Five nights of intensive<i>R</i>- and<i>V</i>-band photometry of QSO 0957+561A,B

Ovaldsen, J. E.; Teuber, J.; Stabell, R.; Evans, A.

doi:10.1046/j.1365-8711.2003.06989.x

Cited by 7 publications

(11 citation statements)

References 13 publications

(24 reference statements)

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“…The expected values of the intrinsic variability are in reasonable agreement with the analysis of light curves for Q0957+561 (Goicoechea et al 2008;Goicoechea 2002;Ovaldsen et al 2003aOvaldsen et al , 2003b, SDSS1004+4112 (Fohlmeister et al 2008), and HE1104-1805 (Poindexter et al 2007). In the case of HE1104-1805, Poindexter et al (2007) specifically studied the effect of intrinsic variability on flux ratios finding a global displacement of 0.1 mag in magnitude differences due to the time delay without apparent changes in chromaticity in the optical (from the J to B photometric bands).…”

Section: Contamination From Other Sources Of Chromaticitysupporting

confidence: 84%

Measuring Microlensing Using Spectra of Multiply Lensed Quasars

Motta

Mediavilla

Falco

et al. 2012

ApJ

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We report on a program of spectroscopic observations of gravitationally lensed QSOs with multiple images. We seek to establish whether microlensing is occurring in each QSO image using only single-epoch observations. We calculate flux ratios for the cores of emission lines in image pairs to set a baseline for no microlensing. The offset of the continuum flux ratios relative to this baseline yields the microlensing magnification free from extinction, as extinction affects the continuum and the lines equally. When we find chromatic microlensing, we attempt to constrain the size of the QSO accretion disk. SDSSJ1004+4112 and HE1104-1805 show chromatic microlensing with amplitudes 0.2 < |Δm| < 0.6 and 0.2 < |Δm| < 0.4 mag, respectively. Modeling the accretion disk with a Gaussian source (I ∝ exp(−R 2 /2r 2 s )) of size r s ∝ λ p and using magnification maps to simulate microlensing, we find r s (λ3363) = 7 ± 3 lt-day(18.1 ± 7.8 × 10 15 cm) and p = 1.1 ± 0.4 for SDSS1004+4112, and r s (λ3363) = 6±2 lt-day(15.5±5.2×1015 cm) and p = 0.7±0.1 for HE1104-1805. For SDSSJ1029+2623, we find strong chromaticity of ∼0.4 mag in the continuum flux ratio, which probably arises from microlensing, although not all the available data fit within this explanation. For Q0957+561, we measure B − A magnitude differences of 0.4 mag, much greater than the ∼0.05 mag amplitude usually inferred from light-curve variability. It may substantially modify the current interpretations of microlensing in this system, likely favoring the hypothesis of smaller sources and/or larger microdeflectors. For HS0818+1227, our data yield possible evidence of microlensing.

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Section: Contamination From Other Sources Of Chromaticitysupporting

confidence: 84%

Measuring Microlensing Using Spectra of Multiply Lensed Quasars

Motta

Mediavilla

Falco

et al. 2012

ApJ

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“…In the past, other authors have also found some zero‐lag correlation between the variations of both components (e.g. Ovaldsen et al 2003a,b, and references therein). The R ‐band residues could be mainly originated by either observational systematic noise or physical phenomena inside the Milky Way.…”

Section: Final Light Curves and Variabilitymentioning

confidence: 87%

“…In this paper ( and ) we present new VR light curves for the two components A and B of QSO 0957+561 ( z s = 1.41). The GLITP‐OM/Q0957+561 project was conceived (amongst other things) to search for gradients in the light curves of the system, so the study by Ovaldsen et al (2003b) and our effort are complementary works. Ovaldsen et al (2003b) discussed the hourly and daily variability, while we address the daily, weekly and monthly variability ().…”

Section: Introductionmentioning

confidence: 99%

“…The GLITP‐OM/Q0957+561 project was conceived (amongst other things) to search for gradients in the light curves of the system, so the study by Ovaldsen et al (2003b) and our effort are complementary works. Ovaldsen et al (2003b) discussed the hourly and daily variability, while we address the daily, weekly and monthly variability (). In , we compare the observed V ‐band gradients and the expected ones after a supernova explosion inside a high‐density medium at z = z s = 1.41.…”

Section: Introductionmentioning

confidence: 99%

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GLITP optical monitoring of QSO 0957+561: VR light curves and variability

Ullán

Goicoechea

Muñoz

et al. 2003

Monthly Notices of the Royal Astronomical Society

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The Gravitational Lenses International Time Project (GLITP) collaboration observed the first gravitational lens system (QSO 0957+561) from 2000 February 3 to March 31. The daily VR observations were made with the 2.56‐m Nordic Optical Telescope at Roque de los Muchachos Observatory, La Palma, Spain. We have derived detailed and robust VR light curves of the two components Q0957+561A and Q0957+561B. In spite of the excellent sampling rate, we have not found evidence in favour of true daily variability. With respect to variability on time‐scales of several weeks, we measure VR gradients of about −0.8 mmag d−1 in Q0957+561A and +0.3 mmag d−1 in Q0957+561B. The gradients are very probably originated in the far source. Thus, adopting this reasonable hypothesis (intrinsic variability), we compare them to the expected gradients during the evolution of a compact supernova remnant at the redshift of the source quasar. The starburst scenario is roughly consistent with some former events, but the new gradients do not seem to be caused by supernova remnant activity.

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“…Thus, the r-SDSS magnitude is inferred through the r SDSS vs. VR relationship: r SDSS = V − 0.89(V − R) + 0.39. This law is based on the r-SDSS magnitudes of the rest of stars and the corresponding VR magnitudes in Tables 1, 2 of Ovaldsen et al (2003b where (x,y) is the 2D position of the star on the CCD. To find the relevant parameters in the g band, i.e., α g (t j ), β g (t j ), and γ g,nm , we may fit the observed magnitude deviations (instrumental − standard) of the seven reference stars to the model incorporating the three systematic terms: zero-point, colour, and inhomogeneity.…”

Section: Discussionmentioning

confidence: 99%

New two-colour light curves of Q0957+561: time delays and the origin of intrinsic variations

Shalyapin¹,

Goicoechea²,

Koptelova³

et al. 2008

A&A

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Aims. We extend the gr-band time coverage of the gravitationally lensed double quasar Q0957+561. New gr light curves permit us to detect significant intrinsic fluctuations, to determine new time delays, and thus to gain perspective on the mechanism of intrinsic variability in Q0957+561. Methods. We use new optical frames of Q0957+561 in the g and r passbands from January 2005 to July 2007. These frames are part of an ongoing long-term monitoring with the Liverpool robotic telescope. We also introduce two photometric pipelines that are applied to the new gr frames of Q0957+561. The transformation pipeline incorporates zero-point, colour, and inhomogeneity corrections to the instrumental magnitudes, so final photometry to the 1-2% level is achieved for both quasar components. The two-colour final records are then used to measure time delays. Results. The gr light curves of Q0957+561 show several prominent events and gradients, and some of them (in the g band) lead to a time delay between components Δt BA = 417 ± 2 d (1σ). We do not find evidence of extrinsic variability in the light curves of Q0957+561. We also explore the possibility of a delay between a large event in the g band and the corresponding event in the r band. The gr cross-correlation reveals a time lag Δt rg = 4.0 ± 2.0 d (1σ; the g-band event is leading) that confirms a previous claim of the existence of a delay between the g and r band in this lensed quasar. Conclusions. The time delays (between quasar components and between optical bands) from the new records and previous ones in similar bands indicate that most observed variations in Q0957+561 (amplitudes of ∼100 mmag and timescales of ∼100 d) are very probably due to reverberation within the gas disc around the supermassive black hole.

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Five nights of intensiveR- andV-band photometry of QSO 0957+561A,B

Cited by 7 publications

References 13 publications

Measuring Microlensing Using Spectra of Multiply Lensed Quasars

Measuring Microlensing Using Spectra of Multiply Lensed Quasars

GLITP optical monitoring of QSO 0957+561: VR light curves and variability

New two-colour light curves of Q0957+561: time delays and the origin of intrinsic variations

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