Optical monitoring of the gravitationally lensed quasar
Q2237+0305 from APO between June 1995 and January 1998

Schmidt, R. W.; Kundić, Tomislav; Pen, Ue-Li; Turner, Edwin L.; Wambsganß, J.; Bergeron, Louis; Colley, Wesley N.; Corson, Charles; Hastings, N. C.; Hoyes, T.; Long, Daniel C.; Loomis, Karen; Malhotra, Sangeeta; Rhoads, James E.; Stanek, K. Z.

doi:10.1051/0004-6361:20020957

Cited by 19 publications

(17 citation statements)

References 19 publications

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“…Despite extensive optical monitoring programmes carried out at the Nordic Optical Telescope (Østensen et al 1996) within the OGLE programme (Woźniak et al 2000), by the GLITP collaboration (Alcalde et al 2002) at the Apache Point Observatory (Schmidt et al 2002), and at Maidanak Observatory (Bliokh et al 1999;Dudinov et al 2000;Vakukik et al 2004), there was no significant intrinsic variability detected in QSO2237+0305. The macrolens models of the system predict the time delays of about one day for all components, so the intrinsic variations in the source should manifest themselves almost at the same time in all four images.…”

Section: Application To the Gravitational Lens System Qso2237+0305mentioning

confidence: 99%

Determining time delay in the gravitationally lensed system QSO2237+0305

Koptelova¹,

Oknyanskij²,

Shimanovskaya³

2006

A&A

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Aims. We considered the possibility of measuring time delays between components of the multiplied quasar QSO2237+0305 and between V and R band variations. Methods. The analysis is based on the flux variations of four components observed by the OGLE collaboration and Maidanak group during the last quarter of 2003. The observed gradients of the brightness variations in this period for OGLE data in V band are 3.4 mmag/day, 2.2 mmag/day, 2.4 mmag/day, and 1.1 mmag/day for the components A, B, C, and D, respectively. The variations are probably intrinsic source variations. The basic method used for time-delay measurements is the cross-correlation technique. To estimate the uncertainty of the time-delay measurements, Monte Carlo simulations were carried out. Results. The calculations showed the impossibility of unambiguously measuring the differential time delays between the components. The observations at shorter wavelengths seem to be the only way to achieve robust time delay measurements in the system. The wavelength-dependent time delays can be used to provide the evidence of an accretion-disk structure of the central optical variable source. The observed V and R band variations of component C show good correlation with the correlation coefficient of 0.83. However, the obtained time delay, about 16.2 days, and its accuracy are far from reliable.

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Section: Application To the Gravitational Lens System Qso2237+0305mentioning

confidence: 99%

Determining time delay in the gravitationally lensed system QSO2237+0305

Koptelova¹,

Oknyanskij²,

Shimanovskaya³

2006

A&A

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“…Microlensing can cause an image to be below or above its average magnification for decades (see Witt & Mao 1994, for an extensive discussion of the effects of microlensing). The recent years have seen monitoring campaigns of both Q 2237+030 and Q 0957+561, which provide irrefutable evidence for microlensing (Colley & Schild 2000;Wozniak et al 2000;Schmidt et al 2002). There are at least a further five multiply imaged quasars for which evidence exists implicating microlensing in the optical range (HE 1104-1805, PG 1115+080, H 1413+117, B 0218+357, B 1600+434).…”

Section: Uncertaintiesmentioning

confidence: 99%

Fitting gravitational lenses: truth or delusion

Evans

Witt

2003

Monthly Notices of the Royal Astronomical Society

117

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The observables in a strong gravitational lens are usually just the image positions and sometimes the flux ratios. We develop a new and simple algorithm which allows a set of models to be fitted exactly to the observations. Taking our cue from the strong body of evidence that early‐type galaxies are close to isothermal, we assume that the lens is scale‐free with a flat rotation curve. External shear can be easily included. Our algorithm allows full flexibility regarding the angular structure of the lensing potential. Importantly, all the free parameters enter linearly into the model and so the lens and flux ratio equations can always be solved by straightforward matrix inversion. The models are only restricted by the fact that the surface mass density must be positive. We use this new algorithm to examine some of the claims made for anomalous flux ratios. It has been argued that such anomalies betray the presence of substantial amounts of substructure in the lensing galaxy. We demonstrate by explicit construction that some of the lens systems for which substructure has been claimed can be well fitted by smooth lens models. This is especially the case when the systematic errors in the flux ratios (caused by microlensing or differential extinction) are taken into account. However, there is certainly one system (B 1422+231) for which the existing smooth models are definitely inadequate and for which substructure may be implicated. Within a few tens of kpc of the lensing galaxy centre, dynamical friction and tidal disruption are known to be very efficient at dissolving any substructure. Very little substructure is projected within the Einstein radius. The numbers of strong lenses for which substructure is currently being claimed may be so large that this contradicts rather than supports cold dark matter theories.

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“…In 2002, the results of monitoring Q2237+0305 by the GLITP (Gravitational Lenses International Time Project) collaboration appeared, which cover the 4-month period October 1999-February 2000 (Alcalde et al 2002). The most recent publication of the results of low-resolution observations with the 3.5-m telescope at the Apache Point Observatory should also be mentioned here, (Schmidt et al 2002); these gave the Gunn r lightcurves of the A and B components for 73 dates between July 1995 and January 1998. In spite of a rather low photometric accuracy, -an error bar of 0.1 m to 0.2 m is reported -the data are of value first of all because they include the brightness peak of the A component in 1996.…”

Section: Introductionmentioning

confidence: 99%

Color effects associated with the 1999 microlensing brightness peaks in gravitationally lensed quasar Q2237+0305

Vakulik¹,

Schild

Dudinov³

et al. 2004

A&A

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Abstract. We present photometry of the Q2237+0305 gravitational lens system in VRI spectral bands with the 1.5-m telescope of the high-altitude Maidanak observatory in 1995−2000. The time interval includes the epoch of the dramatic brightness peaks discovered previously in the A and C image components (Wozniak et al. 2000a,b). By good luck three nights of observation in 1999 were almost at the time of the strong brightness peak of image C, and approximately in the middle of the ascending slope of the brightness peak of image A. Having reached its brightness maximum at the very end of June 1999, the C component had changed its (V − I) color from 0.3 m to 0.12 m since August 1998, and from 0.56 m to 0.12 m since August 1997. It was the bluest component in the system in 1998 and 1999, but by October 2000 that was no longer the case. We do not know the color of the A component exactly at its brightness peak, but we do know that it became 0.47 m brighter in R and 0.15 m bluer in (V − R) between August 1998 and August 2000, about three months before the peak. More intensive monitoring of Q2237+0305 in July-October 2000, made on a nearly daily basis, did not reveal rapid (night-to-night and intranight) brightness variations of the components during this time period, exceeding the photometry error bars. Rather slow changes of magnitudes of the components were observed, in particular, nearly synchronous 0.08 m fading of B and C components, and 0.05 m brightening of D in the R band during July 23−October 7, 2000, while the B component had become the faintest in all filters by the end of this time period. The behavior of the colors of the components was analyzed on the basis of all our VRI observations, made in 1995−2000 on Maidanak. A qualitative tendency of the components to become bluer as their brightness increases, noted in our previous works, was confirmed quantitatively. A correlation between the color variations and variations of magnitudes of the components is demonstrated to be significant and reaches 0.75 for ∆(V − I) vs. ∆R, with a regression line slope of 0.33± 0.08 for these quantities. A plot of (V − I) vs. (V − R) shows the components settled in a cluster, stretchng along a line with a slope of 1.31 ± 0.14. Both slopes are noticeably less steep than those expected if a standard galactic interstellar reddening law were responsible for the differences between the colors of images and their variations over time. We attribute the brightness and color changes to microlensing of the quasar's structure, which we conclude to be more compact at shorter wavelengths, as predicted by most quasar models featuring an energizing central source.

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Optical monitoring of the gravitationally lensed quasar Q2237+0305 from APO between June 1995 and January 1998

Cited by 19 publications

References 19 publications

Determining time delay in the gravitationally lensed system QSO2237+0305

Determining time delay in the gravitationally lensed system QSO2237+0305

Fitting gravitational lenses: truth or delusion

Color effects associated with the 1999 microlensing brightness peaks in gravitationally lensed quasar Q2237+0305

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