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Photocentric variability of quasars caused by variations in their inner structure: consequences for Gaia measurements

LČ Popović, P Jovanović, Marko Stalevski UGent, S Anton, AH Andrei, J Kovačević and Maarten Baes UGent (2012) ASTRONOMY & ASTROPHYSICS. 538.
abstract
Context. We study the photocenter position variability caused by variations in the quasar inner structure. We consider the variability in the accretion disk emissivity and torus structure variability caused by the different illumination by the central source. We discuss the possible detection of these effects by Gaia. Observations of the photocenter variability in two AGNs, SDSS J121855+020002 and SDSS J162011+1724327 have been reported and discussed. Aims. For variations in the quasar inner structure, we explore how much this effect can affect the position determination and whether it can (or not) be detected with the Gaia mission. Methods. We use models of (a) a relativistic disk, including the perturbation that can increase the brightness of part of the disk, and consequently offset the photocenter position, and (b) a dusty torus that absorbs and re-emits the incoming radiation from the accretion disk (central continuum source). We estimate the value of the photocenter offset caused by these two effects. Results. We found that perturbations in the inner structure can cause a significant offset to the photocenter. This offset depends on the characteristics of both the perturbation and accretion disk and on the structure of the torus. In the case of the two considered QSOs, the observed photocenter offsets cannot be explained by variations in the accretion disk and other effects should be considered. We discuss the possibility of exploding stars very close to the AGN source, and also that there are two variable sources at the center of these two AGNs that may indicate a binary supermassive black hole system on a kpc (pc) scale. Conclusions. The Gaia mission seems to be very promising, not only for astrometry, but also for exploring the inner structure of AGNs. We conclude that variations in the quasar inner structure can affect the observed photocenter (by up to several mas). There is a chance to observe such an effect in the case of bright and low-redshift QSOs.
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author
organization
year
type
journalArticle (original)
publication status
published
subject
keyword
accretion disks, ACTIVE GALACTIC NUCLEI, quasars: general, reference systems, accretion, BLACK-HOLE, BROAD EMISSION-LINES, EXTRAGALACTIC RADIO-SOURCES, RADIATIVE-TRANSFER, STAR-FORMATION, STARBURST GALAXIES, LARGE SAMPLE, MODEL, DUST
journal title
ASTRONOMY & ASTROPHYSICS
Astron. Astrophys.
volume
538
article_number
A107
pages
11 pages
Web of Science type
Article
Web of Science id
000300614100107
JCR category
ASTRONOMY & ASTROPHYSICS
JCR impact factor
5.084 (2012)
JCR rank
11/56 (2012)
JCR quartile
1 (2012)
ISSN
0004-6361
DOI
10.1051/0004-6361/201117245
language
English
UGent publication?
yes
classification
A1
copyright statement
I have transferred the copyright for this publication to the publisher
id
2113569
handle
http://hdl.handle.net/1854/LU-2113569
date created
2012-05-25 14:44:09
date last changed
2012-05-30 15:30:22
@article{2113569,
  abstract     = {Context. We study the photocenter position variability caused by variations in the quasar inner structure. We consider the variability in the accretion disk emissivity and torus structure variability caused by the different illumination by the central source. We discuss the possible detection of these effects by Gaia. Observations of the photocenter variability in two AGNs, SDSS J121855+020002 and SDSS J162011+1724327 have been reported and discussed. 
Aims. For variations in the quasar inner structure, we explore how much this effect can affect the position determination and whether it can (or not) be detected with the Gaia mission. 
Methods. We use models of (a) a relativistic disk, including the perturbation that can increase the brightness of part of the disk, and consequently offset the photocenter position, and (b) a dusty torus that absorbs and re-emits the incoming radiation from the accretion disk (central continuum source). We estimate the value of the photocenter offset caused by these two effects. 
Results. We found that perturbations in the inner structure can cause a significant offset to the photocenter. This offset depends on the characteristics of both the perturbation and accretion disk and on the structure of the torus. In the case of the two considered QSOs, the observed photocenter offsets cannot be explained by variations in the accretion disk and other effects should be considered. We discuss the possibility of exploding stars very close to the AGN source, and also that there are two variable sources at the center of these two AGNs that may indicate a binary supermassive black hole system on a kpc (pc) scale. 
Conclusions. The Gaia mission seems to be very promising, not only for astrometry, but also for exploring the inner structure of AGNs. We conclude that variations in the quasar inner structure can affect the observed photocenter (by up to several mas). There is a chance to observe such an effect in the case of bright and low-redshift QSOs.},
  articleno    = {A107},
  author       = {Popovi\'{c}, L\v{C} and Jovanovi\'{c}, P and Stalevski, Marko and Anton, S and Andrei, AH and Kova\v{c}evi\'{c}, J and Baes, Maarten},
  issn         = {0004-6361},
  journal      = {ASTRONOMY \& ASTROPHYSICS},
  keyword      = {accretion disks,ACTIVE GALACTIC NUCLEI,quasars: general,reference systems,accretion,BLACK-HOLE,BROAD EMISSION-LINES,EXTRAGALACTIC RADIO-SOURCES,RADIATIVE-TRANSFER,STAR-FORMATION,STARBURST GALAXIES,LARGE SAMPLE,MODEL,DUST},
  language     = {eng},
  pages        = {11},
  title        = {Photocentric variability of quasars caused by variations in their inner structure: consequences for Gaia measurements},
  url          = {http://dx.doi.org/10.1051/0004-6361/201117245},
  volume       = {538},
  year         = {2012},
}

Chicago
Popović, LČ, P Jovanović, Marko Stalevski, S Anton, AH Andrei, J Kovačević, and Maarten Baes. 2012. “Photocentric Variability of Quasars Caused by Variations in Their Inner Structure: Consequences for Gaia Measurements.” Astronomy & Astrophysics 538.
APA
Popović, L., Jovanović, P., Stalevski, M., Anton, S., Andrei, A., Kovačević, J., & Baes, M. (2012). Photocentric variability of quasars caused by variations in their inner structure: consequences for Gaia measurements. ASTRONOMY & ASTROPHYSICS, 538.
Vancouver
1.
Popović L, Jovanović P, Stalevski M, Anton S, Andrei A, Kovačević J, et al. Photocentric variability of quasars caused by variations in their inner structure: consequences for Gaia measurements. ASTRONOMY & ASTROPHYSICS. 2012;538.
MLA
Popović, LČ, P Jovanović, Marko Stalevski, et al. “Photocentric Variability of Quasars Caused by Variations in Their Inner Structure: Consequences for Gaia Measurements.” ASTRONOMY & ASTROPHYSICS 538 (2012): n. pag. Print.