REVERBERATION RESPONSES IN LIGHT CURVES OF THE Q2237+0305 QUASAR

Abstract

Purpose: Studying the spatial structure of the quasar in the Q2237+0305 gravitational lens system in optical spectral range; estimating the central black hole mass. Design/methodology/approach: The method of reverberation mapping has been used that implies measuring of the time delays between the quasar intrinsic brightness variations in different spectral ranges. We used the macroimage light curves of the Q2237+0305 system in spectral bands V (λeff = 547.7 nm) and R (λeff = 634.9 nm) of Johnson–Cousins photometric system. The reverberation mapping method allows to obtain direct estimates of distances between the quasar regions responsible for radiation in the selected spectral bands. Findings: The time delay between the V and R light curves is estimated to be 5.58±1.69 days, which is more than an order of magnitude larger than that predicted by a standard thin accretion disk model by Shakura–Sunyaev. As an explanation, a suggestion is made that the standard accretion disk model is not entirely adequate when describing an actual quasar structure. Conclusions: Such a large time delay means that reverberation responses arise in extended structures located outside the accretion disk. A suggestion that some extended structure capable to efficiently radiate in optical band may exist around the accretion disks has been reported in a number of works dedicated to the microlensing studies and analysis of flux ratio anomalies in gravitationally lensed quasars. Abolmasov and Shakura have shown analytically that a super-Eddington accretion regime may take place for some quasars, which leads to formation of an envelope. The envelope scatters radiation from the disk, thus making the apparent disk size larger. The further development in studying the spatial structure of the Q2237+0305 quasar with the use of reverberation mapping implies involving the data in spectral band I. This will provide two additional spectral bases thus allowing investigation of a wavelength dependence of the corresponding structure dimensions.

Keywords

• quasar
• black hole
• spatial structure
• accretion disk
• reverberation mapping