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

Ullán, A.; Goicoechea, L. J.; Muñoz, J. A.; Mediavilla, E.; Serra-Ricart, M.; Puga, E.; Alcalde, D.; Oscoz, A.; Barrena, R.

doi:10.1046/j.1365-2966.2003.07091.x

Cited by 8 publications

(12 citation statements)

References 34 publications

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“…The difference of 3.5 mag is consistent with a ratio of fluxes F gal /F A of about 1/25. Thus, in the case of QSO 0957+561, we found a R-band ratio of fluxes F gal /F A of about 1/2.5 (Ullán et al 2003), and now we have F gal /F A ∼ 1/25, which explains our unsuccessful efforts when measuring the flux of the lens galaxy in standard frames.…”

Section: Photometry and Vr Light Curvesmentioning

confidence: 85%

“…The galaxy model could also be inferred from the best images in terms of seeing. Once the relevant information on the galaxy is known, we apply a PSF fitting method to all optical images, setting the galaxy properties to those derived from the HST or the best-quality images, and allowing the remaining parameters to vary (e.g., McLeod et al 1998;Ullán et al 2003). Magain et al (1998) also presented an alternative task (deconvolution) that combines all the frames obtained at different epochs to determine the numerical light distribution of the lensing galaxy, as well as the positions of the point-like sources (quasar components), since these parameters do not vary with time.…”

Section: Photometry and Vr Light Curvesmentioning

confidence: 99%

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Time delay of SBS 0909+532

Ullán

Goicoechea

Zheleznyak

et al. 2006

A&A

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Aims. The time delays between the components of a lensed quasar are basic tools for analysing the expansion of the Universe and the structure of the main lens galaxy halo. In this paper, we focus on the variability and time delay of the double system SBS 0909+532A,B as well as the time behaviour of the field stars. Methods. We use VR optical observations of SBS 0909+532A, B and the field stars in 2003. The frames were taken at Calar Alto, Maidanak, and Wise observatories, and the VR light curves of the field stars and quasar components were derived from aperture and point-spread function fitting methods. We measured the R-band time delay of the system from the χ 2 and dispersion techniques and 1000 synthetic light curves based on the observed records. Results. One nearby field star (SBS 0909+532c) was found to be variable, and the other two nearby field stars are non-variable sources. With respect to the quasar components, the R-band records seem more reliable and are more densely populated than the V-band ones. The observed R-band fluctuations permit a pre-conditioned measurement of the time delay. From the χ 2 minimization, if we assume that the quasar emission is observed first in B and afterwards in A (in agreement with basic observations of the system and the corresponding predictions), we obtain ∆τ BA = −45 +1 −11 days (95% confidence interval). The dispersion technique leads to a similar delay range. A by-product of the analysis is the determination of a totally corrected flux ratio in the R band (corrected by the time delay and the contamination due to the galaxy light). Our 95% measurement ∆m BA = m B (t + ∆τ BA ) − m A (t) = 0.575 ± 0.014 mag is in excellent agreement with previous results from contaminated fluxes at the same time of observation.

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Section: Photometry and Vr Light Curvesmentioning

confidence: 85%

Section: Photometry and Vr Light Curvesmentioning

confidence: 99%

Time delay of SBS 0909+532

Ullán

Goicoechea

Zheleznyak

et al. 2006

A&A

Self Cite

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“…Since the detection of the first lensing induced variability, seen in the quadruply imaged quasar Q2237+0305 (Irwin et al 1989;Corrigan et al 1991), there has been intense theoretical study of this gravitational microlensing, revealing that the degree of brightness fluctuations is strongly dependent upon the size of the source being lensed (Kayser et al 1986;Wambsganss et al 1990;Wambsganss & Paczynski 1991) and the mass function of the lensing objects (Lewis & Irwin 1996;Wyithe & Turner 2001), potentially providing a useful probe of both. Further studies have scrutinized the influence of source size and shape (Refsdal & Stabell 1991, 1993, 1997Agol 2003;Mortonson et al 2005), and more recent programs with dedicated monitoring programs (Woźniak et al 2000;Alcalde et al 2002;Ullán et al 2003) have finally resulted in high quality microlensing light curves that can be compared directly with theoretical models (Wyithe et al 2000;Kochanek 2004).…”

Section: Introductionmentioning

confidence: 99%

Quasar Microlensing: When Compact Masses Mimic Smooth Matter

Lewis

Gil-Merino

2006

ApJ

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The magnification induced by gravitational microlensing is sensitive to the size of a source relative to the Einstein radius, the natural microlensing scale length. This paper investigates the effect of source size in the case where the microlensing masses are distributed with a bimodal mass function, with solar mass stars representing the normal stellar masses, and smaller masses (down to 8.5 × 10 −5 M ⊙ ) representing a dark matter component. It is found that there exists a critical regime where the dark matter is initially seen as individual compact masses, but with an increasing source size the compact dark matter acts as a smooth mass component. This study reveals that interpretation of microlensing light curves, especially claims of small mass dark matter lenses embedded in an overall stellar population, must consider the important influence of the size of the source.

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“…First of all, we take the Q0957+561A fluxes (Ullán et al 2003) that were derived from the photometric approaches: pho2com (Serra-Ricart et al 1999) and psf phot. This leads to two datasets consistent each other.…”

Section: Observations and Reduction Processmentioning

confidence: 99%

“…This leads to two datasets consistent each other. Secondly, we use Ullán et al (2003) GLITP correction laws to extract clean fluxes for the pho2com results of Q0957+561B on 2001 April 10. The combined (pho2com + corr) technique is called pho2comC.…”

Section: Observations and Reduction Processmentioning

confidence: 99%

The Possible Origins of the $VR$ Magnification Ratios of Q0957+561AB

et al. 2004

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Abstract. We present V R magnification ratios of the double quasar Q0957+561AB, which are inferred from frames taken with the 2.56m Nordic Optical Telescope. From two different photometric techniques (pho2comC and psf phot) and a reasonable range for the time delay in the system (415-430 days), we find optical continuum ratios depending on the wavelength. These chromatic ratios are consistent with either differential extinction in a dust system or gravitational microlensing in the deflector. Although the dusty scenario is only viable for a compact dust cloud in the line of sight to the A component, the possible values for the differential extinction and the ratio of total to selective extinction in the V band are surprisingly reasonable. To decide on the true origin of the anomalous ratios (extinction, microlensing or a mixed scenario), we are carrying out new monitoring campaigns and planning detailed observations from the best ground-based and space telescopes.

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

Cited by 8 publications

References 34 publications

Time delay of SBS 0909+532

Time delay of SBS 0909+532

Quasar Microlensing: When Compact Masses Mimic Smooth Matter

The Possible Origins of the $VR$ Magnification Ratios of Q0957+561AB

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