Open AccessEvidence for accretion disc reprocessing in QSO 0957+561
Author(s) -
Collier Stefan
Publication year - 2001
Publication title -
monthly notices of the royal astronomical society
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.058
H-Index - 383
eISSN - 1365-2966
pISSN - 0035-8711
DOI - 10.1046/j.1365-8711.2001.04568.x
Subject(s) - physics , quasar , light curve , astrophysics , amplitude , photometry (optics) , astronomy , accretion (finance) , gravitational lens , stars , galaxy , optics , redshift
We use archival g ‐ and r ‐band photometry of the gravitational lens system QSO 0957+561A, B to estimate the intrinsic variability of the quasar during 1996 February–June. The light curves span 234 d with temporal resolutions of about 2.5 d. Both light curves display a single large‐amplitude event, of ∼0.1 mag (max‐to‐min) in about 100 d, followed by small‐amplitude variations of ∼0.02 mag on time‐scales of tens of days. We find the r ‐band variations lag those at g by 3.4 −1.4 +1.5 d for the large‐amplitude event. This lag is greater than zero at no less than 98 per cent confidence. The delayed coupling of the rest‐frame UV intrinsic variations strongly suggests the existence of a stratified reprocessing region extending ∼light‐days from the putative central black hole source. The observed lag is consistent with that expected from a reverberation within an irradiated accretion disc structure. However, any definitive statement requires further detailed theoretical modelling and high‐quality, signal‐to‐noise ratio of about 100, optical/IR simultaneous monitoring with about 3‐d resolution for approximately 6 months.