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

Popovic, L. C.; Jovanović, P.; Antón, Sonia; Andrei, A. H.; Kovačević, Jelena; Baes, M.

doi:10.1051/0004-6361/201117245

Cited by 34 publications

(38 citation statements)

References 52 publications

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“…Although there are good theoretical reasons to expect that the offsets are generally small (<1 mas; e.g. Kovalev et al 2008;and Popović et al 2012), observational studies tend to find much larger effects (e.g. Taris et al 2011;Orosz & Frey 2013, and the surveys discussed below).…”

Section: Discussion Of the Optical-radio Offsetsmentioning

confidence: 99%

GaiaData Release 1

Mignard

Klioner

Lindegren

et al. 2016

A&A

133

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Context. As part of the data processing for Gaia Data Release 1 (Gaia DR1) a special astrometric solution was computed, the so-called auxiliary quasar solution. This gives positions for selected extragalactic objects, including radio sources in the second realisation of the International Celestial Reference Frame (ICRF2) that have optical counterparts bright enough to be observed with Gaia. A subset of these positions was used to align the positional reference frame of Gaia DR1 with the ICRF2. Although the auxiliary quasar solution was important for internal validation and calibration purposes, the resulting positions are in general not published in Gaia DR1. Aims. We describe the properties of the Gaia auxiliary quasar solution for a subset of sources matched to ICRF2, and compare their optical and radio positions at the sub-mas level. Methods. Descriptive statistics are used to characterise the optical data for the ICRF sources and the optical-radio differences. The most discrepant cases are examined using online resources to find possible alternative explanations than a physical optical-radio offset of the quasars. Results. In the auxiliary quasar solution 2191 sources have good optical positions matched to ICRF2 sources with high probability. Their formal standard errors are better than 0.76 milliarcsec (mas) for 50% of the sources and better than 3.35 mas for 90%. Optical magnitudes are obtained in Gaia's unfiltered photometric G band. The Gaia results for these sources are given as a separate table in Gaia DR1. The comparison with the radio positions of the defining sources shows no systematic differences larger than a few tenths of a mas. The fraction of questionable solutions, not readily accounted for by the statistics, is less than 6%. Normalised differences have extended tails requiring case-by-case investigations for around 100 sources, but we have not seen any difference indisputably linked to an optical-radio offset in the sources. Conclusions. With less than a quarter of the data expected from the nominal mission it has been possible to obtain positions at the sub-mas level for most of the ICRF sources having an optical counterpart brighter than 20.5 mag.

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Section: Discussion Of the Optical-radio Offsetsmentioning

confidence: 99%

GaiaData Release 1

Mignard

Klioner

Lindegren

et al. 2016

A&A

133

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“…Different continuum variability scenarios are discussed in the literature. Most likely a variable accretion rate or instabilities of the accretion disk are responsible for the spectral changes; for some objects, gravitational microlensing, supernova bursts, or jet instabilities are also possible explanations (e.g., Andrei et al 2009;Popović et al 2012). Furthermore, a hot corona above the SMBH produces X-ray photons.…”

Section: Quasar Variabilitymentioning

confidence: 99%

“…In total, the simulated Gaia catalog by Robin et al (2012) contains 10 6 quasars, of which 5200 objects are bright enough to be detected in the RVS. From these bright quasars, 579 objects have broad lines in the RVS wavelength area.…”

Section: Quasars With Broad Emission Lines In the Gaia High-resolutiomentioning

confidence: 99%

“…The quasars in this simulated Gaia catalog were produced mainly with similar statistical properties as SDSS (e.g., colors, apparent brightness, redshifts), but extrapolated to G = 20.5 mag (Slezak & Mignard 2007). Additionally, Robin et al (2012) considered a sky coverage for Gaia quasars of about only 2/3 because of crowding in the Galactic plane. We searched through all SDSS quasars for BELs detectable in Gaia's RVS considering these redshifts and magnitudes.…”

Section: Quasars With Broad Emission Lines In the Gaia High-resolutiomentioning

confidence: 99%

“…Table 2 shows the described wavelength ranges for Hα, Hβ, MgII, CIII], and CIV, where at least one wing (∼50% of the BEL) is located in the RVS interval. Furthermore, we listed the number of expected quasars from the simulated Gaia catalog (Robin et al 2012) and the SDSS objects in the different wavelength ranges. As expected, because of the large number of bright quasars in this redshift range, most of the simulated Gaia or SDSS quasars with a line in the RVS range have the broad Hα line in this interval.…”

Section: Quasars With Broad Emission Lines In the Gaia High-resolutiomentioning

confidence: 99%

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Exploration of quasars with theGaiamission

Proft

Wambsganß

2015

A&A

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We analyze the opportunities in and limits to investigating quasars with the Gaia satellite by studying Gaia's low-and high-resolution quasar spectra, with consideration of their signal-to-noise ratios. Furthermore, we explore bright quasars from the Sloan Digital Sky Survey with broad emission lines (BELs) redshifted into the spectral range of Gaia's Radial Velocity Spectrograph (RVS). We find that Gaia low-resolution spectra of quasars enable a determination of equivalent widths, continuum variability, and the Baldwin effect. Additionally, it will be feasible to analyze BEL reverberation mapping with Gaia data for a small sample of objects. These quasars should have a high cadence of measurements or higher time lags due to large redshifts, high quasar luminosities, or selected lowionization lines. More than 500 known quasars will also get high-resolution spectra of individual BELs in the small wavelength range of the RVS. This allows an investigation of broad emission line shapes and their variabilities to get information on the spatial structure and kinematics of the broad line region. We identify six known variable SDSS quasars with BELs in the RVS that have interesting spectra for a potential intrinsic line variability investigation. However, the signal-to-noise ratio of the RVS is too small for studying narrow and broad absorption lines in quasar spectra.

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