ark:/67375/XBH-GTWS0RDP-M">oup</p></availability><date>2004</date></publicationStmt><notesStmt><note type="research-article" scheme="https://content-type.data.istex.fr/ark:/67375/XTP-1JC4F85T-7">research-article</note><note type="journal" scheme="https://publication-type.data.istex.fr/ark:/67375/JMC-0GLKJH51-B">journal</note></notesStmt><sourceDesc><biblStruct type="inbook"><analytic><title level="a">Gravitational microlensing of quasar broad-line regions at large optical depths</title><author xml:id="author-0000" corresp="yes"><persName><forename type="first">Geraint F.</forename><surname>Lewis</surname></persName><email>gfl@physics.usyd.edu.au</email><email>gfl@physics.usyd.edu.au</email><email>gfl@physics.usyd.edu.au</email><affiliation>Institute of Astronomy, School of Physics, University of Sydney, NSW 2006, Australia</affiliation></author><author xml:id="author-0001" corresp="yes"><persName><forename type="first">R. A.</forename><surname>Ibata</surname></persName><email>gfl@physics.usyd.edu.au</email><email>gfl@physics.usyd.edu.au</email><email>gfl@physics.usyd.edu.au</email><affiliation>Observatoire de Strasbourg, 11, rue de l'Université, F-67000, Strasbourg, France</affiliation></author><idno type="istex">640DEAF2BD289F2CE173958D49A6B22D6A65E819</idno><idno type="ark">ark:/67375/HXZ-92T7XMMM-Z</idno><idno type="DOI">10.1111/j.1365-2966.2004.07349.x</idno></analytic><monogr><title level="j">Monthly Notices of the Royal Astronomical Society</title><title level="j" type="abbrev">Mon. Not. R. Astron. Soc.</title><idno type="pISSN">0035-8711</idno><idno type="eISSN">1365-2966</idno><idno type="publisher-id">mnras</idno><idno type="PublisherID-hwp">mnras</idno><imprint><publisher>Blackwell Science Ltd</publisher><pubPlace>Oxford, UK</pubPlace><date type="published" when="2004-02-11"></date><biblScope unit="volume">348</biblScope><biblScope unit="issue">1</biblScope><biblScope unit="page" from="24">24</biblScope><biblScope unit="page" to="33">33</biblScope></imprint></monogr></biblStruct></sourceDesc></fileDesc><profileDesc><creation><date>2004</date></creation><abstract><p>Recent estimates of the scale of structures at the heart of quasars suggest that the regions responsible for the broad-line emission are smaller than previously thought. With this revision of scale, the broad-line region is amenable to the influence of gravitational microlensing. This study investigates the influence on microlensing at high optical depth on a number of current models of the broad-line region (BLR). It is found that the BLR can be significantly magnified by the action of microlensing, although the degree of magnification is dependent upon the spatial and kinematic structure of the BLR. Furthermore, while there is a correlation between the microlensing fluctuations of the continuum source and the BLR, there is substantial scatter about this relation, revealing that broad-band photometric monitoring is not necessarily a guide to microlensing of the BLR. The results of this study demonstrate that the spatial and kinematic structure within the BLR may be determined via spectroscopic monitoring of microlensed quasars.</p></abstract><textClass xml:lang="en"><keywords scheme="keyword"><list><head>Key words</head><item><term>gravitational lensing</term></item><item><term>quasars: emission lines</term></item><item><term>quasars: individual: Q2237+0305</term></item></list></keywords></textClass></profileDesc><revisionDesc><change when="2004-02-11">Published</change></revisionDesc></teiHeader></istex:fulltextTEI><json:item><extension>txt</extension><original>false</original><mimetype>text/plain</mimetype><uri>https://api.istex.fr/document/640DEAF2BD289F2CE173958D49A6B22D6A65E819/fulltext/txt</uri></json:item></fulltext><metadata><istex:metadataXml wicri:clean="corpus oup, element #text not found" wicri:toSee="no header"><istex:xmlDeclaration>version="1.0"</istex:xmlDeclaration><istex:docType PUBLIC="-//NLM//DTD Journal Publishing DTD v2.3 20070202//EN" URI="journalpublishing.dtd" name="istex:docType"></istex:docType><istex:document><article article-type="research-article">
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<article-title>Gravitational microlensing of quasar broad-line regions at large optical depths</article-title>
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<contrib-group>
<contrib contrib-type="author" corresp="yes">
<name><surname>Lewis</surname><given-names>Geraint F.</given-names></name><xref ref-type="aff" rid="a1"><sup>1</sup></xref><xref ref-type="corresp" rid="cor1"><sup>⋆</sup></xref>
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<contrib contrib-type="author" corresp="yes">
<name><surname>Ibata</surname><given-names>R. A.</given-names></name><xref ref-type="aff" rid="a2"><sup>2</sup></xref><xref ref-type="corresp" rid="cor1"><sup>⋆</sup></xref>
</contrib>
<aff id="a1"><label><sup>1</sup></label>Institute of Astronomy, School of Physics, University of Sydney, NSW 2006, Australia</aff>
<aff id="a2"><label><sup>2</sup></label>Observatoire de Strasbourg, 11, rue de l'Université, F-67000, Strasbourg, France</aff>
</contrib-group>
<author-notes>
<corresp id="cor1"><label><sup>⋆</sup></label>E-mail: <email>gfl@physics.usyd.edu.au</email> (GFL); <email>ibata@astro.u-strasbg.fr</email> (RAI)</corresp>
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<day>21</day>
<month>10</month>
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<date date-type="accepted">
<day>22</day>
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<abstract>
<title>Abstract</title>
<p>Recent estimates of the scale of structures at the heart of quasars suggest that the regions responsible for the broad-line emission are smaller than previously thought. With this revision of scale, the broad-line region is amenable to the influence of gravitational microlensing. This study investigates the influence on microlensing at high optical depth on a number of current models of the broad-line region (BLR). It is found that the BLR can be significantly magnified by the action of microlensing, although the degree of magnification is dependent upon the spatial and kinematic structure of the BLR. Furthermore, while there is a correlation between the microlensing fluctuations of the continuum source and the BLR, there is substantial scatter about this relation, revealing that broad-band photometric monitoring is not necessarily a guide to microlensing of the BLR. The results of this study demonstrate that the spatial and kinematic structure within the BLR may be determined via spectroscopic monitoring of microlensed quasars.</p>
</abstract>
<kwd-group xml:lang="en">
<title>Key words</title>
<kwd>gravitational lensing</kwd>
<kwd>quasars: emission lines</kwd>
<kwd>quasars: individual: Q2237+0305</kwd>
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<body>
<sec id="ss1" sec-type="intro">
<label>1</label>
<title>Introduction</title>
<p>Quasars are amongst the most luminous sources in the Universe. At cosmological distances, their relatively small size ensures the regions responsible for producing the various spectral line components remain effectively unresolved with modern telescopes. Gravitational microlensing, however, can significantly magnify the inner regions, providing clues to the various scales of structure located at the hearts of quasars, giving some of the best estimates of the scale of the central continuum emitting region (e.g. <xref ref-type="bibr" rid="bib7">Jaroszynski, Wambsganss & Paczynski 1992</xref>; <xref ref-type="bibr" rid="bib25">Yonehara 1999</xref>; <xref ref-type="bibr" rid="bib24">Wyithe et al. 2000</xref>), as well as offering the possibility of probing the nature of other small-scale structure in quasars (<xref ref-type="bibr" rid="bib3">Belle & Lewis 2000</xref>; <xref ref-type="bibr" rid="bib23">Wyithe & Loeb 2002</xref>).</p>
<p>The degree of microlensing magnification is dependent upon the scale-size of the source, with smaller sources being more susceptible to large magnifications (e.g. <xref ref-type="bibr" rid="bib19">Wambsganss & Paczynski 1991</xref>). While the continuum emitting region of a quasar is small enough to undergo significant magnification, the more extensive line emitting regions, specifically the broad-line region (BLR) with a scalelength of 0.1 pc to a few pc, were considered to be too large to suffer substantial magnification. <xref ref-type="bibr" rid="bib13">Nemiroff (1988)</xref> undertook a study to determine the degree of microlensing of various models of the BLR, examining the influence of a single microlensing mass in front of the emission region. When considering microlensing in multiply imaged quasars, however, many stars are expected to influence the light beam of a distant source, and these combine in a very non-linear fashion and the single-star approximation is a poor one (e.g. <xref ref-type="bibr" rid="bib20">Wambsganss, Paczynski & Katz 1990</xref>). <xref ref-type="bibr" rid="bib17">Schneider & Wambsganss (1990)</xref> considered the microlensing of a BLR at substantial optical depth. These studies found that while gravitational microlensing did result in the modification of the BLR emission-line profiles, the overall magnification of the region was small, typically less than 30 per cent.</p>
<p>These microlensing studies employed estimates of the size of the quasar BLR based upon simple ionization models [see <xref ref-type="bibr" rid="bib4">Davidson & Netzer (1979)</xref>]. Reverberation mapping, however, provides a more direct measure of the geometry of the BLR and early studies suggested these simple ionization models had overestimated the scale of the BLR by roughly an order of magnitude (e.g. <xref ref-type="bibr" rid="bib14">Peterson et al. 1985</xref>), prompting a revision of BLR physics (<xref ref-type="bibr" rid="bib15">Rees, Netzer & Ferland 1989</xref>). More recent reverberation measurements have refined the size of the BLRs in active galaxies, finding it to be ∼10<sup>−4</sup> pc in low-luminosity active galactic nuclei (AGN), and up to ∼10<sup>−1</sup> pc in luminous quasars, with the size of the BLR scaling with the luminosity of the quasar, such that <italic>R</italic><sub>BLR</sub>∝<italic>L</italic><sup>0.7</sup> (<xref ref-type="bibr" rid="bib21">Wandel, Peterson & Malkan 1999</xref>; <xref ref-type="bibr" rid="bib8">Kaspi et al. 2000</xref>). Furthermore, these results demonstrate that the BLR possesses a stratified structure, with high-ionization lines being an order of magnitude smaller than lower-ionization lines. Following this discovery, <xref ref-type="bibr" rid="bib1">Abajas et al. (2002)</xref> reexamined the question of the microlensing of the BLR region in light of this revised scale. Undertaking an analysis similar to <xref ref-type="bibr" rid="bib13">Nemiroff (1988)</xref>, they considered the influence of a single microlensing mass located in the BLR, finding that significant modification of the BLR line profile results.</p>
<p>As with the approach of <xref ref-type="bibr" rid="bib13">Nemiroff (1988)</xref>, the study of <xref ref-type="bibr" rid="bib1">Abajas et al. (2002)</xref> is a poor representation of microlensing at significant optical depth, the situation for multiply imaged quasars. This paper, therefore, also examines the question of microlensing of the BLR, extending the previous work of <xref ref-type="bibr" rid="bib1">Abajas et al. (2002)</xref> into the higher-optical-depth regime. The approach to this question is described in <xref ref-type="sec" rid="ss2">Section 2</xref>, whereas the results are discussed in <xref ref-type="sec" rid="ss3">Section 3</xref>. The conclusions to this study are presented in <xref ref-type="sec" rid="ss4">Section 4</xref>.</p>
</sec>
<sec id="ss2">
<label>2</label>
<title>Method</title>
<sec id="ss2-1">
<label>2.1</label>
<title> Microlensing maps</title>
<p>The known number of multiply imaged quasars has been steadily growing in recent years (<xref ref-type="bibr" rid="bib12">Muñoz et al. 1998</xref>). For the majority of these, little temporal data have been obtained and so this study focuses upon the quadruple quasar Q2237+0305, the first system in which microlensing was confirmed (<xref ref-type="bibr" rid="bib6">Irwin et al. 1989</xref>). The microlensing parameters, the surface mass density σ and the shearing due to external mass γ, were taken from the model of <xref ref-type="bibr" rid="bib16">Schmidt, Webster & Lewis (1998)</xref>; for images C and D the values for (σ, γ) were (0.69, 0.71) and (0.59, 0.61) respectively. Images A and B have similar microlensing parameters, chosen to be (0.36, 0.41) for the purpose of this study. These microlensing parameters may seem quite specific and hence not applicable to the population of lensed quasars in general. However, for multiply imaged systems the microlensing parameters must be substantial and hence the simulations in this paper can be taken as representative.</p>
<p>Furthermore, the important length-scale in microlensing problems is the Einstein radius (ER) of a single star projected on to the source plane, with sources substantially smaller than this size susceptible to significant magnification, whereas larger sources are more mildly affected by lensing (<xref ref-type="bibr" rid="bib19">Wambsganss & Paczynski 1991</xref>; <xref ref-type="bibr" rid="bib18">Wambsganss 1992</xref>). For Q2237+0305, this length-scale (for a solar-mass star) is η<sub>0</sub>= 0.06 pc (a concordance cosmology, with Ω<sub>0</sub>= 0.3, Λ<sub>0</sub>= 0.7 and <italic>H</italic><sub>0</sub>= 72 km s<sup>−1</sup> Mpc<sup>−1</sup>, is assumed) and is comparable to the revised scale of the BLR in quasars. As Q2237+0305 remains one of the few multiply imaged quasars in which microlensing has been unambiguously detected, potentially it offers the best chance of observing the influence of microlensing of the BLR.</p>
<p><xref ref-type="bibr" rid="bib1">Abajas et al. (2002)</xref> presented a detailed discussion on the observability of BLR microlensing for various gravitational lens systems. <xref ref-type="fig" rid="fig1">Fig. 1</xref> presents the ER for a solar-mass star for a range of source redshifts, with lenses at <italic>z</italic>= 0.1, 0.4, 0.7 and 1.0. The two panels on the right-hand side present the expected size for the high-ionization BLR (column topped with Hi) and low-ionization BLR (Lo), for a range of absolute V-band magnitudes; these were calculated using the measured BLR sizes of NGC 5548 and the <italic>R</italic><sub>BLR</sub>∝<italic>L</italic><sup>0.7</sup> scaling (<xref ref-type="bibr" rid="bib21">Wandel et al. 1999</xref>; <xref ref-type="bibr" rid="bib8">Kaspi et al. 2000</xref>). Clearly, the low-ionization BLR become quite extensive in moderately bright quasars (<italic>M<sub>V</sub></italic>≳−25), up to 10 times larger than the ER for the majority of cases. For some configurations, with relatively nearby lenses, the difference is only a factor of four, a BLR source size that is investigated in this paper. The size of the high-ionization BLR, however, is similar to the ER for many lensing geometries, and is amenable to microlensing for quite luminous quasars. It should be noted that the ER scales with the square root of the microlensing mass; even accounting for a typical microlensing mass of ∼0.1 M<sub>⊙</sub>, the high-ionization BLR for relatively bright quasars should be susceptible to microlensing. As an example, Q2237+0305, the quasar considered in this paper, has an absolute magnitude of <italic>M</italic>∼−26[accounting for a magnification of ∼16 (<xref ref-type="bibr" rid="bib16">Schmidt et al. 1998</xref>)], with its ER being comparable the scale of its high-ionization BLR, although the low-ionization BLR may be too extensive to be significantly magnified.
<fig id="fig1" position="float">
<label>Figure 1.</label>
<caption><p>The Einstein radius for a solar-mass star for lenses at <italic>z</italic>= 0.1, 0.4, 0.7 and 1.0, denoted by the location of the start of each curve, for sources at a range of redshifts. The panels on the right-hand side present the expected size of the high-ionization (column topped with Hi) and low-ionization (Lo) BLRs, for the denoted absolute magnitudes.</p></caption>
<graphic mimetype="image" xlink:href="348-1-24-fig001.tif"></graphic>
</fig>
</p>
<p>Magnification maps were constructed using a ray-tracing algorithm (<xref ref-type="bibr" rid="bib9">Kayser, Refsdal & Stabell 1986</xref>; <xref ref-type="bibr" rid="bib20">Wambsganss, Paczynski & Katz 1990</xref>). For each image, a square region 20 ER on a side was generated. The resolution was chosen such that one ER corresponded to 128 pixels and the number of rays traced ensured that the Poissonian error in the mean magnification was less than 0.5 per cent.</p>
</sec>
<sec id="ss2-2">
<label>2.2</label>
<title>BLR models</title>
<p>To address the question of how microlensing influences the BLR it is important to determine how the region appears at particular velocities. To undertake this, the BLR models of <xref ref-type="bibr" rid="bib1">Abajas et al. (2002)</xref> were adopted; the mathematics of these models is presented in this earlier paper and will not be reproduced here. The BLRs were constructed via a Monte Carlo approach, randomly distributing large numbers of clouds with the appropriate spatial, emissivity and velocity characteristics. By selecting in velocity, images of the source in 100 velocity slices were constructed. As per the earlier study of <xref ref-type="bibr" rid="bib1">Abajas et al. (2002)</xref>, two sizes for the BLR were considered, a smaller source with a radius of 1 ER, as well as a larger source of radius 4 ER. A summary of the eight models employed in this study is presented in <xref ref-type="fig" rid="tbl1">Table 1</xref>; this labelling will be used through the rest of this study. <xref ref-type="fig" rid="fig2">Fig. 2</xref> graphically presents the spatial properties of the various BLR models as a function of velocity.
<fig id="tbl1" position="float">
<label>Table 1.</label>
<caption><p>Summary of BLR models. For each model, <italic>p</italic> denotes the radial form of the velocity field, such that <italic>v</italic>∝<italic>r<sup>p</sup></italic>, while θ represents the orientation of non-spherically symmetric models (see <xref ref-type="bibr" rid="bib1">Abajas et al. 2002</xref>).</p></caption>
<graphic mimetype="image" xlink:href="348-1-24-tbl001.tif"></graphic>
</fig>
<fig id="fig2" position="float">
<label>Figure 2.</label>
<caption><p>The appearance of each of the BLR models as a function of velocity. The models are presented vertically, with the model label given at the top of each column; the details of the models are given in <xref ref-type="fig" rid="tbl1">Table 1</xref>, with the SS models representing spherical shells of clouds, the BS models being biconical shells, whereas the KD and KM models are thin discs. The five velocity slices consider the range from 0 to 1 in units of 0.2; as the models are symmetric in velocity, the appearance of the BLR at negative velocities is the same as that at positive velocities (this is also true of KD1 and KM1 except the images are flipped about the <italic>y</italic>-axis). The lowest panels present the velocity-integrated surface-brightness distribution of each of the models. Superimposed upon these are the spectral line profiles; these can be compared directly with the results of <xref ref-type="bibr" rid="bib1">Abajas et al. (2002)</xref>.</p></caption>
<graphic mimetype="image" xlink:href="348-1-24-fig002.tif"></graphic>
</fig>
</p>
</sec>
</sec>
<sec id="ss3">
<label>3</label>
<title>Results</title>
<p>To calculate the influence of the gravitational-microlensing magnification upon the BLR, each image of the source (as a function of velocity) was convolved with the magnification maps. For the larger BLR models, the source size becomes comparable to the scale of the magnification maps. Hence, appropriate regions are trimmed from the convolved maps to negate edge effects. For the smaller sources, this means that the central 18<sup>2</sup> ER were employed for analysis, whereas the larger sources yielded a region 12<sup>2</sup> ER. Note that for the purposes of this study, all models are oriented perpendicular to the shear field. Random orientations of the BLR models with respect to the microlensing structure is reserved for a future contribution.</p>
<sec id="ss3-1">
<label>3.1</label>
<title>Magnifications</title>
<p>The magnification distributions of the total flux of the BLR models, determined by convolving the velocity-integrated surface-brightness profile with the magnification maps, are presented in <xref ref-type="fig" rid="fig3">Fig. 3</xref>. Note that each panel presents a pair of models, denoted at the top of each column; this is because in each pair of models the radial emission properties of the clouds are the same so that the velocity-integrated surface-brightness profiles are the same. This can be seen in the lowest series of panels in <xref ref-type="fig" rid="fig2">Fig. 2</xref>. In each panel of <xref ref-type="fig" rid="fig3">Fig. 3</xref>, three curves are given; the lightest is the magnification distribution of a single pixel, whereas the thicker, grey line is the distribution for the smaller BLR models. The thick black line corresponds to the magnification distribution for the larger BLR models.
<fig id="fig3" position="float">
<label>Figure 3.</label>
<caption><p>The magnification distributions of the various BLR models of each of the quasar images in Q2237+0305. The models run vertically, with the model name at the top of each column, while the name of each quasar image is presented down the right-hand side. The thin line in each panel corresponds to the magnification distribution of a point source. The grey lines correspond to the magnification distributions for the BLR models with a radius of 1 ER, whereas the black line is the magnification distribution for BLRs of radius 4 ER.</p></caption>
<graphic mimetype="image" xlink:href="348-1-24-fig003.tif"></graphic>
</fig>
</p>
<p>As the source size increases, the width of the magnification probability distribution decreases; in comparing the single-pixel source with the smaller BLR model, it is clear that the high-magnification tail has been curtailed.<xref ref-type="fn" rid="fn1"><sup>1</sup></xref> The smaller BLR model can, however, suffer significant magnification, with the total flux in the line being boosted by a factor of 1.5–2 in most cases. On the face of it, this is rather surprising as the source radius of 1 ER is relatively large. It is important to remember, however, that unlike numerous previous microlensing studies, the source here is not uniform, but possesses structure on scales substantially smaller than an ER and this can be more significantly magnified.</p>
<p>Examining the magnification probability distributions for the larger BLR models reveals that they too can be substantially magnified, although the magnification distribution is narrower than the case of the smaller BLR sources. In most cases, the BLR can be enhanced by ∼50 per cent. Interestingly, the BS1–BS2 pair of models is particularly broad compared to the other cases; examining <xref ref-type="fig" rid="fig2">Fig. 2</xref> reveals that the surface-brightness distributions for these models are quite centrally concentrated compared to the other models, and this small-scale structure can be substantially magnified. Again, this smaller-scale structure of the BLR surface-brightness distribution results in stronger magnification than a uniform source of the same radius.</p>
<p>This is further illustrated in <xref ref-type="fig" rid="fig4">Fig. 4</xref> which presents the form of the BLR emission-line profile for the smaller BS2 model as microlensed by image C in 2237. The left-hand panel presents the magnification map convolved with the BS2 surface-brightness distribution. The series of coloured circles over the map indicate 16 fiducial locations over the map where the form of the emission-line profile was calculated. These are presented in the right-hand panel, with the solid black line being the unlensed emission-line profile; note that the flux in the microlensed line profiles has been divided by the mean magnification of the microlensing map so that a meaningful comparison between them and the unlensed case can be made.
<fig id="fig4" position="float">
<label>Figure 4.</label>
<caption><p>An example of the modification of the BLR line profile for the smaller BS2 for the microlensing model of image C. In this panel, lighter regions denote regions of magnification, whereas darker regions correspond to regions of demagnification. In the left-hand panel, the magnification map, convolved with the surface-brightness distribution of the BLR, is presented. The right-hand panel presents several microlensed BLR line profiles for the locations indicated by the colour-coded circles over the magnification map. The thick black line corresponds to the unmicrolensed line profile. Note that, due to the symmetric nature of the model surface-brightness distribution in velocity space, the microlensed BLR line profile is symmetric in velocity.</p></caption>
<graphic mimetype="image" xlink:href="348-1-24-fig004.tif"></graphic>
</fig>
</p>
<p>It is clear that there is substantial variation not only in the total emission-line flux, but also in the form of the emission-line profile. The red source in the lower left-hand corner lies primarily in a rather uniform region of demagnification and while its emission-line profile is clearly suppressed it appears to have retained its overall shape. The line profile of the dark blue source on the far left-hand side, while being magnified in the wings of the line, appears to be unmagnified at velocities near zero. Examining the source profile as a function of velocity (<xref ref-type="fig" rid="fig2">Fig. 2</xref>) it is apparent that the BS2 model is very centrally concentrated at velocities near zero, appearing more extensive at the velocity extremes. When examining the magnification map in the vicinity of the blue source it can be seen that the outer regions overlay strong magnification, whereas the central regions lie in regions of mean magnification. The opposite is true for the light green source at the top of the second column from the left. Here, the central regions of the BLR lie within a region of strong magnification, whereas the outer regions are less affected, leading to a strong enhancement of the emission-line profile at velocities near zero.</p>
<p>Typically, gravitational microlensing is observed via the photometric monitoring of multiply imaged quasars (<xref ref-type="bibr" rid="bib22">Woźniak et al. 2000</xref>; <xref ref-type="bibr" rid="bib2">Alcalde et al. 2002</xref>) with no programme of spectroscopic monitoring of any system. To observe microlensing of the BLR, therefore, it is important to know whether expected fluctuations are correlated with those of the central continuum source; this might be expected, as the continuum source, which lies at the centre of the BLR, ‘sees’ similar caustic structure in the inner parts of the BLR. <xref ref-type="fig" rid="fig5">Fig. 5</xref> (smaller BLR source) and <xref ref-type="fig" rid="fig6">Fig. 6</xref> (larger BLR source) present the distributions of the magnifications of the continuum source (taken to be a single pixel in the magnification map) versus the magnification of the BLR for coincident observations. Note that the relative probability, displayed in the grey-scale, is presented logarithmically.
<fig id="fig5" position="float">
<label>Figure 5.</label>
<caption><p>The correlation between the magnification of a point-like source (here one pixel) and the smaller BLR models, for simultaneous observations. Note that the relative probabilities are displayed logarithmically as denoted by the grey-scale at the top of the figure.</p></caption>
<graphic mimetype="image" xlink:href="348-1-24-fig005.tif"></graphic>
</fig>
<fig id="fig6" position="float">
<label>Figure 6.</label>
<caption><p>As for <xref ref-type="fig" rid="fig5">Fig. 5</xref>, except for the larger BLR models.</p></caption>
<graphic mimetype="image" xlink:href="348-1-24-fig006.tif"></graphic>
</fig>
</p>
<p>In examining <xref ref-type="fig" rid="fig5">Figs 5</xref> and <xref ref-type="fig" rid="fig6">6</xref> it is clear that there is small-scale structure in the combined probability distributions; this is due to the finite size of the magnification maps employed, with the structure due to the characteristics of the caustic networks. Overall trends, however, are apparent. First, there is a general correlation between the magnification of the continuum and the BLR. For the smaller BLR source, this is most apparent for the BS1–BS2 models. As discussed previously, these models present a quite compact surface-brightness distribution to the caustic network and are, therefore, more similar in scale to the continuum source. In general, the magnifications are correlated for μ≤ 1; this results from the fact that regions of demagnification can be extended on scales greater than an ER and hence both the BLR and continuum region can be demagnified together. However, the correlation of magnifications is weaker at μ > 1, showing considerable scatter for all of the models. This can be understood in terms of the clustering of the caustic network in regions of high magnification which exhibits structure on quite small scales. With this, the magnification of the continuum mirrors this small-scale caustic structure, whereas the BLR is magnified by a weighted average of the larger-scale caustic structure. Interestingly, for all the models, there is also a non-zero probability that while the continuum source is being strongly magnified, the overall BLR region is undergoing demagnification. The reverse of this, however, appears to be significantly rarer in most models.</p>
<p>The situation is very similar for the larger BLR models (<xref ref-type="fig" rid="fig6">Fig. 6</xref>). As expected from <xref ref-type="fig" rid="fig3">Fig. 3</xref>, the distributions of BLR magnification are somewhat narrower than the smaller BLR model. Again, no clear correlation of the continuum and BLR magnification is apparent with the continuum source undergoing significant magnification while the BLR is relatively unmagnified. It is also apparent that while there is a general correlation between the magnification of the two regions, there is still a significant range over which the continuum source can be substantially magnified while the BLR undergoes a magnification of ∼1. Hence, a microlensing fluctuation observed in broad-band photometric monitoring will not necessarily be an indicator of strong microlensing of the BLR. Rather than spectroscopic monitoring, however, broad-band monitoring could be combined with observations obtained through a narrow-band filter which covers a broad line in the quasar spectrum. With this, a plot similar to those presented in <xref ref-type="fig" rid="fig5">Figs 5</xref> and <xref ref-type="fig" rid="fig6">6</xref> could be constructed and compared to simulations.</p>
</sec>
<sec id="ss3-2">
<label>3.2</label>
<title>Velocity shifts</title>
<p>As well as the total magnification of the emission lines, it is important to characterize the modification of the emission-line profile due to differential magnification effects. This can be seen as a shift in the velocity centroid of the emission line. In undertaking this, however, it is important to note the SS and BS models display surface-brightness structure which is symmetrical in velocity, and any gravitational-lensing magnification results in identical line profile modification at positive and negative velocities, leading to a centroid shift of zero. Therefore, in the following study only the positive velocity component of the emission lines are considered for the SS and BS models, whereas the positive velocity and the total emission-line profile are considered for the KD1 and KM1 models.</p>
<p><xref ref-type="fig" rid="fig7">Fig. 7</xref> presents the distribution of the measured centroid of the positive velocity component of the BLR emission line for each of the models presented in this paper. The black line presents the distributions for the smaller BLR models for each lensed image, whereas the thicker, grey line represents the larger BLR models. The vertical dot-dashed line running vertically through the panels represents the unlensed location of the line centroid. <xref ref-type="fig" rid="tbl2">Table 2</xref> summarizes the distributions presented in <xref ref-type="fig" rid="fig7">Fig. 7</xref>, presenting their root mean square (rms) values; note that in these values are expressed as percentages of the linewidth at positive velocities. Several features are apparent. First, the widths of the distributions are relatively insensitive to the microlensing model, with each presenting very similar forms of the distribution. Furthermore, the centroid shifts for the larger BLR models are similar or are broader than those for the smaller BLR models. This result is somewhat surprising, given that the larger BLR models undergo less microlensing magnification, a point returned to below.
<fig id="fig7" position="float">
<label>Figure 7.</label>
<caption><p>The variation in the centroid velocity for positive velocity half of the emission-line profile for each of the models presented in this paper. The solid black line is for the smaller BLR model, where as the thicker, grey line is for the corresponding larger model. The vertical dot-dashed line indicates the location of the unlensed centroid position, with the label for each model given at the top of the line.</p></caption>
<graphic mimetype="image" xlink:href="348-1-24-fig007.tif"></graphic>
</fig>
<fig id="tbl2" position="float">
<label>Table 2.</label>
<caption><p>The widths of the centroid shift distributions presented in <xref ref-type="fig" rid="fig7">Fig. 7</xref></p></caption>
<graphic mimetype="image" xlink:href="348-1-24-tbl002.tif"></graphic>
</fig>
</p>
<p><xref ref-type="fig" rid="tbl2">Table 2</xref> summarizes the rms width of the distributions presented in <xref ref-type="fig" rid="fig7">Fig. 7</xref> as a percentage of the positive velocity linewidth. The width of the distribution does depend on the BLR model under consideration, with the disc models KD1 and KM1, as well as BS3 displaying significantly broader centroid distributions than the other models. Examining the surface-brightness distributions presented in <xref ref-type="fig" rid="fig2">Fig. 2</xref> it is apparent that the two disc models present quite different surface-brightness structures in each of the velocity slices. Hence these undergo differing degrees of lensing magnification, but as their brightness in each slice is non-negligible this can lead to appreciable centroid shifts. Other models, such as BS3 and BS4 are luminous only in a narrow range of velocity, and magnification of this leads to only slight centroid shifts.</p>
<p><xref ref-type="fig" rid="fig8">Figs 8</xref> and <xref ref-type="fig" rid="fig9">9</xref> present the probability distributions of the centroid shift (presented in <xref ref-type="fig" rid="fig7">Fig. 7</xref>) as a function of the total magnification of the smaller BLR, with the corresponding distributions for the larger BLR presented in <xref ref-type="fig" rid="fig9">Fig. 9</xref>. These distributions are presented logarithmically on the same scale as those in <xref ref-type="fig" rid="fig5">Figs 5</xref> and <xref ref-type="fig" rid="fig6">6</xref>. Again, it is clear that some of the structure in these distributions is due to the limited size of the magnification maps, but some features are present. First, it appears that the largest centroid shifts occur typically at lower overall magnification. In this regime, only a small range in velocity must be magnified, leading to a centroid shift but no substantial increase in the total line flux. For the total line flux to be enhanced, a substantial proportion of all velocity structure must be magnified; with this, the centroid shift would be small. Further, the distribution of the centroid shifts appears, in a number of cases, to be quite asymmetric. This is again related to the surface-brightness distribution as a function of velocity.
<fig id="fig8" position="float">
<label>Figure 8.</label>
<caption><p>The centroid shift in velocity versus the total magnification of the BLR for each of the models presented in this paper. This figure considers solely the smaller BLR models. The grey-scale is identical to that presented in <xref ref-type="fig" rid="fig5">Fig. 5</xref>.</p></caption>
<graphic mimetype="image" xlink:href="348-1-24-fig008.tif"></graphic>
</fig>
<fig id="fig9" position="float">
<label>Figure 9.</label>
<caption><p>As for <xref ref-type="fig" rid="fig8">Fig. 8</xref>, except for the larger BLR models.</p></caption>
<graphic mimetype="image" xlink:href="348-1-24-fig009.tif"></graphic>
</fig>
</p>
<p>For the asymmetric surface-brightness distributions (KD1 and KM1) the line asymmetry was defined to be
<disp-formula id="m1">
<label>(1)</label>
<graphic mimetype="image" xlink:href="348-1-24-eq001.tif"></graphic>
</disp-formula>
where <italic>ƒ</italic><sub>+</sub> is the flux in the positive velocity fraction of the emission line and <italic>ƒ</italic><sub>−</sub> is the flux in the negative velocity region. Noting that the KD1 and KM1 models are identical in either integrated positive or negative velocity, only one of these need be considered further. <xref ref-type="fig" rid="fig10">Fig. 10</xref> presents the probability distribution of the line asymmetry for the disc models presented in this paper, with each horizontal panel representing the results for various microlensing models. In each panel, the black line is for the smaller BLR models, whereas the thicker, grey line is for the larger BLR models. The distributions for the various models are not dissimilar, showing that substantial asymmetries in line flux (up to ∼20–30 per cent) can result for the smaller BLR models when they are microlensed. It is, however, surprising that while the magnification of the larger BLR models is typically smaller for the more extended BLR models, substantial line asymmetries still result. This regime mirrors that earlier probed by <xref ref-type="bibr" rid="bib17">Schneider & Wambsganss (1990)</xref> who found that, for the larger BLR models they were considering, the total magnification may be mild, but substantial asymmetric modification of the emission-line profile can result.
<fig id="fig10" position="float">
<label>Figure 10.</label>
<caption><p>The asymmetry in the BLR emission line for the two disc models presented in this paper. The black line denotes the asymmetry for the smaller BLR radius models, whereas the thicker grey line represents the larger models.</p></caption>
<graphic mimetype="image" xlink:href="348-1-24-fig010.tif"></graphic>
</fig>
</p>
</sec>
</sec>
<sec id="ss4">
<label>4</label>
<title>Conclusions</title>
<p>Recent studies have reappraised the scales of structure in quasars, with the indication that the BLR, responsible for the broad emission lines seen in quasar spectra, is smaller than previously thought. This reduction in size makes the region more sensitive to the influence of gravitational microlensing. This paper has examined this influence on eight models of the BLR, considering the microlensing parameters of the multiply imaged quasar Q2237+0305, extending previous studies into the high-optical-depth regime.</p>
<p>For the purpose of this study, two source sizes were adopted: a small source with a radius of 1 ER and a larger source with a radius of 4 ER. It was found that the smaller source can undergo significant magnification, with the total line flux being enhanced by a factor of 2 on occasions. At the other extreme, this smaller source can be substantially demagnified (with respect to the mean magnification) such that its total flux is reduced to 20 per cent of the mean magnified value. As expected, the variations are less dramatic for the larger sources, with a typical demagnification to ∼80 per cent, with magnification extremes of 1.5× to 2×. In earlier studies which considered larger BLR models, the total line flux was found to remain relatively unchanged during microlensing. If, however, the revised BLR sizes are correct, this paper has demonstrated that substantial fluctuations in the total line flux should result. This has an important consequence for studies of gravitational lensing as it implies that the relative broad-line flux between images is not a measure of the relative image macromagnifications, a quantity important to gravitational-lensing modelling.</p>
<p>Furthermore, this paper investigated the degree of modification of the form of the BLR emission line via a measurement of its centroid. The majority of models considered possess symmetric surface-brightness structure in velocity space, and the overall velocity centroid of the emission line remains unchanged during microlensing. However, considering only one-half of the emission line it was found that substantial modification of the emission-line profile can result. Additionally, considering disc models that present asymmetric surface-brightness structure as a function of velocity, it is seen that substantial centroid shifts of the entire emission line of ∼20 per cent can result.</p>
<p>Important differences were found in the microlensed behaviour for the models under consideration in this paper, with the degree of magnification and shift in the line centroid being dependent upon the surface-brightness distribution as a function of velocity. An obvious example of this would be the detection of asymmetric modification of the overall emission-line profile, indicating a surface-brightness distribution which is asymmetric in velocity, such as a structure possessing rotation. While it goes beyond this current paper, these results reveal the possibility of undertaking detailed microlensing tomography of the BLR via spectroscopic monitoring of multiply imaged quasars. However, current microlensing monitoring programs focus upon obtaining broad-band photometry, effectively determining the microlensing light curves for the continuum source. Previous spectroscopic studies have revealed interesting BLR profile line differences between various images (e.g. <xref ref-type="bibr" rid="bib5">Filippenko 1989</xref>), although no systematic spectroscopic programme has been undertaken, with most studies consisting of single- or double-epoch observations (e.g. <xref ref-type="bibr" rid="bib11">Lewis et al. 1998</xref>). To determine the observational implications of this study fully, an investigation of the temporal relationship between the microlensing of the BLR and the continuum emitting source is required, allowing the development of an optimum override strategy such that spectroscopic observations can be obtained. This is the subject of a forthcoming article.</p>
</sec>
</body>
<back>
<ack>
<sec id="ss5">
<title>Acknowledgments</title>
<p>Joachim Wambsganss is thanked for providing a copy of his microlensing ray-tracing code which was employed in this study and Scott Croom is thanked for helping unravel what ‘bright’ means when talking about quasars. The authors are extremely grateful to the Centre for Astrophysics and Supercomputing at Swinburne University of Technology for making substantial computational resources available to this project, and apologize to B. Conn, J. Chapman and I. Klamer for the Mondas's screeching alarm when its CPUs overheated.</p>
</sec>
</ack>
<ref-list>
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<label><sup>1</sup></label><p>Note that the magnification distributions in this paper are normalized with respect to the mean microlensing magnification μ<sub>th</sub>=[(1−σ)<sup>2</sup>−γ<sup>2</sup>]<sup>−1</sup>; hence the source can undergo substantial demagnification as well as magnification and deviations are with respect to the mean behaviour of the emission line.</p>
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</article></istex:document></istex:metadataXml><mods version="3.6"><titleInfo><title>Gravitational microlensing of quasar broad-line regions at large optical depths</title></titleInfo><titleInfo type="alternative" contentType="CDATA"><title>Gravitational microlensing of quasar broad-line regions at large optical depths</title></titleInfo><name type="personal" displayLabel="corresp"><namePart type="given">Geraint F.</namePart><namePart type="family">Lewis</namePart><affiliation>Institute of Astronomy, School of Physics, University of Sydney, NSW 2006, Australia</affiliation><affiliation>E-mail: gfl@physics.usyd.edu.au</affiliation><affiliation>E-mail: gfl@physics.usyd.edu.au</affiliation><affiliation>E-mail: gfl@physics.usyd.edu.au</affiliation><role><roleTerm type="text">author</roleTerm></role></name><name type="personal" displayLabel="corresp"><namePart type="given">R. A.</namePart><namePart type="family">Ibata</namePart><affiliation>Observatoire de Strasbourg, 11, rue de l'Université, F-67000, Strasbourg, France</affiliation><affiliation>E-mail: gfl@physics.usyd.edu.au</affiliation><affiliation>E-mail: gfl@physics.usyd.edu.au</affiliation><affiliation>E-mail: gfl@physics.usyd.edu.au</affiliation><role><roleTerm type="text">author</roleTerm></role></name><typeOfResource>text</typeOfResource><genre type="research-article" displayLabel="research-article" authority="ISTEX" authorityURI="https://content-type.data.istex.fr" valueURI="https://content-type.data.istex.fr/ark:/67375/XTP-1JC4F85T-7">research-article</genre><originInfo><publisher>Blackwell Science Ltd</publisher><place><placeTerm type="text">Oxford, UK</placeTerm></place><dateIssued encoding="w3cdtf">2004-02-11</dateIssued><copyrightDate encoding="w3cdtf">2004</copyrightDate></originInfo><abstract>Recent estimates of the scale of structures at the heart of quasars suggest that the regions responsible for the broad-line emission are smaller than previously thought. With this revision of scale, the broad-line region is amenable to the influence of gravitational microlensing. This study investigates the influence on microlensing at high optical depth on a number of current models of the broad-line region (BLR). It is found that the BLR can be significantly magnified by the action of microlensing, although the degree of magnification is dependent upon the spatial and kinematic structure of the BLR. Furthermore, while there is a correlation between the microlensing fluctuations of the continuum source and the BLR, there is substantial scatter about this relation, revealing that broad-band photometric monitoring is not necessarily a guide to microlensing of the BLR. The results of this study demonstrate that the spatial and kinematic structure within the BLR may be determined via spectroscopic monitoring of microlensed quasars.</abstract><subject lang="en"><genre>Key words</genre><topic>gravitational lensing</topic><topic>quasars: emission lines</topic><topic>quasars: individual: Q2237+0305</topic></subject><relatedItem type="host"><titleInfo><title>Monthly Notices of the Royal Astronomical Society</title></titleInfo><titleInfo type="abbreviated"><title>Mon. Not. R. Astron. Soc.</title></titleInfo><genre type="journal" authority="ISTEX" authorityURI="https://publication-type.data.istex.fr" valueURI="https://publication-type.data.istex.fr/ark:/67375/JMC-0GLKJH51-B">journal</genre><identifier type="ISSN">0035-8711</identifier><identifier type="eISSN">1365-2966</identifier><identifier type="PublisherID">mnras</identifier><identifier type="PublisherID-hwp">mnras</identifier><part><date>2004</date><detail type="volume"><caption>vol.</caption><number>348</number></detail><detail type="issue"><caption>no.</caption><number>1</number></detail><extent unit="pages"><start>24</start><end>33</end></extent></part></relatedItem><identifier type="istex">640DEAF2BD289F2CE173958D49A6B22D6A65E819</identifier><identifier type="DOI">10.1111/j.1365-2966.2004.07349.x</identifier><accessCondition type="use and reproduction" contentType="copyright">© 2004 RAS</accessCondition><recordInfo><recordContentSource authority="ISTEX" authorityURI="https://loaded-corpus.data.istex.fr" valueURI="https://loaded-corpus.data.istex.fr/ark:/67375/XBH-GTWS0RDP-M">oup</recordContentSource><recordOrigin>© 2004 RAS</recordOrigin></recordInfo></mods><json:item><extension>json</extension><original>false</original><mimetype>application/json</mimetype><uri>https://api.istex.fr/document/640DEAF2BD289F2CE173958D49A6B22D6A65E819/metadata/json</uri></json:item></metadata><annexes><json:item><extension>jpeg</extension><original>true</original><mimetype>image/jpeg</mimetype><uri>https://api.istex.fr/document/640DEAF2BD289F2CE173958D49A6B22D6A65E819/annexes/jpeg</uri></json:item><json:item><extension>gif</extension><original>true</original><mimetype>image/gif</mimetype><uri>https://api.istex.fr/document/640DEAF2BD289F2CE173958D49A6B22D6A65E819/annexes/gif</uri></json:item></annexes><serie></serie></istex></record>Pour manipuler ce document sous Unix (Dilib)
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