QSO 0957+561 is first discovered gravitational lens system by Walsh, Carswell, & Weymann in 1979. The quasar QSO 0957+561 appears twin (QSO 0957+561A and QSO 0957+561B) due to gravitational lensing by host galaxy YGKOW G1 that is located directly between Earth and the quasar. The expected distance of QSO 0957+561 from earth is around 9.0 billion Ly.
The photometric analysis of such lensed quasars a like QSO 0957+561 are studied to estimate the more accurate value of Hubble constant. Two images are photometrically examined for long time to estimate the time delay which is proportional to difference between distances travelled by to twin counterparts and mass lens model (which depends on host galaxy). The time delay approach is independent of both methods, like plank ΛCDM (Lambda cold dark matter) or Lambda-CDM model flat results and distance ladder + Type Ia SNe results, which are previously used to estimate Hubble constant (for more watch video link added below).
For more reading:
https://wwwmpa.mpa-garching.mpg.de/~komatsu/meetings/ds2013/schedule/suyu_desitterii.pdf
https://iopscience.iop.org/article/10.1086/320462/pdf
We imaged the QSO 0957+561A and QSO 0957+561B. An astrometric reduction of two optical centers of twin quasars in FITS image estimates the separation of 6 arc second due to gravitational lensing by host galaxy. We used photometric R band filter as expecting that redder part of optical spectrum should be more dominated due to high redshift z=1.4.
Instrument:
Catalog: SIMBAD
Bessell (B): +*.*, Bessell (V): +*.*
Bessell (R): +16.4, Bessell (I): +*.*
CCD: ATIK-383L+
FILTERS: R
TELESCOPE: C11, 1623.0mm
PRiSMv10, Astrometrica
Site:
ORIGIN: Cepheid Observatory, India, Vorion Scientific, India
SITELAT: +24:55:00:00
SITELONG:+75:33:58:99
Observers:
V.K.Agnihotri, B. Kumar, S. Mahawar, K.Vora
Remark:
Sky Clear.
End
Cosmology with Time Delay Strong Lensing by Kenneth Wong