Bibcode
DOI
Oscoz, A.; Alcalde, D.; Serra-Ricart, M.; Mediavilla, E.; Abajas, C.; Barrena, R.; Licandro, J.; Motta, V.; Muñoz, J. A.
Bibliographical reference
The Astrophysical Journal, Volume 552, Issue 1, pp. 81-90.
Advertised on:
5
2001
Journal
Citations
37
Refereed citations
34
Description
Photometric optical data of QSO 0957+561 covering the period 1984-1999
are analyzed to discern between the two values of the time delay (417
and 424 days) mostly accepted in the recent literature. The
observations, performed by groups from three different
institutions-Princeton University, Harvard-Smithsonian Center for
Astrophysics, and Instituto de Astrofísica de Canarias-and
including new unpublished 1998-1999 data from the IAC80 Telescope, were
obtained in five filters (V, R, I, g, and r). The different light curves
have been divided into observational seasons, and two restrictions have
been applied to calculate the time delay better: (1) points with a
strange photometric behavior have been removed, and (2) data sets
without large gaps have been selected. Simulated data were generated to
test several numerical methods intended to compute the time delay
(ΔτAB). The methods giving the best results-the
discrete correlation function, δ2, z-transformed
discrete correlation function, and linear interpolation-were then
applied to real data. A first analysis of the 23 different time delays
derived from each technique shows that ΔτAB must be
in the interval 420-424 days. From our statistical study, a most
probable value of ΔτAB=422.6+/-0.6 days is
inferred.