Hourly Variability in Q0957+561

Colley, Wesley N.; Schild, Rudolph E.

doi:10.1086/309305

Cited by 16 publications

(37 citation statements)

References 12 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…This is not in agreement with e.g. Kundic et al (1997), Pelt et al (1998) and Colley & Schild (2000).…”

Section: Summary and Discussioncontrasting

confidence: 61%

“…Since 1995 different groups have reported values of τ in the range 416-425 days. The results seem again to concentrate around two values; 417 days (Kundic et al 1997;Pelt et al 1998;Colley & Schild 2000) and 424 days (Pelt et al 1996;Oscoz et al 1997;Pijpers 1997;Serra-Ricart et al 1999;Oscoz et al 2001).…”

Section: Introductionmentioning

confidence: 92%

“…For completeness, a least squares second order polynomial fit was computed using all the data points (see also Colley & Schild 2000). The formula for the intensity corrections, δI, reads where s = FWHM ( ).…”

Section: Crosstalk and Galaxy Contaminationmentioning

confidence: 99%

“…for the whole range of seeing conditions. Comparable corrections for subtracting the lens galaxy contribution were discussed in detail by Colley & Schild (2000), whereas the original RES reductions incorporated subtraction of a fixed 18.34 magnitude correction for the lens galaxy contribution to the B aperture flux.…”

Section: Crosstalk and Galaxy Contaminationmentioning

confidence: 99%

“…Results are ambiguous when it comes to the short time scale (lasting a few months) and rapid (less than a few weeks) microlensing events. Schild & Thomson (1995a), Schild (1996) and Colley & Schild (2000) have reported interesting high-frequency features in the brightness record, having amplitudes of only 0.03−0.05 mag and time scales of months and even weeks. Goicoechea et al (1998) also found fluctuations which could be associated with microlensing events.…”

Section: Introductionmentioning

confidence: 99%

See 4 more Smart Citations

New aperture photometry of QSO 0957+561; application to time delay and microlensing

Ovaldsen

Teuber

Schild

et al. 2003

A&A

View full text Add to dashboard Cite

Abstract. We present a re-reduction of archival CCD frames of the doubly imaged quasar 0957+561 using a new photometry code. Aperture photometry with corrections for both cross contamination between the quasar images and galaxy contamination is performed on about 2650 R-band images from a five year period (1992)(1993)(1994)(1995)(1996)(1997). From the brightness data a time delay of 424.9 ± 1.2 days is derived using two different statistical techniques. The amount of gravitational microlensing in the quasar light curves is briefly investigated, and we find unambiguous evidence of both long term and short term microlensing. We also note the unusual circumstance regarding time delay estimates for this gravitational lens. Estimates by different observers from different data sets or even with the same data sets give lag estimates differing by typically 8 days, and error bars of only a day or two. This probably indicates several complexities where the result of each estimate depends upon the details of the calculation.

show abstract

“…This is not in agreement with e.g. Kundic et al (1997), Pelt et al (1998) and Colley & Schild (2000).…”

Section: Summary and Discussioncontrasting

confidence: 61%

Section: Introductionmentioning

confidence: 92%

Section: Crosstalk and Galaxy Contaminationmentioning

confidence: 99%

Section: Crosstalk and Galaxy Contaminationmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 3 more Smart Citations

New aperture photometry of QSO 0957+561; application to time delay and microlensing

Ovaldsen

Teuber

Schild

et al. 2003

A&A

View full text Add to dashboard Cite

show abstract

Fitting gravitational lenses: truth or delusion

Evans

Witt

2003

Monthly Notices of the Royal Astronomical Society

117

View full text Add to dashboard Cite

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.

show abstract

Short time-scale fluctuations in the difference light curves of QSO 0957+561A,B: microlensing or noise?

Gil-Merino

Goicoechea

Serra-Ricart

et al. 2001

Monthly Notices of the Royal Astronomical Society

View full text Add to dashboard Cite

A B S T R A C TFrom optical R-band data of the double quasar QSO 09571561A,B, we made two new difference light curves (with an overlap of about 330 d between the time-shifted light curve for the A image and the magnitude-shifted light curve for the B image). We observed noisy behaviours around the zero line and no short time-scale events (with a duration of months), where the term`event' refers to a prominent feature that may be a result of microlensing or another source of variability. Only one event lasting two weeks and rising 233 mmag was found. Measured constraints on the possible microlensing variability can be used to obtain information on the granularity of the dark matter in the main lensing galaxy and the size of the source. In addition, one can also test the ability of the observational noise to cause the rms averages and the local features of the difference signals. We focused on this last issue. The combined photometries were related to a process consisting of an intrinsic signal plus a Gaussian observational noise. The intrinsic signal has been assumed to be either a smooth function (polynomial), a smooth function plus a stationary noise process, or a correlated stationary process. Using these three pictures without microlensing, we derived some models totally consistent with the observations. We finally discussed the sensitivity of our telescope (at Teide Observatory) to several classes of microlensing variability.

show abstract

Hourly Variability in Q0957+561

Cited by 16 publications

References 12 publications

New aperture photometry of QSO 0957+561; application to time delay and microlensing

New aperture photometry of QSO 0957+561; application to time delay and microlensing

Fitting gravitational lenses: truth or delusion

Short time-scale fluctuations in the difference light curves of QSO 0957+561A,B: microlensing or noise?

Contact Info

Product

Resources

About